Mechanistic Insight into the Superior Catalytic Activity of Au/Co3O4 Interface in Glucose Sensors

The electrocatalyst on a nonenzymatic electrode is critical to the instant sensing of glucose. Metal/oxide composite catalysts, such as Au/Co3O4, show activity in glucose oxidation on electrodes superior to that of single-component catalysts, but the mechanism is still not clear. In this work, commonly applied gold (Au), cobalt oxide (Co3O4), and their composite (Au/Co3O4) were modeled over the carbon (C) electrode within explicit solvent water molecules to mimic the realistic catalytic condition. Density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations were applied to investigate the free energy profiles of the hemiacetal hydroxyl group oxidation on glucose (CHC-OHO + 2OH^- → C═O + 2H2O + 2e^-). The simulation showed that the dissociation of hydrogen on O (HO) was an acid-base proton transfer process and easy in kinetics. The dissociation of hydrogen on C (HC) was exergonic but suffered from a relatively high free energy barrier, which limits the catalytic activity. By comparing catalysts, the composite Au/Co3O4/C catalyst exhibited a lower overall free energy barrier than those of the single-component Au/C and Co3O4/C. The Bader charge analyses showed that the superior activity of the composite catalyst came from the active electron transfer at the Au/Co3O4 interface, where the Au nanoparticle worked as the positive charge transport station to assist the HC oxidation. These mechanistic insights demonstrate the critical role of the metal/oxide composite interface in promoting catalytic activity on electrodes, which assists in the rational design of glucose sensors.