Rh-based Catalysts Toward Complete Electrooxidation Of Ethanol In Alkaline Condition

In recent decades,with the growing demand for clean energy,direct ethanol fuel cell（DEFCs）have attracted extensive attention due to their advantages of high energy density,low safety and environmental protection.The investigation of ethanol oxidation reaction（EOR）catalyst is of great significance for its commercial application.However,the traditional Pt-based and Pd-based catalysts of EOR have very low C1 pathway selectivity,poor ability to break C-C bond and the toxic deactivation,etc.,which greatly limit their large-scale application in DEFCs.Therefore,it is very important to fabricat EOR catalysts with high activity and stability.Rhodium（Rh）might resolve the long existing problem of poor C1 pathway efficiency toward EOR.Rh has been confirmed to break the C-C bond,however,pristine Rh catalysts still exhibit negligible EOR activity is far from meeting the requirements of large-scale commercialization of DEFCs,the reported mass activity is less than 300 m A·mg _Rh^-1,mainly due to the poisoning effect of C1intermediates(CO_ad and CH_x species).To solve this dilemma,Rh-based catalysts for EOR was fabricated under the guidance of Langmuir-Hinshelwood mechanism.This thesis embarks on the electronic structure to design adjusted the catalysts,combined with a series of in-situ and ex-situ techniques were used to clarify the EOR mechanism,so as to further clarify the influence of catalyst structure and component on EOR mechanism,and provide scientific guidance for the design of catalysts with excellent activity and durability.The main contents are as follows:1.Through simple alcohol reduction method in Vulcan XC-72 carbon black surface constructed Rh Pb alloy nanoparticles and PbO_x nanoparticles symbiotic catalyst（Rh Pb-PbO₂/C）,which significantly improved the catalytic activity,stability and CO₂ product selectivity of ethanol electrooxidation under alkaline medium.It exhibits an ever-highest EOR peak mass activity of 2636 m A mg_Rh^-1 in alkaline media,which was 30 times that of Rh/C.Compared with Pd/C sample,the EOR onset oxidation potential on Rh Pb–PbO₂/C catalyst could lower as many as120 m V.After 3 hours of stability test,the catalytic anodic current remained 58%,the apparent faraday efficiency of EOR C1 pathway is estimated to be as high as 20%（at 0.53 V versus RHE）.In situ infrared adsorption spectral（IRAS）results demonstrate that it could significantly improve the production of CO₂and CO₃^2-,compared with Rh/C and the commercial Pd/C.The work is confirmed on the Rh modification such as Pb or PbO_x oxyphilic species can effectively improve ethanol electrooxidation of electrochemical performance and completely oxidized to CO₂selectivity,to develop more efficient EOR catalyst provides a feasible strategy.2.On the basis of the above Rh-PbO_xwork,the Rh-Bi（OH）₃/C composite catalyst was prepared by sodium borohydride reduction method.Thanks to the synergistic effect of Rh and Bi（OH）₃,Rh-Bi（OH）₃/C catalyst showed excellent catalytic activity and stronger toxicity resistance.Under alkaline conditions,the mass activity of EOR reached 3500 m A·mg _Rh^-1,which was nearly twice that of Pd/C-JM sample.The initial oxidation potential was about 100 m V earlier than that of Pd/C-JM sample.At the same time,EOR exhibited excellent stability.Combined with CO Stripping experiment and in-situ infrared spectroscopy（IRAS）,the results show that modification of Bi（OH）₃ on Rh nanoparticles is favorable for the oxidation removal of intermediate products such as CO,which could be attributed to the formation of abundant oxygen-containing species(OH_ad)on the modified Bi（OH）₃ site for rapid oxidation removal of C1 intermediates,thus improving the stability of the catalyst.More importantly,the Faraday efficiency of C1 pathway of the Rh-Bi（OH）₃/C catalyst reached 26.2%at 0.67 V（vs.RHE）.This work could promote the large-scale commercial use of DEFCs.