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

Abstract

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.