The Study On Cabon-based Oxygen Reduction Catalysts Based On Non-precious Metal Doping And Its Application In Energy Devices

Hydrogen fuel is considered one of the best ways to store energy produced from renewable sources,it can be converted into electrical energy via direct electrochemical conversion in proton exchange membrane fuel cells(PEMFCs)at high efficiency and releases water as the only byproduct.The development of fuel cell technology is restricted by precious platinum based electrocatalysts required to sluggish oxygen reduction reaction(ORR).Metal-air batteries,as another new energy technology,is also restricted by precious metal-based ORR catalysts.The development of fuel cells and metal-air batteries is limited by the platinum precious metal that has low reserve,high price,poor durability and poor toxicity resistance to methanol.Therefore,it is very important to develop non-precious metal-based ORR catalysts with low-cost,earth-abundance,good performance,excellent stability and toxicity resistance to methanol.In this paper,a series of non-precious metal-based ORR catalysts have been designed and synthesized based on non-precious metal doping methods and applied in PEMFCs and Zn-air batteries:1.We developed a porous N,S,F tri-doped metal-free carbon-based catalyst(NSF-PC)for ORR,which was obtained by pyrolysis for a complex of edge-selectively carboxylated graphite(ECG)and poly(ionic liquid)(PIL)via electrostatic self-assembling and templated-free approach.The N,S,F tri-doped carbon possessed rich defect,highly doping,high conductivity and hydrophilicity.The optimized NSF-PC catalyst obtained from pyrolysis in NH3 atmosphere exhibited excellent electrocatalytic activities for ORR with the half-wave potential of 0.885 V and 0.72 V(vs.RHE)in alkaline and acidic medium,respectively.More importantly,the catalyst showed high selectivity via a 4e-process,good stability and endurance to methanol.The catalyst further used as the cathode electrode for rechargeable Zn-air battery,exhibiting that the discharge power and charge-discharge stability were better than that of the commercial 20%Pt/C catalyst.The catalyst was also used as the ORR catalyst for PMEFC,which showed a maximum power density of 292 mW/cm2 and good stability.2.We also developed a graphene-like based sulfur-doped Fe-N-C catalyst(S-Fe-N/C)by pyrolysis of a complex of in-situ polymerized polyaniline,iron phthalocyanine,trithiocyanuric acid and graphene oxide(GO).The as prepared S-Fe-N/C catalyst possessed rich folds,porous and high degree of defect.In the process of synthesis,the aniline was in-situ polymerized onto the surface of graphene oxide.Subsequently,hydrothermal process reduced graphene oxide to graphene and produced defect-rich graphene-like carbon matrix with hierarchical porous structure.In the process of synthesis,the iron phthalocyanine molecules were anchored onto the surface of graphene,which could avoid the aggregation of Fe atoms,forming Fe-Nx as active center with high ORR activity.Due to the characteristics of the above structure and chemical composition,the S-Fe-N/C catalyst exhibited excellent ORR activities with a half-wave potential of 0.92 V and 0.785 V(vs.RHE)in alkaline and acidic medium,respectively.The testing results showed that the S-Fe-N/C catalyst was superior to commercial 20%Pt/C catalyst in terms of selectivity of reaction pathway,stability and toxicity resistance.The catalyst was further used as the ORR cathode electrode for assembling PEMFC,which performed a good performance with a maximum power density of 855 mW/cm2 at a low loading.It was also proved that sulfur doping could promote the performance of Fe-N-C catalysts.This work provided a new idea for the preparation of high performance non-precious metal catalysts.