Preparation Of Carbon Supported Titania Composite Photocatalyst And Their Applications In Energy Conversion

As a main contributor of greenhouse effect,the rapid consumption of fossil fuels has led to a significant increase of emitted carbon dioxide（CO₂）into the atmosphere and the depletion of fossil fuel reserves raise serious,consequently causing not only the global energy shortage but also a serious greenhouse effect,and has become of great public concern in the 21 st century.It is particularly important to develop clean alternative energy sources and make rational use of CO₂.Polymer electrolyte membrane fuel cells（PEMFCs）have been widely investigated as promising energy conversion systems to produce electricity due to their pollution-free process and high efficiency（⁸0%）.on the other hand,chemical conversion of carbon dioxide（CO₂）into lowcarbon fuels,such as methane（CH4）and Carbon monoxide（CO）,at high efficiency and high product selectivity is an ideal solution to global warming and shortages of fossil fuels and carbon resources.Therefore,this paper mainly discusses the construction of carbon-loaded titania composites and their application in energy conversion.The main research work in this paper is listed in the following:（1）.Using solar energy as reaction kinetic energy,photochemical deposition of noble metals is a very effective way to improve the activity and stability of catalysts.The activity and stability of Pt electrocatalysts are crucial issues for energy conversion systems involving oxygen reduction reaction（ORR）.In this work,the ultrafine Pt nanoparticles were in situ reduced by the p hotogenerated electrons on Ti O₂ surface so that most of them selectively anchored around the Ti O₂ nanocrystals.The presence of ul-tradispersed Ti O₂ on carbon surface strengthened the metal-support interaction,giving rise to the improved O RR catalytic activity with ⁴9 m V positive shift of half-wave potential as compared to commercial 20 wt% Pt/C.More importantly,the Pt/Ti O 2-C catalysts exhibited a more durable performance after 10,000 cycles in terms of the decrease in electrochemical surface area（0.8%）and mass activity（0.9%）,much lower than those of Pt/C（10.2% and 33.3%）.The high-temperature durability test also revealed a much higher retention of ORR activity.The results demonstrated that anchoring Pt on ultradispersed Ti O₂-decorated carbon would be an effective strategy to enhance the ORR performance by strong metal-support interaction,which facilitated the electron transfer during catalytic reactions as well as prevented Pt aggregation during durability test.（2）.The separation and transfer o f charge carriers and adsorption of CO₂ molecules are crucial factors that affect the CO₂ photoreduction process.The surface atomic structure of Ti O₂ catalyst can be controlled by adjusting and facets to modulate the interfacial charge carrier transfer,CO₂ adsorption and CO and CH4 desorption.In this work,we demonstrated the reduced graphene oxide（r GO）/Ti O 2 nanoparicles were fabricated through a simple solvothermal synthetic route.Ti O₂ particles with an average diameter of 15 nm were uniformly dispersed on the r GO sheet.RGO-Ti O₂ composite photocatalyst as efficient Photocatalyst for the reduction of carbon dioxide（CO 2）to carbon monoxide（CO）and methane（CH4）,yielding CO and CH4 evolution rates of 5.62 and 26.7 μmol h-1 gcat-1,respectively.（3）.Significant efforts have been devoted to develop efficient visible-light-driven photocatalysts for the conversion of CO₂ to chemical fuels.The photocatalytic efficiency for this transformation largely depends on CO₂ adsorption and diffusion.However,the CO₂ adsorption on the surface of photocatalysts is generally low due to their low specific surface area and the lack of matched pores.To overcome this limitation,a well-defined porous hypercrosslinked polymer-Ti O₂-graphene（HCP-Ti O₂-FG）sandwiched structure is reported with relatively high surface area i.e.,988 m2 g-1 and CO₂ uptake capacity i.e.,12.87 wt%.This sandwiched structure shows high photocatalytic performance especially for CH4 production,i.e.,27.62 μmol g-1 h-1,under mild reaction conditions without the use of sacrificial reagents or precious metal co-catalysts.The enhanced CO₂ reactivity can be ascribed to their improved CO₂ adsorption and diffusion,visible-light absorption,and photo-generated charge separation efficiency.This strategy provides new insights into the design and synthesis of well-defined porous photocatalysts for CO₂ uptake and conversion,and highlights the importance of MOPs in combination with photocatalysts for solar energy conversion.