Preparation And Electrochemical Properties Of NiCo₂O₄ Nanocomposites Based Bifunctional Electrocatalysts For Water Splitting

Electrocatalytic water splitting for hydrogen production is one of the effective ways to solve environmental pollution and energy crisis.Electrocatalysts can lower the large overpotentials in water splitting reactions.The noble metals are effective in water splitting reactions,but the commercial use of these noble metal-based catalysts are limited by their extremely high price and scarceness.Therefore,it's important to find alternative efficient non-precious electrocatalysts.Recent years,nickel,cobalt and other transition metal oxides have drawn enormous attention,owing to their low cost,high yield and good catalytic prospect.This dissertation focuses on the key scientific issues of NiCo2O4-based composites,such as material synthesis controllable and electrochemical performance optimization.The effectively tailoring of structure,composition and electrochemical performance of the NiCo2O4-based composites.The therotical insight gained in this work could have general impact on other Janus bifunctional electrocatalysts.The detail contents and results are as follows:(1)The NiCo2O4/NiO/Ni composite with three-dimensional multilayer composite array structure is obtained by simple hydrothermal method,chemical bath deposition and electrodeposition method.An alkaline electrolyzer constructed by two symmetric NiCo2O4/NiO/Ni electrodes delivers splendid activity toward overall water splitting with a current of 10 mA cm-2 at only 1.60 V and almost no deactivation after 10 h.The supported NiO nanosheets increase the active surface area of the electrode,and the metal Ni particles provide many active sites.The structure is benefit for the effective contact between electrode material and electrolyte,prohibiting the active material agglomeration,facilitating the rapid transfer of ions and electrons,and maintaining the structural stability during the catalytic reaction.(2)NiCo2O4/Ni2P with core-shell array structure is constructed by hydrothermal method,chemical bath deposition and phosphating method.When the NiCo2O4/Ni2P is adopted as both anode and cathode in a two-electrode cell for overall water splitting,it only needs 1.59 V to reach a current density of 10 mA cm-2.The structure provides a large number of surface defects and active sites.The synergistic interactions between NiCo2O4 and Ni2P layers,and efficient electron transfer contribute to the enhanced activity.(3)A hierarchical core-shell hollow Ni@NiCo2O4 nanorod array is fabricated by a simple process,which combines hydrothermal and electrodeposition techniques by adopting ZnO nanorods arrays as templates.The hollow Ni@NiCo2O4 electrode as a bifunctional catalyst can achieve a current density of 10 mA.cm2 with a voltage of only 1.58 V.This nanostructure ensures improved electronic conductivity owing to the contribution of hollow Ni(Ni0)nanorod and the electroactive nanostructures that directly attached to the conductive Ni foam.The NiCo2O4 nanosheets also provide large surface area.The hollow structure has a good structure stability,it can prevents the agglomeration of the active material and maintains the electrochemical stability of the electrode material.