Selective electrosynthesis of hydroxylamine from aqueous nitrate/nitrite by suppressing further reduction
Yirong Tang, Zhan Jiang, Yubo Yuan, Xu Li, Chuyao Jin, Bulin Chen, Zhichao Lin, Jie Zao, Jianwei Du, Xiao Zhang, Xiang Gao, Yongye Liang
Abstract
The electrocatalytic reduction of nitrogenous waste offers a sustainable approach to producing nitrogen-containing chemicals. The selective synthesis of high-value hydroxylamine (NH2OH) is challenging due to the instability of NH2OH as an intermediate. Here, we present a rational electrocatalyst design strategy for promoting NH2OH electrosynthesis by suppressing the competing pathways of further reduction. We screen zinc phthalocyanines (ZnPc) with a high energy barrier for NH2OH reduction by regulating their intrinsic activity. Additionally, we discover that carbon nanotube substrates exhibit significant NH3-producing activity, which can be effectively inhibited by the high coverage of ZnPc molecules. In-situ characterizations reveal that NH2OH and HNO are generated as intermediates in nitrate reduction to NH3, and NH2OH 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 NH2OH with a partial current density exceeding 270 mA cm−2 and a turnover frequency of 7.5 ± 0.2 s−1. It also enables the rapid electrosynthesis of cyclohexanone oxime from nitrite with a FE of 64 ± 1.0%. Electroreduction of nitrate or nitrite offers an appealing route for hydroxylamine synthesis but remains challenging due to its intermediate nature. Here, authors present a selective and fast electrosynthesis of hydroxylamine by tuning metal phthalocyanine activity and removing side reaction sites.