fuel cell system for low power applications

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Available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/ijhydene

A complete miniaturized microstructured methanol fuel processor/fuel cell system for low power applications Yong Men, Gunther Kolb, Ralf Zapf, David Tiemann, Martin Wichert, Volker Hessel, Holger Lo¨we Institut fu¨r Mikrotechnik Mainz GmbH, Carl Zeiss Str. 18-20, D-55129, Mainz, Germany

ar t ic l e i n f o

abs tra ct

Article history:

A complete miniaturized methanol fuel processor/fuel cell system was developed and put

Received 17 July 2006

into operation as compact hydrogen supplier for low power application. The whole system

Received in revised form

consisting of a micro-structured evaporator, a micro-structured reformer and two stages of

3 October 2007

preferential oxidation of CO (PROX) reactor, micro-structured catalytic burner, and fuel cell

Accepted 9 December 2007

was operated to evaluate the performance of the whole production line from methanol to

Available online 7 February 2008

electricity. The performance of micro methanol steam reformer and PROX reactor was

Keywords: Microstructured reactor Hydrogen production Fuel processor Methanol steam reforming

systematically investigated. The effect of reaction temperature, steam to carbon ratio, and contact time on the methanol steam reformer performance is presented in terms of catalytic activity, selectivity, and reformate yield. The performance of PROX reactor fed with the reformate produced by the reformer reactor was evaluated by the variation of reaction temperature and oxygen to CO ratio. The results demonstrate that microstructured device may be an attractive power source candidate for low power application. & 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

1.

Introduction

Nowadays focus of research on fuel processing has moved away from drive train applications towards devices for electrical power supply, so-called auxiliary power units (APU) [1]. Small size PEMFCs (polymer electrolyte membrane fuel cells) would be a promising power source for portable electronic devices. In order to power multi-functional portable devices in the future, fuel cells can be potential candidates for replacing batteries [2]. However, there are still significant technical barriers in developing small PEMFCs. One of the major technical challenges for the systems is the development of a compact and light weight hydrogen supply system. Hence, several systems including metal hydrides, chemical hydrides and hydrocarbon fuel processors have been considered as small size hydrogen suppliers. Among them, fuel processors have received considerable attention due to their

high energy density and instant recharge time of liquid fuel [3]. Hydrogen generation as an alternative to hydrogen storage especially for portable fuel-cell systems requires highly compact and integrated reactors and components such as heat exchangers and evaporators. However, conventional fuel processors have high reactor volume frequently owing to mass transfer limitations and temperature management. Thus, microstructured reactors have been employed to minimize the complicated chemical plants mainly due to its advantages for chemical reactions such as its several orders of magnitude higher surface to volume ratio compared to traditional chemical reactors and enhanced heat transfer and mass transfer in the reduced dimensions of microchannels [4]. The process intensification benefits of micro process engineering for gas phase reactions [5–7] are consequently within focus of the world-wide research related to fuel processing for small and medium sized application.

Corresponding author. Tel.: +49 6131 990 441; fax: +49 6131 990 205.

E-mail address: [email protected] (Y. Men). 0360-3199/$ - see front matter & 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2007.12.024

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There are several kinds of hydrocarbon fuels as potential hydrogen sources for PEMFC systems. Among them methanol is an attractive fuel for the small fuel processor because of its low reforming temperature, low steam to carbon ratio, good miscibility with water and low content of sulfur compounds [8]. Although several efforts have been made to develop the micro scale hydrogen supplier for small PEMFC, only few publications were found in the public literature devoting to a complete methanol steam reforming fuel processor/fuel cell system. Various efforts have been made to develop the compact and efficient microchannel methanol steam reformer for portable PEMFC applications. Pacific Northwest National Laboratory (PNNL) demonstrated 40 W equivalent microchannel fuel processor made of stainless steel which consisted of a vaporizer, a steam reformer and a recuperative heat exchanger [9]. Recently, they also reported sub-watt class methanol processors showing high thermal efficiencies up to 33% and low carbon monoxide below 100 ppm [10]. Motorola Labs disclosed an integrated fuel cell system with ceramic based methanol processor comprising fuel vaporizer, heat exchanger, reformer and catalytic combustor. The system was operated for 1 week generating 0.7 W electrical power [11]. Reuse et al. have fabricated an integrated fuel processor with methanol steam reformer and methanol combustor employing two independent passages using microstructured stainless steel plates. Kinetic models for steam reforming and complete combustion were also investigated in the microchannel reactor [12]. CASIO is also developing a multi-layered microchannel reactor being integrated with methanol reformer, CO cleaner, vaporizer and catalytic combustor made of glass for a 10 W class PEMFC system for laptop PC [13]. This work presents the fabrication and performance evaluation of a complete miniaturized methanol fuel processors/fuel cell system including a micro-structured evaporator, a micro-structured methanol steam reformer, two-stage PROX reactor, and a catalytic after-burner. The performance tests with respect to the activity and selectivity for each individual component are thoroughly investigated by variation of reaction temperature, contact time, and feed compositions.

2.

Experimental

2.1.

Catalyst preparation

Three types of microchannel reactors for the methanol steam reforming, PROX and total combustion reactions were fabricated employing the same microchannel sheet design and fabrication method. These reactors used stainless steel sheet patterned microchannel by a wet chemical etching. The elliptic microchannels (600 mm width, 250 mm depth) are separated by 250 mm fins with the total length of 44 mm. The microchannel shape and dimension were decided by computer simulation of flow distribution and pressure drop of the reactants in the microchannel sheet. The microchannel sheets of the reformer, PROX reactor and burner were coated with the respective catalysts to facilitate the appropriate chemical reactions. The procedure applied for wash-coating of the self-made steam reforming Cu/ZnO,

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PROX, and Pt-based combustion catalysts was performed manually by filling the micro-channels with alumina carrier suspension and removing the excess suspension and calcinations at a temperature of 450  C in air to avoid the release of unknown species in the subsequent treatment. The alumina carrier coating was then impregnated with metal salt solutions and calcined in air at 450  C for 6 h. Details of catalyst development and this wash-coating procedure were described in our previous studies [14–16]. The prepared microchannel sheets were stacked and welded by laser to seal the basic reactors such as evaporator, reformer, PROX reactor, and burner. To make high performance micro-reactors, the inlet and outlet geometry of the micro-structured reactors was optimized by computational fluid dynamics and numerical simulation to ensure the uniform flow distribution in the reactor. The dimensions of the micro-structured reactors for methanol steam reforming and catalytic combustion excluding fittings were about 120 mm  36 mm  25 mm, respectively. Both sides of end-plates have two holes for rod-type electric heaters respectively. The dimensions of the microstructured PROX reactor excluding fittings were about 104 mm  80 mm  15 mm, respectively.

2.2.

Experimental set-up

The experimental apparatus consists of feed sections for steam reforming, two-stage PROX and catalytic combustion, and the analysis section with an on-line gas chromatograph and infrared sensor system as shown in Fig. 1. Methanol and water mixture fed by a liquid mass flow meter was vaporized by the micro-structured evaporator and fed into the micro-reformer. Air required for the PROX and combustion reaction was regulated by the respective mass flow controllers. Prior to the reforming reaction the catalyst inside the reactor was reduced by flowing 20% H2/N2 stream into the reactor at 250  C for 2 h. The steam reforming reaction was conducted in the temperature range of 235–275  C and the reaction temperature was controlled by a PID temperature controller with a K-type thermocouple inserted into the wall of the reactor. The PROX reaction was performed by using the reformate feed produced by the micro-structured reformer under realistic condition. The composition of the reactor effluents were analyzed by an on-line ThermoFinnigan Trace gas chromatograph equipped with two thermal conductivity detectors and one flame ionization detector. The analytical procedure allows for analysis of all species present in the reaction effluents including water. The flow rate of dry reformed gas was measured by a digital soap flow meter. The afterburner was coated with platinum catalyst and converted all residual carbon monoxide and hydrogen from the fuel cell anode off-gas at a reaction temperature of 250  C and a slight excess of air. The conversion of methanol steam reforming was calculated by the following equation: Methanol conversion ð%Þ ¼

Cin  Cout , Cin

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Air (PrOx 1)

Air (PrOx 2)

Reformer

PrOx 1

Water Methanol

Evaporator

PrOx 2

230V

Fuel cell

Condenser CO Analyzer

50 Wel CO<50 ppm

Air (Burner)

Exhaust

Exhaust GC - TCD - FID

Burner

where Cin and Cout are the inlet and outlet concentration, respectively. All selectivities reported were based on carbon atoms except for H2, which was based on hydrogen atoms, Si ¼ P

ni Ci

all product species nj Cj

,

where n is the number of carbon atoms in the species and Cj the concentration of the species in the product stream. The same formula is used to calculate H2 selectivity but n is the number of hydrogen atoms in the species. CO content after the PROX reactor was monitored by an online infrared sensor. The fuel cell with a 10-cell stack was purchased from Heliocentris company and equipped with a reformate tolerant Pt–Ru catalyst. This fuel cell is cooled by cathode air with built-in blower in an open system.

3.

Results and discussion

3.1.

Performance of micro-structured methanol reformer

It is well known that the methanol steam reforming reaction for hydrogen production over the Cu-based catalyst [17–21] involves the following reactions. CH3 OH þ H2 O ! 3H2 þ CO2 ,

(1)

CH3 OH ! CO þ 2H2 ,

(2)

CO þ H2 O ! CO2 þ H2 .

(3)

Eq. (1) is the algebraic summation of Eqs. (2) and (3). Eq. (2) represents methanol decomposition. Eq. (3) represents a

Methanol conversion [%]

Fig. 1 – Flow scheme of miniaturized fuel processor/fuel cell system.

100 90 80 70 60 50 40 30 20 10 0

W/F 0.0057 gcat∗min/ml W/F 0.00285 gcat∗min/ml W/F 0.001425 gcat∗min/ml

230 235 240 245 250 255 260 265 270 275 280 Temperature [°C] Fig. 2 – Steam reforming of methanol at S=C ¼ 2.

water–gas shift reaction. The major products of this process are H2 and CO2. Minor quantities of CO are also produced. For the application of PEMFCs, the composition of produced gas requires high concentration of H2 and low concentration of CO. Hence, the effect of reaction variables on methanol steam reforming was performed to identify the optimum operating conditions for the maximum hydrogen production with minimum CO concentration.

3.1.1.

Influence of reaction temperature and contact time

Methanol steam reforming was performed in the microchannel reactor at the various reaction temperatures from 235 to 275  C by electrical heater at S=C ¼ 2=1 as a function of contact time. The contact time span for all the experiments was chosen to include a wide range of methanol conversions ranging up to full methanol conversion. The comparison of the reactor performance is shown in Fig. 2. Methanol

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conversion increases with increasing temperature. The full methanol conversion is achieved at 275  C with contact time of W=F 0:00285 gcat  min=ml. At a definite temperature, the methanol conversion was enhanced with increasing contact time. At the contact time of W=F ¼ 0:0057 gcat  min=ml, methanol is completely converted in the micro-structured reformer at 255  C. At 275  C, 95% conversion was obtained at shortest contact time of W=F ¼ 0:001425 gcat  min=ml. The influence of reaction temperature and contact time on product selectivity is presented in Figs. 3 and 4. H2 and CO2 are the main product components, together with a small amount of CO and methyl formate (C2H4O2). No other products, such as dimethyl ether and methane were observed over the catalyst tested. Selectivity toward CO2, CO and H2 increases with increasing temperature as well as increasing contact time. The increasing CO content with increasing temperature is mainly because of reverse water–gas shift reaction which enhanced by increased reaction temperature [22]. The formation of methyl formate decreases as temperature and contact time increases, showing the reverse trend compared to other species.

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Takahashi et al. [23] and Jiang et al. [24] suggested methyl formate as a major intermediate of methanol steam reforming reaction. Fisher and Bell study methanol decomposition on Cu/SiO2 and Cu/SiO2/ZrO2 catalyst [25]. The result shows that methyl formate may be produced in the presence of gaseous methanol. It is proposed that methyl formate is formed by the interaction of adsorbed methoxide and formaldehyde species [26,27]. 2CH3 OH ! CH3 OCHO þ 2H2 .

(4)

In this study, considerable amount of methyl formate is formed in the reformate gas under present operating conditions. It is observed that reaction temperature markedly affects methyl formate selectivity. At finite contact time of W=F ¼ 0:00285 gcat  min=ml, the methyl formate selectivity falls from 41% to 2% in the temperature range of 235 and 275  C, while methyl formate selectivity decrease from 2.9% to zero at constant temperature of 275  C as contact time increases from 0.001425 to 0:0057 gcat  min=ml. It is noted that the selectivity of methyl formate is strongly dependent on the methanol conversion, i.e. methanol partial pressure. It

100

1.2 1

80 70

0.8

60

CO2 C2H4O2 H2 CO

50 40 30 20

0.6 0.4

CO selectivity [%]

H2,CO2,C2H4O2 selectivity [%]

90

0.2

10 0 230

235

240

245

250 255 260 Temperature [°C]

265

270

275

0 280

Fig. 3 – Effect of temperature on product selectivity at W=F ¼ 0:00285 gcat  min =ml and S=C ¼ 2. Reformer catalyst loading: 1.11 g.

100

H2 and CO2 selectivity [%]

80 70 60

CO2 H2 CO C2H4O2

3 2.5 2

50 40 30

1.5 1

20 10

0.5

CO and C2H4O2 selectivity [%]

3.5

90

0 0 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 0.0045 0.005 0.0055 0.006 W/F [gcat∗min/ml] Fig. 4 – Effect of contact time on product selectivity at 275  C and S=C ¼ 2.

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100 90 80 70 60 50 40 30 20 10 0

W/F 0.0057 gcat∗min/ml W/F 0.00285 gcat∗min/ml W/F 0.001425 gcat∗min/ml

230 235 240 245 250 255 260 265 270 275 280 Temperature [°C]

or synthesis method. CO2 þ H2 ! CO þ H2 O.

3.1.2.

(5)

Influence of steam to carbon ratio

Water plays an important role in the methanol steam reforming. As a reactant in the methanol steam reforming, it affects the product selectivity towards hydrogen. In Fig. 5, under the identical contact time, the effect of steam to carbon ratio of 1.5 to 1 on the performance of micro-structured reformer was studied. The results in Fig. 5 show that higher reaction temperature and longer contact time are more favorable for higher conversion of methanol during the methanol steam reforming at S=C ¼ 1:5. As compared to Fig. 2, the methanol conversion was deteriorated as steam to carbon ratio decreases, whereas the H2 production was improved as the steam to carbon ratio increases. Only at 275  C and W=F ¼ 0:0057 gcat  min=ml, the catalyst shows 100% conversion at S=C ¼ 1:5. 95% conversion was found at 275  C and W=F ¼ 0:00285 gcat  min=ml with S=C ¼ 1:5. No full conversion was achieved at shorter contact time, regardless of the temperature investigated. This is mainly due to the increase of methanol amount in the methanol water mixture with decreasing steam to carbon ratio. Similar results were obtained about the influence of reaction temperature and contact time on product selectivity, as shown in Figs. 6 and 7. The results summarized in Table 1 reveal that the CO concentration contained in the reformed gas during the reaction was affected by the steam to carbon ratio. CO concentration at S=C ¼ 1:5=1 was found to be generally higher than those obtained at S=C ¼ 2=1 under the same temperature and contact time. The concentration of CO was sensitive to the reaction temperature and steam to carbon ratio whereas CO concentration increased from 0.05% to 0.58% as the reforming temperature increased from 235 to 275  C. This is mainly because of reverse water–gas shift reaction which enhanced by increased reaction temperature. The concentration of CO also increased as the steam to

Fig. 5 – Steam reforming of methanol at S=C ¼ 1:5.

100

1.4

90

1.2

80 1.0

70 60

CO2 C2H4O2 H2 CO

50 40 30

0.8 0.6 0.4

CO selectivity [%]

H2,CO2,C2H4O2 selectivity [%]

Methanol conversion [%]

is not surprising that the route for methyl formate formation does not occur appreciably in the absence of gas-phase methanol, as the surface concentrations of crucial intermediates are small in the absence of methanol in the gas phase when methanol conversion is complete. The formation of CO in methanol steam reforming is the major problem when using the produced hydrogen in a fuel cell because of the poisoning of CO on the Pt electrode catalyst [28–30]. Therefore the CO selectivity in the reformate gas is quite important for the performance of micro-reformer. The selectivity of CO increases with methanol conversion and also with temperature. At 275  C a CO concentration of 0.35 vol.% in the produced reformate was determined. The small amount of CO produced increases with increasing contact time, indicating that CO is a consecutive product formed by the reverse WGS reaction from the products of steam reforming reaction, namely H2 and CO2. This observation is in accordance with Purnama [31,32] and Ross’s results [33]. Purnama et al. have proposed that CO is formed as a consecutive product by the reverse water gas shift reaction during the steam reforming of methanol reaction over a commercial CuO/ZnO/Al2O3 catalyst. It was claimed by these authors that the reaction pathway for CO formation is the same for Cu-based catalysts independent of the support type

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20 0.2

10 0 230

235

240

245

250 260 255 Temperature [°C]

265

270

275

0.0 280

Fig. 6 – Effect of temperature on product selectivity at W=F ¼ 0:00285 gcat  min =ml and S=C ¼ 1:5.

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90 CO2 H2 CO C2H4O2

80 70 60

7 6 5

50

4

40

3

30

2

20 1

10

CO and C2H4O2 selectivity [%]

8

100

H2 and CO2 selectivity [%]

1379

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0 0 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 0.0045 0.005 0.0055 0.006 W/F [gcat∗min/ml] Fig. 7 – Effect of contact time on product selectivity at 275  C and S=C ¼ 1:5.

Table 1 – Comparison of the influence of operating conditions on CO content in microstructured reformer

S=C ¼ 2=1 S=C ¼ 1:5

W=F ¼ 0:001425 ðgcat  min=mlÞ

W=F ¼ 0:00285 ðgcat  min=ml)

W=F ¼ 0:0057 ðgcat  min=mlÞ

235  C

255  C

275  C

235  C

255  C

275  C

235  C

255  C

275  C

0.030 0.046

0.071 0.076

0.268 0.278

0.043 0.056

0.125 0.143

0.352 0.355

0.064 0.067

0.162 0.196

0.556 0.576

carbon ratio decreased. This implies that high steam to carbon ratio can suppress reverse water–gas shift reaction causing low concentration of CO. The performance of micro-reformer at S=C ¼ 1:1 was also investigated and the methanol conversion as a function of temperature and steam to carbon ratio was comparatively presented in Fig. 8. When the steam to carbon ratio in feed was further decreased the methanol conversion was decreased to less than 45% and reformate yield was also both less than those at S=C ¼ 2 and 1.5 under the identical contact time and reaction temperature. The results show that at this S/C ratio methanol conversion was incomplete under all the reaction condition applied and it increases with increasing steam to carbon ratio as well as reaction temperature. The reformate yield follows the order: S=C ¼ 1:54S=C ¼ 24S=C ¼ 1:1. High reaction temperature and medium steam to carbon ratio are more favorable for high amount of H2 production during the methanol steam reforming. But, in order to minimize the CO content in the reformate, the reformer should be operated at low reaction temperature and high steam to carbon ratio to suppress the CO concentration in the reformed gas during the methanol steam reforming. However, the operating condition for low CO concentration is not desirable for the H2 production reaction. Furthermore, the H2 production was deteriorated as the steam to carbon ratio increases. Thus, a compromise between H2 production and CO and methyl formate suppression is necessary for operating the reformer. In addition, further CO reduction process is required for microchannel reformer to reduce the CO concentration down to low temperature PEMFC tolerant level of less than 20 ppm.

Methanol conversion [%]

CO content (%)

100 90 80 70 60 50 40 30 20 10 0

S/C=1.1/1 S/C=1.5/1 S/C=2/1

230 235 240 245 250 255 260 265 270 275 280 Temperature [°C] Fig. 8 – Effect of steam to carbon ratio on methanol conversion.

3.2.

Performance of PROX reactor

A two-stage PROX reactor was fabricated and employed to clean up CO for fuel cell application purpose. A bimetallic Rh/ Pt/Al2O3 catalyst similar to [34] was deposited via combination of washcoating & impregenation into the PROX reactor. These experiments were performed under realistic conditions, since the PROX reactors were fed with the reformate produced by the reformer reactor. It has been shown that the level of CO produced in the micro-structured reformer over commercial catalyst can be affected by a variety of factors: reaction temperature, contact time, methanol conversion, and steam to carbon ratio. In order to maximize the reformate yield and minimize CO content in reformate, it is essential to

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O2/CO ratio

CO [ppm]

2.5

3

3.5

4

4.5 700

60

600

50

500

40

400 Temperature dependence Effect of O2/CO ratio

30

300

20

200

10

100

0 115

CO [ppm]

2

1.5 70

0 120

125

130

140 145 135 Temperature [°C]

150

155

160

Fig. 9 – Performance of PROX1 reactor with respect to O2/CO ratio and reaction temperature.

9.00 First day Second day Third day

8.50 8.00 Voltage [Volt]

select a set of operating parameters in the micro-reformer for further CO clean-up treatment: reaction temperature 275  C, S=C ¼ 2=1, and contact time W=F ¼ 0:00285 gcat  min=ml. Fig. 9 presents the CO concentration contained in the reformed gas eluted from the PROX1 reactor with respect to reaction temperature and O2 to CO ratio. As shown in Fig. 9, CO concentration decreases with increasing O2 to CO ratio at a temperature of 140  C. The maximum CO elimination capacity from the reformate stream on PROX1 reactor was achieved to be around 40 ppm with an O2 to CO ratio of 3. Further raising the amount of O2 inevitably led to a H2 loss since the PROX reaction is then more selective toward hydrogen combustion. At O2 to CO ratio of 3, the effect of reaction temperature was also investigated and the optimized reaction temperature was found to be 135  C. The CO content was reduced to as low as 31 ppm under this reaction condition. Based on the optimum operating conditions obtained from the above results, the performance of the complete fuel processor system was evaluated by examining the CO content in the reformate gas eluted from PROX2 reactor operated at 135  C and O2 =CO ¼ 3. The results showed that CO was always effectively reduced to less than 20 ppm in the complete micro-structured fuel processor system. The amount of air added to this second stage was very small because the CO content after PROX1 reactor was as low as 31 ppm. The catalytic burner always fully converted the residual H2 and CO traces into water and CO2 thus leaving no flammable or toxic gases into the exhaust.

7.50 7.00 6.50 6.00 5.50 5.00 0

100

200

300 400 Time [min]

500

600

700

Fig. 10 – Performance of the reformate powered fuel cell.

sion nor selectivity changed noticeably during this period, which demonstrates its long-term performance durability. The electricity generated by the reformate powered fuel cell produced by the micro-structured fuel processor was monitored as a function of time, as depicted in Fig. 10. The system performance degrades slightly with time on stream but its initial performance was recovered once being restarted the next day. The performance test shows the reversible recovery behavior and exhibits good test stability. This degradation is more likely due to the deteriorating of the fuel cell electrode assembly since no deactivation was observed for both steam reforming reaction and PROX reaction.

3.3. Performance durability of micro-structured fuel processor/fuel cell system

4. One important issue for using a catalyst in fuel processor/fuel cell system is the performance durability and catalyst deactivation with time on stream. This complete miniaturized system has been operated for 100 h and neither conver-

Conclusion

A complete and miniaturized methanol fuel processing/fuel cell system composed of microchannel reactors was designed and fabricated at IMM, which consists of a micro-structured

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evaporator, a micro-structured reformer and two stages of preferential oxidation of CO (PROX) reactor, a micro-structured catalytic burner, and a fuel cell. Each of the microstructured components consists of stacks of microchannel patterned stainless steel sheets. The methanol steam reformer was fabricated by depositing self-made Cu/ZnO catalyst inside the microchannel reactor and for the PROX reactor a bimetallic Rh–Pt/Al2O3 catalyst was applied. The performance test shows that the microreformer effectively converted methanol to hydrogen-rich reformate in the methanol steam reforming process. At S=C ¼ 2, full methanol conversion was achieved at 275  C and W=F ¼ 0:00285 gcat  min=ml whereas 0.35% CO containing reformate was obtained. Under the optimized operating condition, the two PROX reactor stages fed by the hydrogen-rich reformate produced by the microreformer effectively reduced the reformate CO content down to 18 ppm at O2 to CO ratio of 3/1 at 135  C. The fuel processing system run stably for over 100 h and exhibited good operating stability. The reformate flow rate was high enough to gain up to 20 W of electrical power out of the fuel cell. This methanol fuel processor/fuel cell system was designed with external electric heating device, therefore, this system is not designed for the energy optimization purpose. Integrated design concepts for small scale fuel processor/fuel cell systems powered by methanol are being considered for the later application to further enhance the energy efficiency of the microsystem. For instance, the reformer would be operated as a coupled steam reformer/ catalytic burner/micro-structured heat-exchanger in such an integrated device. The results presented in this work demonstrate that micro-structured fuel processor/fuel cell system may serve as an attractive power source candidate for low power application. R E F E R E N C E S

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