Synthesis And Electrocatalytic Performance Of Transition Metal Phosphides/nanocarbon Composites

With the increasing demand for sustainable development,cost-efficient energy technologies have attracted extensive attention worldwide.Water electrolysis and fuel cells are two of the most promising advanced energy technologies.It has been known that oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)are the major impediments for the development of fuel cells and electrolysis of water,respectively.At present,precious metal materials are the most efficient and mature ORR and OER catalysts,but their low natural reserve and high cost severely hinder their practical applications.Therefore,developing economical and high-efficiency non-precious candidates has recently become a hot topic of energy research.Among the numerous non-precious metal oxygen-evolved catalysts,carbon materials have been regarded as one of the most promising candidates due to their unique electronic structure and high conductivity.Benefiting from the excellent corrosion resistance and high catalytic activity,transition metal phosphides have also attracted considerable attention in oxygen-evolved catalysis.Here,we selected the composite system of heteroatom-doped carbon materials and transition metal phosphides as the research object,explored highly efficient and controllable synthesis methods and investigated the structure-activity relationship between morphologies and electrochemical performances.The main work of this thesis is shown as follows:1.By integrating the advantages of dual-doped carbon materials and bimetallic phosphides,we rationally designed a novel hierarchical structure in which CoMnP4 nanoparticles were confined within P,N co-doped defective carbon layers(recorded as CMP@PNC)via a space-confinement phosphorization strategy.It is demonstrated that the confined bimetallic phosphide based hybrid could not only achieve higher ORR/OER catalytic activity in 0.1 mol L"1 KOH solution than most of the reported bifunctional oxygen catalysts,but also exhibited superior long-term durability due to the obstructed aggregation of CoMnP4 nanoparticles during the electrochemical cycling process.Synchrotron radiation-based characterization were utilized to investigate the electronic structure of the bimetallic phosphide and characteristics of heteroatoms doping,and we found that the excellent catalytic performance of obtained materials could be ascribed to the highly active sites,high specific surface area and good electrical conductivity of N,P doped carbon as well as the high corrosion resistance and high catalytic activity of bimetallic phosphides.2.Through template-assisted synthesis,a series of nano hybrids composed of amorphous transition metal phosphide Mn-P and N,P co-doped carbon layer were controllably constructed as a new ORR catalyst with good catalytic stability in alkaline solution.We observed that samples with different metal contents showed different catalytic behaviors.The MP/PNC-2 catalyst with 0.25 mmol Mn element presented the best onset potential and the half-wave potential of 0.98v vs.RHE and 0.86v vs.RHE,respectively,which is similar with Pt-based catalyst.The polarization curve of MP/PNC-2 did not change significantly after working for 3000 cycles,indicating that the composite had good catalytic stability in alkaline environment.