Solvent-free Synthesis Of N-doped And Metal/N Co-doped Mesoporous Carbon Materials For Electrocatalysis

Currently,the overuse of fossil fuel has lead to serious environmental pollutions.Exploring clean and renewable energy sources to replace fossil fuel is urgent.Hydrogen and some electron devices(such as fuel cell and supercapacitor)are appropriate candidates.The efficiency of oxygen reduction reaction(ORR)and hydrogen evolution reaction(HER)plays an important role in fuel cell and water splitting,respectively.Functional mesoporous carbon materials have promising potential applicationa in catalyzing ORR and HER due to their high surface area,tunable pore structure,excellent conductivity and stability.Herein,to overcome the issues of complicated synthetic process,low-density active sites and low stability of carbon-based non-nobel metal cataysts,we demonstrate a simple solvent-free method to prepareda series of novel functional mesoporous carbon materials.These materials show excellent electrocatalytic performance for ORR and HER.First,we developed a general solvent-free assembly approach via directly heating amino acid and mesoporous silica mixtures for the synthesis of a family of highly nitrogen-doped mesoporous carbons.Amino acids have been used as the sole precursors for templating synthesis of a series of ordered mesoporous carbons.During heating,amino acids are melted and strongly interact with silica,leading to effective loading and improved carbon yields(up to ?25 wt%),thus to successful structure replication and nitrogen-doping.Unique solvent-free structure assembly mechanisms are proposed and elucidated semi-quantitatively by using two affinity scales.Significantly high nitrogen-doping levels are achieved,up to 16.0 wt%and 9.4 wt%via carbonization at 700 ? and 900 ?,respectively,which is the highst among reported papers.The diverse types of amino acids,their variable interactions with silica and different pyrolytic behaviors lead to nitrogen-doped mesoporous carbons with tunable surface areas(700-1400 m2/g),pore volumes(0.9-2.5 cm3/g),pore sizes(4.3-10 nm),and particle sizes from a single template.As demonstrations,the typical nitrogen-doped carbons show good performance in CO2 capture with high CO2/N2 selectivities up to ?48.Moreover,they show attractive performance for oxygen reduction reaction,with an onset and a half-wave potential of-0.06 and-0.14 V(vs.Ag/AgCl).Porous carbons doped with nano-sized transition metal carbides and/or metal-nitrogen coordinative sites are promising oxygen reduction electrocatalysts.The doping of such functionalities in carbons with desirable concentration,ultra-small size and stable configuration is still a challenge.Base on the method of preparing N-doped mesoporous carbons above,by grinding and pyrolyzing solid mixtures of an amino acid,an iron salt,and a mesoporous silica template,we demonstrate a solvent-free assembly approach to directly anchor both Fe3C nanoclucters and FeNx sites into N-doped ordered mesoporus graphitic carbons.The carbonaceous electrocatalysts are imparted with several fascinating features,namely,highly dispersed ultra-small Fe3C nanoclusters of 1?3 nm,well-anchored FeNx sites,N-doped well-graphitized carbon frameworks,and ordered mesopores(?5.4 nm)and high surface areas(>1000 m2/g),respectively.The combination of these features makes these electrocatalysts exceptional for oxygen reduction reaction under both alkaline and acidic electrolytes,i.e.superior catalytic activities(one of the most active non-noble metal catalysts among reported papers in alkaline media),outstanding stabilities and excellent methanol tolerance,respectively.Finally,molybdenum disulfide nanosheets have been widely investigated due to their excellent catalytic performance for hydrogen evolution reaction(HER).Currently,the MoS2 edge structure is considered to be the actual active site for HER.As a result,developing a highly conductive material with abundant exposed MoS2 edge is a permanent target.In this thesis,MoS2 nanosheets and mesoporous carbon composites were synthesized by a simple solvent-free in-situ atom-transfer method.As in the catalysts,MoS2 nanosheets were dispersed in the mesopores of carbon uniformly.The mesopores enabled the edge of MoS2 nanosheets more exposed and accessible,and enhanced the mass transport in the system.Resultantly,the catalysts show an excellent catalytic performance for HER.