Transition metal doping enhances pseudocapacitive energy storage in monoclinic molybdenum dioxide

Pseudocapacitive supercapacitors have garnered significant research attention in recent years due to their advantage of simultaneously possessing high energy density and high power density. Molybdenum-based metal oxides exhibit high specific capacitance and low cost, among which MoO₂ demonstrates relatively lower specific capacitance but superior electrical conductivity. In this study, we performed transition metal ion doping (Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺) to enhance the capacitive performance of MoO₂. Characterization results reveal that doping does not alter the crystal structure of MoO₂ but influences its microscopic morphology, thereby significantly modulating its electrochemical properties. Electrochemical tests indicate that the specific capacitance of pristine MoO₂ is 129.6 F g^-1 at a current density of 0.5 A g^-1. After transition metal ion doping, both the current response and specific capacitance of MoO₂ are significantly improved. Notably, Fe²⁺-doped MoO₂ achieved a specific capacitance of 206.4 F g^-1, corresponding to an enhancement of 58.8% compared to the pristine MoO₂.