Biaxial strain tunable quantum capacitance and photocatalytic properties of Hf2CO2 monolayer

MXenes have great potential applications in energy storage and photocatalyst. The photocatalytic activity and the quantum capacitance of Hf2CO2 monolayer under biaxial strain are investigated in this paper. The result indicates that Hf2CO2 monolayer under biaxial strain can reduce H+ to H2 at pH = 0 and has the strongest reducing ability at 12% tensile strain. Hf2CO2 monolayer under strain has the photocatalytic capacity for overall water splitting within appropriate pH range. The tensile strain can enhance the CO2 reduction ability of Hf2CO2 monolayer. The reducing ability of Hf2CO2 for N2 is improved under tensile strain and reduced under compressive strain. The analysis of exciton binding energy further confirms the potential photocatalytic activity of Hf2CO2 monolayer under strain. Hf2CO2 monolayers under strain are potential cathode materials for super -capacitors in aqueous electrolyte, the wide voltage makes Hf2CO2 monolayer under-6% strain transform into electrode material of symmetric supercapacitors. The effect of temperature on the electrode type of materials is further explored.