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 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 Li_xMoO₃/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 Mo⁵⁺ ions, which results in faster NRR kinetics and activates inert MoO₃ into efficient Li_xMoO₃ electrocatalyst towards NH₃ synthesis. This work holds great promise in constructing monolithic PEC device to directly harvest solar light for artificial ammonia photosynthesis.