Preparation Of Carbon Matrix Composites By Molten Salt Method And Their Performance Of Hydrogen And Oxygen Evolution

In recent years,ecological damage and shortage of resources have caused a very serious impact.So renewable energy sources are eagerly sought to replace traditional fossil energy sources.Hydrogen energy is a kind of environmentfriendly renewable energy,so it is urgent to develop various green hydrogen generation technologies.Electrolysis of aquatic hydrogen is an effective and sustainable development approach in the current field.But in the water decomposition reaction,it is necessary to overcome the energy barrier and slow kinetics of the two half reactions of hydrogen and oxygen evolution.Therefore,there is an urgent need to develop efficient,low-cost and stable electrocatalysts for water decomposition,which is an important step towards achieving sustainable development.However,the complex synthesis process of existing electrocatalysts restricts the current development.Based on this,it is an efficient strategy to design a simple synthesis path to obtain excellent catalytic materials.Carbon materials have the advantages of easy access to resources,high conductivity and good environmental compatibility.Therefore,the research on oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)as catalyst support is increasing.In this paper,a series of electrocatalytic materials are synthesized by using molten inorganic salt as melt medium.Specifically,carbon material is used as the carrier to introduce the transition metal composite.These transition metals will become new active sites,and the electrocatalytic reaction will take place at these active sites to promote the catalytic reaction.This study provides effective guidance for the development of carbon matrix composites in electrolytic water.The main research of this paper is as follows.(1)Controlling the chemical environment around active species is an effective regulatory strategy to improve the progress of catalytic reactions.Using porous carbon as a matrix,Co@C-based electrocatalysts containing different cobalt species were synthesized by a one-step molten salt method under the conditions of introducing nitrogen atoms and changing the calcination atmosphere.The results show that only metallic Co is formed by calcination in argon atmosphere,while metallic Co and CoO are simultaneously formed in air atmosphere,and the introduction of nitrogen atoms can control the chemical environment and dispersion of cobalt species.The activity analysis of Co@Cbased electrocatalyst shows that the sample Co/CoO@N-C has the best hydrogen evolution and oxygen evolution activity under alkaline conditions.The main reason is that the introduction of nitrogen atoms plays an important role in metallic Co in the alkaline hydrogen evolution reaction,while CoO plays a decisive role in the oxygen evolution reaction.At the same time,the overall water splitting performance was tested,and a current density of 10 mA·cm-2 was achieved at only 1.83 V.It can be seen that the regulation of the chemical environment around the active site is of great significance for the design of efficient bifunctional catalysts.(2)Iron-doped cobalt phosphide hybrid porous carbon(Fe-CoP/NPC)was synthesized by one-step molten salt method.Nanoscale CoP,uniform doping of metal Fe,and composite with porous carbon made great contributions to the high efficiency of hydrogen(HER)and oxygen evolution(OER)under alkaline environment.In addition,the oxygen-containing compounds generated after in situ electrochemical oxidation of Fe-CoP/NPC has more excellent OER performance.The catalyst can achieve a current density of 10 mA cm-2 at the voltage of HER,OER and total hydrolysis of 268 mV,380 mV and 1.74 V respectively in alkaline electrolyte.(3)A three-phase composite catalyst of MoS2,Co9S8 and NC was synthesized by one-step molten salt method,and the catalytic performance of hydrogen evolution,oxygen evolution and full hydrolysis of MoS2-Co9S8/NC was investigated.Due to its inherent metal properties,transition metal sulfides have different catalytic active sites in different reaction systems.Coupled with the combination with highly conductive carbon materials,this catalyst shows excellent catalytic activities of HER,OER and total hydrolysis of water.HER and OER require an overpotential of 229 mV and 350 mV respectively.When the electrode is used as the working electrode of the full hydrolysis cell,the battery voltage is 1.6V at 10 mA cm-2.This excellent catalytic activity is mainly due to the combination of MoS2 and Co9S8 on NC support to form transferable active centers.Among them,MoS2 is the main active component of HER and Co9S8 is the main active component of OER.The catalytic reactions mainly occur on both,and there are heterojunctions in MoS2 and Co9S8,which further promote the catalytic reactions.