Highly Durable Nanoporous Cu2-x S Films for Efficient Hydrogen Evolution Electrocatalysis under Mild pH Conditions

Copper-based hydrogenevolution electrocatalysts are promisingmaterials to scale-up hydrogen production due to their reported highcurrent densities; however, electrode durability remains a challenge.Here, we report a facile, cost-effective, and scalable synthetic routeto produce Cu2-x S electrocatalysts,exhibiting hydrogen evolution rates that increase for & SIM;1 monthof operation. Our Cu2-x S electrodesreach a state-of-the-art performance of & SIM;400 mA cm(-2) at -1 V vs RHE under mild conditions (pH 8.6), with almost100% Faradaic efficiency for hydrogen evolution. The rise in currentdensity was found to scale with the electrode electrochemically activesurface area. The increased performance of our Cu2-x S electrodes correlates with a decrease in the Tafelslope, while analyses by X-ray photoemission spectroscopy, operando X-ray diffraction, and in situ spectroelectrochemistry cooperatively revealed the Cu-centered natureof the catalytically active species. These results allowed us to increasefundamental understanding of heterogeneous electrocatalyst transformationand consequent structure-activity relationship. This facilesynthesis of highly durable and efficient Cu2-x S electrocatalysts enables the development of competitiveelectrodes for hydrogen evolution under mild pH conditions.