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Transition metal selenides, a new type of electrode material for electrochemical capacitors, have attracted much attention because of their superior capacitive performance, notable electrical conductivity, and abundant reserves. Facile and efficient microwave heating followed by a solvothermal method was used to synthesize the (Ni0.85Se)3(Co0.85Se)/reduced graphene oxide (rGO) composite. Firstly, it can be observed that (Ni0.85Se)3(Co0.85Se)/rGO presents a three-dimensional porous microstructure consisting of stacked nanorods. The as-synthesized (Ni0.85Se)3(Co0.85Se)/rGO has an excellent specific capacitance of 2009 F g−1 at a current density of 2 A g−1, an ultrahigh rate performance of 83% with an increment in current density from 2 A g−1 to 30 A g−1, together with an outstanding long-cycle performance of 79.7% capacitance retention after 5000 cycles at 30 A g−1. Furthermore, the assembled (Ni0.85Se)3(Co0.85Se)/rGO‖‖activated carbon (AC) asymmetric supercapacitor achieves a high energy density of 38 W h kg−1 at a power density of 388 W kg−1. After 5000 cycles at a current density of 10 A g−1, the capacitance retention is 80.8%, which promotes the potential application of (Ni0.85Se)3(Co0.85Se)/rGO for high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

A simple and efficient strategy that takes advantages of the synergistic effect of microwave heating method and hydrothermal method is used to synthesize Ni 2 CoS 4 /graphene oxide (MH-Ni 2 CoS 4 /GO). Firstly, Ni 2 CoS 4 nanoparticles are observed to grow uniformly on the surface of GO. Then the obtained MH-Ni 2 CoS 4 /GO electrode is tested and it demonstrates ultrahigh specific capacitance of 2675.0 F g−1 at the current densities of 2 A g−1, fantastic stability of 95.0% even after 2000 cycles at 30 A g−1 and excellent rate capability of 89.7% with current density increasing from 2 A g−1 to 30 A g−1. Moreover, the assembled AC//MH-Ni 2 CoS 4 /GO asymmetric supercapacitor also delivers a good specific capacitance of 126.5 F g−1 at 0.5 A g−1, outstanding stability of 97.0% after 2000 cycles at 5.0 A g−1, and an ultrahigh energy density of 59.6 Wh kg−1 at power density of 497.6 W kg−1. This work provides an approach to synthesize electrode materials with superior excellent performances and it can be easily scaled up for practical applications in supercapacitors. [ABSTRACT FROM AUTHOR]

Water electrolysis is a green, safe, and practical route for hydrogen refueling station, but now it confronts a big challenge of extremely high electrical energy consumption. Thus, lower the voltage of an electrolyzer is one of the critical routes to solve this issue. Here we apply carbon black Vulcan XC-72, carbon nanotubes, and graphene oxide (named as 3C) to construct an effective bifunctional iron cobalt phosphide (FeCoP/3C) electrocatalyst, the electrocatalytic activity toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) was respectively investigated. The FeCoP/3C electrocatalyst shows overpotential of 220 mV and 120 mV at current density of 10 mA cm−2, Tafel slope of 73 mV dec−1 and 129 mV dec−1 for OER and HER in 1 M KOH electrolyte, respectively. When the electrocatalyst is used to construct an overall water electrolyzer, a cell voltage of 1.597 V can be achieved at current density of 10 mA cm−2. Moreover, the FeCoP/3C displays excellent durability toward overall water splitting, because the current density retains 92% after working for 10 h continuously. This outstanding performance is mainly attributed to the electrocatalyst possessing excellent electrical conductivity, exposing sufficient active sites, facilitating fast ions transportation and electron transfer, as well as speeding up O 2 and H 2 release. Therefore, this FeCoP/3C electrocatalyst can be a promising bifunctional electrocatalyst for practical overall water splitting. [Display omitted] • We first choose carbon black Vulcan XC-72, carbon nanotubes, and graphene oxide (named as 3C) to construct an effective bifunctional iron cobalt phosphide (FeCoP/3C) electrocatalyst by a facile method. • A low voltage of 1.597 V is achieved at 10 mA cm−2 for overall water splitting. • This work provides a strategy to synthesize bifunctional electrocatalyst for practical overall water splitting. [ABSTRACT FROM AUTHOR]