Controllable Preparation And Structure Regulation Of Manganese Dioxide-based Catalysts And Their Electrocatalytic Oxygen Evolution Reaction Performances

The increasingly negative impact of fossil fuels on the environment and people’s increasing energy demand motivate modern researchers to exploit and utilize clean energy for sustainable production urgently.Among various solutions,renewable energy conversion and storage systems have attracted considerable attention,such as regenerative fuel cells,water splitting,and metal-air batteries.These energy systems include oxygen evolution reaction（OER）,oxygen reduction reaction（ORR）,hydrogen evolution reaction（HER）,and other basic electrochemical reactions.OER involves multi-step electron transfer,showing high energy barriers and slow dynamics,which limit the large-scale application of these alternative clean energy technologies.Therefore,it is of great significance to develop efficient,stable and low-cost OER catalysts to improve the efficiency of the energy conversion process.MnO₂-based catalysts with the advantages of high-performance cost ratio and variable crystal morphology are expected to be ideal OER catalysts with low cost,high activity,and durability.However,the OER activity of MnO₂ catalysts is much lower than that of reference catalysts（Ir O₂ and Ru O₂）,due to its poor conductivity,and limited active sites.Based on how to design MnO₂-based catalysis for OER with high activity,this thesis adopts the strategies of crystal structure transformation of MnO₂,metal-doping,and heterostructure construction to regulate the structure of MnO₂ at different angles,and takes the performance of electrocatalytic OER in an alkaline medium（1 M KOH）as the standard.The main work of this thesis includes:（1）MnO₂ was macro-regulated by changing reaction conditions.α-MnO₂ nanowire arrays andδ-MnO₂ nanowire arrays were prepared on carbon paper by changing the reaction temperature and the amount of sulfuric acid,respectively,and were used as OER catalysts to investigate the structure-activity relationship between crystal structure and OER electrocatalytic activity.The OER activity of theα-MnO₂ nanowire was better than that of theδ-MnO₂ nanowire according to the test results in 1 M KOH solution.The high aspect ratio of the nanowire makes the active site fully exposed and the catalytic efficiency is higher.The higher oxygen vacancy concentration and Mn³⁺content are the main reasons for the better OER activity ofα-MnO₂.（2）The microstructure of MnO₂ was regulated by metal-doping.V-dopedα-MnO₂nanowire arrays were prepared on carbon paper by a simple hydrothermal method,and the alkaline OER activity ofα-MnO₂ nanowire arrays modified with different contents of V was investigated.When the V-doping concentration is 8%,the catalytic performance ofα-MnO₂nanowire was significantly improved,and the catalytic activity and stability ofα-MnO₂nanowire were the best in 1 M KOH solution.The main driving forces to improve OER activity are the synergistic effect between V and Mn and the increase of oxygen vacancy and Mn³⁺content caused by V doping.（3）The interface structure of MnO₂ was regulated by composite materials.Uniformly,MnO₂ nanowire arrays were prepared on the carbon fiber papers,and the amorphous Fe OOH nanosheets were supported by impregnation.In 1 M KOH,the as-prepared Fe OOH/MnO₂/CP nanoarrays showed the best OER activity than MnO₂ and Fe OOH alone.The unique heterogeneous structure of Fe OOH/MnO₂/CP composite and the synergistic effect of Fe OOH and MnO₂ enable it to have an excellent catalytic activity as OER electrocatalyst.