Mn-modified nickel oxide for selective methanol oxidation: a route toward integrated formate electrosynthesis and hydrogen generation

Abstract

The overall energy efficiency of water electrolysis is constrained by the inherently slow kinetics of the oxygen evolution reaction (OER), which also generates a product of limited economic value. A promising strategy to overcome this drawback involves replacing OER with a more thermodynamically and kinetically favorable anodic reaction that enables hydrogen generation at lower energy input while simultaneously producing value-added chemicals. In this work, we investigate the electrochemical reforming of methanol under alkaline conditions, using a Mn-doped nickel oxide (Mn–NiO) anode to catalyze methanol oxidation to formate, coupled with hydrogen evolution at a platinum cathode. The Mn-doped NiO electrode achieves a methanol oxidation reaction (MOR) current density of 58 mA cm⁻² at 1.6 V vs. RHE in 1 M KOH with 1 M methanol, significantly outperforming undoped NiO. Both electrodes exhibit excellent faradaic efficiency, with formate generation reaching approximately 97%. The Mn-doped NiO electrode exhibited remarkable stability, maintaining a steady current density of 33.8 mA cm⁻² during continuous chronoamperometric (CA) testing for 100 h at 1.65 V vs. RHE in 1 M KOH containing 1 M methanol. When the electrolyte concentration was increased to 3 M KOH, the electrode delivered a methanol oxidation reaction (MOR) current density of 123 mA cm⁻², which gradually decreased to 61.1 mA cm⁻² after 24 h of CA operation. Density functional theory calculations reveal that Mn incorporation modulates the electronic structure of NiO, effectively lowering the energy barrier for methanol-to-formate conversion. These findings provide valuable insights for the design of low-cost, high-efficiency electrocatalysts that integrate organic oxidation with hydrogen evolution, offering a more energy-efficient and economically attractive route for hydrogen production and chemical valorization.