Durable Thin-Film Porous Transport Electrodes for High Current Density PEM Water Electrolysis

Proton exchange membrane water electrolyzers rely on relatively expensive Ir-based catalysts for efficient and durable hydrogen production. To reduce system costs, Ir loadings can be reduced if performance and durability are maintained. Sputter deposition is a readily scalable method to synthesize uniform, low-loading catalyst layers with controlled composition. A catalyst applied directly to the porous transport layer can have advantages for performance, manufacturing simplicity, and catalyst recovery. Suitable porous transport layer porosity can minimize activity losses when reducing loadings. Here, methods are presented to deposit metallic Ir as well as amorphous and rutile Ir oxides. The activity and durability of these materials in the porous transport electrode architecture is evaluated. The metallic and amorphous forms have better initial activity, however, operation at 3 A cm^-2 with 0.1 mg Ir cm^-2 shows that only rutile IrO₂ maintains performance beyond 100 h with a 50 mV improvement after 700 h. A >10x reduced dissolution rate is shown for rutile IrO₂. With a low-porosity transport layer and 0.4 mg Ir cm^-2, a steady-state voltage decay rate of 6 µV h^-1 is achieved. The results demonstrate that sputter-deposited rutile IrO₂ porous transport electrodes with low Ir loading can be operated at high current density to reduce hydrogen production costs.