Synthesis And Function Control Of N,s Based Ternary Co-doped Graphene Nanosheet Electrocatalytic Materials

Multi-heteroatom doped metal-free carbon material is one of the most promising substitutes for precious-metal catalysts for the electrocatalysis of oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）in electrochemical energy conversion devices such as fuel cells and metal-air batteries due to their competitive activity and no concerns on potential detrimental impact of dissolved metal species from transition metal-based materials.However,tuning their bifunctionity for enhancing kinetics of oxygen redox reaction（oxygen reduction reaction and oxygen evolution reaction）is still a critical issue.One critical reason is the lack of clarifying synergistic effects of multi-heteroatom doping induced hybrid active species in carbon matrix.On the other hand,the choice of precursors is essential to modulate synergistic effects of multi-heteroatom dopants.Therefore,developing new precursors to reveal synergistic effects of multi-heteroatom dopants is highly desirable for the molecular-level design of highly efficient oxygen redox catalysts.So,we undertook the following researches:1.N and S co-doped graphene for oxygen redox reaction on theorywe explored N,S co-doped graphene as cost-effective electrocatalysts for ORR and OER by employing density functional theory（DFT）.The results show that that configuration of the model of graphitic N and thiophenic S co-doped graphene has the lowest ORR and OER overpotentials,0.40V and 0.42V,respectively,which is better than Pt（1 1 1）.The high bifunctionity is due to the energy increase of pz-orbitals of carbon atoms in active sites comprising the specific structure of graphitic N and thiophenic S.2 Synthesis of N,S,F co-doped graphene for oxide reduction reaction by self-doping strategyN,S,F co-doped graphene-like carbon nanosheets（NSF/C）were developed via a bottom-up doping strategy with Na Cl as a soluble template using a new precursor of N,S,F co-containing copolymer of 2,6-Diacetylpyridine（DAP,N source）,2-aminophenyl disulfide（APD,S source）and 2,2’-Bis（trifluoromethyl）benzidine（BTB）.The N,S,F co doped ultrathin graphene like carbon nanosheets were formed by pyrolysis.It has multistage pore structure and suitable ratio of graphite nitrogen to thiophene sulfur.Compared with commercial Pt/C,the catalyst showed excellent catalytic activity and better stability for oxygen reduction reduction.High ORR performance strongly depends on DAP/APD/BTB precursors,which helps to obtain high content of graphite N and thiophene S dopants,and provides a favorable platform for producing strong synergistic effect with F.3 In situ synthesis of N,S,P co-doped graphene for bifunctional oxygen redox reactionN,S,P co-doped graphene-like carbon nanosheets（NSP/C）were developed via a bottom-up doping strategy with Na Cl as a soluble template using a new precursor of N,S co-containing copolymer of 2,6-Diacetylpyridine（DAP,N source）and 2-aminophenyl disulfide（APD,S source）mixed with a P source of phosphonitrilic chloride trimer（PCT）.Through adjusting the ratio of PCT and the copolymer of DAP/APD,a series of N,S,P co-doped graphene-like carbon nanosheets with various doping level can be efficiently prepared via pyrolysis process,and demonstrate obviously differential electrocatalytic selectivity for oxygen redox reaction,in which NSP/C derived from DAP/APD and PCT with the mass ratio of 1:1 presents an ultra-high surface area of 1209 m²·g^-1,around3.0 nm in the thickness of nanosheets,as well as optimized ratio and content of N,S,P dopants,resulting in a high half-wave potential up to 0.88V vs.RHE for ORR and a low overpotential down to 0.35V vs.RHE,as well as remarkable stability,while its overall oxygen redox activity is 0.70 V for both ORR/OER in0.1 M KOH.And the performance was also proved by a practical rechargeable zinc-air battery with a maximum power density output of 156 m W·cm^-2,and long charge-discharge capability at 5 m A·cm^-2,which is better than that of the same-loading commercial catalysts of Pt/C and Ir O₂（mixed with a mass ratio of1:1）.The high bifunctionity is strongly relied on the energy increase of pz-orbitals of carbon atoms in active sites comprising the specific ratio of graphitic N,thiophenic S and graphitic P dopants obtained from the new precursor of DAP/APD,which facilitates to derive the high content of graphitic N and thiophenic S dopants,providing a favorable platform to generate the strong synergistic effect with P and thus effectively reduce the energy barrier of pathways in both ORR and OER.This work not only presents an efficient oxygen redox catalyst for rechargeable Zn-Air battery,but also provides an effective strategy of developing highly open-structure carbon materials with the design of molecular structure of multi-heteroatom containing precursors.It is believable that this strategy can be extended to develop doped graphene nanosheets for other energy conversion and storage application.