High Efficiency Electrocatalysts Derived From Transition Metal Polyphthalocyanine(Polyporphyrin)

As the energy crises and environmental damage resulting from the overuse of fossil fuels,rechargeable metal-air batteries and overall water splitting have been recognized as robust and green energy storage/conversion devices for fossil fuel alternatives.However,their development is hampered by the sluggish kinetics of oxygen reduction reaction?ORR?,oxygen evolution reaction?OER?and hydrogen evolution reaction?HER?.Therefore,developing robust electrocatalysts for ORR,OER and HER is vital for renewable/rechargeable energy systems but remains challenging.Polyporphyrin?PP?and polyphthalocyanine?PPc?have the advantages of high conjugated ?-electron system,large-ring hollow channel,excellent conductivity,good electromagnetic performance and large specific surface area.The catalysts derived from transition metal-coordinated polyphthalocyanine and polyporphyrin can provide abundant carbon,nitrogen and metal sources.Based on above-mentioned advantages of PP and PPc,in the thesis,three catalysts with remarkable catalytic performance are prepared,which are derived from transition metal-coordinated polyporphyrin and polyphthalocyanine,respectively.Many valuable results are obtained and summarized as follows.1.Novel CNTs@?Fe,Co,Ni?PP-T?T represents the pyrolysis temperature?hybrid materials are fabricated by pyrolysis of trimetallic?Fe,Co,Ni?polyporphyrin??Fe,Co,Ni?PP?-encapsulated carbon nanotubes?CNTs?.The composition,morphology and structure of the as-obtained samples are characterized.Electrochemical measurements show that the as-prepared CNTs@?Fe,Co,Ni?PP-800 has excellent catalytic activities for both ORR and OER,with more positive onset potential?0.988 V vs RHE?and half-wave potential?0.837 V vs RHE?for ORR,and with smaller overpotential?355 m V?at 10 m A cm^-2 for OER.The assembled CNTs@?Fe,Co,Ni?PP-800 based zinc-air battery shows high peak power density of 155.13 m W cm^-2 and excellent long-term charge-discharge cycling stability?50 h?,distinctly better than the Pt/C-RuO₂ based one.2.Using nickel foam?NF?as conductive support and the surfactant F127 as morphology tuning reagent of iron polyphthalocyanine?Fe PPc?,Fe PPc/NF-S?S represents surfactant?is prepared by a solvothermal method.A novel electrocatalyst P-Fe PPc/NF-S?P represents phosphorization?for overall water splitting is synthesized by the subsequent phosphorization of Fe PPc/NF-S.The as-generated P-Fe PPc/NF-S catalyst only needs the overpotentials of 293 and 224 m V to achieve the current density of 100 m A cm^-2 for OER and HER,and has excellent durability.Using P-Fe PPc/NF-S as the anode and cathode,respectively,the assembled water electrolyzer only needs the cell voltage of 1.743 V to reach m A cm^-2 for overall water splitting,obviously superior to that of the precious metals?using Pt/C/NF and RuO₂/NF as the cathode and anode?-based water electrolyzer?1.852 V?.3.Using iron and cobalt-coordinated polyporphyron as the precursor,SiO₂@?Fe,Co?PP@SiO₂ is synthesized by the silica template and silica-protected methods.Novel SiO₂@?Fe,Co?PP@SiO₂-T?where T represents the pyrolysis temperature?bifunctional oxygen electrocatalysts are prepared by subsequent pyrolysis of SiO₂@?Fe,Co?PP@SiO₂ and acid washing of the corresponding as-pyrolyzed product.The optimized SiO₂@?Fe,Co?PP@SiO₂-800 electrocatalyst shows the positive onset potential of 0.985 V vs RHE and half-wave potential of 0.861 vs RHE for ORR,and an overpotential of 373 m V at the current density of 10 m A cm^-2 for OER.Utilizing SiO₂@?Fe,Co?PP@SiO₂-800 as the air electrode,the assembled zinc-air battery shows a high open circuit voltage of 1.554 V,and displays a higher peak power density(166.69 m W cm^-2)and better long-term charge-discharge cycling stability?over 83 h?than the Pt/C+RuO₂ air electrode.