Light-Driven Bias-Free Photoelectrochemical Cells for Hemin-Catalyzed Ammonia Generation

With the increase in the world population and humanity’s food demands, the essentiality of ammonia, a crucial compound for advanced agriculture, continues to rise. While the Haber–Bosch process provides a valid solution, alternatives should be explored to decrease high energy demands. Herein, we present the development of a simple and low-cost electrocatalytic process for generation of ammonia from nitrite. For that, hemin was examined as a catalyst in a heterogeneous process. The hemin was functionalized on a carbon electrode support, and ammonia production was determined under varied conditions. Cyclic voltammetry and chronoamperometry measurements were used for characterization, followed by quantification of the ammonia generated. The results revealed that during 24 h of activation at −0.8 V vs Ag/AgCl, 1.8 mM of ammonia could be generated. The generation of ammonia was validated via 1H NMR using marked 15N. The hemin-based cathode was then coupled with a CdS/NiOx-based photoanode to construct a standalone photoelectrochemical cell. The photoelectrochemical cell was activated with a white LED light to enable bias-free ammonia production. The cell was continuously activated, while ascorbic acid was used as an electron donor. The bias-free configuration led to the production of 0.2 mM ammonia during 5 h of cell activation. The electrocatalytic process has shown great promise for further development, which may lead to clean and lower energy consumption in ammonia production.