Direct Electrochemical Oxidation Mechanism on Ni ₃ Se ₂ Nanosheets for Selective Methanol-to-Formate Conversion Coupled with Hydrogen Generation

Gaining insights into the reaction mechanism on nickel-based electrocatalysts is actually imperative for the optimization of the methanol oxidation reaction (MOR) activity, but it still faces challenges in identifying the authentic electroactive species for the MOR. Herein, Ni₃Se₂ nanosheets supported on nickel foam (Ni₃Se₂/NF) were synthesized via a facile hydrothermal method and further employed as an excellent electrocatalyst for selectively catalyzing methanol upgrading into value-added formate. The Ni₃Se₂/NF electrode exhibits outstanding electrocatalytic activity and stability toward the MOR. Impressively, when coupled with the hydrogen evolution reaction (HER), it achieves high faradaic efficiencies of over 95% for formate generation within the voltage range of 1.65 to 1.80 V in a two-electrode electrolyzer. Especially, in situ Raman spectroscopy demonstrates that the electrochemical MOR process does not involve the formation of NiOOH, highlighting a direct MOR mechanism over the Ni₃Se₂/NF electrode rather than an indirect oxidation pathway relying on the surface reconstruction. The electron paramagnetic resonance (EPR) together with multipotential step (STEP) tests reveal that ^•OH radicals are electroactive species for the MOR, and the reaction between methanol oxidation and ^•OH reduction is a nonspontaneous process.