Electrochemical\nHydrogenation of Nitrobenzene: From\nElectrocatalysis to Redox Mediator Catalysis

Introducing polyoxometalates (POMs) as redox mediators\ncan decouple\ndirect electrochemical reactions into surface-homogeneous conversion\nsteps. And the formed redox catalysis is beneficial to achieve more\nefficient hydrogenation of nitrobenzene (Ph-NO<sub>2</sub>) to aniline\n(Ph-NH<sub>2</sub>) at low overpotentials. Notably, the redox potentials\nof POMs can adjust the energy barrier of the hydrogenation reaction,\nthus improving conversion efficiency. In particular, by using phosphotungstic\nacid ({PW<sub>12</sub>}) as the redox mediator, the potential of the\nhydrogenation of Ph-NO<sub>2</sub> to Ph-NH<sub>2</sub> was improved\nto 0.04 V vs RHE with a very high <i>k</i><sub>app</sub> of 0.0339 min<sup>–1</sup>. This indicates its superior kinetic\nperformance over that of most previously reported electrocatalysts.\nIn addition, through comparative mechanistic studies of electrocatalysis\nand redox mediator catalysis, EC-SERS revealed the preferential adsorption\nof mediator molecules and their direct interactions with intermediates.\nThis work is significant to a deep understanding of the mechanistic\nbehaviors and potential tuning effects of redox mediators, which will\nhelp to develop more efficient mediators for the hydrogenation of\nPh-NO<sub>2</sub>.