Construction Of Ru-based Electrocatalysts And Their Electrolysis Water Hydrogen Evolution Performance

The large-scale use of fossil fuels has led to increasingly severe environmental pollution,climate change and depletion of fossil resource.The replacement of fossil energy has attracted intense attention,and the green and pollution-free clean energy（solar and wind energy）is the focus of current and future development.However,solar and wind energy have great fluctuation and discontinuity,which cause great obstacles to their use and waste of resources.Therefore,storing solar and wind energy for controlled release when needed is very important for the use of these clean energy sources.Hydrogen is an ideal energy carrier with the advantages of high energy density,environmental friendliness and renewable properties.Converting solar energy and wind energy into chemical energy through electrolysis of water to produce hydrogen is an important way of storing energy.The main problems faced by electrolysis of water hydrogen production are high cost,poor stability and high energy consumption of electrocatalyst.Therefore,it is of significance to develop new electrolytic water catalysts with low cost,high activity and stability.In this paper,a series of electrocatalyst precursors of Co Ru（OH）_x,Ni Fe Ru（OH）_x and Ru-based salicylic acid coordination compound（SA-Ru）were synthesized on nickel foam（NF）substrate by co-precipitation method,in situ etching growth method and etching co-precipitation method respectively.Co Ru O_x,Ni Fe Ru O_x and P-doped Ru O₂（P-Ru O₂/SA）electrocatalysts with excellent electrocatalytic hydrogen evolution（HER）performance were prepared by roasting or phosphating.The obtained precursors and catalysts were characterized and analyzed by a variety of characterization methods.HER performance of the prepared electrocatalyst in alkaline,neutral and acidic electrolytes was tested.The main research contents are as follows:1.A layer of Co（OH）₂,Co₃Ru（OH）_x,Co₄Ru（OH）_x,Co₅Ru（OH）_x and Ru O₂ precursor films were constructed on NF substrates by co-precipitation method.After roasting at 300℃,Co₃O₄,Co₃Ru O_x,Co₄Ru O_x,Co₅Ru O_x and Ru O₂ electrocatalysts were obtained.It was found that Co₄Ru O_xelectrocatalyst exhibited the best HER performance in alkaline（1 M KOH）,neutral（1 M PBS）and acidic（0.5 M H₂SO₄）electrolytes,especially in alkaline electrolyte.Co₄Ru O_x electrocatalyst requires 78,106 and 130 m V overpotentials to generate current densities of 100,300 and 700 m A·cm^-2,respectively.The overpotentials required to generate 100,300,and 700m A·cm^-2 current densities in neutral and acidic electrolytes are 127,245,and417 m V and 79,113,and 142 m V,respectively.The catalytic activity of Co₄Ru O_x in alkaline and neutral electrolytes is better than that of commercial Pt/C catalyst,while its activity in acidic electrolyte is slightly lower than that of Pt/C catalyst.Co₄Ru O_x electrocatalyst also has low Tafel slope(42.38m V·dec^-1)and high Faraday efficiency（99%）in 1 M KOH.Meanwhile,Co₄Ru O_x showed excellent stability in alkaline electrolyte,and LSV curve did not change significantly after 5000 CV cycles.After 500 h potentiostatic test,the current density only decreased from 300 m A·cm^-2 to 277 m A·cm^-2.The excellent HER performance of Co₄Ru O_x electrocatalyst is attributed to the small size of Ru O₂ nanoparticles which formed a highly dispersed structure with Co₃O₄.Co₄Ru O_x has a strong binding force with NF,good electron transfer ability and large electrochemical active area.2.A series of Ni Fe Ru（OH）_x films with different Fe:Ru molar ratios were synthesized on NF surface by in-situ etching growth method.After roasting at300℃,a series of Ni Fe Ru O_x electrocatalysts with different Fe:Ru molar ratios were obtained.The results showed that Ni Fe_0.33Ru O_x electrocatalyst had the best performance.Moreover,Ni Fe_0.33Ru O_x had excellent HER catalytic activity in alkaline,neutral and acidic media,especially in alkaline solution（1M KOH）.The overpotentials of Ni Fe_0.33Ru O_x electrocatalyst driving the current densities of 100,300 and 700 m A·cm^-2 in alkaline,neutral and acidic media were 76,106,133 m V;130,223,385 m V and 79,120,151 m V.The catalytic activity of Ni Fe_0.33Ru O_x in alkaline and neutral electrolytes was better than that of commercial Pt/C catalysts.The Tafel slope of Ni Fe_0.33Ru O_xin 1 M KOH is 42.54 m V·dec^-1 and the Faraday efficiency is 99.4%.What’s more,after 5000 CV cycles in alkaline electrolyte,Ni Fe_0.33Ru O_xelectrocatalyst only showed weak attenuation of HER performance.After 500h potentiostatic test,the current density of Ni Fe_0.33Ru O_x electrocatalyst decreased slightly from 300 m A·cm^-2 to 292 m A·cm^-2,showing excellent stability.The excellent HER performance of Ni Fe_0.33Ru O_x is attributed to the fact that Ru O₂ nanoparticles are small in size and highly dispersed in Ni O-Fe₃O₄ nanosheets,which fully exposes the active site.In addition,Ni Fe_0.33Ru O_x is tightly bound to NF surface,which has good electrical conductivity and large electrochemical active area.3.Using NF as substrate,a layer of SA-Ru film was deposited on NF surface by etching co-precipitation method,and then P-Ru O₂/SA electrocatalyst was prepared by phosphating with sodium hypophosphate as phosphorus source in nitrogen atmosphere.P-Ru O₂/SA electrocatalyst has outstanding HER catalytic property in alkaline（1 M KOH）,neutral（1 M PBS）and acidic（0.5 M H₂SO₄）electrolytes,especially in alkaline solution.In 1 M KOH,1 M PBS and 0.5 M H₂SO₄ electrolyte,the current densities of P-Ru O₂/SA electrocatalyst driving 100 m A·cm^-2,300 m A·cm^-2 and 700 m A·cm^-2 only need 75,101,128 m V;130,233,456 m V and 65,97,137 m V.The Tafel slope of P-Ru O₂/SA in 1 M KOH is 41.84 m V·dec^-1,and the Faraday efficiency is 96%.P-Ru O₂/SA electrocatalyst has excellent stability in alkaline electrolyte.After 5000 CV cycles,the LSV curve almost coincided with the initial curve.After 500 h potentiostatic test,the current density almost remained unchanged,only decreased from 300 m A·cm^-2 to 298 m A·cm^-2.The excellent HER performance of P-Ru O₂/SA is attributed to the formation of Ru group salicylic acid coordination compound,which makes Ru element atomically dispersed.During phosphating,P-doped Ru O₂ can be formed and more active sites are exposed.The carbon layer obtained from the transformation of salicylic acid ligand can improve the conductivity,accelerate the electron transfer,and facilitate the smooth progress of HER.