Direct ammonia and dihydroxyacetone production in an unbiased photoelectrochemical cell.

Guo, Xiaotian; Gao, Rui-Ting; Ren, Shijie; Nguyen, Nhat Truong; Chen, Haojie; Wu, Limin; Wang, Lei · Nat Commun · 2025

basic_science · Level V

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Abstract

Photoelectrochemical production of ammonia usually suffers from a low solar-to-ammonia efficiency and a high overpotential, which influences the bias-free operation of sustainable photoelectrochemistry. Herein, we realize solar-driven ammonia production from waste nitrate by constructing copper-osmium catalysts deposited on the Sb<sub>2</sub>(S,Se)<sub>3</sub> semiconductor, enabling optimized photo-carrier transport pathways and a beneficial co-adsorption configuration of *NO<sub>3</sub>-H<sub>2</sub>O moieties. The photocathode reaches a photocurrent density of 5.6 mA cm<sup>-2</sup> at 0 V<sub>RHE</sub> with a low onset potential of 0.86 V<sub>RHE</sub> and a Faradaic efficiency of 96.98% at 0.6 V<sub>RHE</sub> under AM 1.5 G illumination. We further employ glycerol oxidation reaction on ruthenium doped bismuth oxide catalyst decorated on titanium oxide photoanode, requiring an onset potential of 0.3 V<sub>RHE</sub> to enable bias-free operation. The unbiased photoelectrochemical system shows Faradaic efficiencies of over 97% for ammonia products and above 77% for glycerol oxidation product under AM 1.5 G illumination. The large-sized photoelectrodes maintain a stability for 24 h without noticeable degradation. Our works indicate that unassisted and stable PEC ammonia production is feasible with in situ glycerol valorization using the photoanode and photocathode.