Enabling Low Iridium Loadings and Reduced Catalyst Material Cost for PEM Water Electrolyzers Via Composite Anode Design with Conductive Additive
Authors: Ferner Kara J , Litster Shawn 
Published: December 2024

The production of inexpensive, clean hydrogen will be vital for supporting wide decarbonization efforts across the sectors of industrial chemicals, transportation, and the electric grid. Proton exchange membrane water electrolysis (PEMWE) has great potential as a low-temperature, high current density option for low-carbon hydrogen production; however, at present one of its most significant barriers to widespread commercial adoption is the high cost associated with the iridium (Ir) anode catalyst1.

Unfortunately, many problems arise when lower Ir loadings are attempted. When considering catalyst layers (CLs) comprised only of IrO2, decreasing Ir loadings directly correlates to diminished mechanical robustness and electrode thickness. In this case, low Ir loading anodes can suffer large performance limitations caused by reduced in-plane electrical conductivity and poor interfacial contact with the porous transport layer (PTL), both of which are known to be crucial for good electrolyzer performance2,3. Some success in reaching sufficient activity with lower loadings has been achieved by synthesizing IrO2 particles on a supporting material4, but these anodes are often limited by high insulating characteristics of viable supports as well as additional chemical processing steps. Towards this end, the next decade’s targets for low Ir loadings and high Ir-specific performance urgently necessitate new designs and methods for fabrication of the PEMWE anode.

Herein, we present the successful implementation of a composite anode structure using a conductive additive to enable low Ir loadings for PEMWE while maintaining robust, high-performance operation. As an initial demonstration, we simply use platinum (Pt) black as the conductive additive given its high known electrical conductivity, acid-stability, and a price that is current one-fifth that of Ir5. Results are compared across various loadings of pure-IrO2 anodes, a composite anode with Pt black, and a pure-Pt-black anode. We show physical characterization results from SEM images and four-point probe measurements for sheet resistance, finding that the addition of Pt black reduced electrode sheet resistance by four orders of magnitude. We also present electrochemical characterization results, which revealed that when compared to a high Ir loading anode, the composite anode facilitated a 95% reduction in Ir loading and 80% cost reduction of the anode catalyst materials while maintaining equal current density performance @Ecell = 1.8 V. With this method, we show promising results towards lowering Ir loadings and material costs, addressing a major barrier to the widespread adoption of PEMWE for clean hydrogen production.

References

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“PGM Management,” Johnson Matthey, https://matthey.com/products-and-markets/pgms-and-circularity/pgm-management (accessed 2024-02-15).