Study On The Surface/interface Structure And Oxygen Electrocatalytic Performance Of Quenching-regulated Transition Metal Oxides

Unstable or slow oxygen evolution reaction（OER）and oxygen reduction reaction（ORR）seriously restrict the development of electrolytic water and metal-air batteries.Transition metal oxides have become one of the potential candidates to replace noble metal electrocatalysts due to their abundant resources and low prices,but their catalytic activity still needs to be improved.As the main site of catalytic reactions,the surface/interface structure of catalysts has received widespread attention,and various surface/interface modification methods have been developed.However,most of these reported strategies still have some shortcomings,such as complex operation,poor universality,and insufficient catalytic activity.Therefore,developing simple,versatile,and efficient novel strategies for tailoring the surface/interface of catalysts is of great significance for improving the catalytic activity of oxygen to promote the development of electrolytic water and metal-air batteries.Quenching technology has been widely used in iron/steel smelting,but its application in nanomaterials modification is lack of systematic research,and the underlying mechanism of nanoscale quenching is still unclear.In this thesis,the quenching technology is applied to the surface/interface regulation of transition metal oxide nanocatalysts.By adjusting quenching factors including temperature,solution（salt,concentration）,times,and nanoparticles（size,crystal surface）,the surface/interface structure evolution of transition metal oxides,before and after quenching,and the influence mechanism of quenching factors on the structure evolution are studied.Moreover,the catalytic relationship between the quenched-induced surface/interface structure and oxygen evolution/reduction reaction has been studied to improve the electrochemical performance of electrolytic water and Zn-air batteries.Therefore,the basic theoretical system of quenching factor,surface/interface regulation and catalytic performance is preliminarily established.The main research contents and conclusions are as follows:（1）The quenching technology is proposed to regulate the surface/interface of oxide catalysts and its universality is verified.High-temperature NiMoO₄ is quenched in Fe（NO₃）₃solutions with different concentrations（0.1-1.0 M）for rapid cooling.The results show that quenching introduces Fe doping on the NiMoO₄ surface,and the amount of doping is positively correlated with the concentration of Fe（NO₃）₃.Quenching also produces a disordered stepped surface on the catalyst with rich defects（especially oxygen vacancies）and optimized local electronic structure（such as metal valence）and coordination environment（such as coordination number）,which synergistically increases the number of catalytic active sites and the intrinsic activity,thereby promoting OER/ORR performance.The NiMoO₄ NPs-Fe-1 catalyst prepared by quenching NiMoO₄ nanoparticles in a 1 M Fe（NO₃）₃ solution has an low OER overpotential of 257 mV at a current density of 10 mA cm^-2 and excellent stability.In addition,NiMoO₄ is also quenched in Co（NO₃）₂,Cr（NO₃）₃,or MnSO₄ solution,and oxides such as spinel type Co₃O₄,Fe₂O₃,and amorphous CoSnO₃ are quenched.It is found that quenching treatment could improve the electrocatalytic activity of the catalyst,demonstrating the universality of quenching to tailor the surface/interface structure of oxides.（2）The interaction between multiple quenching is revealed,and the quenching size effect is found.NiMoO₄ nanoparticles with different sizes are quenched multiple times in Fe（NO₃）₃solution,and it is found that pre-quenching can promote the subsequent quenching regulation process.This is due to the fact that the defect structure generated by pre-quenching is more sensitive to subsequent quenching and is more easily regulated flexibly.In addition,quenching has different effects on nanoparticles with different sizes.For large NiMoO₄ particles（>27 nm）,multiple quenching forms Fe doped NiMoO₄ with the rich disordered stepped surface.When the size of NiMoO₄ is small enough（<27 nm）,the amount of surface and even bulk phase Fe doping caused by multiple quenching can reach a high level in a short time,so it is easy to form a Ni Mo_1/3Fe_4/3O₄ intermediate state,which overcomes the high formation barrier commonly associated with Ni Mo_1/3Fe_4/3O₄,and ultimately transforms into a novel NiFe₂O₄ structure.Finally,a unique NiMoO₄/NiFe₂O₄ heterostructure with the connected NiMoO₄ large particles is formed.The NiMoO₄/NiFe₂O₄ catalyst with rich defects prepared by quenching five times in Fe（NO₃）₃ solution exhibits excellent OER(227 mV at 10 mA cm^-2)and ORR（408 mV at half-wave potential）catalytic activity,with a minimum overpotential difference（ΔE=0.635 V）.Liquid and quasi-solid Zn-air batteries based on NiMoO₄/NiFe₂O₄ catalysts exhibit excellent output power density,cycle performance,and flexibility/foldability.（3）Co₃O₄ single crystals with different exposed crystal faces are quenched in Fe（NO₃）₃solution,and the quenching crystal face effect is found.Co₃O₄ cube exposed{100}crystal faces and Co₃O₄ hexagonal plate exposed{111}crystal faces are synthesized and quenched in Fe（NO₃）₃ solution.Among the two exposed crystal surfaces,the{111}crystal surface is more sensitive to the quenching process,characterized by richer surface defects（O defects and Co defects）,more Fe doping,and more disordered surfaces,while optimizing the electronic structure(more Co²⁺and Fe²⁺)and coordination environment（weaker Co-O bonds）.The main reason is that the{111}crystal surface has a more open crystal configuration,weaker Co-O bond strength,and greater surface energy.At the same time,{111}crystal surface has more unsaturated bonds,and its structure is more unstable,providing more quenching action points,which is conducive to ion doping and diffusion.In addition,the lower Fe doping energy and oxygen defect formation energy of{111}crystal planes are conducive to achieving more Fe doping and defect structures during quenching.Therefore,quenching significantly improves the OER/ORR catalytic activity of{100}and{111}crystal surfaces,especially{111}crystal surface.Zn-air batteries assembled with Co₃O₄-P-Q catalysts have excellent power density and cycle stability.The all-weather zero-emission electrolytic water system of"solar panel-zinc air battery-electrolytic water"based on Co₃O₄-P-Q catalyst can achieve zero-energy consumption and long-term electrolytic water.