Controllable Preparation Of Copper-based Catalysts And The Studies On Their Pre-Oxidation Process And Electro-Oxidation Application

With the development of modern industrialization,environmental pollution becomes more and more serious,and the related global energy crisis is also intensively concerned.Currently,developing renewable and clean energy is urgently demanded.Because of the high energy density,clean and pollution-free feature,hydrogen energy has become an ideal substitute to replace the traditional fossil energy.Among various hydrogen production technologies,hydrogen production via water electrolysis is of high energy conversion efficiency,environmental friendliness and easy operation,which has been regarded as an ideal way to produce hydrogen and alleviate the energy crisis.However,as the half reactions in water electrolysis,anodic electro-oxidation reactions,such as oxygen evolution reaction（OER）,urea oxidation reaction（UOR）,limit the overall efficiency of hydrogen production owing to their sluggish kinetic process and complex reaction mechanism,which have been proved as the bottleneck that restricts the development of hydrogen production.Therefore,the development of highly efficient,cheap and stable catalysts for such electro-oxidation reactions is of great significance to improve the energy conversion efficiency and promote the industrialization of hydrogen production via water electrolysis.Current studies indicate that the high-valence metal ions in the catalysts are the active sites of the catalytic electro-oxidation reactions.Hence,designing the catalysts with abundant high-valence metal ions or enriching the high-valence metal sites via the pre-oxidation process are important routes to improve the catalytic activity.However,owing to the poor thermodynamic stability of the high-valence metal ions,it is difficult to directly increase the content of high-valence metal ions in the catalysts.Therefore,optimizing the electrochemical pre-oxidation process would effectively enrich the high-valence metal ions in situ and thereby improve the electro-oxidation performance.In this thesis,the author selected copper-based catalysts as the material models,promoted the pre-oxidation process via constructing hierarchical nanostructures and unique"pit-dot"morphology,realizing enriched catalytic active sites and improved electro-oxidation performance for OER and UOR.The main contents of this thesis include:1.The authors designed and fabricated Cu Fe Prussian blue analogue（PBA）/Cu（OH）₂nanoarrays as efficient catalysts for both OER and UOR catalysis by constructing hierarchical nanostructures on conductive substrate.Our research indicated that the hierarchical catalyst could enrich the reactive sites for promoted pre-oxidation reactions,which could lead to fast formation and accumulation of the high-valence metal ions for electro-oxidation reactions.In addition,the high conductive copper foam support could facilitate the charge transfer,therefore endowing the hierarchical catalyst with ultralow onset potential,high catalytic current density and excellent intrinsic activity synergistically.In detail,ultralow onset potentials of 1.423 V vs.RHE and 1.248 V vs.RHE can be realized for OER and UOR,and the hierarchical catalyst could achieve stable catalytic current density over 300 h and 150 h for OER and UOR,respectively.Detailed analyses indicated that the optimized Cu Fe PBA/Cu（OH）₂hierarchical catalyst could undergo a complete structural transformation during the OER operation.In contrast,only surface pre-oxidation reaction with incomplete structural transformation can be verified for long-term UOR catalysis,which could be attributed to the presence of reductive urea that limits the pre-oxidation process.This work confirms the importance of pre-oxidation process for the electro-oxidation reactions.2.The author fabricated hydrated copper pyrophosphate（Cu₂P₂O₇·3H₂O）ultrathin nanosheet arrays with unique“pit-dot”morphology as efficient pre-catalysts for OER.The unique morphology could increase the surface area of the nanoarrays and provide abundant reactive sites for the pre-oxidation process,therefore leading to enriched high-valence metal ions via the promoted electro-oxidation process.Furthermore,the highly conductive copper foam substrate could accelerate the charge transfer,and realize significantly improved OER activity.As a result,a 260%activity enhancement can be identified during an ultralong OER operation for 30 days,and much lower overpotential,larger current density,higher intrinsic activity,higher faradaic efficiency and smaller charge transfer resistance can be resulted.The systematic study on the pre-oxidation process in this work could shed light on the design and optimization of（pre-）catalysts for energy-related electro-oxidation reactions.