Remarkable Enhancement of Electrochemical Performance by the Oxygen Vacancy and Nitrogen Doping in ZnCo₂O₄ Nanowire Arrays

To improve overall electrochemical performance, we report and propose zinc cobaltite (ZnCo₂O₄) nanowire arrays with a simple and precisely controllable NH₃ plasma treatment. The NH₃ plasma treatment effectively changes the electronic and chemical properties of the pristine ZnCo₂O₄ by the nitrogen doping and surface functionalization simultaneously. By way of the nanoscale surface/electrical modification of ZnCo₂O₄, the nitrogen (N)-doped ZnCo₂O₄ electrodes not only significantly enhanced the electrical conductivity but also increased the density of the hydroxyl group by appropriately controlling the Co²⁺/Co³⁺ ratio (oxygen vacancies). Compared to pristine ZnCo₂O₄ (1682.2 F g^-1 at 5 A g^-1), the N-doped ZnCo₂O₄ electrode without conductive additives possessed high specific capacitance (3804.6 F g^-1 at 5 A g^-1), excellent rate capability (95.45% capacity retention at 40 A g^-1), and good cycling stability (only 3.3% loss after 3000 cycles at 30 A g^-1). These nanoscale surface state engineering methods may open a new avenue to optimize electrochemical performance for energy storage and conversion.