Preparation Of Carbon Based Pd/TiO₂ Nanomaterials And Their Performance In Hydrogen Evolution

With the continuous development and the progress of human society,the over-exploitation and use of fossil energy with limited reserves has caused serious energy crisis and environmental problems.In the face of these problems,the use of environmental technology to develop new renewable energy has become urgent.Hydrogen energy is the most potential alternative to fossil energy due to its high energy density,abundant reserves and zero pollution.Based on this feature,hydrogen production by electrolysis of water has attracted more and more attention as a green energy conversion technology.Hence,it is crucial to find a cheap,efficient and stable electrocatalyst for hydrogen evolution reaction（HER）in the renewable energy conversion system of electrolytic water hydrogen production.Among the many methods of hydrogen production,electrocatalytic hydrogen production from hydrolysis technology can be used to produce large-scale and high-purity hydrogen in a simple way,however,a highly efficiency electrocatalyst is needed to produce large induced current density at a low overpotential.Platinum and platinum-based materials are the best electrocatalysts for HER in the world,but the widespread use of platinum has been severely hampered by their high price as the scarce reserves,so lots of research work are still needed to find and develop an efficient,stable and non-noble metal catalysts for HER.Palladium nanoparticles have high catalytic activity,and the price is much more cheaper than platinum,therefore,it has broad applications in industrial catalysis,energy and chemical industry.Palladium is usually supported on various organics,carbon nanotubes and other metal alloys,as the supported palladium catalyst has the advantages of good dispersion,size controllability,high catalytic efficiency,and easy separation of products,it is the focus of current palladium catalyst research.Titanium dioxide（Ti O₂）has excellent optical properties,good thermal stability,hydrophilicity,low cost and green non-toxic properties.In recent years,it has been widely used in the field of energy technology,including new dye-sensitized solar cells,rechargeable batteries,supercapacitors,photocatalysts,gas sensors et al.Ti O₂ has been widely studied as electrocatalytic material due to its long cycle life and good durability.Hence,the theme of this work is the preparation of carbon based Pd/Ti O2 nanomaterials and the exploration of their electrolytic hydrogen-evolution properties.The main contents of the work are summarized as follows:（1）N,N’-carbonyl diimidazole（CDI）and propargylamine were used to modify polyvinyl alcohol to obtain an alkynated polyvinyl alcohol（alkyne-PVA）.Then the alkyne-PVA was doped with monolayer GO（GO）as the carrier,and sodium borohydride as the reducing agent.Palladium nanoparticles（Pd-NPs）were successfully loaded on the carbon nanomaterials,Pd-NPs@alkyne-PVA/GO composite material was synthesized under normal temperature and natural light.The alkyne-PVA functional groups on the side chains of alkynated pva form a gel network by selective catalytic coupling of Pd（II）.The Pd（II）ions are coordinated by the alkynyl functional groups of alkyne-PVA and fixed to the gel network.Therefore,when the carbon carrier is formed,the Pd nanoparticles are in situ dispersed,and the Pd particles are closely bound to the carrier.（2）In Pd-NPs@alkyne-PVA/GO composites,the coordination of alkyne-pva results in smaller particle size and better dispersion of palladium,which improves the catalytic performance of the metal,the good conductivity of GO and the synergistic action of precious metals further enhanced the electrocatalytic activity of the composites.Platinum carbon（Pt/C）is the most widely used commercial electrocatalytic catalyst for HER with the highest catalytic performance,in the electrolyte of 0.5 M H₂SO₄,the overpotential is only-26 m V to reach the current density of-10 m A·cm^-2,and the Tafel slope is 35.02 m V·dec^-1.Pd-NPs@alkyne-PVA/GO composite exhibits remarkable catalytic activity under the same conditions,the overpotential is-80 m V,and the Tafel slope is 30.85m V·dec^-1.（3）MXene（Ti₃C₂T_x）nanosheets were obtained by etching MAX（Ti₃Al C₂）with hydrofluoric acid（HF）,using the method of ethanol synthesis,utilizing thermodynamically metastable Ti atoms on MXene（Ti₃C₂T_x）nanosheets surface as the nucleation site,in situ fabricating oxygen vacancy-rich Ti O₂ nanoparticles on Ti₃C₂T_xnanosheets（Ti O₂-NPs/Ti₃C₂T_x）,and formed a strong and intimate coupling interface,which improved the electron transmission efficiency between Ti O₂ and Ti₃C₂T_xnanosheet,and the prepared HER electrocatalyst had extremely high stability.（4）The presence of Ti O₂-NPs can be functionally converted into defective sites on the surface of MXene nanosheet,which can improve the migration rate of electrons on the catalyst surface and serve as the active site for HER.The results show that in the electrolyte of 0.5 M H₂SO₄,the overpotential is only-104 m V to reach the current density of-10 m A cm^-2,and the Tafel slope is 88.68 m V·dec^-1.Ti O₂-NPs/Ti₃C₂T_xcomposite has excellent stability and good hydrogen evolution performance in the transition metal HER electrocatalyst,which also provides a new idea for the practical application of transition metal oxides in hydrogen evolution industry.