Inverted design of oxygen vacancies modulated NiCo2O4 and Co3O4 microspheres with superior specific surface area as competitive bifunctional materials for supercapacitor and hydrogen evolution reaction

NiCo2O4 and Co3O4 have been explored as promising candidates for supercapacitor (SCs) and hydrogen evolution reaction (HER) featured with unique physical and chemical characteristics. However, they suffer from sluggish electrons transfer accompanied by poor active sites. It is the common way that silicon dioxide (SiO2) engaged as a sacrificial core could be tightly wrapped by a shell to prepare the hollow/porous target products with satisfying specific surface area. But to reversely think it, using SiO2 as sacrificial shell could be another way to unlock the bottleneck of NiCo2O4 and Co3O4 in this direction. Herein, a facile encapsulated self-activation strategy coupled with partial reduction method is described to construct order mesoporous NiCo2O4 and Co3O4 microspheres with oxygen vacancies modulation (SA-NiCo2O4 (Ov) and SA-Co3O4 (Ov)), respectively. The specific surface area of SA-NiCo2O4 (Ov) and SA-Co3O4 (Ov) microspheres is significantly increased by a factor of three after introducing encapsulated self-activation strategy, respectively. The superior specific surface area could provide numerous electroactive sites and large electrode/electrolyte interfaces for fast ions diffusion and redox reaction. The oxygen vacancies could offer favorable conductivity and boost ions diffusion. In virtue of intrinsic characteristics and structural advantage, SA-NiCo2O4 (Ov) and SA-Co3O4 (Ov) demonstrate decent specific capacitance (448.2 C/g and 375.3 C/g), and the corresponding asymmetrical devices deliver favorable energy density (31.2 Wh/kg and 29.4 Wh/kg), respectively. Furthermore, SA-NiCo2O4 (Ov) and SA-Co3O4 (Ov) could efficiently catalyze HER with a low overpotential of 141.1 mV and 155.6 mV at 10 mA/cm2 and confirm beneficial dynamics, respectively. This present strategy of using self-activation and oxygen-vacancies to enhance electrochemical properties may open up new opportunities for developing high-performance metal oxide catalysts/electrodes for energy conversion and storage.