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 VRHE 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.