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A calorimetric study of the electrolysis of D2O and H2O at palladium cathodes
167
.I. Electroanal. Chem., 344 (1993) 167-185 Elsevier Sequoia .?.A., Lausanne
JEC 02334
A calorimetric study of the electrolysis of D,O and H,O at palladium cathodes T.I. Quickenden
and T.A. Green
Department of Chemistry, The University of Western Australia, Nedlands, WA 6009, (Australia) (Received 2 April 1992; in revised form 11 June 1992)
Abstract
A search for excess heat production during the electrolysis of D,O or H,O at palladium cathodes was conducted using a sensitive flow calorimeter. A total of 20 long-term experiments using 10 control cells and 10 test cells was performed and the effects of different electrode pretreatments and electrolysis conditions were examined. In all cases, the thermal output from the cell matched the Joule input energy within the experimental error of f 1.5%. These results provided no evidence for any excess heat production over the aggregated cell operating time of 17762 h.
INTRODUCTION
Recently, Fleischmann et al. [l] have reported the production of anomalous heat during the electrolysis of D,O at palladium cathodes. This “excess” heat exceeded the Joule heating dissipated in the electrochemical cell by the electrolysis current by between 5% and 111%. Moreover, this excess heat was often sustained for such long periods of time that megajoules of excess energy were apparently produced. Fleischmann et al. [l] concluded that this excess heat must be of nuclear origin since it exceeded the amount of energy that could be stored chemically by a factor of 10-100. Since this original announcement, a number of research groups [2-141 have also reported the production of excess heat during the electrolysis of D,O at palladium electrodes. However, a larger number of researchers [15-291 have found no evidence for excess heat production, despite using similar electrolysis conditions and calorimetric techniques of comparable sensitivity and accuracy. Some workers [17-20,30-321 have attributed the excess heat to errors in the calorimetric procedures used by Fleischmann et al. [l], although many of these criticisms have been refuted in a subsequent publication [33]. With one possible exception [34], there have been no reports of the formation of nuclear byproducts at levels commensurate with the amount of excess heat 0022-0728/93/$06.00
0 1993 - Elsevier Sequoia S.A. All rights reserved
observed. This discrepancy has led many [17-19,30,31,35-411 to suspect a nonnuclear origin for the excess heat. The most frequently suggested explanations for the excess heat are recombination of the evolved gases [17-19,30,31,35] or the sudden release of energy stored in the cathode during the initial electrolysis period 136-411. It has been speculated that the latter effect might arise from either an accumulation of strain energy in the cathode [36-381 or the formation of an unstable endothermic compound [40,41]. However, in many cases [l-6,331 the magnitude of the excess heat reported exceeded 1 MJ mol-’ of Pd and it appears difficult [38,42] to attribute such large excess energies to any chemical or mechanical processes. Nevertheless, it seems prudent to design experiments in which these chemical effects can be distinguished from genuine excess heat production. The aim of the present investigation was to search for excess heat production using accurate calorimetry. It was decided to employ a flow type calorimeter in these studies as this design circumvents many of the problems and limitations of the simple isoperibolic calorimeters used by Fleischmann et al. [1,33] and other workers [7,8,10,13,17-20,251. For example, unlike isoperibolic calorimeters, flow calorimeters are insensitive to inhomogenous internal temperature profiles and their thermal calibration is essentially independent of the electrolyte level. Another advantage of flow calorimeters is that the rate of heat loss can be controlled precisely by deliberately altering the flow rate of the cooling water. This allows maintenance of near-isothermal conditions, irrespective of the magnitude of the input power. A further incentive to use a flow calorimeter arose because they have already been used successfully by a number of other groups [6,11,16,20,23,27,29] in similar studies. The experimental protocol adopted in these studies attempted to address a number of the concerns/criticisms directed at previous reports of excess heat production. For example, given widespread criticism [30,32,43] of the lack of control experiments in a number of other studies, the concurrent running of control cells containing light water, alongside test cells containing heavy water, was deemed essential. Furthermore, given the possibility of apparent excess heat generation via a storage and subsequent relaxation process involving mechanical or chemical energy, an energy audit was carried out over the entire duration of the experiment. Such a mechanism would then be indicated by a period when the energy balance was negative (a storage phase) followed by a period in which there appeared to be excess energy (a relaxation phase). Finally, a comparison of the amount of solvent added to the cell with the predicted loss via electrolysis and evaporation was also considered necessary to preclude contributions to the excess heat via recombination of the evolved gases. EXPERIMENTAL
Figure 1 is a schematic diagram of the calorimeter and associated equipment used in this study. The electrolysis cell was constructed of borosilicate glass and had an internal diameter of 5 cm and height of 15 cm. The lower part of the cell
169
Data
Logger
Thermititora
Computer
7
-
Calibration
-
Cathode
1k
Pergpex
heater
container
-
. _.
I%“,.._er
Fig. 1. A schematic diagram of the flow calorimeter and data acquisition system.
was surrounded by a glass jacket 1 cm thick through which cooling water was pumped at a controlled rate. The cell was sealed with a polypropylene stopper 5 cm thick which incorporated feedthroughs for the electrical connections to the anode and cathode, the calibration heater and the thermistor probe. In addition, there was a small port to allow the passage of nitrogen gas into the cell headspace and a vent through which the gases were expelled. In order to minimize heat loss to the surroundings, the entire electrolysis cell assembly was placed in a large glass Dewar flask fitted with an insulating lid 6 cm thick made of polyethylene foam. The Dewar flask was in turn mounted in a poly(methy1 methacrylate) cylinder immersed in a constant temperature bath maintained at 25.00 f 0.02”C. Each water bath contained two such calorimeters, one containing a D,O cell and the other an H,O cell. The room in which the calorimetric experiments were performed was maintained at a temperature of 21 * 1.5”C. Thermostatted cooling water was pumped from the water bath and through the jacket of each electrolysis cell using a microprocessor-controlled peristaltic pump (Masterflex L/S). In all experiments, water flow rates of either 0.40 g s-i or 0.20 g s- ’ were used. The flow was checked periodically and found to be constant to within +0.5%. The thermal output from each cell was determined by measuring the temperature difference AT between two calibrated thermistors placed in the cooling water flow at the entry and exit of the water jacket. Each thermistor
170
comprised the fourth arm of a Wheatstone bridge circuit and in this configuration produced an output voltage of 3.1 mV “C-l. With this arrangement, AT values of less than O.Ol”C were readily detectable. In experiments Al-A4, Bl-B4, Cl-C4 and Dl-D4, the cathodes were constructed from palladium rods (99.96% Pd) 0.40 cm in diameter obtained from Johnson Matthey. The cathodes used in the experimental series E were constructed from palladium wire (99.95% Pd) 0.10 cm in diameter obtained from Goodfellows. For experiments Al-A4, Bl-I34 and Cl-C4, the cathodes were cut into 1.4 cm lengths, while in experiments Dl-D4 and El-E4 the cathode length was 1.2 cm. Electrical connection to each cathode was facilitated by attaching 0.05 cm diameter Pt wire by spot welding. The four cathodes used in experiments Al-A4 were used essentially in the “as-received” condition, apart from a brief solvent rinse in acetone followed by D,O or H,O. The cathodes used in experiments Bl-B4 were similarly rinsed and then transferred to the electrolysis cells where they were precharged with H or D at a low current density of 65 mA cm-* for 7 days. Precharging at a low current density was performed to minimize stress fracturing and plastic deformation of the cathode during the loading stage. After this precharging process was complete, the current density was increased and calorimetric measurements were commenced. The cathodes for experiments Cl-C4 were pretreated by annealing them at 1000°C for 3 h under vacuum ( < 5 X lo-’ Torr) and were then transferred rapidly to the electrolysis cells. Annealing was performed to remove any pre-existing hydrogen trapped in the palladium. The cathodes used in experiments Dl-D4 were initially cold-worked by repeated rolling of a Pd rod 0.4 cm in diameter into a flat plate of dimensions 4.8 cm x 0.3 cm X 0.15 cm. This plate was then cut into four 1.2 cm lengths. Platinum wires were attached to each length and the electrodes were rinsed in acetone followed by D,O or H,O. They were then transferred to the electrolysis cells where they were anodized at 10 rnA cm-* for 5 min prior to commencement of the electrolysis. In experiments El-E4, the cathodes were first palladized in a 3.5 mM PdCI, solution for 3 h at a current density of 8 mA cm-*, Subsequently, they were transferred to the electrolysis cells and precharged for 5 days at a current density of65mAcm*. After this precharging process was complete, the current density was increased and calorimetric measurements were commenced. In all cases, the cathodes were mounted centrally in the electrolysis cells and each was surrounded by a cylindrical Pt mesh anode. Both the anode and cathode leads were shrouded in polytetrafluoroethylene tubing to minimize Pt catalysed recombination of the evolved gases. The cell head-space was continuously purged with a flow of 25 ml min-’ of dry high purity nitrogen to prevent build-up of an explosive mixture of D, (or H,) and 0,. Each cell contained a 2 fl resistor for thermal calibration of the calorimeter and a thermistor for monitoring the electrolyte temperature. The heater and the thermistor were each sealed in separate glass tubes which had been filled with small amounts of silicone oil to increase thermal conduction.
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Apart from experiments Dl-D4, all electrolysis cells contained 110 ml of H,O or D,O to which sufficient lithium metal (Merck, > 99% Li) was added to make 0.10 M solutions of LiOH or LiOD. The electrolytes in experiments Dl-D4 were obtained by adding L&SO, (BDH, > 99% Li,SO,l to 110 ml of D,O or H,O to make 0.25 M solutions of Li,SO,. D,O was obtained from The Australian Institute of Nuclear Science and Engineering and had a minimum isotopic purity of 99.75%. The isotopic purity of the electrolyte was checked periodically by proton magnetic resonance measurements and was found always to exceed 99.5%, even when cells had been operating for as long as 6 weeks. All electrolysis experiments were performed galvanostatically using dc power supplies (Thurlby PL 320). Current densities from 65 to 1500 mA cmp2 were employed and resulted in Joule heating powers of 0.2-8 W and cell voltages of 3-12 V. Current densities were calculated with respect to the geometric areas of the electrodes. The loss of electrolyte via electrolysis and evaporation necessitated daily additions of 1.5-8 ml of H,O or D,O. Comparison of the total solvent additions during an entire run with the total amount of electrolytic charge passed through the cell indicated that there was little (< 2%) recombination of the evolved gases in the electrolysis cells. Initially, the calorimeter was calibrated by applying varying amounts of power Pi to the in-situ electrical heater and measuring the resulting steady state value of the temperature difference AT between the input and output water flows. In this way the calibration constant k( = Pi/AT) of the calorimeter was determined. It was found that the calibration curve of AT versus input power was linear over the range O-6 W (Fig. 2). The value of k was subsequently checked every 7 days using a power-matching technique. This involved lowering the electrolysis current to ca. 10% of its initial value and adding power via the heater to maintain a temperature close to the operating temperature. Calibration constants in the vicinity of 1.0 W “C-i were obtained at a cooling water flow rate of 0.20 g s-l, while values of around 1.8 W “C-’ were typical when the flow rate was 0.40 g s-‘. Once the calorimeter had been calibrated, the total power output from the electrolysis cell in any experiment could be obtained as the product kAT. In the present work, the primary sources of error were due to uncertainties in the measurement of AT, Pi and the cooling water flow rate. Uncertainties in the measurement of AT were mainly produced by variations in room temperature. Despite extensive insulation of the calorimeter, AT varied by approximately 0.02”C per 1°C change in room temperature. At the lowest measured value of AT, this amounted to an error of ca. +0.5%. The errors in measuring Pi and the cooling water flow rate were both comparable with the uncertainty in AT, leading to a cumulative error of ca. 1.5%. An operational (and probably more realistic) assessment of the experimental error was obtained by observing the variability in a number of control experiments. The observed variations were no larger than the random errors estimated above. A completely rigorous analysis of the thermodynamics of open electrolysis cells should include a correction term for the heat lost by the evaporation of the solvent
172
AT / Fig.
‘C
2. A typical calibration curve for cell Dl using the internal calibration heater.
[17,33,44]. However, under the conditions of the present experiments, this correction would amount to between 2 and 9 mW corresponding to a maximum error of 0.15%. As this was much smaller than the estimated experimental error (ca. 1.5%), this correction was not performed. Nor was any correction made for the small amount of heat removed by the passage of nitrogen gas through the cell headspace 1441.Calculations show that this correction would not exceed ca. 4 mW. Furthermore, the calibration experiments with the electrical heater were carried out using the same nitrogen flow rate and cancelling would thus occur. Any resulting error would therefore be much less than 4 mW and hence negligible. As pointed out previously, there have been frequent criticisms [30,32,43] of the lack of adequate control experiments in calorimetric studies of cold fusion. For this reason, care was taken to ensure that each D,O cell was accompanied, in the same constant temperature water bath, by a control cell of identical construction but containing H,O rather than D,O solvent. The present study involved the use of two such test cell + control cell pairs in two separate water baths and all were contained in the same air-conditioned room. Although all cells were run at identical current densities, the larger cathodic overpotential for the reduction of D,O compared with H,O and the higher resistance of the LiOD electrolyte compared with LiOH resulted in a higher potential difference across the D,O cells. The concurrent running of H,O control experiments and D,O test experiments in pairs enabled any thermal artefacts due to fluctuations in the flow rate of the cooling water, or in the ambient or bath temperatures, to be distinguished from genuine excess heat production.
173
Cell voltages, currents and temperatures were measured every 2 min using a pair of data loggers (Data Electronics, DT 100) interfaced serially to a microcomputer (IBM PS2 30 286). In addition, the temperature of each water bath and the ambient air temperature were also recorded. The cell data were displayed on the computer monitor in real time and written to a file using a commercial software package (Labtech Notebook). Although the electrolysis cells were run continuously for long periods of time, data acquisition runs were performed in 24 h cycles. At the end of each run, a hard copy of the data displayed on the computer monitor was printed. RESULTS
A total of five experimental series (A-E) were completed in this study, with each series consisting of four cells grouped into two control cell + test cell pairs. Each cell in a series had an identical electrode pretreatment, and was operated under the same electrolysis conditions. The heat output from each of these 20 cells was monitored continuously for periods of between 32 and 40 days. The calorimetric data were analysed in three major ways. Firstly, the instantaneous power balance for each 24 h period was calculated. These data were then used to compute the overall energy balance for each 24 h period in the experimental run. Finally, the total energy balance integrated over the entire duration of the experiment was obtained. Instantaneous power balance
Figure 3 shows the power balance for a typical D,O electrolysis cell over a 24 h period. The full line represents the electrical power Pi released into the cell as Joule heating. This was calculated from the equation Pi=Z(E-Ets)
(I)
where Z is the cell current, E is the potential difference across the cell and Et,, is the thermoneutral potential for the electrolysis of D,O or H,O. The thermoneutral potential provides a thermodynamic correction [24] for the portion of input electrical energy used to electrolyse the D,O or H,O and which is thus unavailable to heat the cell. The value of the thermoneutral potential for the electrolysis of H,O at 25°C is 1.481 V [23,24] and the corresponding value for D,O is 1.527 V [23,24]. The full squares plotted in Fig. 3 represent the values of the thermal output power P, calculated every 20 min from the measured value of AT and the calibration constant of the calorimeter using PO= kAT
(2)
In the absence of any excess heat production, the measured Joule input power and
174
.
2 6.5 -
6.0 L 0
I 4
I 6
I 12
Electrolysis
Time
I 16
/
I 20
I 24
h
Fig. 3. The relationship between the Joule input power (1 and the thermal output power ( n J for test cell B4 over a 24 h period. Cell parameters: Pd cathode; Pt anode; 0.10 M LiOD; current density, 375 mA cm-‘. Representative error bars are shown for the estimated uncertainties in the thermal output power. Errors associated with the Joule input power are not shown for reasons of clarity but correspond to +0.03 W.
the observed output power should coincide within experimental
error. It is clear from Fig. 3 that these two quantities do indeed agree within the estimated errors. The small downward trend shown in Fig. 3 for both the input and output powers over the 24 h period is primarily due to the lowering of solution resistance because of an increase in the concentration of the dissolved electrolyte as the solvent is progressively electrolysed. The sudden ca. 6% increase in input power after 23 h occurred when the cell was replenished with D,O, prior to the commencement of a subsequent 24 h cycle. Figure 4 shows similar results to those in Fig. 3, but is for a control cell containing H,O instead of D,O. It is clear that, for the control cell, the output power (full diamonds) and the line representing the input power are once again in close conformity. Although the results in Figs. 3 and 4 are from only a single 24 h period, they are typical of the daily behaviour of all the cells studied during the aggregated operating time of 17762 h. Daily energy balance as a function of time
Figures 5 and 6 show convenient summaries of the long-duration energy balance for a typical control cell -t test cell pair. The results are expressed as the ratio R of
175
6.0
I
I
I
I
I
I 4
I 6
I 12
I 16
I 20
5.5 -
4.5 -
4.0 0
Electrolysis
Time
24
/ h
> and the thermal output power ( 6 1 for Fig. 4. The relationship between the Joule input power (control cell B3 over a 24 h period. Cell parameters: Pd cathode; Pt anode; 0.10 M LiOH; current density, 375 mA cm-‘. Errors are represented as described for Fig. 3.
1.20
0.80 0
I
I
I
I
I
I
10
20
30
Electrolysis
Time
/ Days
Fig. 5. The daily energy balance for test cell B4 as a function of time. The excess heat ratio R is defined by eqn. (3).
176
a= d
1.10
3 $ 4 Cd 1.00 G : a, z w
0.90
0.80 0
10
Electrolysis
20
Time
/
30
Days
Fig. 6. The daily energy balance for control cell B3 as a function of time. The excess heat ratio R is defined by eqn. (3).
the integrated output power to the integrated period. This ratio is given by the equation R = k jt2AT dt/I /“( E - Et,,) dt fl fl
Joule input power for each 24 h
(3)
where t is the time and t, and t, define the beginning and end of a 24 h period and the other terms have already been defined. The presence of excess heat would be seen in Figs. 5 and 6 as a point (or points) which deviated above the R = 1 line by substantially more than the error bar. Although there is some scatter around the R = 1 line in both figures, this is clearly less than the experimental error. Hence the data in these graphs provide no evidence for the existence of excess heat. Similar behaviour was observed in all other experiments, with no experiment showing any sign of excess heat within experimental error. It might be argued that integrating the energy balance over a 24 h period would tend to “hide” any short-lived excess heat event. However, each separate 24 h trace of AT versus time was individually examined for transient temperatures rises, but after elimination of obvious artefacts, none were observed. The total energy hr ‘mce
Any net excess heat production AQ over an entire run is given by the difference between the total output power and the Joule input power integrated over the
Current density/ mA cm-’ 250
250
250
250
Cell
1.4 cmx0.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H,O
1.4cmX0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
1.4 cmx0.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H ,O
1.4cmx0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
Al
A2
A3
A4
864
864
864
864
Duration/h
10.700
9.883
10.741
7.719
Energy input/ MJ
on cells containing untreated Pd cathodes
Experiment
Summary of the results of heat measurements
TABLE 1
10.717
+0.017
+ 0.035
- 0.023
10.718
9.918
+0.048
AQ/MJ
Excess energy/
1.767
Energy output/ MJ
+ 0.2
+ 0.4
-0.2
+ 0.6
Excess heat/%
Cell
1.4cmX0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in Ha0
1.4cmX0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
1.4cmX0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H,O
1.4 cmX0.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
Experiment
Bl
B2
83
B4 250 375 250
250 375 250
250 375 250
250 375 250
Current density/ mA cmm2
168 168 456
168 168 456
168 168 456
168 168 456
Duration/h
12.035
9.094
12.186
8.491
Energy input/ MJ
12.019
9.062
12.114
8.515
Energy output/ MJ
Summary of the results of heat measurements on cells containing electrolytically precharged Pd cathodes
TABLE 2
Excess energy/
- 0.016
- 0.032
- 0.072
+ 0.024
AQ/MJ
-0.1
-0.4
-0.6
+ 0.3
Excess heat/%
384 312 312 384 312 312
250 375 300 250 375 300 250 375 300
1.4 cmX0.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
1.4 cmxO.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H,O
1.4cmx0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O.
c2
c3
c4
384 312 312
384 312 312
250 375 300
1.4 cmx0.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H *O
Cl
Duration/h
Cell
Experiment
Current density/ mA cm-’
17.722
14.201
19.880
13.159
Energy input/ MJ
17.767
14.126
19.760
13.085
Energy output/ MJ
Summary of the results of heat measurements on cells containing vacuum annealed Pd cathodes
TABLE 3
+ 0.045
- 0.075
- 0.120
- 0.074
AQ/MJ
Excess energy/
+0.2
-0.5
-0.6
-0.6
Excess heat/%
Cell
0.15 cm thick Pd plate cathode, Pt mesh anode, 0.25 M Li,SO, in Ha0
0.15 cm thick Pd plate cathode, Pt mesh anode, 0.25 M Li,SO, in Da0
0.15 cm thick Pd plate cathode, Pt mesh anode, 0.25 M Li,SO, in H,O
0.15 cm thick Pd plate cathode, Pt mesh anode, 0.25 M Li,SO, in D,O
Experiment
Dl
D2
D3
D4 275 340
275 340
275 340
275 340
Current density/ mA cm-*
312 576
312 576
312 576
312 576
Duration/h
12.560
10.822
13.544
11.364
Energy input/ MJ
Summary of the results of heat measurements on cells containing cold-worked Pd cathodes
TABLE 4
12.539
10.829
13.579
11.382
Energy output/ MJ
Excess energy/
- 0.021
+ 0.007
+ 0.035
+ 0.018
AQ/MJ
-0.2
+0.1
+ 0.3
+0.2
Excess heat/%
Cell
1.2 cmXO.1 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H z0
1.2 cmx0.1 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
1.2 cmXO.1 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H,O
1.2cmXO.l cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
Experiment
El
E2
E3
E4 1250 1500
1250 1500
1250 1500
1250 1500
432 456
432 456
432 456
432 456
Duration/h
26.005
19.914
25.016
17.573
Energy input/ MJ
on ceils containing palladized Pd cathodes
Current density/ n~4 cm-*
Summary of the results of heat measurements
TABLE 5
26.148
19.968
25.087
17.699
Energy output/ MJ
+0.143
+ 0.054
+ 0.071
+0.126
AQ/MJ
Excess energy/
+ 0.5
+ 0.3
+0.3
+ 0.7
Excess heat/%
182
total duration t, - t, for a 32-40 day calorimetric study:
(4)
AQ = j*‘P,, dt - jt2Pi dt 11 t1
where Pi is the instantaneous Joule input power and PO is the instantaneous output power. Using eqns. (2) and (3) it then follows that AQ = k jr2AT dt - Zj”( E -Et,,) t1 fl
dt
(5)
Tables l-5 summarize the values of AQ obtained for the 20 calorimetric experiments performed in this study. In all cases AQ = 0 within the estimated experimental error of k 1.5%, which shows that the heat energy recovered from the calorimeters matches the Joule input power. Thus, these results provide no significant evidence for any differences between the D,O test cells and the Hz0 control cells. In both cases, there were some cells that produced small energy excesses and some that produced small energy deficits, but none of these deviations exceeded the estimated experimental error. DISCUSSION
The constant-flow calorimeters used in this work were found to be very satisfactory for studying the thermal characteristics of electrolytic processes. The accuracy of the calorimeters was found to be comparable with the accuracies of other calorimeters used in the cold fusion experiments [l-29] and they also possessed excellent long-term stability. In the majority of published experiments reporting excess heat [l-3,6-14], the thermal output power from the cell exceeded the Joule input power by between 5% and 150%, with a mean value of around 15%. Such excess heat levels would have been readily detectable with the present constant-flow calorimeters; however, no excess heat was observed. A few groups [4,5,33] have occasionally reported excess heat at, or around, the 2% level. Such levels would be below the limit of detection of the present calorimeter and could conceivably have been present. However, excess heat at such a low level would be atypical of nearly all the literature reports of excess heat and also would be of little practical significance. The present study also examined the effect of a number of different electrode pretreatments on excess heat production. Because the mechanism of excess heat production is not understood, it is not obvious which pretreatment procedures might be beneficial and which might be detrimental. Nevertheless, it seemed appropriate to use similar pretreatments to those employed by workers who have observed excess heat production. These include vacuum annealing [2,3,5,6,8,1012,141, cold working [4,7,11,12] and electrolytic precharging at low current densities [l-3,8,11,33]. In addition, palladization of the cathode was also tried, as this is known [45] to enhance the rate of uptake of both H and D during electrolytic
183
charging. As pointed out earlier, none of these pretreatments produced excess heat in the present study (Figs. 3-6 and Tables l-5). Some workers [33,46] have suggested that high current densities and/or longduration experiments are necessary before excess heat production is observed. For example, Fleischmann et al. 1331 have recently reported excess heat following weeks of electrolysis and at current densities in excess of 64 mA cmp2. Some other workers [2,6] have also found excess heat production only after a lengthy induction period. However, there are also a number of reports [3,4,7,12] of excess heat production which commenced almost immediately after the start of electrolysis. In order to cover all these possibilities, the present electrolysis experiments were performed with current densities between 65 and 1500 mA cm-*. These values are similar to the current densities employed in the majority of studies. Furthermore, the present experiments were run for periods of up to 40 days and are thus comparable with some of the longest duration experiments reported in the literature [2,6,13]. It should be noted that what is usually described as excess heat or energy is often only a measurement of excess power. This distinction is important because, as previously pointed out, the excess power observed by many groups might simply represent the sudden release of chemical or mechanical energy stored gradually during the initial electrolysis period. To avoid this possible ambiguity, the energy balance for each electrolysis cell was measured over the entire duration of the experiment. The results of these energy audits are presented in Tables l-5 and show that no total excess heat was produced within the experimental error of + 1.5%. Furthermore, a Student t test showed that the mean excess heat from the 10 test cells was not distinguishable from the mean of the 10 controls cells at greater than the 99.9% confidence level. This indicates that there is no significant difference between the thermal behaviour when Pd is electrolysed in D,O or H,O. A number of workers [17-19,30,31,351 have suggested that the excess heat reported may be due to the recombination of D, or H, with 0, in the cell head-space or in the electrolyte. The observation in the present work that the energy input and output agree within ca. 1% suggests that not only was there no excess heat production, but that, in addition, negligible recombination was occurring in the cells. This latter conclusion is also supported by our records of solvent addition which agreed to within 2% of the predicted losses due to electrolysis and evaporation. This latter calculation assumed that the gases exiting the cell were saturated with D,O or H,O vapour. These conclusions on recombination are in agreement with those of a number of other studies [3,8,21,24,33,44] which have also found minimal recombination in cells of similar type. CONCLUSIONS
This study involved the use of precise calorimetry to search for low level excess heat produced during the electrolysis of D,O at palladium cathodes. A variety of electrode pretreatments and electrolysis conditions were used in an attempt to
184
initiate low level excess heat production. However, no excess heat above the estimated &-1.5% accuracy of the calorimeter was observed. The amount of recombination of the evolved gases was also determined and was found to be negligible ( < 2%). ACKNOWLEDGEMENTS
Financial support by Grant El60 from the Minerals and Energy Research Institute of Western Australia is gratefully acknowledged. REFERENCES 1 M. Fleischmann, S. Potts and M. Hawkins, J. Electroanal. Chem. 261 (1989) 301; Errata, 263 (1989) 187. 2 M.C.H. McKubre, R.C. Rocha-Filho, S. Smedley, F. Tanzella, J. Chao, B. Chexal, T. Passe11 and J. Santucci, Proc. 1st Annu. Conf. on Cold Fusion, National Cold Fusion Institute, Salt Lake City, UT, March 1990. 3 A.J. Appleby, Y.J. Kim, O.J. Murphy and S. Srinivasan, Proc. 1st Annu. Conf. on Cold Fusion, National Cold Fusion Institute, Salt Lake City, UT, March 1990. 4 M. Schreiber, T.M. Gur, G. Lucier, J.A. Ferrante, J. Chao and R.A. Huggins, Proc. 1st Annu. Conf. on Cold Fusion, National Cold Fusion Institute, Salt Lake City, UT, March 1990. 5 R.A. Oriani, J.C. Nelson, S-K. Lee and J.H. Broadhurst, Fusion Tech., 18 (1990) 652. 6 C.D. Scott, J.E. Mrochek, T.C. Scott, G.E. Michaels, E. Newman and M. Petek, Fusion Tech., 18 (1990) 103. 7 A. Belzner, U. Bischler, S. Crouch-Baker, T.M. Gur, G. Lucier, M. Schreiber and R.A. Huggins, J. Fusion Energy, 9 (1990) 219. 8 R.C. Kainthla, 0. Velev, L. Kaba, G.H. Lin, N.J.C. Packham, M. Szklarczyk, J. Wass and JG’M. Bockris, Electrochim. Acta 34 (1989) 1318. 9 L.L. Zahm, A.C. Klein, S.E. Binney, J.N. Reyes Jr., J.F. Higginbotham, A.H. Robinson, M. Daniels and R.B. Peterson, J. Electroanal. Chem. 281 (1990) 313. 10 D.P. Hutchinson, C.A. Bennett, R.K. Richards, J.S. Bullock IV and G.L. Powell, Report ORNL/TM-11356, Oak Ridge National Laboratory, TN 1989. 11 R.D. Eagleton and R.T. Bush, Fusion Tech., 20 (1991) 239. 12 D. Lewis and K. Skold, J. Electroanal. Chem., 294 (1990) 278. 13 M.H. Miles, K.H. Park and D.E. Stilwell, J. Electroanal. Chem., 296 (1990) 241. 14 K-S. Yun, J-B. Ju, B-W. Cho, W-I. Cho and S-Y. Park, J. Electroanal. Chem., 306 (1991) 279. 15 D. Albagli, R. Ballinger, V. Cammarata, X. Chen, R.M. Crooks, C. Fiore, M.P.J. Gaudreau, I. Hwang, C.K. Li, P. Linsay, SC. Luckhardt, R.R. Parker, R.D. Petrasso, M.O. Schloh, K.W. Wenzel and MS. Wrighton, J. Fusion Energy, 9 (1990) 133. 16 D.R. McCracken, J. Paquette, H.A. Boniface, W.R.C. Graham, R.E. Johnson, N.A. Briden, W.C. Gross, A. Arneja, D.C. Tennant, M.A. Lone, W.J.L. Buyers, K.W. Chambers, A.K. McIlwain, E.M. Attas and R. Dutton, J. Fusion Energy, 9 (1990) 121. 17 D.E. Williams, D.J.S. Findlay, D.H. Craston, M.R. Sene, M. Bailey, S. Croft, B.W. Hooton, C.P. Jones, A.R.J. Kucernak, J.A. Mason and R.I. Taylor, Nature (London) 342 (1989) 375. 18 N.S. Lewis, CA. Barnes, M.J. Heben, A. Kumar, S.R. Lunt, G.E. McManis, G.M. Miskelly, R.M. Penner, M.J. Sailor, P.G. Santangelo, G.A. Shreve, B.J. Tufts, M.G. Youngquist, R.W. Kavanagh, S.E. Kellogg, R.B. Vogelaar, T.R. Wang, R. Kondrat and R. New, Nature (London), 340 (1989) 525. 19 G.M. Miskelly, M.J. Heben, A. Kumar, R.M. Penner, M.J. Sailor and N.S. Lewis, Science, 246 (1989) 793. 20 F.T. Wagner, T.E. Moylan, M.E. Hayden, U. Narger and J.L. Booth, J. Electroanal. Chem., 295 (1990) 393.
185 21 L. Redey, K.M. Myles, D. Dees, M. Krumpelt and D.R. Vissers, J. Fusion Energy, 9 (1990) 249. 22 M. Chemla, J. Chevalet, R. Bury and M. Perie, J. Electroanal. Chem., 277 (1990) 93. 23 J.-P. Blaser, 0. Haas, C. Petitjean, C. Barbero, W. Bertl, K. Lou, M. Mathias, P. Baumann, H. Daniel, J. Hartmann, E. Hechtl, P. Ackerbauer, P. Kammel, A. Scrinzi, H. Zmeskal, T. Kozlowski, R. Kipfer, H. Baur, P. Signer and R. Wieler, Chimia, 43 (1989) 262. 24 N.A. Godshall, E.P. Roth, M.J. Kelly, T.R. Guilinger and R.I. Ewing, J. Fusion Energy 9 (1990) 229. 25 G.R. Longhurst, T.J. Dolan and G.L. Henriksen, J. Fusion Energy, 9 (1990) 337. 26 T.R. Jow, E. Plichta, C. Walker, S. Slane and S. Gilman, J. Electrochem. Sot., 137 (1990) 2473. 27 R.D. Armstrong, E.A. Charles, 1. Fells, L. Molyneux and M. Todd, J. Electroanal. Chem., 272 (1989) 293. 28 J.W. Fleming, H.H. Law, J. Sapjeta, P.K. Gallagher and W.F. Marohn, J. Fusion Energy, 9 (1990) 517. 29 J. Divisek, L. Furst and J. Balej, J. Electroanal. Chem., 278 (1990) 99. 30 Report of the Cold Fusion Panel, Report of the Energy Research Advisory Board to the Department of Energy, Washington, DC, November 1989. 31 G. Kreysa, G. Marx and W. Plieth, J. Electroanal. Chem., 266 (1989) 437. 32 M. Keddam, Electrochim. Acta, 34 (1989) 995. 33 M. Fleischmann, S. Pans, M.W. Anderson, L.J. Li and M. Hawkins, J. Electroanal. Chem., 287 (1990) 293. 34 B.F. Bush, J.J. Lagowski, M.H. Miles and G.S. Ostrom, J. Electroanal. Chem. 304 (1991) 271. 35 G. Horanyi, Electrochim. Acta, 34 (1989) 889. 36 E.S. Rittner and A. Meulenberg, J. Fusion Energy 9 (1990) 377. 37 A.F. AbuTaha, J. Fusion Energy, 9 (1990) 345. 38 R.L. Garwin, Nature (London), 338 (1989) 616. 39 R.D. Armstrong, Electrochim. Acta 34 (1989) 1287. 40 P.A. Rock, W.H. Fink, D.A. McQuarrie, D.H. Volman and Y.-F. Hung, J. Electroanal. Chem., 293 (1990) 261. 41 L. Pauling, Nature (London), 339 (1989) 105. 42 R.C. Kainthla, M. Szklarczyk, L. Kaba, G.H. Lin, 0. Veiev, N.J.C. Packham, J.C. Wass and J.Q’M. Bockris, Int. J. Hydrogen Energy, 14 (1989) 771. 43 J. Maddox, Nature (London), 338 (1989) 701. 44 V.J. Cunnane, R.A. Scannell and D.J. Schiffrin, J. Electroanal. Chem., 269 (1989) 163. 45 T.B. Flanagan and F.A. Lewis, Trans. Faraday Sot., 55 (1959) 1400. 46 J.O’M. Bockris, Science, 249 (1990) 463.
.I. Electroanal. Chem., 344 (1993) 167-185 Elsevier Sequoia .?.A., Lausanne
JEC 02334
A calorimetric study of the electrolysis of D,O and H,O at palladium cathodes T.I. Quickenden
and T.A. Green
Department of Chemistry, The University of Western Australia, Nedlands, WA 6009, (Australia) (Received 2 April 1992; in revised form 11 June 1992)
Abstract
A search for excess heat production during the electrolysis of D,O or H,O at palladium cathodes was conducted using a sensitive flow calorimeter. A total of 20 long-term experiments using 10 control cells and 10 test cells was performed and the effects of different electrode pretreatments and electrolysis conditions were examined. In all cases, the thermal output from the cell matched the Joule input energy within the experimental error of f 1.5%. These results provided no evidence for any excess heat production over the aggregated cell operating time of 17762 h.
INTRODUCTION
Recently, Fleischmann et al. [l] have reported the production of anomalous heat during the electrolysis of D,O at palladium cathodes. This “excess” heat exceeded the Joule heating dissipated in the electrochemical cell by the electrolysis current by between 5% and 111%. Moreover, this excess heat was often sustained for such long periods of time that megajoules of excess energy were apparently produced. Fleischmann et al. [l] concluded that this excess heat must be of nuclear origin since it exceeded the amount of energy that could be stored chemically by a factor of 10-100. Since this original announcement, a number of research groups [2-141 have also reported the production of excess heat during the electrolysis of D,O at palladium electrodes. However, a larger number of researchers [15-291 have found no evidence for excess heat production, despite using similar electrolysis conditions and calorimetric techniques of comparable sensitivity and accuracy. Some workers [17-20,30-321 have attributed the excess heat to errors in the calorimetric procedures used by Fleischmann et al. [l], although many of these criticisms have been refuted in a subsequent publication [33]. With one possible exception [34], there have been no reports of the formation of nuclear byproducts at levels commensurate with the amount of excess heat 0022-0728/93/$06.00
0 1993 - Elsevier Sequoia S.A. All rights reserved
observed. This discrepancy has led many [17-19,30,31,35-411 to suspect a nonnuclear origin for the excess heat. The most frequently suggested explanations for the excess heat are recombination of the evolved gases [17-19,30,31,35] or the sudden release of energy stored in the cathode during the initial electrolysis period 136-411. It has been speculated that the latter effect might arise from either an accumulation of strain energy in the cathode [36-381 or the formation of an unstable endothermic compound [40,41]. However, in many cases [l-6,331 the magnitude of the excess heat reported exceeded 1 MJ mol-’ of Pd and it appears difficult [38,42] to attribute such large excess energies to any chemical or mechanical processes. Nevertheless, it seems prudent to design experiments in which these chemical effects can be distinguished from genuine excess heat production. The aim of the present investigation was to search for excess heat production using accurate calorimetry. It was decided to employ a flow type calorimeter in these studies as this design circumvents many of the problems and limitations of the simple isoperibolic calorimeters used by Fleischmann et al. [1,33] and other workers [7,8,10,13,17-20,251. For example, unlike isoperibolic calorimeters, flow calorimeters are insensitive to inhomogenous internal temperature profiles and their thermal calibration is essentially independent of the electrolyte level. Another advantage of flow calorimeters is that the rate of heat loss can be controlled precisely by deliberately altering the flow rate of the cooling water. This allows maintenance of near-isothermal conditions, irrespective of the magnitude of the input power. A further incentive to use a flow calorimeter arose because they have already been used successfully by a number of other groups [6,11,16,20,23,27,29] in similar studies. The experimental protocol adopted in these studies attempted to address a number of the concerns/criticisms directed at previous reports of excess heat production. For example, given widespread criticism [30,32,43] of the lack of control experiments in a number of other studies, the concurrent running of control cells containing light water, alongside test cells containing heavy water, was deemed essential. Furthermore, given the possibility of apparent excess heat generation via a storage and subsequent relaxation process involving mechanical or chemical energy, an energy audit was carried out over the entire duration of the experiment. Such a mechanism would then be indicated by a period when the energy balance was negative (a storage phase) followed by a period in which there appeared to be excess energy (a relaxation phase). Finally, a comparison of the amount of solvent added to the cell with the predicted loss via electrolysis and evaporation was also considered necessary to preclude contributions to the excess heat via recombination of the evolved gases. EXPERIMENTAL
Figure 1 is a schematic diagram of the calorimeter and associated equipment used in this study. The electrolysis cell was constructed of borosilicate glass and had an internal diameter of 5 cm and height of 15 cm. The lower part of the cell
169
Data
Logger
Thermititora
Computer
7
-
Calibration
-
Cathode
1k
Pergpex
heater
container
-
. _.
I%“,.._er
Fig. 1. A schematic diagram of the flow calorimeter and data acquisition system.
was surrounded by a glass jacket 1 cm thick through which cooling water was pumped at a controlled rate. The cell was sealed with a polypropylene stopper 5 cm thick which incorporated feedthroughs for the electrical connections to the anode and cathode, the calibration heater and the thermistor probe. In addition, there was a small port to allow the passage of nitrogen gas into the cell headspace and a vent through which the gases were expelled. In order to minimize heat loss to the surroundings, the entire electrolysis cell assembly was placed in a large glass Dewar flask fitted with an insulating lid 6 cm thick made of polyethylene foam. The Dewar flask was in turn mounted in a poly(methy1 methacrylate) cylinder immersed in a constant temperature bath maintained at 25.00 f 0.02”C. Each water bath contained two such calorimeters, one containing a D,O cell and the other an H,O cell. The room in which the calorimetric experiments were performed was maintained at a temperature of 21 * 1.5”C. Thermostatted cooling water was pumped from the water bath and through the jacket of each electrolysis cell using a microprocessor-controlled peristaltic pump (Masterflex L/S). In all experiments, water flow rates of either 0.40 g s-i or 0.20 g s- ’ were used. The flow was checked periodically and found to be constant to within +0.5%. The thermal output from each cell was determined by measuring the temperature difference AT between two calibrated thermistors placed in the cooling water flow at the entry and exit of the water jacket. Each thermistor
170
comprised the fourth arm of a Wheatstone bridge circuit and in this configuration produced an output voltage of 3.1 mV “C-l. With this arrangement, AT values of less than O.Ol”C were readily detectable. In experiments Al-A4, Bl-B4, Cl-C4 and Dl-D4, the cathodes were constructed from palladium rods (99.96% Pd) 0.40 cm in diameter obtained from Johnson Matthey. The cathodes used in the experimental series E were constructed from palladium wire (99.95% Pd) 0.10 cm in diameter obtained from Goodfellows. For experiments Al-A4, Bl-I34 and Cl-C4, the cathodes were cut into 1.4 cm lengths, while in experiments Dl-D4 and El-E4 the cathode length was 1.2 cm. Electrical connection to each cathode was facilitated by attaching 0.05 cm diameter Pt wire by spot welding. The four cathodes used in experiments Al-A4 were used essentially in the “as-received” condition, apart from a brief solvent rinse in acetone followed by D,O or H,O. The cathodes used in experiments Bl-B4 were similarly rinsed and then transferred to the electrolysis cells where they were precharged with H or D at a low current density of 65 mA cm-* for 7 days. Precharging at a low current density was performed to minimize stress fracturing and plastic deformation of the cathode during the loading stage. After this precharging process was complete, the current density was increased and calorimetric measurements were commenced. The cathodes for experiments Cl-C4 were pretreated by annealing them at 1000°C for 3 h under vacuum ( < 5 X lo-’ Torr) and were then transferred rapidly to the electrolysis cells. Annealing was performed to remove any pre-existing hydrogen trapped in the palladium. The cathodes used in experiments Dl-D4 were initially cold-worked by repeated rolling of a Pd rod 0.4 cm in diameter into a flat plate of dimensions 4.8 cm x 0.3 cm X 0.15 cm. This plate was then cut into four 1.2 cm lengths. Platinum wires were attached to each length and the electrodes were rinsed in acetone followed by D,O or H,O. They were then transferred to the electrolysis cells where they were anodized at 10 rnA cm-* for 5 min prior to commencement of the electrolysis. In experiments El-E4, the cathodes were first palladized in a 3.5 mM PdCI, solution for 3 h at a current density of 8 mA cm-*, Subsequently, they were transferred to the electrolysis cells and precharged for 5 days at a current density of65mAcm*. After this precharging process was complete, the current density was increased and calorimetric measurements were commenced. In all cases, the cathodes were mounted centrally in the electrolysis cells and each was surrounded by a cylindrical Pt mesh anode. Both the anode and cathode leads were shrouded in polytetrafluoroethylene tubing to minimize Pt catalysed recombination of the evolved gases. The cell head-space was continuously purged with a flow of 25 ml min-’ of dry high purity nitrogen to prevent build-up of an explosive mixture of D, (or H,) and 0,. Each cell contained a 2 fl resistor for thermal calibration of the calorimeter and a thermistor for monitoring the electrolyte temperature. The heater and the thermistor were each sealed in separate glass tubes which had been filled with small amounts of silicone oil to increase thermal conduction.
171
Apart from experiments Dl-D4, all electrolysis cells contained 110 ml of H,O or D,O to which sufficient lithium metal (Merck, > 99% Li) was added to make 0.10 M solutions of LiOH or LiOD. The electrolytes in experiments Dl-D4 were obtained by adding L&SO, (BDH, > 99% Li,SO,l to 110 ml of D,O or H,O to make 0.25 M solutions of Li,SO,. D,O was obtained from The Australian Institute of Nuclear Science and Engineering and had a minimum isotopic purity of 99.75%. The isotopic purity of the electrolyte was checked periodically by proton magnetic resonance measurements and was found always to exceed 99.5%, even when cells had been operating for as long as 6 weeks. All electrolysis experiments were performed galvanostatically using dc power supplies (Thurlby PL 320). Current densities from 65 to 1500 mA cmp2 were employed and resulted in Joule heating powers of 0.2-8 W and cell voltages of 3-12 V. Current densities were calculated with respect to the geometric areas of the electrodes. The loss of electrolyte via electrolysis and evaporation necessitated daily additions of 1.5-8 ml of H,O or D,O. Comparison of the total solvent additions during an entire run with the total amount of electrolytic charge passed through the cell indicated that there was little (< 2%) recombination of the evolved gases in the electrolysis cells. Initially, the calorimeter was calibrated by applying varying amounts of power Pi to the in-situ electrical heater and measuring the resulting steady state value of the temperature difference AT between the input and output water flows. In this way the calibration constant k( = Pi/AT) of the calorimeter was determined. It was found that the calibration curve of AT versus input power was linear over the range O-6 W (Fig. 2). The value of k was subsequently checked every 7 days using a power-matching technique. This involved lowering the electrolysis current to ca. 10% of its initial value and adding power via the heater to maintain a temperature close to the operating temperature. Calibration constants in the vicinity of 1.0 W “C-i were obtained at a cooling water flow rate of 0.20 g s-l, while values of around 1.8 W “C-’ were typical when the flow rate was 0.40 g s-‘. Once the calorimeter had been calibrated, the total power output from the electrolysis cell in any experiment could be obtained as the product kAT. In the present work, the primary sources of error were due to uncertainties in the measurement of AT, Pi and the cooling water flow rate. Uncertainties in the measurement of AT were mainly produced by variations in room temperature. Despite extensive insulation of the calorimeter, AT varied by approximately 0.02”C per 1°C change in room temperature. At the lowest measured value of AT, this amounted to an error of ca. +0.5%. The errors in measuring Pi and the cooling water flow rate were both comparable with the uncertainty in AT, leading to a cumulative error of ca. 1.5%. An operational (and probably more realistic) assessment of the experimental error was obtained by observing the variability in a number of control experiments. The observed variations were no larger than the random errors estimated above. A completely rigorous analysis of the thermodynamics of open electrolysis cells should include a correction term for the heat lost by the evaporation of the solvent
172
AT / Fig.
‘C
2. A typical calibration curve for cell Dl using the internal calibration heater.
[17,33,44]. However, under the conditions of the present experiments, this correction would amount to between 2 and 9 mW corresponding to a maximum error of 0.15%. As this was much smaller than the estimated experimental error (ca. 1.5%), this correction was not performed. Nor was any correction made for the small amount of heat removed by the passage of nitrogen gas through the cell headspace 1441.Calculations show that this correction would not exceed ca. 4 mW. Furthermore, the calibration experiments with the electrical heater were carried out using the same nitrogen flow rate and cancelling would thus occur. Any resulting error would therefore be much less than 4 mW and hence negligible. As pointed out previously, there have been frequent criticisms [30,32,43] of the lack of adequate control experiments in calorimetric studies of cold fusion. For this reason, care was taken to ensure that each D,O cell was accompanied, in the same constant temperature water bath, by a control cell of identical construction but containing H,O rather than D,O solvent. The present study involved the use of two such test cell + control cell pairs in two separate water baths and all were contained in the same air-conditioned room. Although all cells were run at identical current densities, the larger cathodic overpotential for the reduction of D,O compared with H,O and the higher resistance of the LiOD electrolyte compared with LiOH resulted in a higher potential difference across the D,O cells. The concurrent running of H,O control experiments and D,O test experiments in pairs enabled any thermal artefacts due to fluctuations in the flow rate of the cooling water, or in the ambient or bath temperatures, to be distinguished from genuine excess heat production.
173
Cell voltages, currents and temperatures were measured every 2 min using a pair of data loggers (Data Electronics, DT 100) interfaced serially to a microcomputer (IBM PS2 30 286). In addition, the temperature of each water bath and the ambient air temperature were also recorded. The cell data were displayed on the computer monitor in real time and written to a file using a commercial software package (Labtech Notebook). Although the electrolysis cells were run continuously for long periods of time, data acquisition runs were performed in 24 h cycles. At the end of each run, a hard copy of the data displayed on the computer monitor was printed. RESULTS
A total of five experimental series (A-E) were completed in this study, with each series consisting of four cells grouped into two control cell + test cell pairs. Each cell in a series had an identical electrode pretreatment, and was operated under the same electrolysis conditions. The heat output from each of these 20 cells was monitored continuously for periods of between 32 and 40 days. The calorimetric data were analysed in three major ways. Firstly, the instantaneous power balance for each 24 h period was calculated. These data were then used to compute the overall energy balance for each 24 h period in the experimental run. Finally, the total energy balance integrated over the entire duration of the experiment was obtained. Instantaneous power balance
Figure 3 shows the power balance for a typical D,O electrolysis cell over a 24 h period. The full line represents the electrical power Pi released into the cell as Joule heating. This was calculated from the equation Pi=Z(E-Ets)
(I)
where Z is the cell current, E is the potential difference across the cell and Et,, is the thermoneutral potential for the electrolysis of D,O or H,O. The thermoneutral potential provides a thermodynamic correction [24] for the portion of input electrical energy used to electrolyse the D,O or H,O and which is thus unavailable to heat the cell. The value of the thermoneutral potential for the electrolysis of H,O at 25°C is 1.481 V [23,24] and the corresponding value for D,O is 1.527 V [23,24]. The full squares plotted in Fig. 3 represent the values of the thermal output power P, calculated every 20 min from the measured value of AT and the calibration constant of the calorimeter using PO= kAT
(2)
In the absence of any excess heat production, the measured Joule input power and
174
.
2 6.5 -
6.0 L 0
I 4
I 6
I 12
Electrolysis
Time
I 16
/
I 20
I 24
h
Fig. 3. The relationship between the Joule input power (1 and the thermal output power ( n J for test cell B4 over a 24 h period. Cell parameters: Pd cathode; Pt anode; 0.10 M LiOD; current density, 375 mA cm-‘. Representative error bars are shown for the estimated uncertainties in the thermal output power. Errors associated with the Joule input power are not shown for reasons of clarity but correspond to +0.03 W.
the observed output power should coincide within experimental
error. It is clear from Fig. 3 that these two quantities do indeed agree within the estimated errors. The small downward trend shown in Fig. 3 for both the input and output powers over the 24 h period is primarily due to the lowering of solution resistance because of an increase in the concentration of the dissolved electrolyte as the solvent is progressively electrolysed. The sudden ca. 6% increase in input power after 23 h occurred when the cell was replenished with D,O, prior to the commencement of a subsequent 24 h cycle. Figure 4 shows similar results to those in Fig. 3, but is for a control cell containing H,O instead of D,O. It is clear that, for the control cell, the output power (full diamonds) and the line representing the input power are once again in close conformity. Although the results in Figs. 3 and 4 are from only a single 24 h period, they are typical of the daily behaviour of all the cells studied during the aggregated operating time of 17762 h. Daily energy balance as a function of time
Figures 5 and 6 show convenient summaries of the long-duration energy balance for a typical control cell -t test cell pair. The results are expressed as the ratio R of
175
6.0
I
I
I
I
I
I 4
I 6
I 12
I 16
I 20
5.5 -
4.5 -
4.0 0
Electrolysis
Time
24
/ h
> and the thermal output power ( 6 1 for Fig. 4. The relationship between the Joule input power (control cell B3 over a 24 h period. Cell parameters: Pd cathode; Pt anode; 0.10 M LiOH; current density, 375 mA cm-‘. Errors are represented as described for Fig. 3.
1.20
0.80 0
I
I
I
I
I
I
10
20
30
Electrolysis
Time
/ Days
Fig. 5. The daily energy balance for test cell B4 as a function of time. The excess heat ratio R is defined by eqn. (3).
176
a= d
1.10
3 $ 4 Cd 1.00 G : a, z w
0.90
0.80 0
10
Electrolysis
20
Time
/
30
Days
Fig. 6. The daily energy balance for control cell B3 as a function of time. The excess heat ratio R is defined by eqn. (3).
the integrated output power to the integrated period. This ratio is given by the equation R = k jt2AT dt/I /“( E - Et,,) dt fl fl
Joule input power for each 24 h
(3)
where t is the time and t, and t, define the beginning and end of a 24 h period and the other terms have already been defined. The presence of excess heat would be seen in Figs. 5 and 6 as a point (or points) which deviated above the R = 1 line by substantially more than the error bar. Although there is some scatter around the R = 1 line in both figures, this is clearly less than the experimental error. Hence the data in these graphs provide no evidence for the existence of excess heat. Similar behaviour was observed in all other experiments, with no experiment showing any sign of excess heat within experimental error. It might be argued that integrating the energy balance over a 24 h period would tend to “hide” any short-lived excess heat event. However, each separate 24 h trace of AT versus time was individually examined for transient temperatures rises, but after elimination of obvious artefacts, none were observed. The total energy hr ‘mce
Any net excess heat production AQ over an entire run is given by the difference between the total output power and the Joule input power integrated over the
Current density/ mA cm-’ 250
250
250
250
Cell
1.4 cmx0.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H,O
1.4cmX0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
1.4 cmx0.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H ,O
1.4cmx0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
Al
A2
A3
A4
864
864
864
864
Duration/h
10.700
9.883
10.741
7.719
Energy input/ MJ
on cells containing untreated Pd cathodes
Experiment
Summary of the results of heat measurements
TABLE 1
10.717
+0.017
+ 0.035
- 0.023
10.718
9.918
+0.048
AQ/MJ
Excess energy/
1.767
Energy output/ MJ
+ 0.2
+ 0.4
-0.2
+ 0.6
Excess heat/%
Cell
1.4cmX0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in Ha0
1.4cmX0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
1.4cmX0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H,O
1.4 cmX0.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
Experiment
Bl
B2
83
B4 250 375 250
250 375 250
250 375 250
250 375 250
Current density/ mA cmm2
168 168 456
168 168 456
168 168 456
168 168 456
Duration/h
12.035
9.094
12.186
8.491
Energy input/ MJ
12.019
9.062
12.114
8.515
Energy output/ MJ
Summary of the results of heat measurements on cells containing electrolytically precharged Pd cathodes
TABLE 2
Excess energy/
- 0.016
- 0.032
- 0.072
+ 0.024
AQ/MJ
-0.1
-0.4
-0.6
+ 0.3
Excess heat/%
384 312 312 384 312 312
250 375 300 250 375 300 250 375 300
1.4 cmX0.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
1.4 cmxO.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H,O
1.4cmx0.4cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O.
c2
c3
c4
384 312 312
384 312 312
250 375 300
1.4 cmx0.4 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H *O
Cl
Duration/h
Cell
Experiment
Current density/ mA cm-’
17.722
14.201
19.880
13.159
Energy input/ MJ
17.767
14.126
19.760
13.085
Energy output/ MJ
Summary of the results of heat measurements on cells containing vacuum annealed Pd cathodes
TABLE 3
+ 0.045
- 0.075
- 0.120
- 0.074
AQ/MJ
Excess energy/
+0.2
-0.5
-0.6
-0.6
Excess heat/%
Cell
0.15 cm thick Pd plate cathode, Pt mesh anode, 0.25 M Li,SO, in Ha0
0.15 cm thick Pd plate cathode, Pt mesh anode, 0.25 M Li,SO, in Da0
0.15 cm thick Pd plate cathode, Pt mesh anode, 0.25 M Li,SO, in H,O
0.15 cm thick Pd plate cathode, Pt mesh anode, 0.25 M Li,SO, in D,O
Experiment
Dl
D2
D3
D4 275 340
275 340
275 340
275 340
Current density/ mA cm-*
312 576
312 576
312 576
312 576
Duration/h
12.560
10.822
13.544
11.364
Energy input/ MJ
Summary of the results of heat measurements on cells containing cold-worked Pd cathodes
TABLE 4
12.539
10.829
13.579
11.382
Energy output/ MJ
Excess energy/
- 0.021
+ 0.007
+ 0.035
+ 0.018
AQ/MJ
-0.2
+0.1
+ 0.3
+0.2
Excess heat/%
Cell
1.2 cmXO.1 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H z0
1.2 cmx0.1 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
1.2 cmXO.1 cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOH in H,O
1.2cmXO.l cm diameter Pd cathode, Pt mesh anode, 0.1 M LiOD in D,O
Experiment
El
E2
E3
E4 1250 1500
1250 1500
1250 1500
1250 1500
432 456
432 456
432 456
432 456
Duration/h
26.005
19.914
25.016
17.573
Energy input/ MJ
on ceils containing palladized Pd cathodes
Current density/ n~4 cm-*
Summary of the results of heat measurements
TABLE 5
26.148
19.968
25.087
17.699
Energy output/ MJ
+0.143
+ 0.054
+ 0.071
+0.126
AQ/MJ
Excess energy/
+ 0.5
+ 0.3
+0.3
+ 0.7
Excess heat/%
182
total duration t, - t, for a 32-40 day calorimetric study:
(4)
AQ = j*‘P,, dt - jt2Pi dt 11 t1
where Pi is the instantaneous Joule input power and PO is the instantaneous output power. Using eqns. (2) and (3) it then follows that AQ = k jr2AT dt - Zj”( E -Et,,) t1 fl
dt
(5)
Tables l-5 summarize the values of AQ obtained for the 20 calorimetric experiments performed in this study. In all cases AQ = 0 within the estimated experimental error of k 1.5%, which shows that the heat energy recovered from the calorimeters matches the Joule input power. Thus, these results provide no significant evidence for any differences between the D,O test cells and the Hz0 control cells. In both cases, there were some cells that produced small energy excesses and some that produced small energy deficits, but none of these deviations exceeded the estimated experimental error. DISCUSSION
The constant-flow calorimeters used in this work were found to be very satisfactory for studying the thermal characteristics of electrolytic processes. The accuracy of the calorimeters was found to be comparable with the accuracies of other calorimeters used in the cold fusion experiments [l-29] and they also possessed excellent long-term stability. In the majority of published experiments reporting excess heat [l-3,6-14], the thermal output power from the cell exceeded the Joule input power by between 5% and 150%, with a mean value of around 15%. Such excess heat levels would have been readily detectable with the present constant-flow calorimeters; however, no excess heat was observed. A few groups [4,5,33] have occasionally reported excess heat at, or around, the 2% level. Such levels would be below the limit of detection of the present calorimeter and could conceivably have been present. However, excess heat at such a low level would be atypical of nearly all the literature reports of excess heat and also would be of little practical significance. The present study also examined the effect of a number of different electrode pretreatments on excess heat production. Because the mechanism of excess heat production is not understood, it is not obvious which pretreatment procedures might be beneficial and which might be detrimental. Nevertheless, it seemed appropriate to use similar pretreatments to those employed by workers who have observed excess heat production. These include vacuum annealing [2,3,5,6,8,1012,141, cold working [4,7,11,12] and electrolytic precharging at low current densities [l-3,8,11,33]. In addition, palladization of the cathode was also tried, as this is known [45] to enhance the rate of uptake of both H and D during electrolytic
183
charging. As pointed out earlier, none of these pretreatments produced excess heat in the present study (Figs. 3-6 and Tables l-5). Some workers [33,46] have suggested that high current densities and/or longduration experiments are necessary before excess heat production is observed. For example, Fleischmann et al. 1331 have recently reported excess heat following weeks of electrolysis and at current densities in excess of 64 mA cmp2. Some other workers [2,6] have also found excess heat production only after a lengthy induction period. However, there are also a number of reports [3,4,7,12] of excess heat production which commenced almost immediately after the start of electrolysis. In order to cover all these possibilities, the present electrolysis experiments were performed with current densities between 65 and 1500 mA cm-*. These values are similar to the current densities employed in the majority of studies. Furthermore, the present experiments were run for periods of up to 40 days and are thus comparable with some of the longest duration experiments reported in the literature [2,6,13]. It should be noted that what is usually described as excess heat or energy is often only a measurement of excess power. This distinction is important because, as previously pointed out, the excess power observed by many groups might simply represent the sudden release of chemical or mechanical energy stored gradually during the initial electrolysis period. To avoid this possible ambiguity, the energy balance for each electrolysis cell was measured over the entire duration of the experiment. The results of these energy audits are presented in Tables l-5 and show that no total excess heat was produced within the experimental error of + 1.5%. Furthermore, a Student t test showed that the mean excess heat from the 10 test cells was not distinguishable from the mean of the 10 controls cells at greater than the 99.9% confidence level. This indicates that there is no significant difference between the thermal behaviour when Pd is electrolysed in D,O or H,O. A number of workers [17-19,30,31,351 have suggested that the excess heat reported may be due to the recombination of D, or H, with 0, in the cell head-space or in the electrolyte. The observation in the present work that the energy input and output agree within ca. 1% suggests that not only was there no excess heat production, but that, in addition, negligible recombination was occurring in the cells. This latter conclusion is also supported by our records of solvent addition which agreed to within 2% of the predicted losses due to electrolysis and evaporation. This latter calculation assumed that the gases exiting the cell were saturated with D,O or H,O vapour. These conclusions on recombination are in agreement with those of a number of other studies [3,8,21,24,33,44] which have also found minimal recombination in cells of similar type. CONCLUSIONS
This study involved the use of precise calorimetry to search for low level excess heat produced during the electrolysis of D,O at palladium cathodes. A variety of electrode pretreatments and electrolysis conditions were used in an attempt to
184
initiate low level excess heat production. However, no excess heat above the estimated &-1.5% accuracy of the calorimeter was observed. The amount of recombination of the evolved gases was also determined and was found to be negligible ( < 2%). ACKNOWLEDGEMENTS
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