Design And Properties Of Platinum Free Efficient Catalysts For Oxygen Reduction Reaction

Recently,the rising global energy crisis and environmental impact of traditional fossil fuels pose serious challenges to human health and social development.Develop novel green energy technologies are badly in need.Fuel cell can directly generate electricity from chemical energy stored in materials by electrochemically redoxing reactions in anode and cathode with water as the only byproduct.This energy conversion technology currently receives intensive development focus and becomes another important energy technology after fossil energy because of its high energy conversion efficiency,virtually no pollution,simple structure,significant stability and easy starting.However,the oxygen reduction reaction(ORR)in the cathode is much more kineticly sluggish than the reaction in anode,which restricts the efficiency and performance of such devices.Traditionally,platimum(Pt)has been commonly used as the best ORR catalyst.Unfortunately,its high cost and instability in the fuel cell environment have also made Pt-based catalysts the primary barrier to commercial mass market of fuel cells.Thus,efforts are needed to identify alternative catalysts that are readily available,cost effective,and show comparable-or even better-catalytic effects than Pt for cathodic in fuel cells.Herein,a series of none Pt catalysts are prepared by doping carbon materials and combine polyoxometalates with different carbon materials used as ORR catalysts in different electrolyte.The main results are as follows:(1)A novel kind of highly efficient metal-free electrocatalysts for ORR has been developed successfully by doping heteroatoms in graphdiyne.Mono-element(N,B,F,S)and dual elements(NS,NB,NF)are introduced in the graphdiyne,leading to series dopant graphdiyne.In particular,the as-prepared NFGD exhibits comparable performance to commercial Pt/C both in half-cell and full-cell(Zn-air battery).It shows a much better stability as well as a higher tolerance to methanol crossover and CO poisoning effects than the commercial Pt/C.The density functional theory(DFT)calculations give proper explaination to the doping effect.Our results show that these doped GDs have great potential for metal-free catalysts to be used as low-cost,effcient,and durable ORR catalysts.(2)Develop a new strategy to prepare catalysts by bottom-up synthesis route.The metal-free catalysts were prepared using a nitrogen containing molecule,terephthalonitrile,as the precursor through different thermal temperature,reaction time and elements doping to get the 3D porous structure material(PTF).On this novel platform,we observe that the nitrogen confgurations can greatly influence the electrocatalytic performances of the catalysts,and quaternary nitrogen(N?)can be the most effecient nitrogen configuration for ORR.In addition,different heteroatoms have disparate influences to the parameters of ORR catalysts:boron doping can improve the catalytic selectivity,while fluorine doping can enhance the catalytic activity.Obviously,the rational design of catalysts via bottom-up strategies developed in this work opens up a new avenue for detailed exploration of the electrochemical mechanisms of metal-free catalysts.Based on the work,we also explored the catalyst used in acid medium by introduced Fe and I to the organic framework.The results showed that the doping sequence of Fe and I has great influence on the catalytic activity of the as prepared cataysts.And the best catalyst is PTF-Fe-I,which introduced Fe firstly,and I next.(3)A novel cathode catalyst made of the noble metal free polyoxometalate(POM)Co7(AlePyZn)2 and low cost carbon materials Vulcan XC-72 is highly active toward the ORR in both neutral and basic media.Owning to the strong electrostatic interaction between POM and carbon,the composite were obtained through one step.The as prepared materials reduced O2 to H2O in both neutal and basic media in a 4e-parthway and the reaction mechanism of POM-based materials used as ORR catalysts was studies.This work opened up a new avenue for the application of POM in electrochemical catalytic field.(4)A new and simple approach for the fabrication of noble metal-free ORR electrocatalysts based on 3d-substituted POMs and carbonaceous materials was developed.The POM-based materials were used as the ORR catalysts in both basic and neutal medium,which presented a good platform to shed light on the influence of different 3d metals(Cu,Co,Ni)and carbon support(Vulcan XC-72,rGO,organic carbon materials)on the catalytic activities.This approach also paves the way for the development of a whole new family of efficient active sites of POM and excellent carbon supports.