Tuning Electronic Structure And Surface State For The Design Of High-Efficiency Electrocatalysts

Energy and environmental issues are fundamental challenges facing people in modern society.Since the industrial revolution,major energy sources have relied on fossil fuels,which are unsustainable and contribute to global warming by emitting large amounts of carbon dioxide.Therefore,it is crucial to develop and utilize renewable energy sources The use of intermittent electrical energy from various renewable energy sources to drive electrochemical reactions that convert common or inexpensive molecules into high value-added products is an ideal way to utilize renewable energy sources.Some of these high value-added products can be directly applied in chemical and pharmaceutical fields,while others can be converted from stored chemical energy to electrical energy and reused using fuel cell technology.However,in practical applications,the kinetics and selectivity of electrochemical reactions as well as the stability and cost of catalysts greatly limit the development and large-scale application of these molecular conversion technologies.In view of this,the design and development of highly active,stable,selective,and low-cost electrocatalysts to accelerate the electrode reaction rate,improve the energy conversion efficiency of the device,and reduce the cost of use is of great importance for the large-scale development and utilization of sustainable energy sources.The subject of this paper is to design and develop efficient and stable catalysts and investigate their catalytic performance for the electroconversion of common or inexpensive molecules into high value-added products.In this thesis,we have applied doping engineering and surface modification methods from both electronic structure and surface state directions to modulate the materials in a relevant way.The reaction mechanism is also investigated using electrochemical in situ IR and in situ Raman.Several materials in this paper surface out excellent performance in electrocatalytic water oxidation,propylene electrooxidation and formaldehyde electroreduction reactions,while these results are instructive to understand the relationship between the structure and electrocatalytic performance of the materials.The main contents contained in this paper are as follows.1.We prepared a series of nickel-based Ruddlesden-Popper chalcogenide materials LanSrNinO3n+1 where n=1,2,3 and ∞ to investgate the relationship between activity of water splitting and crystal dimensionality.We found that the OER activity of the samples gradually increased with increasing n from 1 to ∞.The resistivity versus temperature dependence tests show that the resistivity of the samples increases with the crystal dimension thus achieving the transition from insulator to conductor.The soft X-ray absorption spectroscopy(XAS)reveals the intensity of Ni 3d-O 2p hybridization,which is enhanced with increasing n for metal-oxygen bonds.The series of samples with n=∞ have high electrical conductivity and strong Ni-O covalent bonds,which contribute to the acceleration of the OER kinetic process.2.We have prepared a series of pyrochlore structured catalysts R2Ir2O7(R=rare earth ion)with excellent acidic water oxidation intrinsic activity.As the radius of R ion increases,the Ir 5d bandwidth of these materials increases,leading to a weakening of the electronic correlation,followed by an increase in the degree of hybridization of Ir 5d with O 2p orbitals and a transition of the material properties from insulator to metal,as well as an enhancement of the covalent degree of Ir-O bonding,all of which enhance the intrinsic activity of the materials for acidic OER.3.Designing highly active and selective electrocatalyst for partial oxidation of hydrocarbon to high value-added chemical is attractive,but poses a great challenge.Here,we report one-dimensional(1D)hollandite KRu4O8 nanorods as a super electrocatalyst for partial electrooxidation of propene to 1,2-propandiol.In a 0.5 M H2SO4 electrolyte,the KRu4O8 nanorods exhibit a 1,2-propanediol Faradaic efficiency of 62%with a 1,2-propanediol partial current density as high as 12 mA cm-2.Compared to RuO2,hollandite KRu4O8 shows a significantly improved activity and much better stability.Experimental and theoretical analyese suggest that the high 1,2-propanediol activity and selectivity can be attributed to the optimized binding energy of propene and changes in the adsorption configuration of the intermediate species induced by the large K atoms on the catalyst surface.This work illustrates the importance of the catalyst surface structure for electrochemical transformation of organic small molecules.4.We synthesized a high oxygen content graphene oxide(oGO)for the electrocatalytic formaldehyde to 1,2-propanediol reaction,which not only achieves a high selectivity for 1,2-propanediol,with an FE of oGO for 1,2-propanediol of up to 27%at-0.8 V relative to the RHE potential,which is approximately 13 times higher than that of commercial graphite flakes,but also this method,relative to the industrially available propylene oxide alkane aqueous method production costs are substantially lower and the reaction conditions are mild.By comparing the performance with graphene(rGO)with low oxygen content groups on the surface,oGO has higher catalytic activity while maintaining a high Faraday efficiency at 5 h.The stability has been largely improved.