Study On Preparation Of Biocarbon Catalysts And Their Performance For Electrochemical Carbon Dioxide Reduction Reaction

The conversion of carbon dioxide?CO₂?to high value-added products is a forward-looking work,and has a good application prospect in alleviating the energy crisis and climate issues.Recently,the electrochemical CO₂ reduction reaction?ECRR?has attracted wide attention because of its controllable target products and high conversion efficiency.In the study of ECRR catalysts,biocarbon is a catalyst with great potential due to its abundant sources and reserves,simple preparation process,easy adjustment of porosity and surface functional groups.In this dissertation,a series of catalysts were prepared using commercial low sulfur lignin?plant biomass?and hair?animal biomass?as raw materials for ECRR.The main contents and results are as follows:?1?A series of nitrogen-sulfur co-doped porous biocarbon catalysts?LC?were successfully prepared by using commercial low sulfur lignin as carbon precursor,melamine and urea as nitrogen sources,and Na Cl and Zn Cl₂ as template agents under the different preparation conditions.The results demonstrated that N-doping is beneficial to improve the selectivity of CO in ECRR.In addition,as template agents,Na Cl-Zn Cl₂ can help to form rich pore structure at high temperature,increase specific surface area and pore volume,and further enhance ECRR activity.Under 0.1 M KHCO₃ electrolyte,the optimal catalyst LC-3 has a high Faradaic efficiency?FE?of 95.9%for ECRR to CO at an overpotential of 490 m V.The corresponding average current and the yield of CO are-1.98 m A cm^-2 and 8.8 L m^-2 h^-1,respectively.During18 hours of stability test,there were no significant change in ECRR activity and selectivities to CO and H₂.In addition,the systematic characterization analysis has demonstrated that the adsorbed chlorine on the surface of biocarbon was derived from hydrochloric acid washing,which greatly enhances the ECRR activity,thus increasing the yield of CO.?2?Hair as a raw material was degraded by hydrothermal reaction in ammonia water to obtain the precursor.And then urea,melamine,Na Cl and Zn Cl₂ were added and carbonized at different temperatures to obtain biocarbon catalyst.In this study,it has been demonstrated that graphite nitrogen ratio and the content of thiophene sulfur on the catalyst surface increase with the increase of carbonization temperature,which is beneficial to improve the ECRR activity and the selectivity to CO.The optimal biocatalyst HC-1000 has a high Faradaic efficiency of92.4%for ECRR to CO at-0.60 V.The corresponding H₂ Faraday efficiency is 6.0%,and the yield of CO and H₂ are 3.3 L m^-2 h^-1 and 0.22 L m^-2 h^-1,respectively.During 40 hours of test,the catalytic system maintains a good stability.The activity attenuation of the ECRR system after 40 hours was systematically analyzed.The results have shown that the decrease in stability is mainly due to the loss of KHCO₃ in the anode,which leads to the decrease of conductivity,the increase of internal resistance and the decrease of p H data.Adding electrolyte?such as KHCO₃,Na₂SO₄?to the anolyte can increase the conductivity and reduce the internal resistance,thus restoring the stability for ECRR.On this basis,the reaction paths of the cathode and anode in the ECRR reaction system have been proposed,and the mechanism of stability attenuation has been discussed.This research provides guidance for the rational design of reaction system and the improvement of the stability of the reaction system.