Mechanistic Insight\ninto the Superior Catalytic Activity\nof Au/Co<sub>3</sub>O<sub>4</sub> Interface in Glucose Sensors

The electrocatalyst on a nonenzymatic electrode is critical\nto\nthe instant sensing of glucose. Metal/oxide composite catalysts, such\nas Au/Co<sub>3</sub>O<sub>4</sub>, show activity in glucose oxidation\non electrodes superior to that of single-component catalysts, but\nthe mechanism is still not clear. In this work, commonly applied gold\n(Au), cobalt oxide (Co<sub>3</sub>O<sub>4</sub>), and their composite\n(Au/Co<sub>3</sub>O<sub>4</sub>) were modeled over the carbon (C)\nelectrode within explicit solvent water molecules to mimic the realistic\ncatalytic condition. Density functional theory (DFT) calculations\nand ab initio molecular dynamics (AIMD) simulations were applied to\ninvestigate the free energy profiles of the hemiacetal hydroxyl group\noxidation on glucose (CH<sub>C</sub>-OH<sub>O</sub> + 2OH<sup>–</sup> → CO + 2H<sub>2</sub>O + 2e<sup>–</sup>).\nThe simulation showed that the dissociation of hydrogen on O (H<sub>O</sub>) was an acid–base proton transfer process and easy\nin kinetics. The dissociation of hydrogen on C (H<sub>C</sub>) was\nexergonic but suffered from a relatively high free energy barrier,\nwhich limits the catalytic activity. By comparing catalysts, the composite\nAu/Co<sub>3</sub>O<sub>4</sub>/C catalyst exhibited a lower overall\nfree energy barrier than those of the single-component Au/C and Co<sub>3</sub>O<sub>4</sub>/C. The Bader charge analyses showed that the\nsuperior activity of the composite catalyst came from the active electron\ntransfer at the Au/Co<sub>3</sub>O<sub>4</sub> interface, where the\nAu nanoparticle worked as the positive charge transport station to\nassist the H<sub>C</sub> oxidation. These mechanistic insights demonstrate\nthe critical role of the metal/oxide composite interface in promoting\ncatalytic activity on electrodes, which assists in the rational design\nof glucose sensors.