Effects Of Vacancy Defects Of Nickel,Cobalt,and Copper Metals On Their Hydrogen Evolution Reaction Activity

Resource waste and environmental pollution are two urgent problems in the field of energy.The solution of these problems requires the rapid development of new energy.The electrolysis of water for hydrogen is a simple and recyclable route,which is the current research topic.Transition metals and their composites are a kind of very important and highly active electrode material for electrolysis of water.The experimental results show that porous treatment of transition metals by dealloying method can improve their specific area and the catalytic performances of the electrode.However,dealloying approach is relatively complex.How to develop a simple and effective method to large-scale preparation of micron-nano porous transition metals is a technical problem.In addition,there are few studies on how micro-nano porous structures can improve the catalytic properties of self-supporting electrodes.In this thesis a simple oxidation-reduction method was proposed to micron-nano porous（fibrosis）treatment of nickel,cobalt,and copper metals and the electrochemical properties of these electrodes for the hydrogen evolution reaction（HER）were evaluated.Furthermore,the method of Density Functional Theory（DFT）was used to reveal the related effect mechanism of porous（vacancy defects）structures on HER properties of these electrodes.In this thesis,micro-nano porous nickel foil was prepared by using the high-temperature oxidation-reduction method.The micro structure morphologies and phase of the prepared samples were examined by SEM and XRD.Their electrochemical performance for HER were also evaluated.It was found that when the micron-nano porous Ni metal was used as self-supporting electrode for HER,the electrode specific area was significantly increased by the micron-nano porous treatment,reducing the charge transfer resistance.The overpotential of it was 100.5 m V(at current density of10 m A cm^-2),which is 267.3 m V lower than the value of pure Ni foil（367.8 m V）.The experimental results show that this micron-nano porous treatment greatly improves the HER performance of self-support electrodes based on Ni metals.Furthermore,the DFT calculation is performed,and the micro model of micro-nano porous Ni is constructed.And the effect of vacancy defect of nickel surface on HER properties is evaluated and discussed.The calculation showed that the vacancy defect shifted down the d-band center position of nickel atoms,which weakened the strong adsorption energy on nickel surface,from-2.87 e V to-2.72 e V,thus optimizing the hydrogen absorption property on the nickel surface.Secondly,the commercial cobalt foil was also treated by high-temperature oxidation-reduction method to construct the micro-nano porous architectures.The micro structure morphologies and phase of the prepared samples were examined.The electrochemical performances of the micro-nano porous Co showed that the specific area was increased and more active sites was exposed with the formation of micro-nano porous structures.The overpotential of the cobalt foil after porous treatment at current density of 10 m A cm^-2 was 130 m V,showing a superior performance.The relevant DFT calculation mainly discusses the effect of vacancy defects on the cobalt（111）surface.The calculation show that the vacancy defect will shift down the d-band center of the cobalt atoms,which weakened the adsorption energy from-2.82 e V to-2.69 e V on the cobalt（111）surface,thus improving the intrinsic hydrogen catalytic performance of the cobalt（111）surface.Finally,the copper foam was treated by room temperature oxidation-reduction method,and the nano-fiber was in situ formed on the copper foam.Electrochemical testing and characterization of the prepared nano-fiber copper foam were performed,and the results showed that the specific area of nano-fiber copper foam increased by2.48 times,and the overpotential was 329.1 m V at current density of 10 m A cm^-2 after room temperature oxidation-reduction treatment,which proved that oxidation-reduction treatment has a high effect on its HER performance.The DFT calculation showed that the nano-fiber structure can provide additional hydrogen adsorption sites on the copper surface,increasing the number of active sites on the copper surface,thus finally improving HER activity.