Insight into the Reactivity of Electrocatalytic Glycerol Oxidation—The Strength of the Hydroxyl Group Bonding on Surface

Glycerol is a main byproduct originating from the transesterification process of vegetable oils and animal fat into biodiesel. The production of glycerol byproduct has become greater than the demand as the biodiesel production has increased. Its oversupply has significantly lowered the market price. Therefore, research on electrocatalytic glycerol oxidation reaction (EGOR) has been highlighted recently since it can generate both electricity and valuable chemicals. Glycerol can be used not only as fuel in direct alcohol fuel cells but also as reactants to produce valuable chemicals like dihydroxyacetone, glyceric acid, glycolic acid, and formic acid. However, it is not fully unknown for the reaction pathway on various catalysts due to the complexity of reaction intermediates. Most of the research focused on finding the mechanism for which desired target substance is produced. However, this work is done to comprehend a key mechanism that not only determines glycerol oxidation having various pathways but also might relate to the selectivity of each intermediate in oxidizing process. What to find the main descriptor that affects the glycerol electro-oxidation would be worthy for further design of the electrocatalyst. Combination studies of <i>ab-initio</i> computations and experiments to find the represent descriptor that affect the glycerol electro-oxidation was performed. The adsorption energies of OH and hydroxyl group in the glycerol at the catalyst surface were compared with calculating binding energies and a crystal orbital Hamilton population (COHP) analysis. As a result, the binding energy of OH and that between the hydroxyl group in glycerol and the catalyst surface were proposed as key descriptors to control the glycerol oxidation reaction in PtCu surface model. Both OH and hydroxyl group of the glycerol molecule were most strongly bound on the PtCu₃ surface. The alloy catalyst of Pt and Cu supported on porous carbon was used to support this data. (Pt/PC, Pt₃Cu/PC, PtCu/PC, and PtCu₃/PC) The mass activity of the glycerol oxidation experiment showed the same tendency as the result of the calculation, that the PtCu₃/PC sample showed the highest mass activity among other catalysts. Therefore, the stronger OH binds on the surface, the higher the reactivity of the glycerol oxidation. This study identified that the binding energy of OH on the catalyst surface is the key descriptor in the glycerol oxidation reaction. This is expected to be helpful in predicting and analyzing the reactivity of glycerol as well as various alcohol-based molecules. This research will pave the way for the design and development of future catalysts to produce value-added chemicals for electrocatalytic glycerol conversion reactions.