Oxygen vacancy rich and phosphate ions modulated hierarchical mesoporous NiCo2O4-CoO hollow nanocubes as efficient and stable electrodes for high-performance supercapacitor

NiCo2O4 featured with high theoretical capacity and rich valence has aroused intense interest in the field of supercapacitor (SCs). Nevertheless, the poor electric conductivity hinders its commercial application. Herein, oxygen vacancy and phosphate ions modulated NiCo2O4-CoO hollow nanocubes (abbreviated as NiCo2O4-CoO (Ov) HNs) as the potential electrode for supercapacitor are synthesized through Pearson's Hard-Soft-Acid-Base (HSAB) principle along with partial reduction treatment. Oxygen vacancies could offer satisfactory conductivity and boost ions diffusion rate, and phosphate ions could improve electrochemical reaction reversibility greatly. In addition, the hollow/porous configuration could enrich electroactive sites and shorten ion/charge migration path. Benefitting from the intrinsic characteristics and structural advantages, NiCo2O4-CoO (Ov) HNs demonstrate superior specific capacitance (707C/g at 1 A/g), decent charge/discharge behavior, and favorable life span. Moreover, NiCo2O4-CoO (Ov) HNs//AC delivers an ideal energy density (40.4 Wh/kg at 914.7 W/kg), which surpasses most of the latest NiCo2O4-based devices. Overall, this present strategy may open up new opportunities for developing high-performance metal oxides for energy storage.