Preparation Of Composited And Defective Cobalt-based Electrocatalysts And Their Electrode Performance On Water Splitting

Herein,according to the characteristics of Co-based electrocatalysts,composite structure and different defects such as oxygen(O)vacancy type and doping type were introduced.Combined with advanced characterization technologies and electrochemical testing methods,the hydrogen evolution reaction(HER),oxygen evolution reaction(OER)and total water splitting performance on Co based electrocatalysts with various defects was studied.The main contents are as follows:1.A sol-gel method was used to prepare the Co-Mo2C composite coated in graphitized carbon.It was applied to HER.It was found that the catalytic activity of pure metallic Co or pure Mo2C material was very low,but when the metallic Co and Mo2C were composited with each other,the HER catalytic activity was much higher.It was found that metal Co acted as a cocatalyst,which accelerated the charge transfer efficiency of HER and increased the crystallinity of Mo2C.It promoted the graphitization degree of carbon shell and increased the conductivity of the material.The optimized sample CoMo(0.5:0.5)-800@GC showed a ?10 of 165 mV at pH?13.At the same time,the catalyst could still maintain high HER activity under acidic conditions.2.A salt-assisted method was proposed for the preparation of NiCo2O4 anti spinel,which was full of O vacancies and applied in HER and OER bifunctional catalysis.The KCl crystal on the precursor benefit the formation of smaller NiCo2O4 nanoparticles filling with O vacancy defects,which promoted the conductivity of the oxide and the dissociation of H2O molecules.Thus,it improved HER and OER bifunctional catalytic activity of NiCo2O4.In pH?14,the optimized sample NiCo2O4-2KCl showed the ?10 values of 129 and 304 mV for HER and OER,respectively.3.Co₃O₄ full of inactive rare earth metal doping defects was prepared by a coprecipitation method and applied to HER catalysis.The inactive rare earth metal La was found in the Co₃O₄ grain boundary by the form of La3+ ions,which inhibits the growth of Co₃O₄ grains.This helped obtain Co₃O₄ nanoparticles with a diameter of?20 nm,so as to obtain higher electrochemical active surface area.In order to balance the charge,more O vacancies formed,which promoted the water molecules dissociation and conductivity enhancement.In 1 M KOH,the optimized sample 2%La-Co₃O_4-350 showed a ?10 of 98 mV for HER.4.Co₃O₄ full of non-metallic Se and Te doping defects was synthesized by a hydrothermal method in one pot and applied to OER catalysis.This method omitted the calcination,which shortened production period of oxide electrocatalysts.It was found that the non-metallic Se entered the Co₃O₄ cell in the form of Se2-and replaced the original O2-ion,which made the cell stretched.Te doping made Co₃O₄ become amorphous,which was not beneficial to the improvement of OER activity.In the Se-doped Co₃O_4,Se filled in the O vacancies.The conductivity of oxide was improved owing to the higher metallicity of Se.In addition,the increase of Co3+/Co2+content also promoted the OER activity.The optimized 6%Se-Co-0.5KClO3 showed a ?10 of 281 mV when pH?14,which was lower than that of IrO₂.5.A urea oxidation method was used to prepare Co₃O₄ filled with active metal Mo doping defects,which was applied to HER,OER and overall water splitting catalysis.Using urea as an oxidant,Co2+ was oxidized into Co₃O₄ nanoparticles with a diameter of?5 nm in N2 atmosphere and uniformly distributed on activated carbon.It was found that Mo4+replaced the tetrahedral site Co2+in Co₃O₄ cell.On the one hand,Mo4+ tuned the electronic structure of Co3+and enhanced the ability to dissociate H2O molecules,thus obtaining higher HER activity.On the other hand,Mo4+promoted the formation of O vacancies and pyridinic N,increasing the density of active sites of OER.Thus,it improved the catalytic activity of OER.4%Mo-Co₃O_4/NC showed ?10 values of 91 and 276 mV in 1 m KOH for HER and OER,respectively.