Application Of Catalysts With Low Noble Metal Or Non-noble Metal In Formic Acid Oxidation And Oxygen Reduction Reaction

The frequent occurrence of extreme weather in recent years has made countries on earth pay more attention to environmental protection.Traditional fossil energy is non-renewable and destructive to the environment,which goes against to build environmentally friendly energy systems.The development of technology and population growth have led to increasing energy needs.Hence,the importance of solving the energy crisis and developing green energy to world development is self-evident.Under such objective conditions and the strong support of governments,the new energy field has ushered in a vigorous development.In new energy field,it is considered that fuel cells are one of the most shining stars,which have great potential to solve the energy crisis and relieve environmental pressure for their high energy density,mild operating environment and clean working mode.For the fuel cell to have the possibility of large-scale production,the improvement of the catalyst is essential.According to the present researches,noble metal catalysts are still the most excellent catalysts in fuel cells.However,the high price and scarce reserves of precious metals have hindered the further development of fuel cells.Formic acid oxidation(FAO)is the simplest reaction in small molecule fuel oxidation reduction,while oxygen reduction reaction(ORR)is an indispensable part of most fuel cells.For FAO,catalysts with the best performance is palladium(Pd)-based catalysts.But the increasing price of Pd recently results in a further increase in the cost of catalysts.The progress of ORR is slowly in dynamics and need the help of catalysts.Platinum(Pt)and Pd-based catalysts have the best performance while the price and reserves are also inevitable problems.There are many methods to improve the performance of catalysts,which mainly concentrate on decreasing the amount of noble metal and developing non-precious metal catalysts.Choosing appropriate supports and reducing agents for doping,controlling the morphology of metal particles are efficient solutions to improve the quality activity of precious metals and reduce the amount of precious metal.In the field of developing non-noble metal catalysts,the universal methods to enhance the activity of catalysts are controlling the interaction between carrier and metal through non-metal element doping and trying to obtain highly active catalytic sites.Therefore,this paper introduces several catalysts and their electrocatalytic performance with non-metal element doping as a clue.The mainly work are showing as follows:(1)FAO on Pd particles is relevant with their crystal structures.Here,silicon nanowires are employed as a sacrifice template to grow Pd nanoparticles with various twin structures,including two-fold,three-fold and five-fold ones.The introduction of F can adjust the electron structure and d-band center of Pd,which could promote the catalytic performance.The as-prepared products show an excellent performance on FAO.The peak current of the optimal product is 0.697 A·mgpd-1 in a mixed electrolyte with 0.1 M HClO4 and 0.5 M HCOOH,which is 2.9 times than that of the commercial Pd/C catalyst.The electrochemical active surface area of the catalyst(0.322 m2·mg-1)is 3.5 times than that of the commercial Pd/C(0.091 m2·mg-1)catalyst;(2)The electrocatalytic activity is closely associated with the electronic structure of catalysts.Doping of F and N in catalysts can decrease the d-band center of Pd.The electron-deficient Pd has been proven to show better oxygen reduction reaction performance than the electrophilic one due to the downshift of d-band center.In order to further verify that suitable doping of non-metal elements can improve the performance of catalyst,in this work,Pd nanoparticles are uniformly dispersed in F,N-doping graphene with the assistant of silicon nanowires and hydrofluoric acid(Pd/F,N-doping G).The as-prepared Pd/F,N-doping G-3 catalyst shows a four-electron oxygen reduction pathway with large half-wave potential of 0.87 V and high onset potential of 0.99 V in 0.1 M KOH.In addition,the Pd/F,N-doping G-3 based zinc-air battery exhibits an open potential of 1.40 V and a high power density of 229 mW·cm-2;(3)To futher reduce the cost of the catalysts,we used a comparative novel synthetic method to dope in situ with non-metallic element N for obtaining Fe-N-C Type catalyst.We selected Fe3O4 with ORR catalytic performance,support it on a polyaniline carrier and Fe3O4/NC was obtained after high temperature annealing.The compound has a potential for being an excellent ORR catalyst.