Highly Selective Electrooxidation of Glycerol to Tartronic Acid Over a Single-Atom Rhodium Catalyst Supported on Indium Oxide.

The electrooxidation of biodiesel-derived glycerol offers an effective approach for the sustainable production of valuable C3 compounds. However, highly selective synthesis of a specific C3 compound, such as tartronic acid (TA), by glycerol electrooxidation remains a big challenge due to the competitive dehydrogenation between CαH2(OH) and CβH(OH). Herein this study reports a glycerol electrochemical oxidation reaction (GEOR) for the selective production of TA, which is catalyzed by a single-atom rhodium catalyst supported on indium oxide (Rh1-In2O3) in an alkaline medium. At a potential of 1.40 V versus reversible hydrogen electrode, the Rh1-In2O3-catalyzed GEOR achieves an optimal TA selectivity of 93.2% and a productivity of 4.6 mmol cm-2 h-1, outperforming all previously reported electrocatalytic systems for the GEOR. Experimental results, complemented by density functional theory calculation, reveal that the single-atom Rh catalyst improves glycerol oxidation by facilitating hydroxyl oxidation to active oxygen species and greatly decreasing the energy barrier for CαH2(OH) dehydrogenation in the GEOR process, thus resulting in high TA selectivity. Furthermore, an integrated electrolyzer, combining GEOR with the hydrogen evolution reaction, achieves a current density of 100 mA cm-2 at a cell voltage of 1.50 V. A techno-economic analysis demonstrates the economic feasibility of this integrated system.