Electrochemistry-Assisted Photoelectrochemical Reduction of Nitrogen to Ammonia

Abstract

Ammonia (NH3) is a basic chemical feedstock for the production of fertilizers and pharmaceuticals, and it emerges as a new hydrogen energy carrier for renewable energy sources such as solar and wind power. A photoelectrochemical nitrogen reduction reaction (PEC NRR) under mild operating conditions represents a potentially green and convenient approach for the synthesis of NH3. However, a generally applicable PEC NRR featuring a high NH3 yield and a satisfactory conversion efficiency remains elusive. Herein, we report on a simple and effective electrochemistry-assisted strategy to enhance the PEC fixation of N2 to NH3. Using this strategy, we harness a steel-based cathode-assisted Au/SiO2/Si photocathode to seamlessly combine two critical reaction steps—N2 activation and hydrogenation—to realize an NH3 yield rate of 22.0 μg·cm–2·h–1 and a faradic efficiency of 23.7% at −0.2 V versus a reversible hydrogen electrode under one sun illumination. We also provide an accessible reaction setup to avoid the disturbance of a contamination by air, human breath, and N2 stream, leading to a reliable production of NH3 by the PEC NRR. An operando characterization and a theoretical calculation uncover the active sites and reaction mechanism of the whole system for an electrochemistry-assisted PEC NRR. This work demonstrates the capability of an electrochemistry-assisted excitation in PEC NRR, and it introduces a new design concept for addressing pertinent challenges in photoelectrochemical and other chemical fields.