Tuning the Selectivity of Glycerol Electrooxidation via Catalyst Composition and Operating Conditions

The electrooxidation of glycerol presents a promising route for upgrading a biodiesel byproduct into high-value chemicals while lowering the energy cost of electrochemical hydrogen production, but its mechanistic understanding remains incomplete. This work investigates the influence of temperature and catalyst composition on glycerol electrooxidation using three distinct electrocatalysts: first-row transition-metal NiCo oxide, noble metal AuIn alloy, and hybrid PdNi alloy. Electrochemical, in situ UV-vis reflectance and in situ Raman measurements reveal catalyst-specific oxidation mechanisms: an oxyhydroxide-mediated path for NiCo, an adsorbed hydroxide-mediated path for AuIn which suffers from inhibition, and a dual mechanism for PdNi. Oxyhydroxide mechanisms favor formic acid, whereas adsorbed hydroxide pathways selectively promote C₃ products such as glyceric acid and dihydroxyacetone. Flow cell electrolysis across a range of temperatures and flow rates relevant to industrial application shows that elevated temperature enhances reaction rates and mitigates catalyst inhibition, a relevant effect for the hybrid catalyst. These findings provide key mechanistic insights and practical guidelines for optimizing continuous-flow glycerol electrooxidation systems.