Efficient Electrocatalytic Hydrogenation of Nitroaromatics into Arylamines on a Pseudocrystalline MoSx Cathode in an Alkaline Electrolyte

Abstract

The development of an active Earth-abundant metal electrocatalyst for the hydrogenation of aromatic nitro compounds to aromatic amines using water as a clean and safe hydrogen source can greatly benefit the green synthesis of fine chemicals. Herein, we reported a novel pseudocrystalline structured molybdenum sulfide (p-MoS_x) as a great electrocatalytic hydrogenation catalyst in converting nitrobenzene (Ph-NO₂) to aniline (Ph-NH₂) with a Faraday efficiency (F.E.%) of 82.2% and over 99.1% selectivity at a conversion of 99.6%, outperforming both the amorphous and crystalline MoS_x catalysts. The p-MoS_x was synthesized and deposited on a carbon cloth support via a hydrothermal-only strategy, where the crystallinities of the MoS_x were realized by altering the feeding ratio of ammonium molybdate and thiourea during the synthetic processes. Activity origin investigations with underpotential deposition of hydrogen (HUPD) studies, electrochemical active areas (ECSA) measurements, and electrochemical impedance spectroscopy (EIS) tests revealed that the unique pseudocrystalline structure can optimize the chemisorbed hydrogen (H_ads) formation and nitro group adsorption on the surface, thereby promoting the hydrogenation step and consequently improving the efficiency for converting Ph-NO₂ to Ph-NH₂ with high selectivity (>95%) in a broad potential range. In addition, the p-MoS_x/CC electrode was also found to be efficient in catalyzing electrochemical hydrogenation of other nitro compounds containing fragile functional groups, such as C–X (X = F, Cl, Br), C═O, C═C, C≡N, and C≡C, to the corresponding aromatic amines.