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Highlights Electrodeposited amorphous IrO x thin electrodes are first developed for proton exchange membrane electrolyzer cells. An ultralow loading of 0.075 mg cm−2 archives superior performance to catalyst-coated membrane (2 mg cm−2). > 96% of catalyst savings and > 42-fold higher catalyst utilization are demonstrated.

Highlights 4-nm-thick Pt nanosheets (Pt-NSs) are electrochemically grown on Ti substrates for hydrogen evolution reactions. Highly uniform Pt-NS surface coverage with an ultralow loading of 0.015 mgPt cm−2 is achieved. 99.5% catalyst savings and about 237-fold higher catalyst utilization are demonstrated.

Abstract Interfacial and bulk properties between the catalyst layer and the porous transport layer (PTL) restrict the iridium loading reduction for proton exchange membrane water electrolyzers (PEMWEs), by limiting their mass and charge transport. Using titanium fiber PTLs of varying thickness and porosity, the bulk and interface transport properties are investigated, correlating them to PEMWEs cell performance at ultra‐low Ir loadings of ≈0.05 mgIr cm−2. Electrochemical experiments, tomography, and modeling are combined to study the bulk and interfacial impacts of PTLs on PEMWE performance. It is found that the PEMWE performance is largely dependent on the PTL properties at ultra‐low Ir loadings; bulk structural properties are critical to determine the mass transport and Ohmic resistance of PEMWEs while the surface properties of PTLs are critical to govern the catalyst layer utilization and electrode kinetics. The PTL‐induced variation in kinetic and mass transport overpotential are on the order of ≈40 and 60 mV (at 80 A mgIr−1), respectively, while a nonnegligible 35 mV (at 3 A cm−2) difference in Ohmic overpotential. Thus at least 150 mV improvement in PEMWE performance can be achieved through PTL structural optimization without membrane thickness reduction or advent of new electrocatalysts.