Efficient electrocatalytic oxidation of glycerol toward formic acid over well-defined nickel nanoclusters capped by ligands

The electrocatalytic oxidation of glycerol toward formic acid is one of the most promising pathways for transformation and utilization of glycerol. Herein, a series of well-defined Ni_n(SR)_2n nanoclusters (n = 4, 5, 6; denoted as Ni NCs) were prepared for the electrocatalytic glycerol oxidation toward formic acid, in which Ni₆-PET-50CV afforded the most excellent electrocatalytic performance with a high formic acid selectivity of 93% and a high glycerol conversion of 86%. This was attributed to the lowest charge transfer impedance and the most rapid reaction kinetics. Combined electrochemical measurements and X-ray absorption fine structure measurements revealed that the structures of Ni NCs remained intact after CV scanning pretreatment and electrocatalysis via forming the Ni–O bond. Additionally, the kinetic studies and in-situ Fourier transformed infrared suggested a sequential oxidation mechanism, in which the main reaction steps of glycerol → glyceraldehyde → glyceric acid were very rapid to produce a high selectivity of formic acid even though the low glycerol conversion. This work presents an opportunity to study Ni NCs for the efficient electrocatalytic oxidation of biomass-derived polyhydroxyl platform molecules to produce value-added carboxylic acids.