| Since entering the 21st century,the requirement of people for energy has been growing,and the shortage of fossil fuels can no longer meet the demands of society,which force people to develop green and environmentally friendly new energy systems.Hydrogen is a new type of energy carrier favored by people.Using renewable energy sources such as solar energy or wind energy produces electric energy for electrolyzed water splitting,which is the greenest way to produce hydrogen.In the process of electrolyzed water splitting,the water oxidation at the anode is the oxygen evolution reaction?OER?,which requires a high overpotential.Therefore,developing efficient and inexpensive catalysts improves the energy utilization of electrolyzed water splitting,which has become one of the research hotspots of current researchers.Although there have been many reports of OER catalysts for transition metal compounds,their catalytic performance still needs to be further improved.In particular,there is currently no systematic investigation into the changes on OER catalysts during the catalytic reaction process.To further improve the performance of non-noble transition metal compounds in water oxidation and understand the evolution of the catalyst during water oxidation,in this paper,the transition metal sulfide and hydroxide were as the research objects,and Co S nanosheets,Fe Co-S nanoparticles,and Co Fe Ce-LDHs electrocatalysts were successfully prepared through a simple solution phase route.The catalytic water oxidation performance of the obtained catalyst was systematically investigated.Also,the changes of phase,oxidation state before and after the catalytic water oxidation and oxygen evolution reaction were thoroughly studied,which suggested possible catalytic mechanisms and showed the principle application of layered Co Fe Ce-hydroxide electrocatalyst on zinc-air battery.The specific research contents are as follows:1?By means of a small molecule organic amine-assisted approach,sulfur powder and Co Cl2 were used as reaction precursors to directly synthesize a thin layer of cobalt sulfide nanosheets.The surface chemical environment of the obtained cobalt sulfide material,such as the relative content of different oxidation states of cobalt could be replaced by adjusting the amount of sulfur powder.The obtained cobalt sulfide nanosheets with a thickness of5-12 nm had abundant defects and larger electrochemical specific surface area.The surface Co?II?could be easily converted into Co?III?.At a current density of 10 m A cm-2in alkaline media,the overpotential was only 312 m V.In 1 M KOH solution,when the catalyst loading was 0.37-0.45 mg cm-2,a constant current could be kept constant for at least 36 h.The activity of this electrocatalyst was better than the most reported monometallic cobalt sulfide materials and commercial Ru O2.2?The bimetallic Fe-Co sulfide composite material was synthesized as a OER electrocatalyst by solvothermal method using organic amine.Electrochemical test results showed that when the Co:Fe molar ratio was in the range of 1:2-2:1 and the sulfur content was more,the oxygen evolution activity of the sulfide was better.At a current density of 10m A cm-2 in 1 M KOH solution,the optimized Fe-Co sulfide catalyst had a low overpotential of 288 m V.In addition,the electrocatalyst also showed excellent catalytic stability.The catalyzed catalyst was collected and characterized systematically.The results showed that during electrocatalysis process,the cobalt component in the surface layer of Fe-Co sulfide dissolved and only left iron oxides/hydroxy oxides that may be the true catalytically active phase.There were many causes for the excellent catalytic activity of the catalyst,including the high conductivity of the metal sulfide in the catalyst and the porous structure of the oxide active phase derived in situ during the electrocatalysis process.In addition,the presence of residual sulfur may optimize the electronic structure of the catalytically active site.3?Co Fe Ce-layered hydroxide nanomaterials were prepared by hydrothermal method.Layered hydroxides with different ratios were obtained by keeping the total moles of Co,Fe and Ce to 1.2 mmol,Ce:Fe=1:1 unchanged and changing the molar amount of Ce to 0-0.3mmol.It was found that the introduction of Ce could promote the synergy between Co and Fe components and improved the oxygen evolution performance of catalytic water oxidation by investigating the electrochemical performance of this series of electrocatalysts.At a current density of 10 m A cm-2 in 1 M KOH solution,the overpotential of the obtained Co0.9Fe0.15Ce0.15-layered hydroxide was only 295 m V,which was much smaller than that of Co0.9Fe0.15Ce0?347 m V?.The catalyst and Pt/C catalyst mixture were used as the air cathode catalyst material of zinc-air battery.When the catalyst loading was 1.65 mg cm-2,the open circuit voltage of the battery was 1.40 V and the power density was 88 m W cm-2.At a constant discharge current density of 10 m A cm-2,the specific capacity and energy density were 697 m Ah g-1 and 820 m Wh g-1 respectively.After 853 consecutive charge/discharge cycles?about 143 hours?,the energy efficiency of the battery only dropped from 55.7%to53.6%,which showed its excellent stability and the performance was better than Pt/C?20%?+Ru O2?99.5%?air cathode catalyst material. |
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