The Construction Of Transition-metal-based Nanoplates/Mesoporous Carbon Nanorods Composites And Their Research Of Electrochemical Performances

Global warming and the limited supply of energy based on traditional fossil fuels,such as coal,oil and natural gas,have greatly influenced and limited the development of the world economy and ecology.And it’s urgent to search for new green,non-polluting and renewable energy.With the rapid growth of the portable electronic device market and the development of hybrid electric vehicles,there is an increasing demand for environmentally friendly high-power energy storage and conversion equipments.Among them,both the hydrogen energy and electric energy have caused widespread attention because of their excellent energy storage capacity performance in the aerospace,aviation and new energy vehicles and other fields.Carbon nanomaterials are of great interest as the advanced supports of electrochemical active materials to enhance their performances.However,little knowledge has been put into understanding whether the pores of carbon nanomaterials as supports can tune the performance of energy storage and conversion devices due to the lack of methods for making porous carbon nanomaterials.Herein,this study demonstrates the use of 1D ordered mesoporous carbon nanorods（OMCRs）with high surface area as a new class of supports for 2D ultrathin MoS₂ and MnO₂ nanoplates to create the interesting hierarchical nanohybrids（MoS₂@OMCRs and MnO₂@OMCRs）.Besides,they display outstanding electrochemical performances when applied as catalyst for HER and electrode for asymmetric supercapacitor,respectively.Detailed work is displayed as follows:（1）We successfully prepared the high molecular weight phenolic resin with mesoporous structure by high temperature hydrothermal reaction using the triblock copolymer F127 as the pore template,PVP as the structure directing agent and the low molecular weight phenolic resin.And it was calcined as the carbon source in a multi-gradient high temperature in nitrogen to form an ordered mesoporous carbon nanorods（OMCRs）.The results show that the material has a novel mesoporous structure,and the surface area and pore volume are larger.（2）Without adding any additives and adhesives,we fulfill the modification of ultra-thin MoS₂ nanosheets on the surface of OMCRs,under the electrostatic attraction between them,leading to a novel core-shell hierarchical nanostructured MoS₂@ OMCRs.After its morphological and structural analysis,we are surprised to find that the material still retains its special mesoporous structure.This special feature makes it an outstanding catalyst in HER.MoS₂@OMCRs exhibits an onset potential as low as 105 mV in HER,and a Tafel slope almost close to commercial pt/C（40 mV dec-1）.It also displays excellent cycling stability in long-term HER（1000 CV cycles）and time response（8000 seconds）,with continuous hydrogen bubbles generated.Various data above indicate that MoS₂@OMCRs has good electrocatalytic hydrogen evolution effect.（3）Using KMnO₄ and Mn（NO₃）₂ as raw materials,the ultra-thin MnO₂ nanosheets are uniformly modified on the surface of OMCRs by oxidation-reduction reaction,which constituted a novel core-shell hierarchical nanostructured MnO₂@OMCRs.Taking advantage of the pseudocapacitance of MnO₂@OMCRs and the electric double layer capacitance of OMCRs,they are assembled and used as the positive and negative electrodes to form the asymmetric supercapacitor.The assembled MnO₂@OMCRs//OMCRs ASC has a wide voltage window which extends to 2.0 V and a higher rate performance than other MnO₂-based asymmetric capacitors at different current densities.In addition,at the current density of 2 A g^-1,85% of the capacitance has been maintained after 5000 cycles of constant current charge-discharge cycles,demonstrating good cycle stability.It also has high energy density and high power density.