Synthesis Of Transition Metal Oxides And Electrocatalytic Water Splitting Properties

So far,with the advancement and development of human science and technology,our demand for energy has increased dramatically.Due to the non-renewable nature of traditional fossil fuels and the high level of pollution,our demand for clean,renewable new energy sources is increasing.In new energy sources,hydrogen energy,its high calorific value,zero pollution and other advantages have gradually been paid close attention.Up to now,there are more and more hydrogen production methods.The method of hydrogen production by electrolyzed water has the advantages of high efficiency,simple preparation method,zero pollution,and sustainability.Therefore,research and development and preparation of low-cost,high-efficiency electrocatalytic water decomposition catalysts have become the focus of recent years.Among these,transition metal oxides have good moisture-decomposing hydrogen,catalytic oxygen evolution activity and stability,and have high stability and mechanical strength under alkaline electrolytes,and have a good effect in the field of electrocatalytic water decomposition.The development and application prospects.First,Ca3Co2O6 series transition metal oxide catalyst samples were prepared by optimizing the traditional sol-gel method.The specific optimization process is shown in the experimental part of this article.The product was found to be pure by characterization,and the crystallization effect was good,Ca3Co2O6,but other oxide samples were not obtained.Then,HER and OER electrochemical performance tests were performed under 0.1 M KOH and 1 M KOH,respectively.HER test results:The overpotential(Ej=10)of the sample Ca3Co2O6 at a current density of 10 mA·cm-2 was 0.449 and 0.294 V in 0.1 M and 1 M KOH,respectively,and the Tafel slopes were 150.5 and 73.4 mA·dec-1,showing better HER performance than other samples,but with a noble metal sample 20%Pt/C at 0.1 M and 1 M KOH at a current density of 10 mA·cm-2(Ej=10)For 0.007 and 0.067 V,respectively,the Tafel slopes are 62.3 and 49.0 mA-dec-1,respectively,and there is a certain gap.OER test results:The overpotential(Ej=10)of the sample Ca3Co2O6 at a current density of 10 mA·cm-2 was 0.460 V and 0.460 V,respectively,in 0.1 M and 1 M KOH,and the Tafel slopes were 81.3 and 93.2 mA-dec-1 respectively shows better OER performance compared to other samples,but the overpotential(Ej= 10)at a current density of 10 mA·cm-2 at 0.1 M and 1 M KOH with the precious metal sample RuO2 is at 0.529 and 0.549 V,the Tafel slopes of 62.3 and 49.0 mA·dec-1 respectively show better OER performance in the same laboratory environment.Based on the previous calcium cobaltate,Li-Ca3Co2O6 and Mg-Ca3Co2O6 catalysts were prepared by doping the precursors with sol-gel method at 850 ?by doping other active metals Li and Mg.The influence of the molar ratio of the doped metal and calcium on the composition and catalytic activity of the catalyst was discussed.By means of characterization,it was found that Li was slightly doped in Ca3Co2O6 in the form of LiCoO2.After the electrochemical performance tests,the catalytic activity of the HER and the performance of the whole series was improved by a molar ratio of lithium to calcium,magnesium to calcium of 1:14.The overpotential(Ej=10)of the sample Li-Ca3Co2O6-5(Li:Ca=1:14)at the current density of 10 mA·cm-2 was 0.352 and 0.247 V,respectively,in 0.1 M and 1 M KOH,and the Tafel slope They are 205.4 and 75.6 mA·dec-1,respectively,while OER performance did not increase substantially.Through investigation,it was found that due to the existence of LiCoO2,the overall catalytic performance of the catalyst compared to the single catalyst Ca3Co2O6 has been greatly improved,but the catalytic performance of the OER has not been greatly improved;and Mg-doped Ca3Co2O6 as a control has improved the electrocatalytic performance.Not obvious.Therefore,in order to improve the conductivity,a series of graphene-doped LiCoO2 was used as the HER and OER catalysts based on the previous content and the catalytic performance was explored by changing the Li and Co ratios.By means of characterization,it was shown that the product is purer than graphene-coated core-shell LiCoO2.The electrochemical performance tests of HER and OER were performed at 0.1 M KOH and 1 M KOH,respectively.HER test results:The overpotential(Ej=10)of LiCoO2-rGO-3,2 at the current density of 10 mA·cm-2 is 0.408 and 0.345 V,respectively,in 0.1 M and 1 M KOH,and the Tafel slope They were 141.5 and 99.4 mA·dec-1,respectively,and showed better HER performance than other samples.Although the HER performance was comparable to the previous series,the lower Tafel slope was much better than the samples CCO and Li-CCO series.OER test results:The overpotential(Ej=10)of LiCoO2-rGO-2 at the current density of 10 mA·cm-2 was 0.427 and 0.376 V,respectively,in 0.1 M and 1 M KOH,and the Tafel slopes were 59.8 and 49.6 mA·dec-1 showed better OER performance compared to other samples,which was especially remarkable when compared to previous samples.It can be seen that LiCoO2-rGO series catalysts have good dual-function catalytic properties of HER and OER.