Efficient, Versatile, and Durable Electrocatalytic Nitroaromatic-to-Arylamine Reduction via Heteroatom-Site Hydrogen-Atom Transfer.

Abstract

The selective reduction of nitroaromatics to arylamines affords key intermediates for the industrial production of diverse chemical stocks and materials. The current reduction strategies generally work under harsh conditions, including high temperature, high pressure, and the use of hazardous hydrogen gas, leading to substantial challenges in sustainability and energy efficiency. To this end, direct electrocatalytic nitroaromatic reduction (with water-originated green hydrogen source) is a promising solution to these issues; however, their industrial applications are limited by the low selectivity, low current density, and poor stability of the catalytic electrodes. Here, we report a universally applicable, efficient, and selective electrocatalytic nitroaromatic-to-arylamine reduction approach utilizing highly stable self-standing Ru1Cu alloy electrodes. Superior performance (e.g., >99% selectivity, >99% yield, and >99% Faradaic efficiency for p-nitrophenol-to-p-aminophenol) can be achieved under mild working conditions and industrial-level current densities, which can be upheld over a wide range of working potentials (∼500 mV), pH values (0-14), and substrate concentrations (12.5-250 mM), and further extended to broad scope of nitroaromatics substrates and drugs. Moreover, we demonstrate the durable operation of electrolysis for over 1000 h in a flow reactor and kilogram-level production of p-aminophenol. Mechanistic investigations revealed that the superior catalytic performance originated from a switch from the PCET pathway to the HAT pathway as a result of the ensemble effect in Ru1Cu, enabling a heteroatom-site bimolecular microkinetic model with significantly promoted activation of surface hydrogen species (*H) and balanced surface bimolecular reaction kinetics.