Photoelectrochemical Nitrate Reduction to Ammonia: Materials, Methods, and Metrics

Ammonia is a crucial chemical feedstock, and its production is a major contributor to greenhouse gas emissions. Electrochemical approaches offer greener routes to ammonia synthesis, but direct nitrogen fixation remains highly challenging. An alternative strategy is the reduction of nitrate, a pollutant commonly found in wastewater, into ammonia and related products. When coupled with lightabsorbing materials, this process can be driven photoelectrochemically, enabling modular systems that simultaneously recover waste nitrogen and generate valuable chemicals. In this review, we critically assess the thermodynamic framework underpinning nitrate reduction, clarify reported redox potentials and reaction pathways, examine analytical methodologies for nitrogen product quantification, and summarise the emerging materials and device architectures for (photo)electrocatalytic nitrate reduction. Finally, we provide recommendations to improve experimental standardisation and accelerate progress in the field.