Preparation And Electrocatalytic Performance Of MOFs-derived Transition Metal Selenides

With the development of society and economy,the problems of fossil energy crisis and ecological environment pollution are becoming more and more prominent,and the demand for sustainable and clean energy represented by hydrogen energy is becoming more and more urgent.Hydrogen production by electrolysis of water as an ideal method to obtain hydrogen has become one of research focuses in the world today.However,the electrocatalyst with high activity,low cost and good stability is the key to water electrolysis hydrogen production.Currently,the platinum,ruthenium oxide and other precious metals catalysts are still the main electrocatalysts.Nevertheless,the high prices and scarcity greatly hinder its large-scale commercial application.Hence,it is of great significance to develop other non-noble metal catalysts with excellent performance and low cost.Transition metal selenides have variable electronic states and functional controllability,and shown good electrocatalytic performance in electrolytic water and other electrochemical reactions.Therefore,it is regarded as a new type of non-noble metal electrocatalytic material with great development prospect.However,the catalytic performance of transition metal selenides is still much lower than our expected due to the low exposure active sites.Based on this,the structure and morphology of transition metal selenides derived from MOFs were improved by scientific design and effective experiments control,so as to increase the number of active sites and conductivity of the catalyst,further reduce the catalytic resistance,and make them have better electrocatalytic performance.The main contents of this paper are as follows:（1）[CH₃NH₃][Co（COOH）₃]precursor was firstly synthesized with methylamine was used as cationic template,formic acid as ligand and cobalt nitrate as the center metal ions.Subsequently,Co₃O₄was synthesized by calcining the precursor in air.Finally,after two steps of hydrothermal treatment,Co Se₂-T microcubes（T=140,160,180,200℃）with two different morphology were obtained by adjusting the second step of hydrothermal temperature.Here,the Co Se₂-140 and Co Se₂-160 are composed of nanosheets,and the Co Se₂-180 and Co Se₂-200 are composed of nanorods.The electrochemical test results show that Co Se₂-160 not only has excellent performance of HER and OER,but also has good stability.In 0.5 M H₂SO₄,the overpotential of Co Se₂-160 is 156 m V,and the slope of Tafel is 40 m V dec^-1(under current density of 10m A cm^-2).In 1 M KOH,the overpotential of Co Se₂-160 is 328 m V,and the slope of Tafel is 73 m V dec^-1(under current density of 10 m A cm^-2).The presence of sheet-like nano-architectures and selenium vacancy is the key to the improvement of catalytic performance.（2）The precursors[CH₃NH₃][Zn_xCo_1-x（HCOO）₃]were successfully prepared with methylamine was used as cationic template,formic acid as ligand and cobalt nitrate as well as zinc nitrate as the center metal ions.Subsequently,the Zn_xCo_1-xSe₂microcubes were finally synthesized by solvothermal treatment.It is proved that Zn atoms were successfully doped through a series of characterization of XRD,EDS and XPS.As a bifunctional electrocatalyst,Zn_0.1Co_0.9Se₂showed remarkable HER and OER performance in series Zn_xCo_1-xSe₂samples.When HER was tested in acidic medium and OER was tested in alkaline electrolyte,the overpotentials are 196 m V for HER and308 m V for OER with a current density of 10 m A cm^-2,respectively.And the Tafel slope are 56 m V dec^-1and 80 m V dec^-1,respectively.The outstanding electrocatalytic performance of Zn_0.1Co_0.9Se₂can be attributed to its hollow cubic structure,the synergistic effect between Zn–Co–Se and a small amount of Zn atom doping.