Effect of Iron Impurities on the Electrochemical Oxidation of Glycerol on Ni(OH)₂/NiOOH Electrodes

Herein, the effect of iron (Fe) ions impurities in alkaline electrolyte is investigated for enhancing the activity of nickel-oxyhydroxide (NiOOH) for electrochemical oxidation of glycerol (EOG). Cyclic voltammetry and chronoamperometry analyses show that Fe impurities have a significant effect on both EOG activity and product distribution. We found the presence of Fe impurities in the electrolyte enhance the C−C cleavage bonds within glycerol and its intermediates, thereby favoring the formation of C2 and C1 products. Our results deviate from the conventional observations in Ni-based catalysis for EOG, which instead of the anticipated glycolate and formate products resulting from the C−C scission of glycerate, we observe the generation of oxalate (C2) and formate (C1), therefore suggesting the involvement of aldehyde intermediates in the reaction mechanism, providing a novel perspective on the higher faradaic efficiency of formic acid compared to glycolic acid. These results show the importance of eliminating iron ions from the electrolyte solution, as this step is pivotal in comprehending the cation effect on the electrochemical oxidation of glycerol in alkaline environments.