Synthesis And Electrocatalytic Performance Of Heteroatomic Doping Carbon-based Transition Metal Composite

Fuel cells,water splitting technology and the regenerated fuel cell system which is composed of fuel cells and water splitting can realize the conversion of chemical energy and electric energy and play an important role in the efficient use of energy,mitigation of energy crisis and environmental pollution.The key component of fuel cells and water splitting is the electrode catalyst whose performance determines the efficiency and cost of battery device.The development of novel cost-effective,highly-efficient and highly-durable non-noble-metal multifunctional electrocatalysts has been an important research subject in the above sustainable energy fields.In this paper,we used respectively highly stable nanodiamond?ND?,graphene oxide with high surface area?GO?and nano boron carbide?nano-B₄C?as the basic materials,which were composited with transition metal?Fe,Co?compound.Adding boron or nitrogen precursor to the above composite materials and then through vacuum heat treatment,a series composite material electrocatalysts of heterogeneous doped nanocarbon materials with transition metals and their derivatives have been developed which are low price,high catalytic activity and good stability.The synergistic effect of doped carbon materials and transition metals greatly improved the catalytic activity and stability of the catalyst.We carried on researches on oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?in fuel cells,as well as hydrogen evolution reaction?HER?and oxygen evolution reaction in water electrolysis.The relationship between the composition,structure and the electrocatalytic performance of ORR,OER and HER have been systematically studied.Firstly,inspired by the sp³-bonded nanodiamond with highly stable and the synergistic effect between B/N dual-doped carbon,we fabrided the shell/core structural boron and nitrogen co-doped graphitic carbon/nanodiamond?BN-C/ND?catalyst,by annealing a complex of ND,FeCl₃,boric acid and melamine at 1000?C for 3 h under a nitrogen atmosphere.In the process of the surface graphitization of nanodiamond with catalysis by FeCl₃,B and N atoms from the decomposition of boric acid and melamine were directly introduced into the graphite lattice to form B,N co-doped graphitic carbon shell,while the core still retained the diamond structure.Electrochemical measurements of the BN-C/ND catalyst show much higher electrocatalytic activities towards oxygen reduction reaction?ORR?in alkaline medium than its analogues doped with B or N alone?B-C/ND or N-C/ND?.The high catalytic activity of BN-C/ND is attributed to the synergetic effect caused by co-doping of C/ND with B and N.Meanwhile,the BN-C/ND exhibits an excellent electrochemical stability due to the special shell/core structure.There is almost no alteration occurred in the cyclic voltammetry measurements for BN-C/ND before and after ADT test.To further improve the ORR catalytic activity of C/ND,the NDs deposited Fe?OH?₃nanoparticles though microwave assisted precipitation were mixed with melamine and treated at 800?C in N₂ atmosphere to obtain shell/core structural Fe/N-C/ND catalyst.The Fe element can catalyze the graphitization of ND,and the codoping of Fe,N was realized during the graphitization process.Moreover,it is to form Fe/N doped carbon active sites,synergistically improving the ability of catalyzing ORR.The onset potential of the Fe/N-C/ND for ORR was-0.01 V?vs.Hg/HgO?,which is comparable to the 20wt%Pt/C.And the half-wave potential of the Fe/N-C/ND was-0.10 V?vs.Hg/HgO?,which is lower than that of the 20wt%Pt/C by only 20 mV.In addition,Fe/N-C/ND also shows an excellent electrochemical stability due to the highly stable ND core.Inspired by various Co-based materials including Co,CoO and Co-N complex exhibiting excellent catalytic activity for the HER,ORR,and OER,we used a rapid microwavepolyol method to deposite cobalt particles on GO which has a high specific surface area and rich in oxygen-containing functionalities.Then,the GO supported cobalt particles were heated with melamine at 600?C under an N₂ atmosphere to obtain CoO@Co/N-rGO catalyst.The cobalt particles on graphene were superficially oxidized by the oxygen from the oxygen-containing functionalities of GO to form CoO@Co particles with a core–shell structure.Melamine acts as a nitrogen source for N doping in the graphene lattice,which are partially bonded with the Co atoms to form Co–N moieties.The catalyst exhibits remarkable catalytic activity and superior stability towards the HER in both acidic and alkaline media(?_J10=0.14 V in 0.5 M H₂SO₄),which is much better than the current similar non-noble metal catalyst.The catalyst also shows excellent ORR activity in 0.1 M KOH which is comparable to that of 20wt%Pt/C catalyst,and also a good OER catalytic activity in 0.1 M KOH(?_J10=0.42 V).The unusual catalytic activities arise from the synergetic chemical coupling effects of metallic Co,cobalt oxides and Co/N-doped graphene.This study provides a new attractive multi-functional catalyst material for unitized regenerative fuel cells and overall water splitting technologies.Lastly,based on Co₂B with good OER and HER electro-catalytic activities,the nano-B₄C deposited Co?OH?₂ nanoparticles though a rapid microwave-polyol method were mixed with melamine and treated at 600?C in N₂ atmosphere to obtain Co₂B/Co/N-B-C/B₄C nanocomposites with multiple components coexisting and good interaction with each other.In the process of the heat treatment,the Co₂B and Co nanoparticles are formed in situ and anchored on the generated N and B codoped carbon and undecomposed B₄C.The excellent trifunctional catalytic performances and excellent stability issue from synergetic effects of Co₂B,metal Co,Co/N-doped carbon and B self-doped carbon coexisting in the hybrid with good interaction mutually.The catalyst exhibits remarkable catalytic activity towards the OER(?_J10=0.3 V,which is lower than RuO₂ by 10 mV).In ORR,the onset potentional,diffusion current density and half-wave potential are comparable to that of 20wt%Pt/C catalyst.Furthermore,Co₂B/Co/N-B-C/B₄C as a bifunctional oxygen electrode catalyst exhibits the smallest E_J10,OER-E_J3,ORR with a value of 0.71 V,which is one of the best bifunctional oxygen electrode catalysts.Meanwhile,the catalyst also shows a good HER catalytic activity in 0.1 M KOH(?_J10=0.22 V).Besides,the Co₂B/Co/N-B-C/B₄C hybrid also exhibits perfect stability which may be attributed to the stable Co-B bond and also the B₄C which is left after reaction as a stiff support in the hybrid.