| Along with the increasing concern on energy and environmental issues,oxygen reduction reaction(ORR)electrocatalysts as the energy-conversion devices have been made worldwide application in the past years.Especially,given that most of the best electrocatalysts are expensive and scarce precious metals(e.g.Pt)for the ORR,it is highly desired to develop alternative electrocatalysts with high efficiency and low cost,such as nonprecious metal-based ORR catalysts.In this thesis,we describe the design and synthesis of a serious of efficient sustainable nonprecious metal electrocatalysts based on different sustainable waste biomass,corncob and peanut shell,as well as 2D phthalocyanine/porphyrin polymers doped with nitrogen,phosphorus,transition metal(e.g.Fe/Co/N/P etc)-contaning species.The main research contents in this thesis were summarized below.1.Efficient ORR electrocatalytic activity of peanut shell-based graphitic carbon microstructuresA hierarchical microporous graphitic carbon material intrinsically doped with sulfur and extrinsically doped with dual cobalt species [Co3O4 and Co(PO3)2,termed as Co OP]nanoparticles was prepared from a sustainable waste biomass,peanut shell,with CO2 gas as the activating agent through a thermalreduction method.The resulting Co OP@bio-C exhibits an overall superior ORR catalytic activity,stability and resistance to methanol crossover in alkaline media to commercial 20 wt% Pt/C,with onset and half-wave potentials of 0.91 V and 0.81 V in 0.1 M KOH,a limiting current density of 5.7 m A·cm-2,and a small Tafel slope of 57 m V·dec-1,representing the best result among the biomass-based carbon electrocatalysts.In particular,comparative studies reveal the significant effect of the work function of corresponding catalytic materials on the ORR electrocatalysis.Dual-doped Co OP@bio-C with a work function of 5.42 e V,closer to that of Pt(5.65 e V),displays much better electrocatalytic activity than single-doped Co3O4@bio-C,single-doped Co(PO3)2@bio-C and bio-C-800 catalysts with work functions of 8.35 e V,6.61 e V and 5.02 e V,respectively,due to its good adsorption nature to O2 and desorption nature to the reaction intermediates.The present result will be surely helpful for the design and synthesis of biomass resourcebased ORR catalysts with great application potential.2.Prepartion of cobalt-phosphorus-nitrogen doped biomass-based carbon material for ORRBy using earth-abundant corncob as carbon source,cobalt hydroxide,sodium hypophosphite and melamine as the precursors,KOH as chemical activator,four kinds of heteroatom doped carbon materials were obtained successfully.Among them,the resulting Co PNA@bio-C catalyst exhibits excellent electroactivity with onset and half-wave potentials of 0.92 V and 0.85 V in 0.1 M KOH,a limiting current density of 5.5 m A·cm2,via a4-electron pathway,good stability and good methanol tolerance,representing one of the best results among the Co-doped carbon electrocatalysts.The combination of unique cylindrical structures with multiple holes in the wall and two different functional cobalt phases(Co2O3and Co2N0.67)rends Co PNA@bio-C an excellent ORR performance,in addition to the heterojunction effect from n-type N doping and p-type oxyacidic surface.This work provided a new strategy for the preparation of economical catalysts with high ORR performance by using biomass.3.Preparation of extraordinarily stability oxygen reduction catalyst by a polymerization-pyrolysis-evaporation strategyThe effective anchoring and fixation of heteroatom active sites on porous carbon material is the key to improve the stability of non-noble metal based ORR catalysts.A polymerization-pyrolysis-evaporation(PPE)strategy is developed to synthesize N-doped porous carbon material with Co,Co Fe and γ-Fe2O3 species simultaneously,while the precursor is prepared by a mixture of iron phthalocyanine-based conjugated porous polymer and cobalt-magnesium based nanomaterials obtained by a coordination/polymerization approach.The nitrogen doping with various types(M-N,pyridinic N,graphitic N and oxidized N etc.)are expected to facilitate the anchoring and fixation of the more active metal compound on the substrate and thus improve the stability of the proposed catalysts.The prepared Mg-Co/Co Fe/γ-Fe2O3@NC ORR catalyst exhibits excellent electroactivity with onset and half-wave potentials of 0.95 V and 0.83 V vs RHE,respectively,high limiting current density of 5.73 m A·cm-2,via a 4-electron pathway along with extraordinary stability(>98% retention after 10000 s)and good methanol tolerance,representing the best results among the NPM-doped carbon electrocatalysts.This result provides a new route for the rational design and development of novel highly-stable ORR electrocatalysts,bringing new perspectives for designing various nonprecious metal-based ORR catalyst materials.4.Synthesis of nanoparticles/iron porphyrin polymers induced by phosphorus and study on properties of Zn-Air batteryRational design of electrocatalysts to replace the noble-metal-based materials for oxygen reactions and evolution reactions(ORR and OER,respectively)is highly desirable but challenging for rechargeable Metal-Air batteries.The Fe/Co/N/P co-doped composites are synthesized by one-step method.According to a set of electrochemical tests,the obtained CFe2.5Co/NC can act as dual-functional catalyst to drive OER and ORR with desirable activities and stabilities in alkaline media.Specifically,the CFe2.5Co/NC presents an onset-potential of 1.57 V,a potential of 1.64 V at 10 m A·cm-2,a Tafel slope of 68 m V·dec-1as an OER catalyst,and an onset potential of 0.97 V,a half-wave potential of 0.83 V as an ORR catalyst.The performance is comparable to those of precious metal based electrocatalysts,making it possible for potential application in the renewable energy devices,especially Zn-Air battery. |
