Dual Heterojunction Graphene-Supported Photocatalysts of Copper Oxide Nanowires and Copper Ferrite Nanoparticles for Photoelectrochemical Water Splitting

Photoelectrochemical hydrogen evolution (HER), a half reaction of water splitting, is crucial to the low-cost, environmentally friendly production of clean H2 fuel as part of the solution for transitioning away from a fossil fuel economy. Electrodeposition of a controllable Cu film on graphene followed by thermal annealing at 200–400 °C has been used to produce copper oxide (CuxO, x = 1, 2) nanowires. The relative compositions of CuO and Cu2O layers in the CuxO-Cu/graphene system form a heterojunction structure enabling high efficiency for electron–hole separation and a fast charge transfer rate, where the CuO layer with a proper thickness enhances light absorption, improves the charge separation, and serves as a protective layer for Cu2O photocorrosion while graphene serves as a flexible, highly conductive substrate. A high-performance dual Z-scheme heterojunction photocatalyst to greatly improve charge carrier separation, increase carrier density, and reduce electron–hole recombination is obtained by decorating this CuxO-Cu/graphene system with an efficient cocatalyst based on Cu-based ternary CuFe2O4 nanoparticles, obtained by a solvothermal method. The addition of CuFe2O4 nanoparticles on the best optimized CuxO-Cu/graphene is found to nearly double the photocurrent from −2.64 mA·cm–2 to −4.91 mA·cm–2, making this dual heterojunction catalyst among the best copper-based catalyst systems for HER reported to date.