Design And Application Of Mesoscopic Electrocatalysts With Porous Coatings For Electrochemical Reduction Reactions

The growing challenging regarding global climate change is becoming increasingly problematic due to the excessive and accelerating use of fossil fuels.It is therefore necessary to develop clean,environmental-friendly and renewable energy to shift the infrastructure based on carbon energy.Technologically speaking,electrochemistry uses clean electrical energy to drive reactions,and plays a key role in the sustainable energy technology.This has also led to the promotion of a large number of electrocatalysts.However,current development of electrocatalysts is still facing many challenges:(1)Most of the high performance electrocatalysts were achieved in laboratory research,which may lose the advantages during their translation into the real-world device,and are facing the issue of catalyst poisoning and deactivation in the operation process;(2)The conversion rate for some low-kinetic reactions is far from practical,and lower Faraday Efficiency also causes waste of energy and significant increase of the cost;(3)For multi-step reactions,highly selective and tunable conversion towards intermediate state and target product remain challenging.In this thesis,we target the above problems and aim to design and develop novel electrocatalytic system for solution.A variety of mesoscopic electrocatalysts were designed for different electrochemical reduction reactions to improve the stability,Faraday Efficiency and selectivity of the catalysts.The specific works are as follows:1.Design,synthesis and application of mesoscopic electrocatalysts for HERTo solve the problem that HER catalysts are easy to get poisoned and deactivated,porous inorganic materials coated precious metal(e.g.Pt@Ce O2),were synthesized.Meanwhile,the carbon supports were introduced in catalysts to construct electrical transmission paths and form “active site-shell selection-conductive pathway” mesoscopic materials,(e.g.Pt/C@ZIF-8 and Ru/NCNT@Ti O2 core-shell mesoscopic electrocatalysts).The porous shells were wrapped on the surface of the precious metals to protect them from the poisoning of the anions in the electrolyte,so as to improve the activity of HER.2.Design,synthesis and application of mesoscopic electrocatalysts for NRRIn this chapter,we designed a serial of CNT@MOFs and NCNT@MOFs mesoscopic electrocatalysts for NRR,which achieved high yield and high Faraday efficiency of NH3.The design of catalysts is mainly based on three aspects: first,enrich N2 around active sites to increase the intrinsic concentration,so as to improve the yield;second,build the hydrophobic structure to suppress the competitive HER,so as to improve the Faraday efficiency of NRR;third,develop carbon nanotubes to create simultaneously active sites and conductive pathway.The facile synthesis can be used as a general strategy to a variety of catalysts,which can obtain more optimized electrocatalysts with higher yield and Faraday Efficiency.3.Design,synthesis and application of electrocatalysts for nitrobenzene reduction reactionIn this chapter,we conducted selective reduction of nitrobenzene to nitrosobenzene by Ru/NCNT and NCNT@UIO-66 under mild condition,and only H2 O was needed as the proton source which met the needs of sustainable synthetic process.The yield of nitrosobenzene can reach above 50% through the primary optimization of reaction conditions.