Unveiling complete lactate oxidation through a hybrid catalytic cascade

Although challenging, the generation of energy through the harvesting of electrons from biological fluids via fuel cells is a promising technology for wearable electronics. However, a current challenge is that neither a single molecular catalyst or an enzyme can completely oxidize fuels in biological fluids. With this issue in mind, herein, we report a hybrid bi-catalytic system allowing complete lactate oxidation by combining an organic catalyst, 4-amino-TEMPO (Amino-TEMPO), with a recombinant enzyme, oxalate decarboxylase (OxDc). This hybrid system was chosen due to the high oxidative catalytic activity of the molecular catalyst and the promiscuity of the recombinant enzyme to alternative substrates. The hybrid architecture enhanced the performance of the bioanode, enabling higher efficiency and improved stability of the energy-harvesting fuel cell. The hybrid system showed high catalytic activity, achieving a high and stable current density of 23.0 ± 1.5 mA cm−2 for lactate oxidation after 48 h of bulk electrolysis. Intermediate and product analysis by nuclear magnetic resonance (NMR) and gas chromatography (GC) coupled to a thermal conductivity detector (TCD) confirmed that the hybrid architecture acts in the multiples catabolic steps of lactate oxidation, enabling the complete oxidation of lactate to CO2 by collecting 12 electrons from the fuel molecule.