Surface Design Of Low-Dimensional Inorganic Materials For The Oxygen Electrocatalysis

Finding sustainable development methods to alleviate the small-or large-scale energy crisis has become human's main efforts and goals.It is hopeful that human could reduce dependence on the traditional energy such as fossil in the future.The transformation of electricity from renewable sources(e.g.,solar photovoltaic devices,wind turbines,etc.)has been continuously developed and implemented.However,the energy provided by this renewable energy source is intermittent,while the consumption of electricity is continuous,resulting in a time-duration mismatch between supply and demand.Therefore,in order to realize the utilization of renewable energy,energy conversion and storage devices should be vigorously developed.The electrochemical process can realize the transformation between electrical energy and chemical energy.When the supply of renewable energy exceeds the demand,the electricity by renewable energy can be used to drive spontaneous electrochemical reactions and convert it into chemical energy for storage.The stored energy can be converted back into electrical energy by a spontaneous electrochemical reaction in a galvanic cell.Rechargeable batteries is widely used in small mobile business devices(such as mobile phones,laptops,and even automobiles),electrolysis and cell reactors on large-scale devices still require further developments.At present,hydrogen energy has attracted extensive attention from the energy industry due to its characteristics of zero emission,zero pollution and high energy density.More and more research focused on energy conversion based on hydrogen cycle.In this case,electrochemical water splitting is used as the initial reaction,where chemical energy converted from electrical energy to hydrogen.When electricity demands are high,the hydrogen fuel can be oxidized at the anode.In the above energy conversion reactions,oxygen electrocatalysis plays an important role in both electrolysis and cell reaction.The OER(Oxygen evolution Reaction)and ORR(Oxygen Reduction Reaction)becomes the rate-limiting step of the batteries due to the four-electron transfer process.At present,RuO2 and IrO2 are the main catalysts for OER,while platinum is the main catalyst for ORR.However,the high cost of precious metals has greatly limited the developments and large-scale application of water splitting and fuel cells.Therefore,the developments of inorganic solid catalytic materials for oxygen electrocatalysis have become a key problem in energy conversion and application.Oxygen electrocatalysis is a heterogeneous catalytic reaction process.Because the reaction only occurs on the surface of electrocatalysts,the properties of the catalyst surface play a key role in the whole reaction.For electrolytic oxygen evolution reaction and oxygen reduction reaction,surface/interface structure design of electrocatalysts provides an important path for the exploration of high-performance electrocatalysts.At present,a large number of literatures have reported that the surface modification methods of electrocatalysts can not only optimize the electronic states of active sites on the surface of catalysts,but also retain the bulk characteristics of catalysts.Meanwhile,low-dimensional inorganic materials possess excellent electrochemical catalytic performance due to their quantum limiting effect and large surface area.Therefore,the surface/interface chemical regulation can be an important strategy to optimize of the adsorption energy of intermediates and improve the performance of oxygen electrocatalysis.The specific content of this paper is as follows:(1)Electrochemical surface reorganization is an effective strategy to regulate catalysts'surface and interface.In this paper,the zero-dimensional scale Co2P was used as the model electrocatalyst precursor to highlight the strategy of electrochemical surface oxidation of metallic precursors in alkaline media,which can promote the generation of a large number of surface active sites and improve the performance of OER reaction.We further extended the surface oxidation strategy to one-dimensional CoP nanowire arrays and a series of transition metal phosphates.In this chapter,we fully demonstrate the important role that electrochemical surface oxidation can play in the electrochemical OER process by surface/interface regulation on low-dimensional inorganic materials.(2)The modulation of the surface coordination number is also one of the important means for the design of the surface/interface structure of inorganic solid materials.The optimal coordination site exposure is realized by coordination regulation in porous platinum,which brings high catalytic activity and stability to ORR process of electrochemical reaction of oxygen.The optimal Pt coordination-site exposure in grain boundaries provides suitable adsorption energies for oxygen species and high thermodynamic stability,resulting in high intrinsic activity and durability in the ORR,even superior to Pt(111)sites.Our as-obtained grain-boundary porous platinum(GBP-Pt)consisting of 3 nm crystals exhibits 7 times higher ORR activity than commercial Pt.For fuel cell performance,the GBP-Pt catalyst based MEA exhibits high power density(1.49 W cm2,0.71 A mg-1 Pt for mass activity)and stability(12.9%loss after 30 K cycles),all of which far surpass the U.S.DOE target in 2020(0.44 A mg-1 Pt for mass activity and 40%loss for stability).In this chapter,we mainly demonstrated that the regulation of the surface coordination number can also be used as a method of surface interface of low-dimensional inorganic catalytic materials,and further improve their catalytic activity to the electrochemical ORR process.(3)It is also an effective surface/interface regulation method to combine low-dimensional inorganic catalytic materials and optimize the electronic structure of catalytic sites.In this paper,a zero-dimensional MnO nanoparticle confined to porous carbon nanosheet material was synthesized to realize the interface composite.The porous graphite carbon layer is activated by the manganese oxygen nanoparticles to become the active site in the ORR catalysis process,and the conductivity and stability of the manganese oxygen nanoparticles are further improved.In addition,under the enhancements of manganese oxide compounds,the hydrogen peroxide of the side reaction is rapidly decomposed,and the catalytic materials show excellent catalytic characteristics and long-term stability,which solves the bottleneck problem of carbon materials as catalysts for oxygen reduction reaction.This paper fully exhibits that the interfacial composition of low-dimensional inorganic materials can improve performance of oxygen electrochemical ORR process and become one of the effective means of chemical regulation of the surface or interfaces.