Synthesis And Studies Of Nickel-Cobalt Based Oxides/phosphides (Sulfides) Catalysts Completed For Electrocatalytic Water Splitting

Water electrolysis is considered as one of the most efficient technologies for hydrogen production.High efficient and stable catalysts are needed to increase kinetic rates and decrease overpotentials of HER and OER.In this thesis,several series of nickel-cobalt based catalysts were prepared and used to catalyze HER,OER and overall water splitting.The catalysts have exhibited greatly improved catalytic performances benefited from their optimized compositions and formation of heterojunctions.The overpotentials of HER and OER have been greatly decreased.The thesis including following three works.?1?A series of NiCoP/NiO heterostructural catalysts were fabricated by a successive hydrothermal,oxidation,and phosphidation procedure.The as-prepared catalysts have shown excellent bifunctional electrocatalytic performances for HER and OER in alkaline conditions.Especially,the optimized catalyst NiCoP/NiO-310has exhibited excellent catalytic performance in 1 M KOH,and only 147 and 267mV overpotential is needed for HER and OER respectively to reach a current density of 10 mA/cm².Furthermore,when the catalyst was employed as a bifunctional catalyst for overall water splitting,only 1.63 V cell voltage is needed to reach a current density of 10 mA/cm².?2?A series of NiCo₂O_4-xS_x nanosheets with heterostructures were synthesized by partially sulfurization of spinel NiCo₂O₄.The as-prepared catalysts have shown excellent bifunctional electrocatalytic performances for HER and OER in alkaline conditions.Especially,the optimized catalyst NiCo₂O_4-xS_x-0.8 has exhibited excellent catalytic performance in 1 M KOH,and only 104 and 286 mV overpotential is needed for HER and OER respectively to reach a current density of 10 mA/cm².Furthermore,when the catalyst was employed as a bifunctional catalyst for overall water splitting,only 1.46 V cell voltage is needed to reach a current density of 10 mA/cm².?3?NiCo₂S₄ nanoflowers and nanoparticles were prepared by solvothermal method.Compared with NiCo₂S₄ nanoparticles,the NiCo₂S₄ nanoflowers are demonstrated as a more efficient bifunctional electrocatalyst for overall water splitting in 1 M KOH,which needs overpotentials of 83 mV and 230 mV for HER and OER respectively to afford the current density of 10 mA/cm².Furthermore,the NiCo₂S₄ nanoflower exhibits excellent overall water splitting activity with a cell voltage of 1.52 V to reach a current density of 10 mA/cm².