Intensifying N 2 Transport and Stabilizing Triple Phase Boundary via Introducing a Gas-Diffusion Electrode into a Photoelectrochemical Cell for Ammonia Production

The photoelectrochemical (PEC) cell for the nitrogen reduction reaction is an attractive route to green ammonia synthesis, but is challenged by low N2 solubility and a competitive hydrogen evolution reaction. Herein we introduce a gas-diffusion electrode (GDE) into a flow PEC cell as a cathode to intensify nitrogen transport. In this type of PEC cell, a hydrophobically treated carbon paper loaded with Bi2S3/MXene functions as the GDE, while a CdS/S-doped TiO2 nanotube array serves as the photoanode. The flow PEC cell with a GDE achieves an ammonia production rate of 8.339 μg·h–1·cm–2 and a Faradaic efficiency of 5.65%, representing 25.4% and 42.9% higher values than the H-type PEC cell, respectively. Although increasing the applied cell voltage and light intensity can boost the ammonia production rate, the Faradaic efficiency decreases. This work demonstrates that GDE provides a robust reactor-level approach to enhance ammonia production and offers engineering insights into the design and operation of the PEC cell toward a green ammonia synthesis.