| Electrochemical water splitting has been a clean,efficient and sustainable strategy to produce hydrogen.Electrolysis of water includes hydrogen evolution reaction at the cathode（HER）and oxygen evolution reaction at the anode（OER）.The key to improve the efficiency of hydrogen production is exploring highly active and durable catalysts,which can overcome kinetic obstacles,and promote reaction kinetics,especially for the four-electron OER process.The atoms at the exposed crystal faces of the metastable metal nanoparticles have abundant electronic states near the Fermi level,which optimizes the adsorption energy of the reaction substrate intermediates,thereby improving the catalytic performance.Therefore,the phase control of the electrocatalyst will provide a new way to improve electrocatalytic performance.The main contents of the thesis are as follows:（1）Nickel hydroxide nanoflowers was synthesized by solvothermal method.Then CH4plasma was used for the conversion of Ni（OH）2 nanoflowers to hexagonal（hcp）porous nickel nanosheets.Under controlled reaction temperature,face centered cubic（fcc）nickel can also be obtained.Alkaline HER performance test shows that,the overpotential of metastable hcp Ni is 33 mV lower than that of cubic nickel at 10mA/cm~2,demonstrating the merits of the metastable phase.Theoretical calculations show that the surface of hcp Ni is more conducive to the adsorption of water molecules.In the process of HER,the center of the d-band of metastable hcp Ni is closer to the Fermi level,which is beneficial for the decomposition of water molecules.（2）Carbon quantum dots（CQDs）was used to assemble Co（OH）2 nanosheets under solvothermal conditions.The plasma of Ar-H2 has been applied to reduce CQDs-Co（OH）2,producing heterojunction of hexagonal Co@CoO.Under controlled reaction temperature,the catalysts with different morphologies and crystal phase structures can be obtained.It is found that noble metal Ir doping can improve its electrocatalytic performance.For example,the as-synthesized Ir-Co@CoO catalyst exhibits an overpotential of 188 mV for OER at current density of 10mA/cm~2,which exceeds most reported catalysts.Its activity does not decrease when the reaction was maintained for90 h,showing good stability.This work aims to provide a general strategy for the preparation of metastable phase metal nanomaterials.Based on the rational design of metastable phase heterostructures,heir relevant properties and applications can be extended to other fields,such as catalysis,electronic and biomedicine. |
