| At present,the energy and environmental problems caused by the excessive use of fossil fuels have forced people to turn their attention to research and develop green and sustainable energy sources.H2O,as a rich substance on the earth,will certainly provide a new solution to the energy problem if it can be utilized and converted into hydrogen energy.And as a major component of greenhouse gases,CO2 can be converted into carbon forms that can be used sustainably to reduce environmental pollution and solve energy problems.Therefore,the conversion of H2O and CO3 gradually become the focus of research.In these conversion reactions,solar energy can be directly converted into storable chemical energy by means of photoelectrocatalytic water decomposition and carbon dioxide reduction with the help of solar artificial photosynthesis system.In this process,the performance of the catalyst directly affects the selectivity and efficiency of the reaction.As a new class of catalyst,most of the polyoxometalate molecules have good photosensitivity and electrochemical activity,and at the same time,they contain a large amount of transition metal and non-metal elements.Therefore,they are expected to be a new type of green photoelectrocatalytic materials.But the polyoxometalate also has some weaknesses,such as low activity,poor conductivity,small area and so on.Therefore,we can start from the material design point of view to optimize the polyoxometalates to improve their catalytic performances and give full play to their unique nature.Here we prepared a series of pom-based nanohybrids and studied their photoelectrocatalytic properties.The main research contents are as follows:(1)First of all,we have successfully synthesized graphene-CdS-pom composite films by layer-by-layer self-assembly method through the electrostatic interaction between the materials.The experimental results show that the photocurrent response of graphene-CdS-pom composite films increases five-fold in comparison with the single CdS films.This is because the electron transfer between the CdS and pom promotes the separation efficiency of charges in the CdS quantum dots,and the introduction of graphene further promotes the transfer of charges to the external circuit and thus improves the photocatalytic activity of the composite thin film.This work opens up a new path for the design of photoanode materials with efficient water decomposition and pollutant degradation properties.(2)Then we successfully synthesized a mixed Co/Cu containing polyoxometalate,denoted as Cu6Co7.The pom was dropped on a carbon cloth as a working electrode.We find that Cu6Co7/CC show good catalytic activity for both HER and OER under neutral conditions.More importantly,this Cu6Co7 catalyst has a very good biocompatibility.When combined with bacteria Ralstonia eutropha,Cu6Co7/CC can reduce CO2 into biomass efficiently.The overall photo-to-biomass efficiency can reach 10%,which is nearly 10 times higher than the natural plants performance.This work paves the way for the development of polyxoxmetalate-based artificial photosynthetic systems with high efficiencies.(3)Based on the work(2),we see that although the pom has good catalytic performance,it still needs a large overpotential in the electrocatalytic water splitting,which makes the energy utilization efficiency lower.Therefore,we consider starting from the pom and combining the pom with a ZIF material,which has a permanent porosity and a high surface area,to give full play to their respective advantages,or to produce greater synergy to prepare a bifunctional catalyst.The resulting catalyst,Co-Mo2C@NC,exhibits not only excellent electrocatalytic properties under alkaline conditions but also in neutral conditions.Compared with Cu6Co7,the overpotential of Co-Mo2C@NC significantly reduced.The research of this work provides a new idea for people to develop and utilize the Earth's rich transition metal elements as the research of producing hydrogen energy in neutral condition. |
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