An integrated Si photocathode with lithiation-activated molybdenum oxide nanosheets for efficient ammonia synthesis

As an alternative to the conventional industrial Haber-Bosch process, photoelectrochemical (PEC) routes that are powered by renewable solar energy hold great promise for N 2 reduction reaction (NRR) towards NH 3 synthesis at ambient conditions. However, great challenges remain in promoting NH 3 production rate for the PEC NRR devices, especially with the earth-abundant catalysts. Here we report an integrated Li x MoO 3 / n + np + -Si photocathode could achieve an unprecedented PEC NH 3 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 NH 3 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 MoO 3 into efficient Li x MoO 3 electrocatalyst towards NH 3 synthesis. This work holds great promise in constructing monolithic PEC device to directly harvest solar light for artificial ammonia photosynthesis. A lithiation strategy is adopted to activate inert MoO 3 nanosheets into efficient Li x MoO 3 electrocatalyst towards NH 3 synthesis, and this process causes dramatic structural distortion with abundant oxygen vacancies. With an optically and electrocatalytically decoupled configuration, the integrated Li x MoO 3 / n + np + -Si photocathode enables both sufficient sunlight harvesting and fast N 2 reduction kinetics, leading to an efficient photoelectrochemical NH 3 synthesis performance. • A facile lithiation strategy to activate MoO 3 nanosheets into efficient Li x MoO 3 nanosheets towards NRR. • The rational integration of Si photocathode with Li x MoO 3 nanosheets leads to an efficient photoelectrochemical NH 3 synthesis. • The decoupled configuration of Si photocathode and Li x MoO 3 nanosheets enable both sunlight harvesting and fast N 2 reduction kinetics.