Light-Driven\nBias-Free Photoelectrochemical Cells\nfor Hemin-Catalyzed Ammonia Generation

With\nthe increase in the world population and humanity’s\nfood demands, the essentiality of ammonia, a crucial compound for\nadvanced agriculture, continues to rise. While the Haber–Bosch\nprocess provides a valid solution, alternatives should be explored\nto decrease high energy demands. Herein, we present the development\nof a simple and low-cost electrocatalytic process for generation of\nammonia from nitrite. For that, hemin was examined as a catalyst in\na heterogeneous process. The hemin was functionalized on a carbon\nelectrode support, and ammonia production was determined under varied\nconditions. Cyclic voltammetry and chronoamperometry measurements\nwere used for characterization, followed by quantification of the\nammonia generated. The results revealed that during 24 h of activation\nat −0.8 V vs Ag/AgCl, 1.8 mM of ammonia could be generated.\nThe generation of ammonia was validated via <sup>1</sup>H NMR using\nmarked <sup>15</sup>N. The hemin-based cathode was then coupled with\na CdS/NiOx-based photoanode to construct a standalone photoelectrochemical\ncell. The photoelectrochemical cell was activated with a white LED\nlight to enable bias-free ammonia production. The cell was continuously\nactivated, while ascorbic acid was used as an electron donor. The\nbias-free configuration led to the production of 0.2 mM ammonia during\n5 h of cell activation. The electrocatalytic process has shown great\npromise for further development, which may lead to clean and lower\nenergy consumption in ammonia production.