Designed Synthesis And Application Research On Tantalum Compounds Anchored Platinum Electrocatalyst

Nowadays,faced with serious energy and environmental challenges,the development of green and clean renewable energy is urgently needed.Hydrogen has been regarded as an ideal energy carrier due to its zero emission and high energy density.The hydrogen economy,that is to explore a renewable technology for high-purity hydrogen production such as water electrolysis,and finally to promote the utilization of hydrogen fuels through renewable energy conversion devices such as fuel cells.In order to improve the energy efficiency of these renewable conversion devices,such as fuel cells and electrolyzed water,developing high active and durable platinum-based electrocatalyst is of great significance to accelerate the sluggish kinetics of electrochemical process.In this paper,we proposed a strategy of utilizing tantalum compounds as platinum electrocatalyst support by virtue of their high acid resistance and chemical stability.The porous sheets with large specific surface area and hollow structured microspheres with macro-and meso-pores were prepared by a template method with heat treatment.The atomic-scale interfaces between platinum and tantalum compounds were tailored by using different crystallinity of tantalum oxide,which can generate an electronic coupling between platinum and tantalum atoms,thus boosting the electrochemical performance.The interaction between platinum and tantalum compounds was strongly enhanced by adjusting the components of tantalum compounds.By establishing a platinum-based electrocatalytic system using tantalum compounds as support,the goal of preparing platinum-based electrocatalyst with high activity and high stability can be achieved,which provides a theoretical basis for the modification and structural design of platinum-based electrocatalyst.The main results obtained are as follows:(1)The mesoporous tantalum oxide sheets were prepared by sacrificial template method.After crystallization treatment,tantalum oxide still maintains a good mesoporous structure with a high specific surface area of 71.494 m2 g-1.Compared with commercial tantalum oxide support,mesoporous tantalum oxide support(Pt/OM-Ta2O5-20)exhibited a higher response currents and better activity toward oxygen reduction,due to its large specific surface area and good dispersion of platinum nanoparticles.(2)To further investigate the support effect of porous structure on platinum performance,the ultra-low loading of platinum was dispersed on the surface of the macro-and meso-porous tantalum oxide hollow microspheres by ultraviolet reduction method,and this was used as electrocatalyst toward hydrogen evolution reaction.Compared with tantalum oxide nanoparticles(Ta2O5 NPs)and solid microshperes(S-Ta2O5)supports,hollow structured tantalum oxide microspheres showed a better mass transfer rate during the hydrogen evolution reaction due to larger specific surface area for a good dispersion of platinum.The strong electronic coupling between tantalum oxide and platinum enhanced the adsorption of hydrogen atoms on the platinum surface,thereby promoting the hydrogen evolution reaction performance of platinum electrocatalyst.The electrocatalyst with a platinum loading of 0.07 wt.%(HS-Ta2O5-0.07Pt)exhibited the highest mass activity and TOF value,even better than commercial platinum/carbon electrocatalyst.(3)The tantalum pentoxide/carbon nanotube nanocomposite was prepared via microwave-assisted hydrothermal method to uniformly disperse tantalum oxide nanoparticles on the surface of functionalized carbon nanotubes.Through the investigation of the tantalum oxide loading and heat-treatment temperature,-the optimal preparation conditions of the tantalum pentoxide/carbon nanotube nanocomposite were determined with the loading of 17.3%and the heating temperature of 800?;tantalum oxide shows a good crystallinity and uniformed dispersion(average size of 8 nm).Tantalum pentoxide/platinum interfaces were characterized by HADDF-STEM,showing the preferential anchoring of platinum at the interfaces of carbon nanotubes and tantalum pentoxide with a large amount of Pt-Ta2O5-CNT triple junctions.The electron-deficient state on platinum surface can effectively enhance the adsorption of oxygen molecules on platinum and accelerate the cleavage of O-O bonds.Moreover,the electron-rich state of tantalum pentoxide surface can enhance the electron conductivity of oxide support and facilitate electron transport during oxygen reduction reaction.The mass activity of the Pt-Ta2O5/CNT electrocatalyst at 0.9 V vs.RHE was 0.23 A mg-1,which was 3.4 times and 2.2 times the mass activity of the Pt/C and Pt/CNT electrocatalysts,respectively.After the potential scanning cycle tests of 10000 cycles,the half-wave potential of the as-prepared platinum electrocatalyst showed only a 15 mV decrease,suggesting an extraordinary stability of our electrocatalyst.(4)Polystyrene-divinylbenzene microspheres(PS-DVB)were introduced to prepare tantalum oxide capped PS-DVB precursor by a solvothermal method.The PS-DVB were served as a hollow structured template as well as a carbon source to obtain Ta2O5/C hollow nanocomposites.The presence of hollow structure provides a large surface area for the uniform dispersion of platinum,thereby effectively increasing the platinum utilization.Furthermore,the inner carbon shell can enhance the conductivity of oxide support,thereby accelerating the electron transport during the oxygen reduction reaction.Meanwhile,the outer tantalum oxide shell can avoid the direct contact of carbon with acid electrolyte,thus effectively inhibiting its electrochemical corrosion process.The prepared HS-Ta2O5/C-Pt electrocatalyst exhibited an excellent oxygen reduction activity in alkaline solutions.(5)Based on the previous section,to improve the electrical conductivity of support,the Ta2O5-TaC hybrids capped hollow carbon microsphere were prepared by controlling the in-situ phase transfomation process of tantalum pentoxide to highly conductive tantalum carbide.The presence of tantalum carbide is beneficial to enhance the electrical conductivity of tantalum pentoxide interparticles.The optimal components of support were determined by investigating the electrocatalytic performance of platinum electrocatalysts using different phase components of tantalum compound as supports.With the coexistence of these two phases,oxides can induce spillover effect and release more platinum active sites for oxygen,while carbides can serve as an electron donor to provide a rapid electron supply for platinum during the oxygen reduction reaction,thereby accelerating oxygen reduction process.Due to the synergistic effects between Ta2O5 and TaC,after the potential cycle scanning of 10000 cycles,the half-wave potential of the Pt/Ta2O5-TaC/C electrocatalyst showed only a 3 mV decrease,indicating an excellent stability toward oxygen reduction reaction.