Simultaneously introducing N dopants and O vacancies in CoMoO4 for high-performance hybrid capacitors

With high redox activities, environmental friendliness, and low cost, metal molybdates have been regarded as promising electrode materials for various electrochemical devices. However poor intrinsic charge transport kinetics, limited active sites, and insufficient structural durability render the inferior performance of metal molybdates. Here, we developed a one-step method to create N doping and O vacancies in CoMoO₄ (N-CoMoO_4-x) by annealing the CoMoO₄ precursor in NH₃. The abundant defects effectively boost the charge transport kinetics and redox activity, leading to superior reversible capacity and rate performance. The developed N-doped CoMoO₄ with enriched O vacancies presented conspicuously enhanced performances (2185 mF cm⁻² at 5 mA cm⁻², 1375 mF cm⁻² at 40 mA cm⁻²) compared to that of the CoMoO₄ electrode (360 mF cm⁻² at 1 mA cm⁻²). Meanwhile, the hybrid capacitor using N-CoMoO_4-x as the battery-type cathode and activated carbon (AC) as the capacitor-type anode displays a high areal capacitance of 177 mF cm⁻² even at 100 mA cm⁻² and only decays about 7 % after 10,000 cycles, superior to that of many previous reported full device performances using metal molybdates as electrodes. This work can be a good reference for the design of metal molybdates applied in electrochemical fields.