Synthesis Of Transition-Metal-Based Catalysts For Electrocatalytic Water Splitting

Fossil fuel,which is a kind of non-renewable energy resource,is the foundation that human society depends on for existence and development.However,energy consumption is gradually increasing.And the air pollution caused by fossil fuel seriously threatens our environment.Therefore,it is a great challenge to solve the problem that relates to the increasing demand for energy and the urgent environmental pollution.In response to these problems,new energy sources-such as solar energy,wind energy,geothermal energy,biomass energy,ocean energy and nuclear fusion energy-attract more and more attention from all countries.We know that hydrogen energy is a clean and sustainable energy resource,and its principle combustion product is water that is not poisonous.So,it is feasible to produce hydrogen from electrolyzing water,which is a clean and reversible route.Although the traditional precious metal electrocatalysts have high catalytic activity,the development of hydrogen production from electrolyzing water has been greatly limited due to their high price and scarce crustal content.Therefore,the design and synthesis of electrocatalysts based on non-noble metals with high catalytic activity and stability is a research hotspot at present.Given the above,bimetallic phosphides,oxides and nitrides catalysts are designed and synthesized through morphology control and electronic transport tuning to achieve overall water splitting.Our research includes three parts:1.Hollow Ni-Co-P nanotube arrays are synthesized using electrodeposited copper hydroxide template.The three-dimensional（3D）hierarchical earth-abundant transition bimetallic GDs/Co_0.8Ni_0.2P arrays are constructed by hollow nanotubes which consist of two dimensional（2D）nanosheets.With the decoration of zero-dimensional（0D）graphene quantum dots,an efficient overall-water-splitting catalysts are finally constructed.Owing to the large specific surface area,good electron transport ability,highly dispersed graphene quantum dots,and the confinement effect of graphene quantum dots,the integrated GDs/Co_0.8Ni_0.2P nanoarrays show good catalytic activity for both HER and OER,and the potential attained 1.54 V at the current density of 10 mA cm^-2 for overall water splitting.2.The CuCoO_x nanowire arrays are synthesized by hydrothermal method.After hydrogen treatment and carbon layer coating,the Mott-Schottky electrocatalysts with core-shell structure are successfully constructed.For HER and OER,the overpotentials of the NC/CuCo/CuCoO_x nanowire arrays present 112 mV and 190 mV at 10 mA cm^-2,respectively.The good catalytic activity and stability of NC/CuCo/CuCoO_x nanowire arrays attributes to the high conductivity,large specific surface area,a large number of active sites,and a good electron transport channel constructed by synergetic effect of metal,semiconductor,and nitrogen-doped carbon layers.3.NC-NiCu-NiCuN nanowires are constructed by carbonization/nitridation-induced in situ growth strategies.Through the dual modulation of electrical properties and electron transport,the in-situ coupling of NiCu nanoalloys,NiCuN and nitrogen-doped carbon layers not only facilitates the consecutive electronic transmission in the whole system,but also promotes the conductivity and the exposure of active sites.Due to the synergistic effect of the catalysts,NC-NiCu-NiCuN nanowires have good HER and OER catalytic activity.The overpotentials are 93 mV for HER and 232 mV for OER at a current density of 10 mA cm^-2,respectively.The two-electrode cell using NC-NiCu-NiCuN requires only 1.56 V at 10 mA cm^-2 and has significant durability over 50 h.