Amorphous and Crystalline Anode Catalysts in Proton Exchange Membrane Electrolysis: Performance and Long-Term Durability: Article No. 241202

Iridium oxide is typically the anode catalyst benchmark in proton exchange membrane water electrolyzers (PEMWE). This work evaluates critical material and electrode properties, assessing the performance and long-term durability (2000 - 4000 h) differences of six commercial catalysts (around 0.4 mgIr/cm2 on anode catalyst layer). The amorphous and crystalline types show distinguishable performance decay under a steady hold at 3 A/cm2. The amorphous group consistently demonstrated higher cell efficiency within 250 h, mainly attributed to a combination of higher reactivity and site access. Although the crystalline group generally had lower initial kinetic performances, one catalyst (Pajarito) exhibits a good initial kinetic performance (385 mV at 3A/cm2) and a modest degradation rate (7 ..mu..V/h), around 65% lower than the amorphous baseline. Equivalent circuit modeling (ECM) and distribution of relaxation times (DRT) further revealed lower polarization resistances, lower catalyst layer resistances and higher capacitances with the amorphous group, however, the kinetic benefit tended to degrade faster. This type of degradation speaks to crystallization processes, verified by high-resolution microscopy, X-ray scattering, and spectroscopy techniques. The evaluation of catalyst development efforts at the device level is critical for next-generation materials in PEMWEs and benefits an understanding of cost/lifetime tradeoffs and degradation mitigation strategies.