Selective electrosynthesis of hydroxylamine from aqueous nitrate/nitrite by suppressing further reduction.

The electrocatalytic reduction of nitrogenous waste offers a sustainable approach to producing nitrogen-containing chemicals. The selective synthesis of high-value hydroxylamine (NHOH) is challenging due to the instability of NHOH as an intermediate. Here, we present a rational electrocatalyst design strategy for promoting NHOH electrosynthesis by suppressing the competing pathways of further reduction. We screen zinc phthalocyanines (ZnPc) with a high energy barrier for NHOH reduction by regulating their intrinsic activity. Additionally, we discover that carbon nanotube substrates exhibit significant NH-producing activity, which can be effectively inhibited by the high coverage of ZnPc molecules. In-situ characterizations reveal that NHOH and HNO are generated as intermediates in nitrate reduction to NH, and NHOH can be enriched in the ZnPc electrode. In the H-cell, the optimized ZnPc catalyst demonstrates a Faradaic efficiency (FE) of 53 ± 1.7% for NHOH with a partial current density exceeding 270 mA cm and a turnover frequency of 7.5 ± 0.2 s. It also enables the rapid electrosynthesis of cyclohexanone oxime from nitrite with a FE of 64 ± 1.0%.