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Voltammetric study of the reduction of molecular oxygen on bright platinum in perchloric acid solution
Electrochmnca
Acta,
1964, Vol
9, PP
441 to 450
Pergamon
Press
Ltd
Prmted
m Northern
Ireland
VOLTAMMETRIC STUDY OF THE REDUCTION OF MOLECULAR OXYGEN ON BRIGHT PLATINUM IN PERCHLORIC ACID SOLUTION* M W BREITER General Electric Research Laboratory, Schenectady, New York, U S A Abstract-The cathodic reduction of molecular oxygen was studled on bright platmum under voltammetnc contitlons m 1 N HCIO, Periodic current-potential curves were measured at 30 mV/s, and the ohnuc and capacitive components of the impedance platmum/solutlon were determmed under the same con&tlon at 1000 c/s m the potential range between hydrogen and oxygen evolution It follows from the mpedance measurements m the presence and absence of Oa reduction (oxygen or hehum saturation of the electrolyte) that the oxygen coverage or the hydrogen coverage at a given potential are the same m the presence and absence of O2 reduction This eliminates reduction mechanisms m which the formation of adsorbed oxygen atoms as mtermedlates or the participation of adsorbed hydrogen atoms are postulated A mechanism compatible with the experimental results 1s discussed Oxygen coverage mhlblts 0, reduction Adsorption of chlonde Ions has a slmllar effect R&urn&On ttudle sur Pt poh, sous des conditions voltam&rlques en HC104 N, la reduction cathodlque de l’oxyg&ne gazeux Des courbes perlodlques courant-tension sont etabhes a 30 mV/s et les composantes ohmlques et capacitive de l’lmpbdance Pt/solutlon a 1000 c/s dans l’mtervalle de tensions comprls entre les evolutions d’hydrogene et d’oxygene, sont mesurks sous les msmes condltlons De ces dern&es mesures, 11apparait que les recouvrements d’oxygene et d’hydrogene, & tension don&e, sont les m&mes en pr&.ence ou en absence de reduction de 0, (&ectrolyte sature d’hehum) Les mecamsmes posslbles sont amsl mleux canton&, on en propose un type qul paralt compatible avec les rCsultats obtenus Le recouvrement d’oxygkne mhlbe la reduction de 0, et l’adsorptlon de Cl- a un effet analogue Zusammenfassung-Man untersuchte die kathodlsche Reduktlon von molekularem Sauerstoff an blanken Platmelektroden m 1 N HC104 unter voltametrlschen Bedmgungen Perlodlsche StromSpannungskurven wurden mlt 30 mV/s aufgenommen, und die ohm’schen und kapazltlven Komponeten der Impedanz Platm/Losung wurden unter glelchen Bedmgungen bei 1000 Hz lm Potentlalbereich zwlschen Wasserstoff- und Sauerstoffentwlcklung bestlmmt Aus den Impedanzmessungen be1 Anwesenhelt bzw Abwesenhelt der Sauerstoffreduktlon (Sauerstoff- bzw Helium-Sattlgung der Losung) geht hervor, dass die Bedeckung durch Sauerstoff bzw durch Masserstoff bei emem gegebenen Potential m belden Fallen glelch blelbt Dlese Tatsache schhesst Reduktlonsmechamsmen aus, be1 Welchen die Bddung von adsorblerten Sauerstoffatomen als Zwlschenprodukt, bzw die Tellnahme adsorblerter Wasserstoffatome postuhert wu-d Man dlskutlert emen Reduktlonsmechamsmus, der mlt den gefundenen Gegebenhelten verembar 1st Die Sauerstoffbedeckung der Elektrode mhlblert die O,-Reduktlon, die Adsorption von Cl-Ionen hat den glelchen Effekt INTRODUCTION
m the mechanism of the cathodic reduction of molecular oxygen on mert electrodes has been mtenslfied by the practical use of this process m fuel cells. A large number of papers deal with the kmetlcs of platmum l-l’ Three different types of mechamsms have been postulated. I Adsorbed oxygen atoms are formed as mtermedlates by dlssoclatlve adsorptlon II O2 molecules are not spht mto adsorbed oxygen atoms durmg the reduction III The reduction mvolves adsorbed hydrogen atoms Dlscusslons of some paths of mechanisms I and II have been glven8J2 on the assumption that the fraction of the surface that IS free of oxygen atoms or other mtermedlates 1s practically Independent of potential However, It follows from the results m this paper as well as from other data m the literature that the above assumption does not hold for a large part of the potential range m which oxygen 1s reduced on platinum * Manuscript received 4 July 1963 INTEREST
441
442
M W BREITER
It appeared feasible to the author that a drstmctlon between mechamsms I and IT 1s possible on the basis of a comparative study of the surface coverage with oxygen atoms m the presence and absence of OS reduction (solution saturated with molecular oxygen or helium) In general, the coverage should be different m the two cases if mechanism I apphes It need not be different for mechamsm II This point ~111 be elaborated m more detail m the Discussion Mechamsm III 1s not likely since the hydrogen coverage 1s very small m the potential range of 0, reduction (U > 0 4 V). Krad’shlkovls argues that hydrogen adsorptlon may exist for U > 0 4 V if molecular oxygen is present m the electrolyte. The results of this paper do not substantiate Krawl’shlkov’s assumption Voltammetrlc measurements were chosen here because of the satisfactory reproduclblhty of the results Perlodlc current-potential curves were taken at 30 mV/s m 1 N HClO, saturated with punfied helium or oxygen The ohmic and capacitive component of the impedance electrode/solution were determmed as a function of potential at 1000 c/s under the same condltlons as the I/U curves InformatIon on the adsorption of oxygen or hydrogen atoms was obtained and compared m the same potential range m the presence and m the absence of OS reduction The mhlbltmg effect of the oxygen coverage on the 0, reduction and a similar effect of adsorbed chloride ions are discussed EXPERIMENTAL
The experiments were carried out m a Pyrex vessel of conventlonal design, thermostatted at 30°C The electrode potential was measured against a hydrogen electrode m the same solution as the test electrode Fresh solution was used whenever a change from 0, stirring to He stirring was necessary The clrcmt for the impedance measurements has been described m a previous commumcatlon lg The current density and the ohmic (RJ or capacitive (l/coC,) component of the Impedance m a series clrcult were recorded as a function of potential when the curves became time-independent after some minutes of cycling RESULTS
Curves (a), (b), (c) and (a’), (b’) and (c’) of Fig. 1 were obtained m unstirred solution The electrolyte was saturated with hehum for curves (a), (b) and (c) and with oxygen for curves (a’), (b’) and (c’) (pHe = po, M 1 atm) Curves a and a’ represent penodlc I/U curves The ~/WC, us U curve m the presence of helium, (b), comcldes with the one m the presence of oxygen, (b’), m unstirred solution. The same statement holds for the R,/U curves (c) and (c’) The anodlc potential sweep 1s shown by a solid line, the cathodic sweep by a dashed line The curves are reproductions of the orlgmal traces which were photographed on the screen of the oscdloscope The I/U curve of Fig 2 was obtamed m a solution stirred with oxygen. The width of the current fluctuations due to the gas stirring 1s marked The current density 1s an average one between 0 2 V and 0 8 V m Fig 2 The correspondmg I/U curve for hehum stirring looks like curve (a) m Fig 1 and 1s not given. Again the two I/C&~ US U curves or the two R,IU curves are the same for 0, stirring and He stlrrmg. They are very similar to the curves (b) and (c) of Fig. 1, but not as smooth This 1s due to the somewhat irregular stlrrmg by gas bubbles The correspondmg ~/WC, USU curves and R,IU curves are not reproduced here
Reduction of Op on bright Pt m HCIOl solution
443
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(b)
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RJU curves (c), (c’) at 30 mV/s m unskrred 1 N HCIOl saturated with hehum (a, b, c) or oxygen (a’, b’, c’) anodlc sweep - - - - - - cathodic sweep
FIG 1 Peno&c Z/U curves (a), (a’), 1/WC. us U curves (b), (b’) and
+os-
04
aa.
VU
._
IZ
._
16
1
u,v
FIG 2 Penodlc Z/U curve with Oa stn-rmg m 1 N HClO, at 30 mV/s. anodlc sweep - - - - - - cathodic sweep
M W BREITER
444
The followmg experiments were carried out to study the mhlbltmg role of the oxygen layer on the 0, reduction under reproducible condltlons m unstirred solution A periodic potential sweep was applied at 30 mV/s between about 0 6 V and about 1 5 V The I/U curve (a) m Fig. 3 was measured m the presence of helmm, curve (c) The l/oC, US U curve (b) 1s the same m the presence of m the presence of oxygen (0)
FIG 3 Penodlc I/U curves (a) (helium) and (c) (oxygen) and l/oC. (hehum or oxygen) at 30 mV/s m unstirred 1 N HClO, anodlc sweep ______ catbodlc sweep Respective curves (d), (e), (f), after potential shift - - - - - - I sweep, cathodic 2 sweep, anodlc - - - - - 3 sweep, cathodic
us U curve (b)
He or 0, In curve (d) (helium) the potential was rapidly decreased by a rectangular voltage pulse of 0 5 V when the potential of reversal was reached at the end of the anodlc sweep The subsequent three sweeps (cathodic, anodlc, cathodic) were photographed Then the sweep was applied again between 0 6 V and 1 5 V for several cycles
Reduction of 0, on bright Pt m HCIO, solution
445
before the I/WC, USU curve (e) was taken as described The lj~X,jU curve (e) 1s the same m the presence of helium or oxygen Curve (f) was determmed m the presence of oxygen m the same way as for helium
+I80
00
I
1
w
I.2
I6 1
U.V
0
L-J---08
0
FIG 4 Perlo&c I/U cnrves (a), (d), (helmm) and (c), (f) (oxygen) and l/oC. LS U curves (b), (e), (oxygen or hehnm) at 30 mV/s in unstirred 1 N HCIOl + 1O-4 N HCI (a, b, c) or m sunstlrred 1 N HCIOl + 103N HCl (d, e, f) anodlc sweep - - - - - - cathodic sweep Curves (a), (b), (c) m Fig 4 were obtamed in unstirred 1 N HCIO, + 10-d N HCl, curves (d), (e) and (f) m 1 N HCIO, + 10F3N HCl The solutions were saturated with hehum for curves (a) and (d), with oxygen for curves (c) and (f) There IS no difference m the l/oC, US U curves for helium or oxygen saturation of the solution DISCUSSION
Dlstmctron between mechamsms I, II and III Curves (a), (b), (c) of Fig 1, referrmg to 1 N HCIO, saturated with helium, have been dlscussed1s-21 m recent papers A short repetltlon of certam conclusions IS desirable here The reaction H+ + e- = Had (1)
446
M W BREITER
occurs practically reversibly between about 0.38 V and 0 1 V (curve (a) of Fig. 1). Thrs leads to large values of the capacitance and small values of the ohmic component of the faradalc impedance assoclated22 with reactron (1) (curves b and c) l/oC, decreases with potential between 0 4 V and about 0.84 V m the so-called double layer regron (compare curve (a)) durmg the anodrc sweep. Thus decrease was attnbutedlg to a change of the structure of the Helmholtz double layer, caused by the begmnmg formation of the oxygen layer The mcrease of ~/WC,wrth U for U > 0 84 V 1srelated to the decrease of the double layer capacitance wrth mcreasmg oxygen coverage (curve (a)) ~/UC, changes httle with U between 1 5 V and 0 9 V during the cathodic sweep when the oxygen layer remains nearly unchanged (curve (a)) Then the I/&, US Ucurve exhrbrts a broad mmlmum closely to the potentral where the cathodic current peak of curve (a) IS located The R,/U curve shows clearly the separation between hydrogen and double layer region. It was suggested 21 that the oxygen layer is formed or reduced m acid solutions accordmg to the reactions Pt + H,O = Pt-0
+ 2H+ + 2e-.
(2)
Reaction (2) is anodtc for U 2 0 8 V durmg the anodrc sweep. During the cathodic sweep the reduction of the oxygen layer starts at about 1 0 V Reaction (2) can be cathodic between 1 0 V and 0.8 V because its thermodynamic eqmhbrmm potential is shifted towards more posrtrve values with increasing oxygen coverage. The oxygen coverage at a constant potential between 0 8 V and 1 5 V after some trme has values whrch are not much larger than those durmg an anodic low-speed sweep at the same potentral It may be pointed out that reaction (2) is the sum of the first two steps of several paths of oxygen evolution discussed by BockriG and Rlddrford l2 Curve (a’) of Fig 1 m the presence of 0, shows the hydrogen and oxygen regron as does curve (a) However, the currents for the formatron or reduction of the respective layers are superimposed upon the cathodic current of 0, reduction The 0, reduction leads partly to H202 and partly to H,O by the sequence of reaction&‘J’ 0, + 2H+ + 2e- = H,O, , H,O, + 2Hf + 2e- = H,O.
(3) (4)
Water 1s formedsp7p17mainly between 0.1 V and about 0 6 V m the region of the hmrtmg O,-drffusron current when the potential 1s sufficiently cathodic to the thermodynamic eqmhbrmm potential of reactron (4). The separation of the net current density IO,of 0, reduction mto partial current densities I3 and Z4of reactions (3) and (4) 1s not known between 0 6 V and 0 9 V under voltammetrrc condmons. The superposrtlon of the currents m the hydrogen region obscures shghtly the appearance of the hmltmg drffuslon current of 0, m Fig 1 Durmg the anodrc sweep, the cathodic net current decreases with mcreasmg potential between 0 8 V and 0 9 V and becomes posrtlve for U > 0 9 V The anodrc current density m curve (a’) IS practrcally equal to that m curve (a) between 1-OV and 1 5 V and shows the potentral dependence charactenstlc for reaction (2) The current IS very small between 1 5 V and 1.0 V during the cathodic sweep Reactions (3) and (4) are strongly mhrbrted by the oxygen coverage, as also found by Vlelstrch l6 This result ehmmates O,-reduction mechamsms m whrch the partrcrpatlon of the oxygen layer is postulated, as for instance
Reduction of 0, on bnght Pt in HClO, solution
447
111the electrochemtcal metal peroxide path * The cathodic current peak of curve (a’) has the same locatron as the one of curve (a) The small cathodic current of curve (a’) 1s nearly equal to the one of curve (a) between 10 V and 0 8 V This means that reactrons (3) and (4) contribute to the cathodic current only for U < 0 8 V when sites free of adsorbed oxygen are present (see curve (a)). After the peak the current decreases with decreasing potential and tends towards its hmrtmg value between 0 6 V and 0 4 V The current peak of curve (a’) 1s probably due to a depletron of molecular oxygen close to the surface during the rapid production of sites free of oxygen atoms between 0 9 V and 0 75 V during the cathodic sweep The peak herght depends upon the rate of formation of free sites The disappearance of the peak m stirred solutions (see Fig 2) where the thickness of the diffusion layer remains constant substantiates the above interpretation Comparison of curves (b) and (b’) and of (c) and (c’) shows that they are the same This is true also for stirred solutions, and suggests that both the oxygen coverage and the hydrogen coverage at a given potential are determmed solely by processes that occur m the absence of 0, reduction 0, reduction does not seem to influence reactions (1) or (2). An equrvalent conclusion was drawn by Vrelstrchls from faster potential sweeps (sweep rate about 1 V/s) that make the currents of layer formation or reduction appear more pronounced relatively to the current of It may be pointed out that Vrelstrch’s conclusion cannot be transO,-reduction. ferred without additional assumptions to slow-speed sweeps Since hydrogen adsorptton 1s not favourably influenced by the presence of molecular oxygen m the electrolyte and does not extend beyond 0 4 V, mechanism III can be ruled out_ In the potential region of oxygen adsorptton the followmg equation holds during the sweeps m solutions saturated with an inert gas.
Here 8 designates the oxygen coverage, Fl7, 1s the number of C/cm2 for monolayer formatron, la is the partial current density of reaction (2) and depends upon the oxygen coverage 8 and U, t is the time If reactions (3) and (4) occur m the presence of molecular oxygen m addition to reaction (2), the assumption of a drssocratlve adsorptton of oxygen molecules leads to the equation
FL g = 12V3, u) + z’(e, u,PO,) Here I’ designates the net rate m A/cm2 by which the oxygen coverage IS influenced under the above assumption by reactions (3) and (4) I’ will differ for different ratedetermining steps of the O,-reduction mechanism In general I’ will be a function of 0, U and po, It is drfficult to conceive kmettc equations which lead to the same oxygen coverage at a given potential under conditions (5) or (6) Therefore rt is concluded on the basis of the Impedance measurements that a drssoclatrve adsorptton of oxygen is not mvolved m the O,-reduction mechamsm. The latter conclusion is also made very probable by its direct proofs3 for carbon electrodes with the aid of isotopic measurements The followmg mechanism of O,-reduction, suggestedM m a less explicit form earlier, is compatible with the experimental results with the additional postulate
M W BREITER
448
that the coverage with mtermedlates (Ozad,0,H etc) IS much smaller than the coverage with oxygen atoms Pt + 0, = Pt-0, (7) Pt-0,
+ 2H+ + 2e- = Pt-O,H, Pt-O,H,
Pt-O,H,
= Pt + H,O,
+ 2H+ + 2e- = Pt + 2H,O.
(8) (9) (10)
Reactions (6), (7) and (9) may occur m several steps which are not yet known Part of the hydrogen peroxlde produced may be desorbed (9) while the remainder IS reduced to water (10) The oxygen coverage IS only determined by eq (5) if the above mechanism apphes with the addltlonal postulate The absence of addltlonal small humps m the l/oC, U#U curves m the presence of O,-reduction demonstrates that the surface coverage with intermediates IS much smaller than the coverage with oxygen atoms at a given potential. A slmllar mechanism has been postulated for platinum by other authors.7J5a25 Inhcbltmng effect of the oxygen
layer
The mhlbltmg effect of the oxygen layer on the O,-reduction has already been described shortly m the preceding sectlon Figure 2 shows clearly that the rate of O,reduction 1s larger at the same potential for U > 0 7 V durmg the anodlc than durmg the cathodic sweep. The same statement holds for U > 0 8 V m unstirred solution (curve (a’) m Fig 1) if allowance IS made for the superimposed cathodic current of reactlon (2) between 1 0 V and 0 8 V durmg the cathodic sweep The hysteresis described IS attributed to the mhlbltmg effect of the oxygen layer Curves (d), (e) and Since the l/oC, z)s U curves (f) of Fig 3 present direct evidence for this mterpretatlon are the same m the presence and absence of O2 reduction (one curve (e) IS only shown), curve (d) gives direct mformatlon about the oxygen coverage at any potential of curve (f) 0, reduction starts at more anodlc potentials during the first cathodic sweep than during the subsequent cathodic sweep because more sites free of oxygen atoms are available The hysteresis between the anodlc sweep and the subsequent cathodic sweep becomes small m the steep portion of the I/U curves between-90 ,uAlcm2 and-270-~A~cm2. The srmdanty of the current decrease with Increasing potential above 0 8 V during the anodlc sweep 1s great between the cathodic 0, reduction and the anodlc H, oxldatlon 26 The current fluctuations due to n-regular stlrrmg disappear at about 0 8 V where a small amount of oxygen atoms IS present on the surface The current density IO, was computed by forming I-I, with the aid of curves (a) and (a’) of Fig 1 and IS plotted USU m Fig 5 for the anodlc sweep The large decrease of current with potential occurs between 0 8 V and 0 9 V where about 10 per cent of an oxygen monolayer IS formed The results described suggest that the current decrease between 0 8 V and 0 9 V during the anodlc sweep 1s due to mhlbltlon by the oxygen layer There IS no contradlctlon Involved m this conclusion smce the adsorbed oxygen atoms do not participate as mtermedlates m the 0, reduction Infrunce
of chlorrde eons
A voltammetrlc
mvestlgatlon
of the adsorptlon
of chloride Ions on smooth
Reduction of 0% on bright Pt m HCIO, solution
449
platinum m perchlorlc acid solutions has been made2’ recently It was found that the presence of Cl- Ions leads to a change of the shape of the Z/U curves m the hydrogen region and the oxygen region (see curves (a) and (d) m Fig 4) Adsorptlon of chloride ions IS demonstrated by the decrease of the double layer capacitance in the double layer region and the region of oxygen adsorption (compare curves (b) and (e) in Fig 4 with curve (b) m Fig 1) Nearly a monolayer of adsorbed Cl- 1s present m the double layer region during the anodlc sweep for ,,ccl_ >‘ 10e2 M The Z/U curves (c) and (f) m Fig 4 have a shape slmllar to curve (a’) m Fig 1. However, the current decreases with increasing potential already between 0 6 V and UV
FIG 5 Current density of Oa reduction durmg the anodlc sweep at 30 mV/s m unstirred 1 N HClOp
0 8 V during the anodlc sweep Then the current becomes posltlve This means a shift of the current decrease by about 0 2 V to less positive potentials m the presence of chloride ions Slmllarly, the increase of the current with potential during the cathodic sweep and the current peak are located at less posltlve potentials m Fig 4 than m Fig 1. The height of the current peaks of curves (c) and (f) of Fig 4 IS smaller than that of curve (a’) m Fig 1 Agam the I/WC, USU curves do not differ m the presence of hehum or oxygen Only one l/c&, z1.sU curve 1s shown for each solution Tt can be concluded from curves (a) and (d) m Fig 4 that the oxygen coverage 1s small between 0 6 V and 0 8 V during the anodlc sweep The l/r& USU curves (b) and (e) demonstrate adsorption of chloride ions m the said range Thus the absorption of Cl- exerts a strong mhlbltlon on the O2 reduction, probably by the blocking of active sites and by the q-effect. 28 The results are similar to results obtained for the reduction wave of oxygen to hydrogen peroxide on mercury 28 There the half-wave potential IS shifted towards a more positive potential m acid solutions contammg chloride Ions. The 0, reduction occurs at a higher rate at any potential durmg the cathodic than during the anodlc sweep The I/UC, USU curves demonstrate that part of the
M
450
W
BREITER
adsorbed Cl- is desorbed durmg the anodlc sweep between about 0 9 V and 1.5 V and that readsorption starts durmg the cathodic sweep at about 0 8 V Therefore less ClIS adsorbed between 0 8 V and 0 7 V durmg the cathodic than dunng the anodlc sweep. This explains the observed hysteresis of the I/U curves m the presence of ClAcknowledgement-The
author IS grateful for the helpful comments
of Dr
F
G
Wdl, General
Electnc Research Laboratory REFERENCES 1 T P HOAR, Proc Roy Sot A142,628 (1933) 2 W A ROITERand R B JAMPOJXAJA,Acta Phys-Chrm URSS 7,247 (1937) 3 P DELAHAY,J Electrochem Sot 97, 198 (1950) 4 A I KR.UIL’SHIKOV and W A ANDREEVA,Zh AZ Khmm 27,389 (1953) Zh AZ Khzm 28,1286 (1954) 5 T N BELINAand A I KRASIL’SHIKOV, 6 J O’M BOCKRI~and A K M SHAMSHUL HUQ, Proc Roy Sot A237,277 (1956) Z Elektrochem 60, 731 (1956) 7 D WINKELMANN, 8 J O’M Bocm, J Chem Phys 24,817 (1956) Z phys Chem (N F ) 15,409 (1958) 9 W VIELSTICH, 10 T P HOAR, Proc 8th Meetmg CZTCE 1956, p 439 Butterworths, London (1958) 11 J GINER,2 Efektrochem 63,386 (1959) 12 A C RIDDIFORD, Electrochzm Actu 4, 170 (1961) J Electroanalyt Chem 2, 310 (1961) 13 D T SAWYERand L V INTERRANTE, J P HOARE,J EIectrochem Sot 110,858 (1962) and V I VESSEUIVSKY, Dokl Akad Nauk SSSR 148, 152 :: Yu A MASITOV,K I ROSENTHAL (1963) 16 W VIELSTICH, Z InstrumKde, 71,29 (1963) 17 L N NEKRASXIVand L MULLER,Dokl Akad Nauk SSSR 149, 1107 (1963) 18 A I KRAUL’SHIKOV, Proceedmgs of the 4th Conference on Electrochemrstry, Moscow 1956, p 272 Academy of Sciences, Moscow (1959) 19 M W BREITER, J Electroanalyt Chem, m press 20 F G WILL and C A KNORR,Z Elektrochem 64,258 (1960) 21 W BOLDand M BREITER, Electrochzm Acta 5, 145 (1961) 22 P DOLIN and B ERSHLER, Acta Phys-Chrm URSS 13,747 (1940) 23 M 0 DAVIES, M CLARK, E YEAGERand F HOVORKA,J Electrochem Sot 106, 56 (1959). 24 W G BERL,Trans Electrochem Sot 83,253 (1943) 25 S SCHULDINER and R M ROE, Extended Abstracts of Theoretrcal D~rsron of Electrochem Sot Vol 1, No 1, Abstract 149 (1963) 26 M W BREITER, Efectrochrm Acta 7, 601 (1962) 27 M W BREITER, Electrochzm Acta 8,925 (1963) 28 V S BAGOTSKNand I E YABLOKOVA, Zh Fu Chum 27, 1663 (1953)
Acta,
1964, Vol
9, PP
441 to 450
Pergamon
Press
Ltd
Prmted
m Northern
Ireland
VOLTAMMETRIC STUDY OF THE REDUCTION OF MOLECULAR OXYGEN ON BRIGHT PLATINUM IN PERCHLORIC ACID SOLUTION* M W BREITER General Electric Research Laboratory, Schenectady, New York, U S A Abstract-The cathodic reduction of molecular oxygen was studled on bright platmum under voltammetnc contitlons m 1 N HCIO, Periodic current-potential curves were measured at 30 mV/s, and the ohnuc and capacitive components of the impedance platmum/solutlon were determmed under the same con&tlon at 1000 c/s m the potential range between hydrogen and oxygen evolution It follows from the mpedance measurements m the presence and absence of Oa reduction (oxygen or hehum saturation of the electrolyte) that the oxygen coverage or the hydrogen coverage at a given potential are the same m the presence and absence of O2 reduction This eliminates reduction mechanisms m which the formation of adsorbed oxygen atoms as mtermedlates or the participation of adsorbed hydrogen atoms are postulated A mechanism compatible with the experimental results 1s discussed Oxygen coverage mhlblts 0, reduction Adsorption of chlonde Ions has a slmllar effect R&urn&On ttudle sur Pt poh, sous des conditions voltam&rlques en HC104 N, la reduction cathodlque de l’oxyg&ne gazeux Des courbes perlodlques courant-tension sont etabhes a 30 mV/s et les composantes ohmlques et capacitive de l’lmpbdance Pt/solutlon a 1000 c/s dans l’mtervalle de tensions comprls entre les evolutions d’hydrogene et d’oxygene, sont mesurks sous les msmes condltlons De ces dern&es mesures, 11apparait que les recouvrements d’oxygene et d’hydrogene, & tension don&e, sont les m&mes en pr&.ence ou en absence de reduction de 0, (&ectrolyte sature d’hehum) Les mecamsmes posslbles sont amsl mleux canton&, on en propose un type qul paralt compatible avec les rCsultats obtenus Le recouvrement d’oxygkne mhlbe la reduction de 0, et l’adsorptlon de Cl- a un effet analogue Zusammenfassung-Man untersuchte die kathodlsche Reduktlon von molekularem Sauerstoff an blanken Platmelektroden m 1 N HC104 unter voltametrlschen Bedmgungen Perlodlsche StromSpannungskurven wurden mlt 30 mV/s aufgenommen, und die ohm’schen und kapazltlven Komponeten der Impedanz Platm/Losung wurden unter glelchen Bedmgungen bei 1000 Hz lm Potentlalbereich zwlschen Wasserstoff- und Sauerstoffentwlcklung bestlmmt Aus den Impedanzmessungen be1 Anwesenhelt bzw Abwesenhelt der Sauerstoffreduktlon (Sauerstoff- bzw Helium-Sattlgung der Losung) geht hervor, dass die Bedeckung durch Sauerstoff bzw durch Masserstoff bei emem gegebenen Potential m belden Fallen glelch blelbt Dlese Tatsache schhesst Reduktlonsmechamsmen aus, be1 Welchen die Bddung von adsorblerten Sauerstoffatomen als Zwlschenprodukt, bzw die Tellnahme adsorblerter Wasserstoffatome postuhert wu-d Man dlskutlert emen Reduktlonsmechamsmus, der mlt den gefundenen Gegebenhelten verembar 1st Die Sauerstoffbedeckung der Elektrode mhlblert die O,-Reduktlon, die Adsorption von Cl-Ionen hat den glelchen Effekt INTRODUCTION
m the mechanism of the cathodic reduction of molecular oxygen on mert electrodes has been mtenslfied by the practical use of this process m fuel cells. A large number of papers deal with the kmetlcs of platmum l-l’ Three different types of mechamsms have been postulated. I Adsorbed oxygen atoms are formed as mtermedlates by dlssoclatlve adsorptlon II O2 molecules are not spht mto adsorbed oxygen atoms durmg the reduction III The reduction mvolves adsorbed hydrogen atoms Dlscusslons of some paths of mechanisms I and II have been glven8J2 on the assumption that the fraction of the surface that IS free of oxygen atoms or other mtermedlates 1s practically Independent of potential However, It follows from the results m this paper as well as from other data m the literature that the above assumption does not hold for a large part of the potential range m which oxygen 1s reduced on platinum * Manuscript received 4 July 1963 INTEREST
441
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M W BREITER
It appeared feasible to the author that a drstmctlon between mechamsms I and IT 1s possible on the basis of a comparative study of the surface coverage with oxygen atoms m the presence and absence of OS reduction (solution saturated with molecular oxygen or helium) In general, the coverage should be different m the two cases if mechanism I apphes It need not be different for mechamsm II This point ~111 be elaborated m more detail m the Discussion Mechamsm III 1s not likely since the hydrogen coverage 1s very small m the potential range of 0, reduction (U > 0 4 V). Krad’shlkovls argues that hydrogen adsorptlon may exist for U > 0 4 V if molecular oxygen is present m the electrolyte. The results of this paper do not substantiate Krawl’shlkov’s assumption Voltammetrlc measurements were chosen here because of the satisfactory reproduclblhty of the results Perlodlc current-potential curves were taken at 30 mV/s m 1 N HClO, saturated with punfied helium or oxygen The ohmic and capacitive component of the impedance electrode/solution were determmed as a function of potential at 1000 c/s under the same condltlons as the I/U curves InformatIon on the adsorption of oxygen or hydrogen atoms was obtained and compared m the same potential range m the presence and m the absence of OS reduction The mhlbltmg effect of the oxygen coverage on the 0, reduction and a similar effect of adsorbed chloride ions are discussed EXPERIMENTAL
The experiments were carried out m a Pyrex vessel of conventlonal design, thermostatted at 30°C The electrode potential was measured against a hydrogen electrode m the same solution as the test electrode Fresh solution was used whenever a change from 0, stirring to He stirring was necessary The clrcmt for the impedance measurements has been described m a previous commumcatlon lg The current density and the ohmic (RJ or capacitive (l/coC,) component of the Impedance m a series clrcult were recorded as a function of potential when the curves became time-independent after some minutes of cycling RESULTS
Curves (a), (b), (c) and (a’), (b’) and (c’) of Fig. 1 were obtained m unstirred solution The electrolyte was saturated with hehum for curves (a), (b) and (c) and with oxygen for curves (a’), (b’) and (c’) (pHe = po, M 1 atm) Curves a and a’ represent penodlc I/U curves The ~/WC, us U curve m the presence of helium, (b), comcldes with the one m the presence of oxygen, (b’), m unstirred solution. The same statement holds for the R,/U curves (c) and (c’) The anodlc potential sweep 1s shown by a solid line, the cathodic sweep by a dashed line The curves are reproductions of the orlgmal traces which were photographed on the screen of the oscdloscope The I/U curve of Fig 2 was obtamed m a solution stirred with oxygen. The width of the current fluctuations due to the gas stirring 1s marked The current density 1s an average one between 0 2 V and 0 8 V m Fig 2 The correspondmg I/U curve for hehum stirring looks like curve (a) m Fig 1 and 1s not given. Again the two I/C&~ US U curves or the two R,IU curves are the same for 0, stirring and He stlrrmg. They are very similar to the curves (b) and (c) of Fig. 1, but not as smooth This 1s due to the somewhat irregular stlrrmg by gas bubbles The correspondmg ~/WC, USU curves and R,IU curves are not reproduced here
Reduction of Op on bright Pt m HCIOl solution
443
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RJU curves (c), (c’) at 30 mV/s m unskrred 1 N HCIOl saturated with hehum (a, b, c) or oxygen (a’, b’, c’) anodlc sweep - - - - - - cathodic sweep
FIG 1 Peno&c Z/U curves (a), (a’), 1/WC. us U curves (b), (b’) and
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M W BREITER
444
The followmg experiments were carried out to study the mhlbltmg role of the oxygen layer on the 0, reduction under reproducible condltlons m unstirred solution A periodic potential sweep was applied at 30 mV/s between about 0 6 V and about 1 5 V The I/U curve (a) m Fig. 3 was measured m the presence of helmm, curve (c) The l/oC, US U curve (b) 1s the same m the presence of m the presence of oxygen (0)
FIG 3 Penodlc I/U curves (a) (helium) and (c) (oxygen) and l/oC. (hehum or oxygen) at 30 mV/s m unstirred 1 N HClO, anodlc sweep ______ catbodlc sweep Respective curves (d), (e), (f), after potential shift - - - - - - I sweep, cathodic 2 sweep, anodlc - - - - - 3 sweep, cathodic
us U curve (b)
He or 0, In curve (d) (helium) the potential was rapidly decreased by a rectangular voltage pulse of 0 5 V when the potential of reversal was reached at the end of the anodlc sweep The subsequent three sweeps (cathodic, anodlc, cathodic) were photographed Then the sweep was applied again between 0 6 V and 1 5 V for several cycles
Reduction of 0, on bright Pt m HCIO, solution
445
before the I/WC, USU curve (e) was taken as described The lj~X,jU curve (e) 1s the same m the presence of helium or oxygen Curve (f) was determmed m the presence of oxygen m the same way as for helium
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FIG 4 Perlo&c I/U cnrves (a), (d), (helmm) and (c), (f) (oxygen) and l/oC. LS U curves (b), (e), (oxygen or hehnm) at 30 mV/s in unstirred 1 N HCIOl + 1O-4 N HCI (a, b, c) or m sunstlrred 1 N HCIOl + 103N HCl (d, e, f) anodlc sweep - - - - - - cathodic sweep Curves (a), (b), (c) m Fig 4 were obtamed in unstirred 1 N HCIO, + 10-d N HCl, curves (d), (e) and (f) m 1 N HCIO, + 10F3N HCl The solutions were saturated with hehum for curves (a) and (d), with oxygen for curves (c) and (f) There IS no difference m the l/oC, US U curves for helium or oxygen saturation of the solution DISCUSSION
Dlstmctron between mechamsms I, II and III Curves (a), (b), (c) of Fig 1, referrmg to 1 N HCIO, saturated with helium, have been dlscussed1s-21 m recent papers A short repetltlon of certam conclusions IS desirable here The reaction H+ + e- = Had (1)
446
M W BREITER
occurs practically reversibly between about 0.38 V and 0 1 V (curve (a) of Fig. 1). Thrs leads to large values of the capacitance and small values of the ohmic component of the faradalc impedance assoclated22 with reactron (1) (curves b and c) l/oC, decreases with potential between 0 4 V and about 0.84 V m the so-called double layer regron (compare curve (a)) durmg the anodrc sweep. Thus decrease was attnbutedlg to a change of the structure of the Helmholtz double layer, caused by the begmnmg formation of the oxygen layer The mcrease of ~/WC,wrth U for U > 0 84 V 1srelated to the decrease of the double layer capacitance wrth mcreasmg oxygen coverage (curve (a)) ~/UC, changes httle with U between 1 5 V and 0 9 V during the cathodic sweep when the oxygen layer remains nearly unchanged (curve (a)) Then the I/&, US Ucurve exhrbrts a broad mmlmum closely to the potentral where the cathodic current peak of curve (a) IS located The R,/U curve shows clearly the separation between hydrogen and double layer region. It was suggested 21 that the oxygen layer is formed or reduced m acid solutions accordmg to the reactions Pt + H,O = Pt-0
+ 2H+ + 2e-.
(2)
Reaction (2) is anodtc for U 2 0 8 V durmg the anodrc sweep. During the cathodic sweep the reduction of the oxygen layer starts at about 1 0 V Reaction (2) can be cathodic between 1 0 V and 0.8 V because its thermodynamic eqmhbrmm potential is shifted towards more posrtrve values with increasing oxygen coverage. The oxygen coverage at a constant potential between 0 8 V and 1 5 V after some trme has values whrch are not much larger than those durmg an anodic low-speed sweep at the same potentral It may be pointed out that reaction (2) is the sum of the first two steps of several paths of oxygen evolution discussed by BockriG and Rlddrford l2 Curve (a’) of Fig 1 m the presence of 0, shows the hydrogen and oxygen regron as does curve (a) However, the currents for the formatron or reduction of the respective layers are superimposed upon the cathodic current of 0, reduction The 0, reduction leads partly to H202 and partly to H,O by the sequence of reaction&‘J’ 0, + 2H+ + 2e- = H,O, , H,O, + 2Hf + 2e- = H,O.
(3) (4)
Water 1s formedsp7p17mainly between 0.1 V and about 0 6 V m the region of the hmrtmg O,-drffusron current when the potential 1s sufficiently cathodic to the thermodynamic eqmhbrmm potential of reactron (4). The separation of the net current density IO,of 0, reduction mto partial current densities I3 and Z4of reactions (3) and (4) 1s not known between 0 6 V and 0 9 V under voltammetrrc condmons. The superposrtlon of the currents m the hydrogen region obscures shghtly the appearance of the hmltmg drffuslon current of 0, m Fig 1 Durmg the anodrc sweep, the cathodic net current decreases with mcreasmg potential between 0 8 V and 0 9 V and becomes posrtlve for U > 0 9 V The anodrc current density m curve (a’) IS practrcally equal to that m curve (a) between 1-OV and 1 5 V and shows the potentral dependence charactenstlc for reaction (2) The current IS very small between 1 5 V and 1.0 V during the cathodic sweep Reactions (3) and (4) are strongly mhrbrted by the oxygen coverage, as also found by Vlelstrch l6 This result ehmmates O,-reduction mechamsms m whrch the partrcrpatlon of the oxygen layer is postulated, as for instance
Reduction of 0, on bnght Pt in HClO, solution
447
111the electrochemtcal metal peroxide path * The cathodic current peak of curve (a’) has the same locatron as the one of curve (a) The small cathodic current of curve (a’) 1s nearly equal to the one of curve (a) between 10 V and 0 8 V This means that reactrons (3) and (4) contribute to the cathodic current only for U < 0 8 V when sites free of adsorbed oxygen are present (see curve (a)). After the peak the current decreases with decreasing potential and tends towards its hmrtmg value between 0 6 V and 0 4 V The current peak of curve (a’) 1s probably due to a depletron of molecular oxygen close to the surface during the rapid production of sites free of oxygen atoms between 0 9 V and 0 75 V during the cathodic sweep The peak herght depends upon the rate of formation of free sites The disappearance of the peak m stirred solutions (see Fig 2) where the thickness of the diffusion layer remains constant substantiates the above interpretation Comparison of curves (b) and (b’) and of (c) and (c’) shows that they are the same This is true also for stirred solutions, and suggests that both the oxygen coverage and the hydrogen coverage at a given potential are determmed solely by processes that occur m the absence of 0, reduction 0, reduction does not seem to influence reactions (1) or (2). An equrvalent conclusion was drawn by Vrelstrchls from faster potential sweeps (sweep rate about 1 V/s) that make the currents of layer formation or reduction appear more pronounced relatively to the current of It may be pointed out that Vrelstrch’s conclusion cannot be transO,-reduction. ferred without additional assumptions to slow-speed sweeps Since hydrogen adsorptton 1s not favourably influenced by the presence of molecular oxygen m the electrolyte and does not extend beyond 0 4 V, mechanism III can be ruled out_ In the potential region of oxygen adsorptton the followmg equation holds during the sweeps m solutions saturated with an inert gas.
Here 8 designates the oxygen coverage, Fl7, 1s the number of C/cm2 for monolayer formatron, la is the partial current density of reaction (2) and depends upon the oxygen coverage 8 and U, t is the time If reactions (3) and (4) occur m the presence of molecular oxygen m addition to reaction (2), the assumption of a drssocratlve adsorptton of oxygen molecules leads to the equation
FL g = 12V3, u) + z’(e, u,PO,) Here I’ designates the net rate m A/cm2 by which the oxygen coverage IS influenced under the above assumption by reactions (3) and (4) I’ will differ for different ratedetermining steps of the O,-reduction mechanism In general I’ will be a function of 0, U and po, It is drfficult to conceive kmettc equations which lead to the same oxygen coverage at a given potential under conditions (5) or (6) Therefore rt is concluded on the basis of the Impedance measurements that a drssoclatrve adsorptton of oxygen is not mvolved m the O,-reduction mechamsm. The latter conclusion is also made very probable by its direct proofs3 for carbon electrodes with the aid of isotopic measurements The followmg mechanism of O,-reduction, suggestedM m a less explicit form earlier, is compatible with the experimental results with the additional postulate
M W BREITER
448
that the coverage with mtermedlates (Ozad,0,H etc) IS much smaller than the coverage with oxygen atoms Pt + 0, = Pt-0, (7) Pt-0,
+ 2H+ + 2e- = Pt-O,H, Pt-O,H,
Pt-O,H,
= Pt + H,O,
+ 2H+ + 2e- = Pt + 2H,O.
(8) (9) (10)
Reactions (6), (7) and (9) may occur m several steps which are not yet known Part of the hydrogen peroxlde produced may be desorbed (9) while the remainder IS reduced to water (10) The oxygen coverage IS only determined by eq (5) if the above mechanism apphes with the addltlonal postulate The absence of addltlonal small humps m the l/oC, U#U curves m the presence of O,-reduction demonstrates that the surface coverage with intermediates IS much smaller than the coverage with oxygen atoms at a given potential. A slmllar mechanism has been postulated for platinum by other authors.7J5a25 Inhcbltmng effect of the oxygen
layer
The mhlbltmg effect of the oxygen layer on the O,-reduction has already been described shortly m the preceding sectlon Figure 2 shows clearly that the rate of O,reduction 1s larger at the same potential for U > 0 7 V durmg the anodlc than durmg the cathodic sweep. The same statement holds for U > 0 8 V m unstirred solution (curve (a’) m Fig 1) if allowance IS made for the superimposed cathodic current of reactlon (2) between 1 0 V and 0 8 V durmg the cathodic sweep The hysteresis described IS attributed to the mhlbltmg effect of the oxygen layer Curves (d), (e) and Since the l/oC, z)s U curves (f) of Fig 3 present direct evidence for this mterpretatlon are the same m the presence and absence of O2 reduction (one curve (e) IS only shown), curve (d) gives direct mformatlon about the oxygen coverage at any potential of curve (f) 0, reduction starts at more anodlc potentials during the first cathodic sweep than during the subsequent cathodic sweep because more sites free of oxygen atoms are available The hysteresis between the anodlc sweep and the subsequent cathodic sweep becomes small m the steep portion of the I/U curves between-90 ,uAlcm2 and-270-~A~cm2. The srmdanty of the current decrease with Increasing potential above 0 8 V during the anodlc sweep 1s great between the cathodic 0, reduction and the anodlc H, oxldatlon 26 The current fluctuations due to n-regular stlrrmg disappear at about 0 8 V where a small amount of oxygen atoms IS present on the surface The current density IO, was computed by forming I-I, with the aid of curves (a) and (a’) of Fig 1 and IS plotted USU m Fig 5 for the anodlc sweep The large decrease of current with potential occurs between 0 8 V and 0 9 V where about 10 per cent of an oxygen monolayer IS formed The results described suggest that the current decrease between 0 8 V and 0 9 V during the anodlc sweep 1s due to mhlbltlon by the oxygen layer There IS no contradlctlon Involved m this conclusion smce the adsorbed oxygen atoms do not participate as mtermedlates m the 0, reduction Infrunce
of chlorrde eons
A voltammetrlc
mvestlgatlon
of the adsorptlon
of chloride Ions on smooth
Reduction of 0% on bright Pt m HCIO, solution
449
platinum m perchlorlc acid solutions has been made2’ recently It was found that the presence of Cl- Ions leads to a change of the shape of the Z/U curves m the hydrogen region and the oxygen region (see curves (a) and (d) m Fig 4) Adsorptlon of chloride ions IS demonstrated by the decrease of the double layer capacitance in the double layer region and the region of oxygen adsorption (compare curves (b) and (e) in Fig 4 with curve (b) m Fig 1) Nearly a monolayer of adsorbed Cl- 1s present m the double layer region during the anodlc sweep for ,,ccl_ >‘ 10e2 M The Z/U curves (c) and (f) m Fig 4 have a shape slmllar to curve (a’) m Fig 1. However, the current decreases with increasing potential already between 0 6 V and UV
FIG 5 Current density of Oa reduction durmg the anodlc sweep at 30 mV/s m unstirred 1 N HClOp
0 8 V during the anodlc sweep Then the current becomes posltlve This means a shift of the current decrease by about 0 2 V to less positive potentials m the presence of chloride ions Slmllarly, the increase of the current with potential during the cathodic sweep and the current peak are located at less posltlve potentials m Fig 4 than m Fig 1. The height of the current peaks of curves (c) and (f) of Fig 4 IS smaller than that of curve (a’) m Fig 1 Agam the I/WC, USU curves do not differ m the presence of hehum or oxygen Only one l/c&, z1.sU curve 1s shown for each solution Tt can be concluded from curves (a) and (d) m Fig 4 that the oxygen coverage 1s small between 0 6 V and 0 8 V during the anodlc sweep The l/r& USU curves (b) and (e) demonstrate adsorption of chloride ions m the said range Thus the absorption of Cl- exerts a strong mhlbltlon on the O2 reduction, probably by the blocking of active sites and by the q-effect. 28 The results are similar to results obtained for the reduction wave of oxygen to hydrogen peroxide on mercury 28 There the half-wave potential IS shifted towards a more positive potential m acid solutions contammg chloride Ions. The 0, reduction occurs at a higher rate at any potential durmg the cathodic than during the anodlc sweep The I/UC, USU curves demonstrate that part of the
M
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BREITER
adsorbed Cl- is desorbed durmg the anodlc sweep between about 0 9 V and 1.5 V and that readsorption starts durmg the cathodic sweep at about 0 8 V Therefore less ClIS adsorbed between 0 8 V and 0 7 V durmg the cathodic than dunng the anodlc sweep. This explains the observed hysteresis of the I/U curves m the presence of ClAcknowledgement-The
author IS grateful for the helpful comments
of Dr
F
G
Wdl, General
Electnc Research Laboratory REFERENCES 1 T P HOAR, Proc Roy Sot A142,628 (1933) 2 W A ROITERand R B JAMPOJXAJA,Acta Phys-Chrm URSS 7,247 (1937) 3 P DELAHAY,J Electrochem Sot 97, 198 (1950) 4 A I KR.UIL’SHIKOV and W A ANDREEVA,Zh AZ Khmm 27,389 (1953) Zh AZ Khzm 28,1286 (1954) 5 T N BELINAand A I KRASIL’SHIKOV, 6 J O’M BOCKRI~and A K M SHAMSHUL HUQ, Proc Roy Sot A237,277 (1956) Z Elektrochem 60, 731 (1956) 7 D WINKELMANN, 8 J O’M Bocm, J Chem Phys 24,817 (1956) Z phys Chem (N F ) 15,409 (1958) 9 W VIELSTICH, 10 T P HOAR, Proc 8th Meetmg CZTCE 1956, p 439 Butterworths, London (1958) 11 J GINER,2 Efektrochem 63,386 (1959) 12 A C RIDDIFORD, Electrochzm Actu 4, 170 (1961) J Electroanalyt Chem 2, 310 (1961) 13 D T SAWYERand L V INTERRANTE, J P HOARE,J EIectrochem Sot 110,858 (1962) and V I VESSEUIVSKY, Dokl Akad Nauk SSSR 148, 152 :: Yu A MASITOV,K I ROSENTHAL (1963) 16 W VIELSTICH, Z InstrumKde, 71,29 (1963) 17 L N NEKRASXIVand L MULLER,Dokl Akad Nauk SSSR 149, 1107 (1963) 18 A I KRAUL’SHIKOV, Proceedmgs of the 4th Conference on Electrochemrstry, Moscow 1956, p 272 Academy of Sciences, Moscow (1959) 19 M W BREITER, J Electroanalyt Chem, m press 20 F G WILL and C A KNORR,Z Elektrochem 64,258 (1960) 21 W BOLDand M BREITER, Electrochzm Acta 5, 145 (1961) 22 P DOLIN and B ERSHLER, Acta Phys-Chrm URSS 13,747 (1940) 23 M 0 DAVIES, M CLARK, E YEAGERand F HOVORKA,J Electrochem Sot 106, 56 (1959). 24 W G BERL,Trans Electrochem Sot 83,253 (1943) 25 S SCHULDINER and R M ROE, Extended Abstracts of Theoretrcal D~rsron of Electrochem Sot Vol 1, No 1, Abstract 149 (1963) 26 M W BREITER, Efectrochrm Acta 7, 601 (1962) 27 M W BREITER, Electrochzm Acta 8,925 (1963) 28 V S BAGOTSKNand I E YABLOKOVA, Zh Fu Chum 27, 1663 (1953)