Oxygen vacancies-rich NiCo2O4-4x nanowires assembled on porous carbon derived from cigarette ash: A competitive candidate for hydrogen evolution reaction and supercapacitor

NiCo2O4 has aroused intense interest for hydrogen evolution reaction (HER) and supercapacitor (SCs). Nevertheless, the poor electric conductivity and insufficient electroactive sites hinder its commercial application. In this work, oxygen vacancies-rich NiCo2O4-4x nanowires assembled on porous carbon derived from discarded cigarette ash (named as Ov-NCO/PC-Y) are achieved via hydrothermal treatment combined with partial reduction process. The rich oxygen vacancies could offer remarkable conductivity, rapid ions transport rates, and rich electroactive sites. The introduction of phosphate ions is favorable for weakening the activation energy of their redox reactions, and therefore greatly promoting their surface reactivity and electrochemical reaction reversibility. Moreover, the interconnected 3D porous network structure of porous carbon (PC) could offer large surface area and short transport channel of ions/electrons. In virtue of intrinsic characteristic and structural advantage, Ov-NCO/PC-0.1 can be regarded as an effective HER catalyst with a low overpotential of 135.9 mV to reach 10 mA/cm2. Furthermore, Ov-NCO/PC-0.1 demonstrates superior specific capacitance of 1002.2 F/g, and Ov-NCO/PC-0.1//AC-based aqueous asymmetrical supercapacitor delivers the energy density of 32.7 Wh/kg at the power density of 160.2 W/kg. Moreover, the specific capacitances of Ov-NCO/PC-0.1//AC-based aqueous asymmetrical supercapacitor nearly keep unchanged after 3500 cycles. Overall, these findings shed fundamental insight on constructing high-performance bifunctional transition metal oxides for optimizing electrochemical energy conversion and storage.