Investigation Of Electrochemical Water Splitting Properties Of Carbon Nanotubes Confined Functionalized Poms

The creation of sustainable energy sources has steadily come to the forefront of people’s minds due to global warming and the rapid consumption of fossil fuels.With the increase of environmental protection requirements and the widespread use of hydrogen fuel,the development of low-cost,clean and efficient hydrogen production technologies has gradually become a hot spot of attention for researchers.At present,the common hydrogen production technologies are:methane steam reforming,coal gasification and electrolysis of water.In the process of hydrogen production by electrolysis of water,oxygen evolution reaction occurs at the anode and hydrogen evolution reaction occurs at the cathode,which can realize the efficient use of electricity and is one of the most environmentally friendly and convenient technology for hydrogen production.Currently,Pt catalysts are used for commercial electrolytic hydrogen production.Although Pt has excellent electrocatalytic effect,it has the problems of high price and industrialization cost,therefore,it greatly limits the practical application.Therefore,the development of low-cost,high-activity and high-stability electrocatalysts is the key to industrial application of electrolytic water for hydrogen production.POMs are mono-disperse nanoclusters with well-defined structures,abundant species and unique redox activities,which are widely used in electrocatalysis.However,POMs suffer from high solubility,poor electrical conductivity and easy agglomeration when used as electrocatalysts.Therefore,in this thesis,a series of carbon nanotubes confined functionalized POMs composites were designed and synthesized by a confinement strategy.The obtained composites have substantially improved electrical conductivity,while reducing the solubility of POMs,improving dispersion and stability,and exhibiting excellent catalytic performance when applied to electrolytic water reactions.The main research of this thesis is divided into two points as follows:1.A series of carbon nanotube-confined transition metal Co,Ni and Cu substituted Keggin-type phosphotungstic acids were constructed through a confinement strategy.The existence of electron transfer interactions between the two composites was confirmed by XPS and XAFS characterization.The synergistic catalytic effect between carbon nanotubes and POMs was revealed by electrocatalytic performance tests,and the variation of electron and ion transport rates within the electrocatalytic system was elaborated.The magnitude of the adsorption and desorption capacities of the POM-based composites with different transition metal substitutions for the hydrogen evolution intermediates were shown by DFT calculations.Ultimately,a new approach is provided for the preparation of highly efficient POM-based catalysts for electrolytic catalyst for hydrogen evolution.2.Keggin-type phosphomolybdic acids(PMo₁₁V,PMo₁₀V₂,PMo₉V₃)substituted with different numbers of vanadium atoms in the confinement of carbon nanotubes was constructed by using a confinement strategy.The synergistic catalytic effect of vanadium atoms in POMs and the"barrier effect"of carbon nanotubes on the POMs were confirmed by electrocatalytic oxygen precipitation performance tests,and the contribution of highly conductive carbon nanotubes to the current density in the electrocatalytic system was elucidated.The effect of vanadium atoms on the electronic structure of the POM composites was revealed by XPS tests,showing the effect of the number of vanadium atoms on the electrocatalytic oxygen precipitation performance.Finally,a novel method for preparing highly effective vanadium-based electrocatalytic oxygen evolution catalysts is provided.