Doping Modification Of Two-dimensional Materials And Its Effct On Electrocatalytic Performance

Represented by oil and natural gas,among the most important energy sources in the world,fossil fuels still play a pivotal role.Because of limited fossil fuel resources,the burning of fossil fuels is accompanied by the emission of greenhouse gases,which seriously threatens the security of the ecological environment and the sustainable development of energy.The energy transition and energy reform program aim to alleviate the social crisis and enable energy freedom.Among them,fuel cells and the use of electrochemical water splitting to produce hydrogen are considered to be expected to replace traditional fossil fuels and promote the development of a green and environmentally friendly society.For fuel cells,the slow oxygen reduction reaction（ORR）kinetics of the cathode restricts the energy conversion efficiency and power density.Therefore,finding highly active oxygen reduction catalysts is considered to be the key to optimize the performance of fuel cells.Oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）are the main half-reactions that occur at the anode and cathode,respectively,in the electrochemical water splitting reaction.Compared with HER,the complex and slow process of OER involves multiple proton/electron coupling steps and is also a more energy-intensive process.Therefore,improving the efficiency of OER electrocatalysts can greatly contribute to improving the overall efficiency of the water electrolysis reaction.Two-dimensional（2D）materials are considered as promising catalyst candidates due to their large specific surface area,highly exposed surface atoms,and two-dimensional charge transport pathways.Tuning the electronic structure and even the surface morphology of two-dimensional materials by doping has effectively improved the catalytic performance of the materials.In this paper,aiming at improving the catalytic performance by doping modification,a series of electrocatalytic materials with excellent performance were obtained by introducing different elements in different ways.The innovative preparation process and mechanism exploration have brought a broader perspective to the field of electrochemical catalysts.The foremost consequent of this study are as follows:1.Graphene oxide（GO）has shown great promise in many practical applications,but it has long been considered to have no ORR catalytic activity.In this study,graphene oxide was assembled into the cathode of a lithium-ion battery and disassembled after several cycles of operation.Compared with pure graphene oxide,the onset potential of activated graphene oxide is shifted forward by about 0.16 V,which even exceeds that of graphene after high temperature nitridation（0.84 V）.During this process,oxygen-containing functional groups in graphene oxide provide doping sites for Li.The presence of Li stabilizes the-COOH group and maintains the catalytic activity of the material.This is the first time that lithium-doped carbon with high ORR activity has been proposed,and the interdisciplinary research on the combination of batteries and catalysis has brought a broader perspective to the field of electrochemistry.2.Layered double hydroxides（LDHs）have attracted extensive research interest in recent years due to their interesting electrocatalytic activity,abundance,ultra-stability,and low toxicity.Tuning the electronic structure of LDHs by elemental doping is a widely adopted method,adding metal dopants X（X=W,Mo,Nb,Ta,Re,Ir,Ru,Mn and V）with high valence charges To tune the electronic structure,the energy of its valence-charge transition is reduced,thereby improving the catalytic OER performance.At present,Ti is only used for the direct preparation of LDH（for photoelectric catalysis）,and the electronic interaction between Ti and LDHs sheets with other metals has not been studied,and it has not been used as a third element for doping.This work innovatively proposes Ti-doped NiFe-LDH to further improve the OER performance.We can see that titanium-doped nickel-iron layered double hydroxide（Ti-NiFe LDH）is more suitable for OER catalyst from the experimental results.The onset potential is very early and its value is 1.41 V,the polarization curve shows a rapidly increasing current density,A high current density of 30 m A cm^-2 can be achieved with a small overpotential,which is only 270 m V.The electrochemical impedance test results show that the charge transfer resistance of Ti-NiFe LDH is smaller than that of NiFe-LDH,and the electron transfer rate during electrochemical process is faster.