| Under the background of the increasing consumption of fossil energy and the increasing environmental pollution,the research and development of new clean energy that conforms to the concept of sustainable development is an urgent task.Hydrogen(H2)has become the best candidate for new energy due to its outstanding advantages of high calorific value,low pollution and wide sources.With the rapid development of electrochemical technology,electrolysis of water for hydrogen production has attracted extensive attention due to its significant scientific and industrial importance.The electrolysis of water includes oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).Highly active electrocatalysts can effectively reduce energy consumption during water electrolysis.OER is a four-electron transfer process with relatively sluggish kinetics,which is the bottleneck of water electrolysis for hydrogen production,and the development of corresponding OER electrocatalysts is not yet as mature as HER electrocatalysts.Therefore,to overcome this dilemma,it is urgent to develop efficient and stable OER catalysts.On the other hand,the hydrazine oxidation reaction(HzOR),which can also be used as an electrocatalytic anode reaction,has an equilibrium potential of only-0.33 V(vs RHE),which is significantly lower than that of OER(1.23 V),and can also be coupled with HER.The only by-product is carbonfree N2,which is highly in line with the development strategy of carbon-peak and carbon neutralization and can be used as an alternative reaction for OER.However,the lack of efficient catalysts also restricts its wide application.The activities of OER and HzOR catalysts are highly dependent on the electronic structure of their active sites,which provides a theoretical basis for the design and preparation of highly active catalysts.For example,RuO2 is recognized as an excellent OER electrocatalyst.Although it has been studied for many years,its performance still has a lot of room for improvement,especially the poor stability in the acidic OER process restricts its large-scale application.The intrinsic activity of RuO2 can be improved by regulating the electronic structure of active site Ru by heteroatomic doping.As for the HzOR process,this is a process in which N2H4 is dehydrogenated into N2 through multiple steps.It can also be used to obtain high-efficiency catalysts by regulating the electronic structure of the active site.In this dissertation,a series of electrocatalysts were prepared by doping and constructing heterojunction to regulate the electronic structure of the active site,and evaluating their catalytic activities.Combined with structural characterization and theoretical calculations,the relationship between structure and catalytic activity was explored.The specific research contents are as follows:The details are as follows:1.Rutile-type RuO2 has outstanding electrocatalytic OER activity,but it has poor stability in acidic electrolytes.The root cause is that the interaction between the active site Ru and the adsorbed O is too strong,which makes the reaction activation energy of the OER rate-determining step(RDS)higher.In this chapter,a highly active Mn-RuO2 nanocatalyst was prepared by doping RuO2 with Mn to change the electronic structure of Ru at the active site,thereby regulating its adsorption energy for O.At a current density of 10 mA cm-2,the OER required an overpotential of 158 mV,enabling 5000 CV cycles and chronopotentiodynamic cycling for up to 10 hours in 0.5 mol L-1 sulfuric acid electrolyte.Structural characterization and theoretical calculations reveal that doping leads to a decrease in the d-band center of Ru and an increase in the distance from the Fermi level,which optimizes the adsorption energy to the intermediate,thereby reducing the activation energy required for the RDS of the OER,and ultimately reducing the overpotential of OER.The study also found that Mn doping effectively inhibits the conversion of Ru4+into easily soluble higher-valence Ru ions,ensuring good structural and catalytic activity stability.2.In order to realize the device application of OER catalysts,high reaction current density and high mass activity are also required.This requires the catalyst to maintain structural stability and initial high activity at a large reaction potential,and the mass fraction of the noble metal Ru in the catalyst should be as low as possible to effectively reduce the application cost.Based on the analysis of active site electronic structure regulation,increasing active site density and promoting electron transfer,this chapter proposes to use In-doped RuO2 nanoribbons to solve the above problems,and prepare In0.17Ru0.83O2-350 nanoribbons.At the current density of 10 mA cm-2,the overpotential required for OER reaction is 177 mV,and more importantly,the current density is up to 400 mA cm-2,and the mass activity is up to 1094.90 A gRu-1(under an overpotential of 300 mV).The research revealed that,firstly,the doping of In realized the electronic structure regulation of Ru at the active site,reduced the d-band center of Ru,optimized the adsorption energy of reaction intermediates,and reduced the reaction activation energy of the RDS.Secondly,the work function of the catalyst is reduced,accelerating the transfer of electrons from the reactants to the catalyst surface.Thirdly,the nanoribbon structure can expose more active sites and increase the surface electric field strength,thereby improving the mass activity and reaction current density.3.The reaction equilibrium potential of electrocatalytic hydrazine oxidation reaction(HzOR)is only-0.33 V(vs RHE),which is significantly lower than that of OER reaction(1.23 V),so it can be used as an anode replacement reaction to realize hydrogen production with low energy consumption.And HzOR can also be used in direct hydrazine fuel cells(DHFC)to obtain high energy density.However,the HzOR working potential of existing electrocatalysts is much higher than the theoretical value.In this chapter,a Mott-Schottky junction electrocatalyst(CoP/Co-20)composed of two phases of cobalt nanoparticles and cobalt phosphide was prepared.The HzOR working potentials are-69 and 177 mV at reaction current densities of 10 and 100 mA cm-2,respectively,which is outstanding in a series of Co-based materials.The CoP/Co interface acts as the active site of HzOR,and its electronic structure is effectively regulated.The difference between the work functions of the two phases forms a builtin electric field that can effectively drive electron transfer at the interface until the Fermi level and work function reach equilibrium.The reduction of Co valence electrons can reduce the occupancy of the central eg orbital of Co,thereby accelerating the reaction kinetics of the HzOR process.The density functional theory(DFT)calculation results further reveal the interfacial charge polarization,which plays a positive role in the multi-step dehydrogenation reaction of N2H4. |
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