Enhanced charge- carrier dynamics and efficient solar- to- urea conversion on Si- based photocathodes

Photoelectrochemical (PEC) coupling of CO2 and nitrate can provide a useful and green source of urea, but the process is affected by the photocathodes with poor charge- carrier dynamics and low conversion efficiency. Here, a NiFe diatomic catalysts/TiO2 layer/nanostructured n+p- Si photocathode is rationally designed, achieving a good charge- separation efficiency of 78.8% and charge- injection efficiency of 56.9% in the process of PEC urea synthesis. Compared with the electrocatalytic urea synthesis by using the same catalysts, the Si- based photocathode shows a similar urea yield rate (81.1 mg center dot h-1 center dot cm-2) with a higher faradic efficiency (24.2%, almost twice than the electrocatalysis) at a lower applied potential under 1 sun illumination, meaning that a lower energy- consumption method acquires more aimed productions. Integrating the PEC measurements and characterization results, the synergistic effect of hierarchical structure is the dominating factor for enhancing the charge- carrier separation, transfer, and injection by the matched band structure and favorable electron- migration channels. This work provides a direct and efficient route of solar- to- urea conversion.