Highly Durable Nanoporous Cu(2–x)S Films for Efficient Hydrogen Evolution Electrocatalysis under Mild pH Conditions

[Image: see text] Copper-based hydrogen evolution electrocatalysts are promising materials to scale-up hydrogen production due to their reported high current densities; however, electrode durability remains a challenge. Here, we report a facile, cost-effective, and scalable synthetic route to produce Cu(2–x)S electrocatalysts, exhibiting hydrogen evolution rates that increase for ∼1 month of operation. Our Cu(2–x)S electrodes reach a state-of-the-art performance of ∼400 mA cm(–2) at −1 V vs RHE under mild conditions (pH 8.6), with almost 100% Faradaic efficiency for hydrogen evolution. The rise in current density was found to scale with the electrode electrochemically active surface area. The increased performance of our Cu(2–x)S electrodes correlates with a decrease in the Tafel slope, while analyses by X-ray photoemission spectroscopy, operando X-ray diffraction, and in situ spectroelectrochemistry cooperatively revealed the Cu-centered nature of the catalytically active species. These results allowed us to increase fundamental understanding of heterogeneous electrocatalyst transformation and consequent structure–activity relationship. This facile synthesis of highly durable and efficient Cu(2–x)S electrocatalysts enables the development of competitive electrodes for hydrogen evolution under mild pH conditions.