PEM Water Electrolysis - Durability Under Heavily Reduced Anode Catalyst Loading

When coupled to renewable but nonetheless intermittent power sources such as wind or solar, polymer electrolyte membrane (PEM) electrolyzers are intended to be in operation for tens of thousands of hours¹. Hence, the long term behavior of membrane electrode assemblies (MEAs) under these power operating characteristics is of great importance. At moderate conditions (25 cell stack, around 50°C and 1.3 A/cm²)², commercial PEM electrolyzers show little to no significant degradation (< 4 µVh) after 55,000 h². However the anode catalyst loading in commercial systems is generally high (> 2 mg/cm²)³ and the state-of-the-art catalyst material, iridium, is expensive and rare. A reduced catalyst loading will contribute to reduce the costs of electrolyzer stacks, but to this date the effect of anode catalyst loading on the durability of PEM electrolysis has not yet been thoroughly investigated in literature.

This study aims to show the durability of PEM electrolysis single cells under reduced anodic catalyst loadings. As shown in Fig. 1 (top), with IrO₂ loadings as low as 0.6 mg/cm² we were able to reach identical performance when compared to our standard catalyst loading of 2.25 mg/cm² IrO₂. Moreover, stable cell performances over 680 h in an initial life time test were obtained (Fig. 1 bottom). Further reductions in catalyst loading show deteriorating cell performances in 1000 h long term testing. In this study the performance degradation data of MEAs with lower anode loadings were shown and the degradation effects differentiated. The degradation characteristics were also partially localized using electrochemical impedance spectroscopy and reference electrode measurements⁴ in order to separate cathodic and anodic overvoltages.

We aim to contribute to the understanding of the degradation mechanisms and to possible cost reductions of MEAs for PEM electrolysis by showing the relation between anode loading and long term stability. This information shall assist in making PEM water electrolysis both cost effective and durable.

Fig. 1: Top: single cell performance under a heavily reduced anode loading of 0,60 mg/cm² IrO₂. We were able to obtain similar cell performances as for the regular loadings of 2,25 mg/cm² IrO₂ and stable cell performances over time (bottom).

References:

1. M. Carmo, D. Fritz, J. Mergel and D. Stolten, International Journal of Hydrogen Energy, 38, 4901-4934 (2013)

2. K. Ayers, PEM Electrolysis R&D Webinar, presented at the DOE Fuel Cell Technologies Program Webinar, May 23 (2011)

3. Debe, M. K.; Hendricks, S. M.; Vernstrom, G. D.; Meyers, M.; Brostrom, M.; Stephens, M. et al.:. In: J. Electrochem. Soc. 159 (6) (2012)

4. Jung, Myunghee; van Zee, John W., 216th ECS Meeting, 1585–1593 (2009)