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 NH3 synthesis at ambient conditions. However, great challenges remain in promoting NH3 production rate for the PEC NRR de-vices, especially with the earth-abundant catalysts. Here we report an integrated LixMoO3/n(+)np(+)-Si photo-cathode could achieve an unprecedented PEC NH3 yield rate of 8.7 mu g 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 accom-panying the abundant oxygen vacancies and Mo5+ ions, which results in faster NRR kinetics and activates inert MoO3 into efficient LixMoO3 electrocatalyst towards NH3 synthesis. This work holds great promise in con-structing monolithic PEC device to directly harvest solar light for artificial ammonia photosynthesis.

Automated summary

Photoelectrochemical routes powered by renewable solar energy offer a promising alternative to conventional industrial processes for N-2 reduction reaction (NRR) towards NH3 synthesis at ambient conditions. In this study, an integrated LixMoO3/n(+)np(+)-Si photo-cathode achieved a high PEC NH3 yield rate by efficiently harnessing sunlight and promoting catalytic kinetics, without the use of precious noble metals. The lithiation strategy played a crucial role in enhancing NRR kinetics and activating MoO3 into an efficient electrocatalyst for NH3 synthesis. This work has significant potential for constructing monolithic PEC devices for solar-driven artificial ammonia photosynthesis.