Charge Photoaccumulation in Covalent Polymer Networks for Boosting Photocatalytic Nitrate Reduction to Ammonia

Abstract In the design of photoelectrocatalytic cells, a key element is effective photogeneration of electron‐hole pairs to drive redox activation of catalysts. Despite recent progress in photoelectrocatalysis, experimental realization of a high‐performance photocathode for multi‐electron reduction of chemicals, such as nitrate reduction to ammonia, has remained a challenge due to difficulty in obtaining efficient electrode configurations for extraction of high‐throughput electrons from absorbed photons. This work describes a new design for catalytic photoelectrodes using chromophore assembly‐functionalized covalent networks for boosting eight‐electron reduction of nitrate to ammonia. Upon sunlight irradiation, the photoelectrode stores a mass of reducing equivalents at the photoexcited chromophore assembly for multielectron reduction of a copper catalyst, enabling efficient nitrate reduction to ammonia. By introducing the new photoelectrode structure, it is demonstrated that the electronic interplay between charge photo‐accumulating assembly and multi‐electron redox catalysts can be optimized to achieve proper balance between electron transfer dynamics and thermodynamic output of photoelectrocatalytic systems.