A novel hierarchical porous Co(OH)2/CoSe2 heterostructure composites are prepared by ion exchange method, and the precursor Co(CO3)0.5(OH)∙0.11H2O (CoCHH) is synthesized by hydrothermal method. Because the precursor CoCHH has the advantages of mild preparation conditions and controllable morphology and structure, it is possible to prepare a complex hierarchical structure of Co(OH)2/CoSe2. The porous Co(OH)2/CoSe2 heterostructure nanosheet and Co(OH)2/CoSe2 heterostructure nanotube have an excellent specific surface area of 90.5 m2 g−1 and 78.7 m2 g−1, which is significantly better than the precursor CoCHH nanosheet and CoCHH nanorod. The porous Co(OH)2/CoSe2 heterostructure nanosheet as cathode of supercapacitor has high specific capacity of 1283.3 C g−1 at current density 1 A g−1 in 3 M KOH solution, and the Co(OH)2/CoSe2 heterostructure nanotube only required 48 mV (vs. Reversible Hydrogen Electrode) to reach the 10 mA cm−2 for HER in 1 M KOH solution. In addition, with porous Co(OH)2/CoSe2 heterostructure nanosheet as cathode and CNTs as anode, the as prepared asymmetric supercapacitor has satisfactory energy density (68.9 Wh kg−1 at power density of 189.7 W kg−1). Moreover, the electrochemical hydrolysis (ECH) system can be formed by using Co(OH)2/Co3S4 nanorod and Co(OH)2/CoSe2 heterostructure nanotube as electrocatalysts and as-prepared supercapacitors in series, and the water decomposition can be driven directly by the supercapacitor. The electrochemical hydrolysis effect is obvious, and significantly improves the performance of the electrochemical hydrolysis system.
