Design And Application Of High-efficiency Electrocatalyst Based On Self-supporting Structure

In recent years,due to the depletion of fossil fuels,people pay more and more attention to the development of clean energy to replace fossil fuels.Hydrogen is a clean and efficient energy carrier which may replace fossil energy to some extent in the future.The electrolysis of water splitting is an effective way to large-scale hydrogen production in sustainable energy conversion technologies.Not only that,zinc-air batteries have attracted extensive attention due to their high energy density,abundant raw materials,safety and environmental protection.However,electrolysis of water splitting for hydrogen production and zinc-air batteries are both limited by their respective two half-reactions.The hydrogen evolution reaction（HER）at the cathode and the oxygen evolution reaction（OER）at the anode are important half-reactions in the process of hydrogen production from water electrolysis.Oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）on the anode are two important reactions of air batteries in zinc-air batteries.Although noble metal materials（Pt,Ru O₂ and Ir O₂）exhibit excellent overpotentials during HER,OER and ORR processes,their poor cycling stability,monofunctionality and high price still limit their large-scale applications.Therefore,the development of efficient and stable non-precious metal catalysts is the key to solving the problem.Self-supporting materials（metal foam or carbon-based materials）have excellent electrical conductivity,large specific surface area and pore structure.The catalyst supported on its surface will increase the electron/matter transfer rate of the catalyst,accelerate the adsorption and escape of gas（H₂ or O₂）,and greatly increase the active area of the catalyst.Based on the above ideas,we explored the application of self-supporting base materials in water electrolysis and zinc-air batteries（ZABs）,and achieved the following results:1.In this work,we used Ni foam（NF）as a substrate to grow Ni Mn_1.5PO₄ thin layers on the surface of NF by a facile method.The Ni Mn_1.5PO₄ thin layer uniformly grows and covers on the surface of NF,thus form a three dimensional（3D）network structure.The 3D structure has a large specific surface area and a porous framework structure,which exhibited very low overpotentials and highly efficient hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.The overpotentials of Ni Mn_1.5PO₄/NF catalysts were 72 m V and 198 m V at 10 m A cm^-2 for HER and OER process,respectively.When Ni Mn_1.5PO₄/NF was used as both anode and cathode electrocatalyst in 1 M KOH,a low cell voltage of 1.48 V was achieved at current density of 10 m A cm^-2 and showed a good long-term stability for 50 h.In the process of overall water splitting,the H₂ yield can be reached 4.17μmol min^-1.2.In the second work,KNi Fe（CN）₆/C/NF catalyst is prepared by a simple hydrothermal reaction.In this catalyst,the cubic structure of KNi Fe（CN）₆ grows on the surface of the nickel foam（NF）to form a three-dimensional network structure.The formation of KNi Fe（CN）₆ is based on the substitution of K⁺by Ni²⁺in K3[Fe（CN）₆].During this substitution process,some K⁺vacancies will be formed in KNi Fe（CN）₆,so that the catalytic activity can be improved.The KNi Fe（CN）₆/C/NF catalyst shows exhibited efficient electrocatalytic activity for oxygen evolution reaction,requiring low overpotentials of 69 and 231 m V to achieve 10 and 100 m A cm^-2 current densities in 1.0M KOH solution.When it is used as a catalyst for ZABs,KNi Fe（CN）₆/C/NF shows excellent high stability within 1000 cycles with a charge-discharge overpotential gap of0.85 V at 5 m A cm^-2.The flexible battery assembled based on the KNi Fe（CN）₆/C/NF catalyst also has excellent performance,which can maintain stable charge and discharge within 50 cycles at a current density of 5 m A cm^-2.3.We prepared carbon-coated Co₄N nanoparticles（Co₄NC）dispersed in N-doped cubic carbon shell composites（Co₄NC@NC）using Prussian blue derivatives（PBAs）as precursors.The composite of the double-layer carbon shell with Co₄N not only improves the conductivity of the catalyst,but also greatly slows down the corrosion of Co₄N nanoparticles by alkaline solution.The test found that,Co₄NC@NC exhibits the significantly enhanced electrocatalytic activities for HER,OER and ORR.Especially,the overpotential is only 166 m V for OER at current density of 10 m A cm^-2.ZABs assembled with Co₄NC@NC shows excellent stability during 1050 cycles at 5 m A cm^-2.Furthermore,Co₄NC@CN also used as a HER catalyst for water splitting.The above results indicate that Co₄NC@CN can be used as a high performance three-functional catalyst for ZABs and overall water splitting.