Preparation And Electrocatalytic Properties Of ZIFs Derivatives Supported Copper And Nickel Oxides

The rapid development of modern society leads to the increasing consumption of fossil energy.At the same time,a series of environmental pollution problems caused by it make people pay more and more attention to sustainable development,and reach a consensus on actively seeking clean and efficient renewable energy.In the new energy industry,fuel cell as the main force has been widely studied.Direct methanol fuel cell(DMFC),with its high energy density,short start-up time and environmental friendliness,has great application potential in portable electronic devices.At present,the most commonly used and effective catalyst in DMFC is the precious metal platinum(Pt)based catalyst.However,to promote its commercialization process,the main problems of catalyst such as high cost,limited reserves,easy poisoning,low MOR activity and cathode methanol penetration should be solved.Therefore,the research and development of ORR catalysts and MOR catalyst supports with low-cost,high catalytic efficiency are of vital practical significance for the further development of DMFC.In this paper,two kinds of catalysts with higher catalytic activity of MOR and ORR than commercial Pt/C were prepared,and physical characterization of the materials was carried out by a variety of means,including X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),contact angles,scanning electron microscopy(SEM)and transmission electron microscopy(TEM).At the same time,the tests of MOR and ORR performance of the materials were carried out by electrochemical means,including cyclic voltammetry(CV),linear voltammetry(LSV),electrochemical impedance spectroscopy(EIS)and rotating ring disk electrode test(RRDE).In this paper,CoZn-ZIFs were used as templates,and the precursor was first pyrolyzed in nitrogen atmosphere and etched with hydrochloric acid(HCl).Then the Co₃O₄@NPC/Cu O catalyst was synthesized for ORR by adding Cu(NO₃)₂·6H₂O and secondary calcination at 300-500?.Then the Pt nanoparticles were uniformly loaded onto its surface by sodium borohydride reduction method to obtain Pt-Co₃O₄@NPC/Cu O catalyst for MOR.For cathode ORR,Co₃O₄@NPC/Cu O-400(400?)shows better ORR activity and stability than commercial Pt/C(10 wt.%),and the reduction peak potential and half-wave potential reach 0.82 V and 0.83 V,respectively.During the ORR process,the high specific surface area and mesoporous structure of Co₃O₄@NPC/Cu O-400 are favorable for the substances transport and the exposure of active sites.Cu O nanoparticles can not only provide the variable valence states(Cu⁰,Cu⁺and Cu²⁺)that ORR may need,but also act as a protective layer for the highly active substances(CO²⁺)to improve the stability of the catalyst.For anode MOR,Pt-Co₃O₄@NPC/Cu O-400(5 wt.%)has much higher mass activity than Pt/C,reaching 1947 m A mg _Pt^-1.During the MOR,the high surface area of the Co₃O₄@NPC/Cu O-400 supports effectively improves the dispersion of Pt nanoparticles,and thus significantly reduce the shedding and agglomeration of Pt nanoparticles during the reaction.The strong interaction between metal(Pt)and metal oxides(Cu O)weakens the adsorption strength of intermediate product CO_ads at Pt active sites,thus effectively promoting the release of Pt active sites to enhance MOR catalytic activity.In this work,CoZn-ZIFs was used as a template to first pyrolyze the precursor at high temperature(950?),then in the presence of polyvinylpyrrolidone(PVP),the Ni O nanosheet precursor was added,and the Co Ox@NGC/Ni O catalyst was synthesized by a secondary calcination method at 300-500?for ORR.The Pt nanoparticles were uniformly loaded onto the surface by sodium borohydride reduction method to obtain Pt-Co Ox@NGC/Ni O catalyst for MOR.For cathode ORR,Co Ox@NGC/Ni O-400(400?)has better ORR activity and stability than commercial Pt/C(10 wt.%),and the reduction peak potential and half-wave potential reach 0.84 V and 0.85 V,respectively.In the ORR process,the high specific surface area and mesoporous structure provided by the three-dimensional flower-like structure provide transport channels for O₂,electrolyte and charge transfer.The transfer of electrons from Co atoms to C atoms will reduce the local work function on the carbon surface,which is beneficial to the adsorption of O₂.For anode MOR,the mass activity of Pt-Co Ox@NGC/Ni O-400(5 wt.%)reaches 1645 m A mg _Pt^-1,which is 2.4 times that of Pt/C.The binary solid state redox pairs of Co³⁺/Co²⁺and Ni³⁺/Ni²⁺on Co O_X@NGC/Ni O-400 surface can provide abundant active sites for MOR.Co O_X@NGC/Ni O-400 supports with high specific surface area can facilitate the dispersion of Pt nanoparticles to improve the MOR activity.In this paper,ZIFs was used as a template to prepare bimetallic oxide composites by a two-step pyrolysmic-oxidation method,which showed excellent ORR/MOR catalytic activity,indicating that this kind of catalyst has great application potential in DMFCs.