An integrated Si photocathode with lithiation-activated molybdenum oxide nanosheets for efficient ammonia synthesis. (November 2022) - Mao, Yuyin
Abstract: As an alternative to the conventional industrial Haber-Bosch process, photoelectrochemical (PEC) routes that are powered by renewable solar energy hold great promise for N2 reduction reaction (NRR) towards NH3 synthesis at ambient conditions. However, great challenges remain in promoting NH3 production rate for the PEC NRR devices, especially with the earth-abundant catalysts. Here we report an integrated Lix MoO3 / n + np + -Si photocathode could achieve an unprecedented PEC NH3 yield rate of 8.7 μg cm −2 h −1, which is among the highest PEC NRR systems ever reported. With an optically and electrocatalytically decoupled configuration, the integrated PEC photocathode could harvest the sunlight sufficiently and simultaneously promote the catalytic kinetics, thus leading to the improved NH3 synthesis. More importantly, such high PEC NRR performance is derived from earth-abundant elements without precious noble metals. Verified by the electrochemical experiments and density functional theory (DFT) calculations, the lithiation strategy gives rise to dramatic structural distortion accompanying the abundant oxygen vacancies and Mo 5+ ions, which results in faster NRR kinetics and activates inert MoO3 into efficient Lix MoO3 electrocatalyst towards NH3 synthesis. This work holds great promise in constructing monolithic PEC device to directly harvest solar light for artificial ammonia photosynthesis. Graphical Abstract: A lithiation strategy is adopted to activate inert MoO3 nanosheets into efficient Lix MoO3 electrocatalyst towards NH3 synthesis, and this process causes dramatic structural distortion with abundant oxygen vacancies. With an optically and electrocatalytically decoupled configuration, the integrated Lix MoO3 / n + np + -Si photocathode enables both sufficient sunlight harvesting and fast N2 reduction kinetics, leading to an efficient photoelectrochemical NH3 synthesis performance. ga1 Highlights: A facile lithiation strategy to activate MoO3 nanosheets into efficient Lix MoO3 nanosheets towards NRR. The rational integration of Si photocathode with Lix MoO3 nanosheets leads to an efficient photoelectrochemical NH3 synthesis. The decoupled configuration of Si photocathode and Lix MoO3 nanosheets enable both sunlight harvesting and fast N2 reduction kinetics.