Preparation Of Transition Metal Phosphide And The Electrocatalytic Activity For Hydrogen Evolution

The development and application of new clean energy sources are urgent with the increasingly serious energy crisis and environmental problems.Hydrogen energy with a high calorific value per unit mass,clean and pollution-free,and abundant storage capacity has attracted much attention.Among many hydrogen production technologies,hydrogen production by electrolysis of water is considered to be the most ideal way to produce hydrogen.However,the challenge remains to reduce the hydrolysis energy barrier and enhance the efficiency of hydrogen production during the electrolysis of water.Currently,the development and application of non-precious metal catalysts to replace expensive precious metal catalysts is the key to achieving large-scale electrolytic hydrogen production from water.In this paper,the preparation of transition metal phosphides（TMPs）is the core of this work,and the direction of material structure design and catalytic activity modulation is used to prepare high catalytic performance TMPs electrodes for hydrogen precipitation.The focus is on using the structural tunability of metal-organic framework materials（MOFs）to reasonably prepare catalytic electrodes with three-dimensional structures,and regulating the electronic structure of catalytic sites through elemental doping and construction of heterogeneous interfaces to enhance the intrinsic catalytic activity.Finally,structural characterization,electrochemical performance testing and electrochemical mechanism analysis are combined to systematically analyze the catalyst activity sources and the conformational relationships between them.Details of the study are as follows:（1）Ni Coprecursor arrays were first hydrothermally synthesized using nickel foam（NF）as the conducting substrate,and then Prussian blue-like（PBA）was introduced in situ using this as the sacrificial template,and finally the FeP₄/NiCoP/NF heterogeneous catalysts were obtained by low-temperature phosphorylation.In this process,PBA utilizes the precursor sacrificial template to achieve a regular arrangement,and its uniformly distributed organic coordination transition metals facilitate the formation of FeP₄/NiCoP heterostructures.The strong electron coupling in the heterogeneous interface enhances the charge transfer rate during the catalytic process and ultimately significantly enhances the HER performance of the electrode.Electrochemical performance tests showed that the FeP₄/NiCoP/NF electrode had an overpotential of only 129 mV at a current density of 100m A cm^-2 and a Tafel slope value of 87 mV dec^-1.The fitted EIS test data indicated that the charge transfer impedance(R_ct=1.1Ωcm^-2)of the FeP₄/NiCoP/NF electrode was much smaller than that of other control electrodes.In addition,the in situ grown array structure enabled the FeP₄/NiCoP/NF electrode to exhibit outstanding electrochemical stability,which remained structurally stable during 250 h of continuous catalysis.（2）In order to further improve the electrochemical activity area of the catalyst,the PBA array introduced in situ was etched by anion exchange technique to obtain a PBA-S/NF catalyst precursor with a larger specific surface area,and finally it was low-temperature phosphorylated to obtain a Co₂P@CoNi₂S₄/NF heterogeneous catalytic hydrogen precipitation electrode.During the etching process of PBA,sodium sulfide was chosen as the etching agent,and the ionic radius and exchange rate difference between S^2-and ferricyanide in PBA were used to complete the etching and reconstruction of the catalyst,during which a large number of pores were formed due to the migration of large ferricyanide groups,and the surface reconstruction was accompanied by the formation of a large number of folded nanosheets to further increase the specific surface area of the electrode.The electrochemical active area test showed that the bilayer capacitance(C_dl)of the PBA-S/NF electrode increased from 20.46 mF cm^-2 for PBA/NF to 52.61 mF cm^-2 after etching,and the structural analysis of the catalyst showed that the CoNi₂S₄ prepared by the exchange process was less crystalline and formed a Co₂P@CoNi₂S₄/NF heterogeneous catalyst in the subsequent phosphorylation process.Electrochemical tests showed that the Co₂P@CoNi₂S₄/NF heterogeneous electrode with a high specific surface area had very outstanding HER catalytic performance and electrochemical stability,with an overpotential of 203 mV at a current density of 100 mA cm^-2,and remained stable after 140 h of stability testing.（3）In order to design catalysts with more outstanding HER performance,the electronic structure of the catalytic sites was tuned to further enhance the HER performance of the electrodes based on the construction of catalysts with a large specific surface area.Firstly,CoZn array precursors with hierarchical structure were synthesized on nickel foam as templates,and then ZIF-67 was synthesized in situ by introducing dimethylimidazole ligands,and SEM showed that ZIF-67 dodecahedra were oriented vertically under the action of templates.So far,the anion-exchange method was used to etch ZIF-67 to obtain a skeletonized coral cluster-like structure precursor,which significantly increased the specific surface areas of the catalyst.Finally,low-temperature annealing phosphorylation treatment was used to obtain CoPS@ZnO/NF catalytic hydrogen precipitation electrodes.The structural analysis of the catalyst revealed that the PS^3-dimer formed after phosphorylation modulates the electronic structure of the Cosite,which strongly promotes the conversion rate of intermediates in the HER catalytic process.The electrochemical performance test results showed that CoPS@ZnO/NF had very outstanding HER performance with an overpotential of 163 mV at 100 mA cm^-2 current density,and the EIS fitting data indicated that the charge transfer impedance of the electrode was significantly reduced after phosphorylation.In addition,the in situ grown three-dimensional support structure makes the CoPS@ZnO/NF electrode have very outstanding catalytic stability,and the structure remains stable after 160 h of continuous testing.