The Complete Oxidation of Glycerol to CO2: A Hybrid Enzymatic and Organic Electrocatalytic Cascade

There has been a significant interest lately in the complete oxidation of biofuels to CO₂. The use of multiple biocatalysts allows for deeper biofuel oxidation and thus maximizes the energy density that can be extracted per molecule of biofuel. However, there are still many biofuels for which a suitable biocatalyst is not known. We have recently taken an alternative approach to combine the high catalytic activity of enzymatic biocatalysts with the promiscuous nature of small molecule organic catalysts. We demonstrate the complete electrochemical oxidation of the biofuel glycerol to CO₂ using a hybrid enzymatic and small-molecule catalytic system. Combining an enzyme, oxalate oxidase, and an organic oxidation catalyst, 4-amino-TEMPO, we are able to electrochemically oxidize glycerol at a carbon electrode, while collecting as many as 16 e^-s per molecule of fuel. Additionally, we investigate the anomalous electrocatalytic properties that allow 4-amino-TEMPO to be active under the acidic conditions required for oxalate oxidase to function.