Preparation Of Modified TMPs As Electrocatalyst And Study Of Electrocatalytic Performance

Nowadays,fossil fuels are still the main energy source in the world,making great contributions to human development.However,too much dependence on fossil fuels has caused many problems,including energy shortage,environmental contamination and even energy war.Hydrogen energy stands out in many new energy sources and becomes the most promising clean energy in the 21st century.Among the technologies to produce hydrogen,electrochemical water splitting is the simplest and most economical method,which requires a highly efficient electrocatalyst to achieve large cathodic current densities at low overpotentials.Currently,the precious metal Pt and Pt-based catalysts are the most active electrocatalyst for HER,but the high costs limit their commercialization.In the last few years,transition metal phosphides（TMPs）have been widely studied for their noble-metal-like properties and are considered to be promising catalysts for HER for replacing Pt and Pt-based catalysts.TMPs are formed by alloying transition metal with phosphorus and it have excellent electrical conductivity,which is very beneficial to the electrical transport of the electrode and can effectively improve the kinetic speed of electrochemical reaction on the electrode.Some studying show that the hydrogen adsorption energy barrier on the surface of TMPs is lower than other catalysts,which can benefit to electrochemical splitting water.Recently,to further enhance the water splitting performance of TMPs,foreign atoms doping and carbon coating were frequently used.Therefore,based on the above analysis,in this master’s thesis,we studied the methods of doping new elements and carbon coating to improve of TMPs performance.The main contents of the paper are summarized as follows:（1）Preparation of Al-doped CoP₃ nanowires array as follows:the precursor of Al（OH）F nanowires array was firstly prepared by hydrothermal method,and then the samples was synthesized with red phosphorus as a phosphorus source by vacuum tube sealing method in the condition of high temperature without oxygen.At the same time,by adjusting the mass ratio of Al in the precursor and the calcination temperature,the optimum ratio is applied to electrocatalysis.The results indicate that the electrocatalytic performance of Co P₃ can be dramatically enhanced via Al doping.It only needs an overpotential of only 40 m V to achieve the current density of 10 m A cm^-2 for the Al（10%）-Co P₃ nanowire arrays.The test results show doped Al atoms can donate electrons to nearby Co and P atoms and it can increase electrons transfer rate.Doped Al atoms also can weaken the bonds between surface and H atoms,which benefit for hydrogen evolution.Moreover,doped Al atom provides a larger special surface area for Co P₃nanowire arrays,which provides more exposure to catalytically active sites and facilitates the transfer of electrons.（2）N doped C coated with WP₂,WP₂ nanoparticles were firstly synthesized by vacuum sealing technology,then coated with N-doped C shell by gas-solid reaction method,which was used as a new type of electrocatalyst.By adjusting the mass ratio of dicyandiamide in the precursor to find the best ratio for electrocatalysis.N doped C coated with WP₂ only needs an overpotential of only 57 m V to achieve the current density of 10 m A cm^-2 and shows good stability in the acid,neutral and alkaline electrolyte.The test results show modification of the carbon can make the BEs of W 4f and P 2p negatively shift,which increase the adsorption capacity of H ion and provide a way for charge transfer,thus increasing the conductivity of the WP₂.And the N-doped C shell can activate the adjacent C atoms to increase the density of active sites.Moreover,the presence of carbon shell also increases the corrosion resistance of the catalyst.