Engineering diamond-based photocathodes for visible light-driven hydrogen generation

Diamond-based materials feature manifold attractive properties for different electrochemical applications, thanks to its chemical inertness and large operational bias window. Nevertheless, the blindness to Visible (Vis) light typically hinders their application in photo-electrochemistry using a sustainable source like solar radiation. In the present work, we propose an original all‑carbon solution for the development of efficient photocathodes for hydrogen evolution with the functional integration of Vis light harvesting, charge transport, and interfacial processes in a single platform. The electrode is based on the implementation of surface nanostructuring by ultra-short pulsed laser on free-standing polycrystalline chemical vapor deposition (CVD) diamond plates. In particular, the photocathode is made up of micro-distributed graphitic paths in the inner material regions to reduce the series resistance and of a nitrogen-incorporated ultra-nanocrystalline layer as active element for the catalytic process. In photo-activated hydrogen evolution under Vis irradiation, the engineered cathode subjected to hydrogen plasma treatment yields a photocurrent of −0.14 mA/cm2 at 0 V vs. the reversible hydrogen electrode (RHE) and a Tafel slope of −273 mV/dec. The present outcomes, related to the formation of defect-related surface states, open the door to the application of the proposed diamond-based structures in sustainable energy generation.