The crystalline nature of the surface of Co3O4-TiO2/Ti cathode was examined by X-ray diffraction (XRD) measurement and the 2θ values acquired within the range of 10° to 80° using a Bruker D2 PHASER X-ray diffractometer that uses Cu Kα radiation. The morphology of the cathode surface was depicted by a scanning electron microscopy (SEM,FEI QUANTA FEG250) and high-resolution transmission electron microscope (HRTEM, JEM-2100 F). The X-ray photoelectron spectroscopy (XPS) was obtained using a Thermo Fisher ESCALAB 250Xi system with Al Kα as an X-ray source. C 1s peak at 284.8 eV from residual carbon was conducted to correct the binding energy of other elements. The details of DFT calculation were provided in the supplementary material.