Ultralow-Potential Photoelectrochemical Synthesis of Hydroxylamine and Oximes

The efficient and environmentally friendly synthesis of hydroxylamine (NH₂OH) remains a challenge in sustainable chemical production. Electrochemical nitrate reduction to NH₂OH suffers from dependence on external hydrogen sources, which often lead to the nitrite accumulation or over-reduction of NH₂OH to ammonia due to unbalanced hydrogenation intensity. Herein, we report the photoelectrochemical nitrate reduction to NH₂OH (PENRH) using a bimetallic Bi- and Cu-modified TiO₂/CdS/Sb₂(S,Se)₃ semiconductor. Under AM 1.5 G illumination, the resulting photocathode achieves a Faradaic efficiency of 91.9% and a selectivity of 92.7% at 0.3 V_RHE for NH₂OH, while effectively suppressing side reactions. In situ characterization and theoretical calculations reveal that the synergy between Bi and Cu sites optimizes the adsorption of intermediates, promotes NO₃ ^- protonation, and facilitates the rapid desorption of NH₂OH, thereby preventing its over-reduction. This system is successfully extended to the oxime synthesis by coupling in situ generated NH₂OH with aldehydes or ketones, enabling efficient preparation of various oximes and demonstrating the broad applicability of PENRH. This work not only introduces a green photoelectrochemical approach for NH₂OH synthesis, but also offers a new paradigm for the resource utilization of nitrate.