Synthesis Of Bimetal Based Micro/Nano Porous Electrocatalysts And Their Catalytic Properties In Electrochemical Water Splitting

Hydrogen energy has attracted global attention because it holds the promise of a clean and effective energy future.Water electrolysis can produce high-purity hydrogen without additional carbon emission.Therefore,by using sustainable energy like solar power and wind power as electricity supply,water electrolysis may play a major part in the future hydrogen-electricity energy system.Water electrolysis using alkaline electrolyzers has been the most commercial and mature technology to produce hydrogen for many years.To further lower the cost of this technology,developing effective and cheap electrocatalysts that can endure in alkaline media for cathodic half-reaction（Hydrogen Evolution Reaction,HER）and anodic half reaction（Oxygen Evolution Reaction,OER）to substitute noble-metal based electrocatalysts（Pt based and Ru based,etc.）has been focused by researchers.Earth-abundant 3d transition metals（TM）are cheap and also catalytically active.In this circumstance,I focused on four typical 3d transition elements（Ni,Co,Cu,Fe）in this dissertation:Designing stable and effective electrocatalysts in alkaline media which are derived from these four elements by optimizing the component and structure of the materials.Based on the potential synergistic effects from different active components,bimetallic electrocatalysts were chosen as research objects in this dissertation.Different porous micro/nano structured（including core-shell structure,hollow structure）TM alloys,phosphides and selenides were prepared,with the aim of increasing the number of active sites.The influences of components and micro/nano structures from these catalysts on their electrochemical performance were investigated.Sequentially,their performance was further optimized.In addition,the methods adopted in this thesis to prepare different micro/nano structures may shed some light on controlled and facile synthesis of TM based electrocatalysts with typical nanostructures.The main research contents are presented as follows:（1）CoNi glycolate nanosheets/carbon nanotube（CNT）composites with core-shell structure were prepared via solvothermal reaction.Followed by annealing in NH₃ atmosphere,the reduction of precursors into alloys and the nitrogen doping into CNTs were achieved simultaneously.Therefore,a core-shell structure with Co₂Ni alloy nanoparticles anchored on N-doped CNTs was synthesized.The attachment of alloys on CNTs can effectively restrain the agglomeration of alloy nanoparticles,thus increasing the exposed active sites to enhance catalytic activity.The performance comparison of different samples showed that Co₂Ni alloy might have a potential synergistic effect in different steps of HER because of the combination of active Ni and Co.The N-doped CNTs can also bring additional activity in HER.Therefore,the advantages of the components and this core-shell structure made the composite kinetically favorable and stable in alkaline HER.（2）By introducing Cu ions into the solvothermal reaction of preparing Co glycerate spheres precursor,CuCo hollow glycerate spheres were obtained.The hollow spheres were then transformed into double-shell hollow spheres according to Kirkendall effect after a sequential hydrothermal reaction.Followed by selenization procedure,the CuCo selenide double-shell hollow spheres were successfully synthesized.The phase and alkaline OER performance of samples with different Cu content were studied.Samples that consisted of Cu_2-xSe and（Co,Cu）Se₂ phases showed superior catalytic performance.It can be inferred that the proper amount of Cu may help the absorption of intermediates in OER,which further improves the OER performance of Co based materials.（3）A facile template-engaged strategy was developed to modulate the component and morphology of yolk-shell structured Ni glycerate spheres using different Fe ions as modulators.The as-obtained hollow NiFe glycerate spheres were transformed into hollow NiFe oxyphosphide spheres consequently via a following phosphorization procedure.The reaction mechanism of different Fe ions was probed by monitoring the reaction process.It was found that the etching and ion-exchange effect caused by Fe³⁺and Fe²⁺,respectively,led to the formation of hollow spheres and the incorporation of Fe.Then the as-obtained hollow NiFe oxyphosphide spheres with an optimized Ni/Fe ratio showed excellent catalytic performance for OER,benefitting from the high intrinsic catalytic activity of NiFe-based materials.