Performance losses at H2/O2 alkaline membrane fuel cell

doi:10.1016/j.elecom.2014.12.006

Electrochemistry Communications

Volume 51, February 2015, Pages 117-120

https://doi.org/10.1016/j.elecom.2014.12.006 Get rights and content

Highlights

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Significant potential loss in AMFC caused by low ionic conductivity of membrane and catalyst layer
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Severe performance loss is also caused by low water concentration at catalyst surface.
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Operation at high temperature essential to increase the water concentration in humidified oxidant

Abstract

H₂/O₂ alkaline membrane fuel cell (AMFC) is evaluated by polarization curves and conductivity measurements to determine the performance limiting factors. The analysis of IR corrected polarization curves shows that at medium to high current region significant potential loss in AMFC is caused by low ionic conductivity of membrane and catalyst layer, and limitations from mass transport of water. In low to medium current region the severe performance loss is caused by low water concentration at catalyst surface due to insufficient water concentration in the fully humidified oxidant at ≤ 60 °C.

Introduction

Much research has been focused on alkaline membrane fuel cell (AMFC) which allows the use of non-precious metal catalyst for oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR). Presently, the performance of H₂–O₂ AMFC employing commercial anion exchange membrane (AEM) and anion exchange ionomer (AEI) is low in relation to proton exchange membrane fuel cell (PEMFC) even with benchmark catalyst like Pt/C [1], [2], [3]. Major reasons for low performance suggested in the literature are insufficient water supply at cathode even with humidified Air/O₂ at practical stoichiometries [4], large anodic over potential due to water flooding at anode [5], and low ionic conductivity of membrane and ionomer [6]. However, systematic quantification of all these losses at the fuel cell level is scarce in literature. In this work, AMFC performance is systematically evaluated at various catalyst loadings to measure anodic and cathodic overpotential. Furthermore, performance losses due to the ionic resistance of membrane and ionomer are quantified by determining ionic resistance of catalyst layer (CL) and membrane.

Section snippets

Experimental

Two types of fuel cell membrane electrode assemblies (MEAs) were prepared, Type-1 with various low anode and cathode catalyst loadings and Type-2 with high anode and cathode catalyst loadings. Type-1 MEAs were prepared by spray coating the required amount of catalyst ink on A201 membrane (Tokuyama Corp Japan) or Nafion-115 membrane (QuinTech Germany) maintained at 65 °C. Typical catalyst ink was prepared by sonicating the mixture comprised of 50 mg Pt/C (60 wt.% Pt, Alfa Aesar, United Kingdom), 250

Performance evaluation

Performance evaluations of AMFC were carried out with Type-1 MEAs with low loadings between 0.07 and 0.16 mg_Pt·cm^− 2. Fig. 1(a) shows the I–V curve for two MEAs with varying catalyst loading at anode. The obtained power density of 90 mW·cm^− 2 at 0.6 V is reasonable compared to literature values [1], [2], [3] considering the low loading of catalyst used here. Performance is mostly not sensitive to change in anode loading. This indicates that mass transport of H₂ is facile and kinetic limitation from

Discussion

The performance of AMFC is significantly lower below 0.85 V in relation to PEMFC even after correcting for ionic resistance of membrane and CL (Fig. 3(b)) and the mass transfer effect in AMFC starts to become dominant only below 0.5 V as shown above in Fig. 2(a). Hence, a major performance loss between 0.85 V and 0.5 V is attributed to low water concentration at the catalyst surface. In PEMFC, the ORR is dependent on O₂ and H⁺ concentration where H⁺ ions are abundantly available via proton exchange

Conclusions

Measurement of performance curves with various anode and cathode loading shows that the HOR kinetics in AMFC is fast and can be neglected for potential losses at least at high anode flow rates. Significant improvement in AMFC performance can be obtained by increasing the H₂O concentration in oxidant for example by operating at higher temperatures. Analysis of the AMFC performance curves corrected for catalyst layer and membrane resistance show that in relation to PEMFC, at a given current the

Conflict of interest

No conflict of interest.

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In spite of significant achievements in alkaline exchange membrane fuel cells (AEMFCs) in recent years, they are still lagging behind proton exchange membrane fuel cells (PEMFCs) due to performance instability. Among the relevant operational parameters of AEMFC, the researchers have found that poor water management within the cell was the main reason for failure of the system. In the past five years, numerous modeling and experimental works were reported proposing different strategies to improve water management of AEMFC. With proper water management, the achievable power output in AEMFCs is comparable with that of PEMFCs or even more. Efforts have to be continued, but AEMFCs can become a strong competitor in the market place. This review paper discusses the strategies and developments impacting water management of AEMFCs providing knowledge source for upcoming studies.
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Short communicationPerformance losses at H2/O2 alkaline membrane fuel cell

Highlights

Abstract

Introduction

Section snippets

Experimental

Performance evaluation

Discussion

Conclusions

Conflict of interest

J. Power Sources

Electrochem. Commun.

J. Membr. Sci.

Electrochim. Acta

Steady-state dc and impedance investigations of H2/O2 alkaline membrane fuel cells with commercial Pt/C, Ag/C, and Au/C

J. Phys. Chem. B

Pt-free cathode catalyst performance in H2/O2 anion-exchange membrane fuel cells (AMFCs)

ECS Trans.

Short communication
Performance losses at H₂/O₂ alkaline membrane fuel cell

Steady-state dc and impedance investigations of H₂/O₂ alkaline membrane fuel cells with commercial Pt/C, Ag/C, and Au/C

Pt-free cathode catalyst performance in H₂/O₂ anion-exchange membrane fuel cells (AMFCs)