Preparation Of Novel Transition Metal Compounds And Their Use In Electrocatalytic Water Decomposition

To solve the energy and environmental problems related to the massive use of fossil fuels,humankind needs to develop sustainable energy resources,such as solar,wind and tide,to generate electricity.As electricity has limitations in delivery and storage,we have to convert electricity into alternative energy forms,such as hydrogen.Hydrogen gas has long been considered as an ideal energy carrier due to its cleanness and recyclability,high energy density,feasibility in transportation and storage,and high energy conversion efficiency in fuel cells,water electrolysis is a feasible way for large-scale production of hydrogen gas.If the electricity is provided by a solar cell,we can convert the sustainable solar energy into chemical energy.In this technology,the development of water splitting electrocatalysts contributes significantly to enhance the solar-to-hydrogen efficiency.A typical water electrolysis cell consists of a cathode for hydrogen evolution reaction(HER)and an anode for oxygen evolution reaction(OER).Both HER and OER kinetics,especially the latter,have hindered the overall efficiency of water splitting,electrocatalysts for hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)need to be studied to increase the energy conversion efficiency in water electrolysis cells.Compared to the reduction of water to hydrogen,the oxidation of water to O2(2H2O ? 4H+ + 4e-+ O2)is a more complicated reaction as four electrons are needed for the formation of an oxygen molecule,the water oxidation process is limited by sluggish kinetics and requires large overpotentials.To improve the reaction rate and/or lower the over-potential,highly efficient water oxidation electrocatalysts must be exploited.Many noble metal-based,noble metal-free or even metal-free complexes and materials have been widely studied for electrocatalytic HER and OER,due to the limited reservation of noble metals on earth,their applications for large-scale production of hydrogen are not affordable and sustainable,cheap element-based systems have thus attracted great attention with application prospects.Electrocatalysts can be homogeneous complexes in electrolytes or heterogeneous solids on electrode surfaces.Electrocatalysts can be homogeneous complexes in electrolytes or heterogeneous solids on electrode surfaces,compared with homogeneous molecular catalysts,which have the merit towards better understanding of HER/OER mechanisms from insightful structure-performance correlation,solid material electrocatalysts usually have higher activity and stability with more accessibility.In these regards,the Ni-and Co-based materials,including phosphides,sulfides,(oxy)hydroxides and selenides had been developed for electrocatalytic HER and OER in the past few years.Herein,the methods of electrodeposition and solvent-thermal synthesis were used to prepare Ni-and Co-based electrocatalysts:(1)An electrodeposited NiSe/NF electrode was obtained with superior electrocatalytic activities for both water reduction and oxidation.A water electrolysis cell was fabricated using this cheap,easily-obtained,efficient and robust electrode as both anode and cathode to achieve high water splitting current density of 20 mA cm-2 at cell voltage around 1.50 V,(2)A Zn doped porous three-dimensional flower-like CoO which is a kind of high efficient water oxidation catalyst was synthesized by hydrothermal method,about 330 mV over-potential was needed to reach the current density of 10 mA cm-2,this electrocatalysts is still stable after long time electrocatalysis.