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

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.