Toward Intrinsic Activity: An Experimental Descriptor for the Hydrogen Evolution Reaction

Efficient hydrogen evolution reaction (HER) catalysts are critical for water electrolysis in hydrogen production. Pt-based high-entropy alloys (Pt-HEAs) offer efficient catalysis with reduced Pt usage, and their performance and cost-effectiveness can be further enhanced through support strategies. However, evaluating the intrinsic activity of supported Pt-HEAs for HERs remains challenging due to the difficulty in accurately measuring the electrochemically active surface area (ECSA). To overcome this challenge, we employed surface-interrogation scanning electrochemical microscopy (SI-SECM) to in situ titrate surface-adsorbed hydrogen (H*); in combination with the Frumkin adsorption isotherm, we established an experimental descriptor based on the effective half-coverage potential (E1/2eff.). This descriptor originates from the H adsorption thermodynamics on the real catalyst surface and accounts for non-ideal adsorption behavior, enabling the correlation of intrinsic HER activity independently of ECSA. This descriptor was successfully validated in Pt, Au, Ag, and Pt0.9Ir0.1 model systems, and it was used to compare and screen the intrinsic activity of 35 Pt-HEA samples. Additionally, a statistical correlation between the elemental combinations and catalytic intrinsic activity was revealed. This study provides an experimental approach for high-throughput screening of multi-component catalytic systems without relying on ECSA normalization, laying a crucial experimental foundation for the precise design of high-performance catalytic materials.