Preparation Of Tungsten-based Electrode Materials And Electrochemical Hydrogen Evolution Activity

With the deterioration of the global environment and the increasing energy demand,renewable clean energy has attracted much attention.Hydrogen is considered as a clean energy carrier that is expected to replace traditional fossil fuels.Hydrogen production by electrochemical water electrolysis is a green method that can continuously obtain hydrogen.In order to drive the electrocatalytic hydrogen evolution reaction（HER）with minimum overpotential and apply it to industrial large-scale electrolysis,developing catalysts with high activity,high stability and low cost is the main goal at present.Tungsten-based electrocatalytic materials have been widely studied and used in HER because of their abundant natural reserves,environmental friendliness and high catalytic activity.In this paper,starting from the metal tungsten,different tungsten-based electrode materials were prepared by magnetron sputtering and replacement methods.Through the synergistic effect between tungsten and other metals and the interaction between the substrate of tungsten-based material and the metal supported on it,the electrocatalytic hydrogen evolution activity of tungsten-based electrode materials was improved.The main research contents are as follows:（1）A series of WM complexes were prepared by combining W with Co,Mo,Ni forΔ_H*<0 and Cu,Au,Ag forΔ_H*>0 by magnetron sputtering.The changes of hydrogen evolution activity of W after alloying with differentΔ_H*metals were systematically compared.Firstly,XRD results show that WNi,WCo,WCu,WAg and WAu form an alloy structure.The electrochemical test results show that the order of hydrogen evolution activity of WM complex is WNi>WAu>WCu>WCo>WAg>WMo.Ni forΔ_H*<0 and Au forΔ_H*>0 have the most prominent hydrogen evolution activity after combining W,which is much higher than other WM alloys.Among them,W₂₀Ni₈₀/NF and W₄₀Au₆₀/NF are the metal proportional electrodes with the best activity,respectively.The current densities of W₂₀Ni₈₀/NF and W₄₀Au₆₀/NF are 364.85 m Acm^-2and 283.50 m Acm^-2respectively at an overpotential of 300 m V,and the overpotential at a current density of 10 m A cm^-2is 64 m V and 136 m V respectively.The improvement of hydrogen evolution activity is attributed to the synergistic effect between metals caused by the formation of alloy structure.Therefore,Δ_H*of single metal is not a factor affecting HER activity of W alloy.（2）In order to further improve the HER activity of the tungsten-based catalyst,a small amount of noble metal was modified on its surface to prepare the noble metal modified tungsten-based catalyst.In this chapter,tungsten-based materials W and WOx were selected as substrates,and the HER activity of electrodes loaded with various low-loading noble metals M（M=Ag,Au,Ru,Pd,Ir,Pt）was systematically investigated by magnetron sputtering.The electrochemical test results show that the combination of WO_x,W and precious metal M can produce interaction,which improves the hydrogen evolution activity compared with pure M.Among them,Pt _MS@W/NF has the highest hydrogen evolution activity,while Pd _MS@W/NF has a similar hydrogen evolution activity to Pt _MS@W/NF,and both of them are obviously higher than other electrode combinations.The overpotential at the current density of10 m A cm^-2is 71 m V for Pt _MS@W/NF and 79 m V for Pd _MS@W/NF,respectively.The mass specific activity of Pt _MS@W/Ti and Pd _MS@W/Ti at 300 m V overpotential is52.50 A mg _Pt^-1and 48.62 A mg _Pd^-1,respectively.At an overpotential of 200 m V,the current density of Pd _Sub@W/NF(526.0 m A cm^-2)is 2.80 times that of Pd _Sub@NF electrode(187.4 m A cm^-2)and 1.49 times that of Pt/C electrode(353.4 m A cm^-2).At10 m A cm^-2,the overpotential of Pd _Sub@W/NF（16 m V）is close to that of Pt/C（15 m V）and much lower than that of Pd _Sub@NF electrode（65 m V）.XPS results show that the addition of W makes Pd lose electrons,while W gains electrons,and there is a strong interaction between Pd and W,thus improving the problem of Pd’s strong adsorption of hydrogen.SEM results show that W substrate makes Pd more dispersed.The lattice stripes of Pd and W were observed by TEM,and the catalyst was supported on NF with three-dimensional network porous structure,which made the catalyst more dispersed,smaller in particle size and increased in the number of reactive sites.（3）In order to further prepare tungsten-based catalysts with higher hydrogen activity than Pt/C.Pd _Sub@WNi（Au）/NF was prepared by substitution method,in order to increase the interaction between Pd and WNi（Au）substrate compared with Pd and W,thus improving the hydrogen evolution activity.Firstly,WNi and WAu electrodes with different atomic ratios were prepared.Among them,W₂₀Ni₈₀/NF and W₄₀Au₆₀/NF are the metal combinations with the highest hydrogen evolution activity,which are much higher than those of single metals W,Ni and Au.The current density at 200 m V overpotential is 121.7 and 77.4 m A cm^-2for W₂₀Ni₈₀/NF and W₄₀Au₆₀/NF,respectively.XPS results show that the electron Ni grains electrons of W loses its electrons.In WAu alloy,the electronic structure of W changes and the valence state becomes more stable.Secondly,the electrochemical hydrogen evolution activity of Pd _Sub@WNi（Au）/NF was investigated.At an overpotential of 200 m V,the apparent current density of hydrogen evolution of Pd _Sub@W₈₅Ni₁₅/NF(798.5 m A cm^-2)is much higher than that of Pd _Sub@NF(187.4 m A cm^-2),Pd _Sub@W/NF(526.0 m A cm^-2)and Pt/C(265.6 m A cm^-2)with the same noble metal loading.At 10 m A cm^-2current density,the overpotential of Pd _Sub@W₈₅Ni₁₅/NF is only 3 m V,which is lower than that of Pt/C（17 m V）,Pd _Sub@NF（65 m V）and Pd _Sub@W/NF（16 m V）.Pd _Sub@W₈₅Ni₁₅/NF also has a small Tafel slope(33.2m V dec^-1)and excellent stability.As the interplanar distance of WNi（Au）decreases from 2.36 to 2.03（?）,the mass specific hydrogen evolution activity of Pd _Sub@WNi（Au）/NF increases at first and then decreases.When the content of Ni is 15%,the mass specific activity of Pd _Sub@W₈₅Ni₁₅/NF is the highest,which is 39.27 A mg _Pd^-1.When the substrates were W₂₀Ni₈₀/NF and W₄₀Au₆₀/NF with the highest activity,the specific mass activities of Pd _Sub@W₂₀Ni₈₀/NF and Pd _Sub@W₄₀Au₆₀/NF were 8.24 and 14.9 A mg _Pd^-1,respectively,which were much lower than those of Pd _Sub@W₈₅Ni₁₅/NF.Therefore,for Pd _Sub@W₈₅Ni₁₅/NF,the interaction between Pd and substrate is not a simple synergistic effect,but a hydrogen spillover effect,and the crystal plane spacing（2.24（?））of（111）crystal plane of Pd is consistent with that of W₈₅Ni₁₅crystal plane spacing（2.24（?））.Therefore,the reason for the improvement of hydrogen evolution activity of Pd _Sub@W₈₅Ni₁₅comes from the"crystal face spacing matching effect"of hydrogen spillover between Pd and the base alloy,and there is a strong interaction between Pd and the base W₈₅Ni₁₅.XPS results show that in Pd _Sub@W₈₅Ni₁₅/NF,Pd loses electrons and W₈₅Ni₁₅gains electrons.TEM results show that the interplanar spacing of Pd（2.24（?））and W₈₅Ni₁₅（2.23（?））are observed.