The Preparation Of Transition Metal Electrocatalysts And Their Application In Electrocatalytic Water Splitting

Due to the advancement of science and technology,the explosion of population,the limited amount of fossil energy contained in the earth has been consumed,and the environmental pollution has deteriorated rapidly.Therefore,the development of renewable and clean energy is imminent.As a new type of clean energy source,hydrogen energy has a wide range of sources,high calorific value,and no pollution in combustion.Therefore,it has become a research hotspot for renewable clean energy in recent years.Hydrogen production from electrolyzed water is currently the most widely studied hydrogen production method,but there are still problems such as expensive catalysts and electrode polarization.Because of its rich source,low price and great potential for catalytic performance,transition metal catalysts have become a hot spot for HER/OER catalyst research in recent years.In the preparation of bimetallic nitrogen-doped carbon composites,bimetallic precursors were prepared by heating reflow.The final CoNi-N-doped composites(CoNi-NC)were prepared by high-temperature calcination of precursors.The above catalysts were characterized by XRD,XPS,SEM and Raman.The HER/OER electrochemical performance of the catalyst was tested by electrochemical tests.Electrochemical data showed that the HER/OER performances of CoFe-NC and FeNi-NC prepared by the same method are not as good as CoNi-NC in the N2 saturated 0.1 mol KOH alkaline solution.In the test of the effect of calcination temperature on the HER/OER electrochemical performance of CoNi-NC,the HER/OER electrochemical performance of the CoNi-NC series catalysts first increases and then decreased with the increase of the calcination temperature.800' C was the optimum calcination temperature.At the current density of 10 mA·cm-2,the HER overpotential of CoNi-NC-800 was 175 mV,and the Tafel slope is 207 mV dec-1.The OER overpotential of CoNi-NC-800 was 423 mV,and the Tafel slope was 97 mV·dec-1.These data all indicate that CoNi-NC-800 is an excellent HER/OER bifunctional catalyst.In the preparation of bimetallic nanoparticles,the CoNi double metal hydroxides and FeNi double metal oxides were synthesized hydrothermally.This experiment focused on the effects of reaction conditions such as the amount of oleic acid,the amount of TOPO,and the bimetallic molar ratio on the structure of the catalyst material and the HER/OER electrochemical performance.The results showed that the HER activity of FeNi-NPs was the best,when the molar ratio of oleic acid was 2 mL and the molar ratio of FeNi was 3:1.The HER overpotential was 427 mV and the Tafel slope was 156 mV dec-1 when the the current density is 10 mA cm-2.When the molar ratio of FeNi was 1:1,the OER activity of FeNi-NPs was the best.Under the current density of 10mA·cm-2,the OER overpotential was 416 mV and the Tafel slope was 113 mV dec-1.The microstructure of CoNi-DHs gradually changed from nanosphere structure to nanorod shape.The HER activity of CoNi-DHs with a TOPO addition of 3.5 mmol and a CoNi molar ratio of 1:1 was the best.At a current density of 10 mA·cm-2,the HER overpotential was 463 mV and the Tafel slope was 71 mV Dec-1.The OER activity of CoNi-DHs with a CoNi mole ratio of 1:3 was the best.at a current density of 10 mA·cm-2,the OER overpotential was 379 mV,and the Tafel slope was 56 mV·dec-1.As the molar ratio of CoNi increased,the microstructure of CoNi-DHs gradually changed from a hexagonal nanosheet structure to a nanobeam.The Co@ZIF-67 was prepared through the self-assembly of elemental cobalt and dimethylimidazole by reflux,and the cobalt was made from reduction of cobalt acetate tetrahydrate by sodium borohydride.By XRD,TEM and other characterization methods,the microstructure was positive dodecahedron.When the ratio of cobalt to dimethylimidazole was 1:2 and 1:4,both the HER and OER of the catalyst exhibited good activity.Among them,at the current density of 10 mA cm-2,The HER overpotential of the Co@ZIF-67-3 catalyst was 446 mV,and the OER overpotential was 402 mV.The HER overpotential of the Co@ZIF-67-4 catalyst was 442 mV and the OER overpotential was 409 mV.