Wafer-Level Artificial Photosynthesis for CO₂ Reduction into CH₄ and CO Using GaN Nanowires

We report on the first demonstration of high-conversion-rate photochemical reduction of carbon dioxide (CO 2 ) on gallium nitride (GaN) nanowire arrays into methane (CH 4 ) and carbon monoxide (CO). It was observed that the reduction of CO 2 to CO dominates on as-grown GaN nanowires under ultraviolet light irradiation. However, the production of CH 4 is significantly increased by using the Rh/Cr 2 O 3 core/shell cocatalyst, with an average rate of ∼3.5 μmol g cat –1 h –1 in 24 h. In this process, the rate of CO 2 to CO conversion is suppressed by nearly an order of magnitude. The rate of photoreduction of CO 2 to CH 4 can be further enhanced and can reach ∼14.8 μmol g cat –1 h –1 by promoting Pt nanoparticles on the lateral m -plane surfaces of GaN nanowires, which is nearly an order of magnitude higher than that measured on as-grown GaN nanowire arrays. This work establishes the potential use of metal-nitride nanowire arrays as a highly efficient photocatalyst for the direct photoreduction of CO 2 into chemical fuels. It also reveals the potential of engineered core/shell cocatalysts in improving the selectivity toward more valuable fuels.