Nanoscale Regulation And Electrochemical Oxygen Evolution Reaction (OER) Properties Of Transition Metal-based Compounds

The rapid consumption of fossil fuels caused by increasing number of population and growing need for advanced technologies have led to global resource and environment problems.Therefore,the development of green and renewable energy with high energy conversion rate and corresponding technologies are increasingly becoming the focuses of global attention.Electrochemical oxygen evolution reaction?OER?has captured remarkable interest because of its wide application in the fields of new energy?hydrogen production from electrochemical water splitting,metal-air batteries,etc.?.Catalytic materials with high efficiency are keys to speed up the OER process.To now,Ru-and Ir-based oxides are widely used as OER electrocatalysts,however,their application in large-scale industrial production is limited by high cost and poor chemical stability.To address this issue,researchers have synthesized a variety of non-noble metal-based materials to serve as OER electrocatalysts,and further proposed different performance optimization methods according to material characteristics,among which,researches on cobalt-based materials are always at the cutting edge of this field.However,from the perspective of practical application,the catalytic performance and synthetic process of cobalt-based catalysts still need to be further improved and optimized.This dissertation is involved in extracting favorable factors through integrating various OER performance optimization strategies as far as possible to improve the synthetic process of existing catalytic materials or to optimize the original active sites for further improvement of catalytic performance,and then make them be closer to the needs of practical application.The dissertation includes the following contents:A series of Ni Co bimetal sulfides?Ni Co₂S₄?with different morphology are loaded on nickel foam?NF?.The effects on morphology and OER electrocatalytic performance were studied in detail.Benefiting from more mass-transport channels and more active sites provide by lager electrochemical active surface area,the results show that Ni Co₂S₄ with 3D interconnecting structure consisting of 1D nanoneedles and 2D nanosheets exhibits the most electrocatalytic activity toward OER in alkaline environment.Only overpotential of 279 m V is needed to achieve a current density of 50 m A·cm^-2,and Tafel slope is as low as 68 m V·dec^-1.Additionally,the catalyst can be used in continuous OER at 50 m A·cm^-2 for at least 20 h without obvious decline of catalytic activity.S-treated 2D Co Fe-PBA grown on carbon fiber paper?CFP??S-Co Fe-PBA/CFP?was obtained by a two-step process including solution method at room temperature and a subsequent mild sulfuration process.The effects on structure,constitution and electrocatalytic activity toward OER caused by S-treated process were discussed.S-Co Fe-PBA/CFP only requires overpotentials of 235 m V,259 m V and 272 m V to drive the current densities of 10 m A·cm^-2,50 m A·cm^-2 and 100 m A·cm^-2,respectively,along with a super low Tafel slope of 35.2 m V·dec^-1,such activities of S-Co Fe-PBA/CFP are comparable with the-state-of-the-art OER electrocatalysts.The remarkable electrocatalytic performance can be ascribed to two kinds of effects caused by S-treated process.On one hand,H⁺from intermediates of*OH and*OOH can be captured by-SO_x on the surface of catalyst,and the activation energy is thereby reduced;On the other hand,partial phase transformation of Co Fe-PBA leads to in-situ formation of amorphous Co S_x nanogauze on its surface,the interaction between two phases contribute to improving charge transfer and the adsorption for OER intermediates,thus speeding up the process.