Bias-Free Solar-Driven Ammonia Coupled to C₃-Dihydroxyacetone Production through Photoelectrochemistry

Conversion of solar energy into value-added chemicals through photoelectrochemistry (PEC) holds great potential for advancing sustainable development but limits by high onset potential which affects energy conversion efficiencies. Herein, we utilized a CuPd cocatalyst-modified Sb₂(S,Se)₃ photocathode (CuPd/TSSS) to achieve an ultra-low onset potential of 0.83 V_RHE for photoelectrochemical ammonia synthesis. Meanwhile, we achieved unbiased NH₃ production by synthesizing major value-added C₃-dihydroxyacetone (DHA) through glycerol oxidation on the BiVO₄ photoanode with the loading Pd cocatalyst, instead of a traditional solar water oxidation reaction. The PEC integrated system stably produced 11.98 μmol cm^-2 of NH₃ and 201.9 mmol m^-2 of DHA over 5 h with ~80 % faradaic efficiency without applying additional bias. In situ analysis and theoretical calculations confirmed high catalytic activity for ammonia synthesis at the CuPd/TSSS photocathode and enhanced selectivity for DHA at the Pd/BiVO₄ photoanode. This design represents a breakthrough in directly utilizing solar energy, nitrate-containing wastewater, and biomass waste for ammonia and highly value-added C₃ production, which addresses increasing energy demands while decreasing environmental impact.