| In view of the current problems of rapid increase in energy demand,shortage of fossil fuels and environmental pollution,this paper seeks to develop the clean and efficient renewable energy,hydrogen,by means of water electrolysis.The process of electrolyzing water includes a hydrogen evolution reaction?HER?process on the cathode and an oxygen evolution reaction?OER?process on the anode.The above process involves one-or multi-electron transfer,and each electron transfer needs to overcome a certain degree of activation energy,which can be reflected by overpotential?the difference between practical and theoretical potentials?.The overpotential for OER is much larger than that of HER,thus,the energy consumption is large.In this regards,if hydrogen production by water electrolysis is to achieve effective industrial promotion,it will be necessary to obtain an efficient oxygen evolution electrocatalyst.Currently,RuO2 and IrO2 are among the best reported OER catalysts,but their widespread use is limited by high prices and resource scarcity.In the face of the above challenges,the research is mainly focused on potential electrocatalysts based on transition metals such as Fe/Co/Ni,which are rich in reserves,low in price and their electronic structure is easy to be tunned due to the existence of 3d electrons.As a research object,the structure of Fe/Co/Ni-based nanomaterials is modulated to achieve high efficiency electrocatalytic OER performance.The structural tunning methods of nanomaterials in this paper mainly include:?1?synergistic effect of multi-metals to enhance the electrocatalytic activity;?2?in-situ electrochemical regulation to enhance the electrocatalytic activity;?3?enriched surface or interface sites to enhance the electrocatalytic activity.Based on the above three tunning methods,we have mainly completed the following work:?1?Cu/Co based hierarchical bimetallic selenide nanotubes were successfully constructed,and the structure remained unchanged while Cu/Co?oxy?hydroxides were formed in the electrocatalytic process.The material exhibited excellent OER performance:low overpotential(238 mV@10 mA cm-2),fast reaction kinetics(Tafel slope 62 m dec-1),strong charge transfer capability?2.3??,and large electrochemically active area(ECSA 4.95 mF cm-2),excellent stability?continuous testing for 20 h,no increase in polarization?.The excellent properties of Cu/Co based hierarchical bimetallic selenide nanotubes are mainly derived from the hierarchical nanotube structure assembled by nanosheets,which has the advantage of large specific surface area and can effectively expose more active sites in electrocatalytic reactions;the bimetallic synergistic effect can enhance the charge transport;the in situ formed?oxy?hydroxides during the oxygen evolution reaction can provide more electrocatalytic active sites and improve electrocatalytic performance.?2?Ni/Mo based bimetallic porous nanowires were in situ constructed via electrochemical process.During the electrochemical activation of NiMoN b imetallic nitride solid nanowires,Mo element with high valence states was dissolved and the corresponding pores were left,meanwhile,high-activity?oxy?hydroxides were in situ formed.The material exhibits excellent OER catalytic activity:low overpotential(280mV@20 mA cm-2),fast reaction kinetics(Tafel slope of 45 mV dec-1),large electrochemically active area(ECSA of 4.23 mF cm-2),excellent stability?continuous testing for 20 h,no increase in polarization?.The Ni/Mo porous nanowires also exhibit high efficiency of HER activity and excellent full electrolysis performance of water:the onset potential of hydrogen evolution is close to 0 V vs.RHE,and the total decomposition water potential at 10 mA cm-2 is only 1.547 V vs.RHE.The excellent properties of Ni/Mo based bimetallic porous nanowires are mainly derived from:the pores formed by the in situ dissolution of Mo,which provides larger active area and more active sites;the bimetallic synergistic effect can enhance the charge transport;the in situ formed?oxy?hydroxides during the oxygen evolution reaction can provide more electrocatalytic active sites and improve electrocatalytic performance.?3?Ni/Fe bimetallic coordination complexes were successfully constructed.Similar to amorphous metal–organic frameworks?aMOFs?,metal coordination complexes?MCCs?consist of central metals and surrounding ligands,and have long-range disordered structures.One of the main differences between MCCs and aMOFs is that the ligands of MCCs can be any other kinds of chemical groups in addition to the organic units.Although MCCs are long-range disordered,they still retain short-or medium-range ordered structures.Long-range disordered,short-range ordered nanomaterials possess rich grain boundaries,more abundant defects and active sites,and the electocatalytic performance can be greatly improved:the Ni/Fe based bimetallic coordination complexes constructed in this paper achieves an extremely low OER overpotential of 229 mV at 10 mA cm-2.?4?Topological conversion derived Fe/Co/Ni based trimetallic coordination complex nanosheets were constructed,which possesses the property of MCCs with rich active sites,and has the advantage of mult-metallic synergistic effect as well as fast charge transport of two-dimensional nanostructures.The catalytic activity is considerably enhanced:overpotential at 10 mA cm-2 current density is only 220 mV,with fast reaction kinetics(Tafel slope of 60 mV dec-1),large electrochemical effective active area(ECSA of 8.23 mF cm-2),excellent stability?continuous testing for 30 h,no increase of polarization?.This thesis provides the guidance to the structural regulation of Fe/Co/Ni based nanomaterials and the reality of highly efficient electrocatalytic activity,as well as lays a foundation for the the promotion of industrial catalysts. |
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