ZIF-derived Cobalt-Based Catalysts For Direct Electrocatalysis Of Methanol To Ethanol

Ethanol,as a fuel,chemical raw material and solvent,has beenwidely used in various fields.However,traditional production methods for ethanol,such as grain fermentation and ethylene hydrate,have problems such as low selectivity of ethanol,high production cost and complex process.Therefore,novel ethanol production method has become a research hotspot.In this experiment,ZIF-8 support prepared by a simple precipitation method was immersed with Co metal after calcination,and finally the Co3ZnC/NC catalysts with good dispersibility was obtained,which were used for the direct electrocatalytic methanol to ethanol.And the effect of catalyst calcination atmosphere on the electrocatalytic performance of methanol was investigated.The Co3ZnC/NC catalysts were characterized by XRD,BET,ICP,elemental analysis,XPS,HS-LEIS,TEM,ESR,Raman,Contact angle analysis and other characterization methods.The reaction mechanism of direct electrocatalytic methanol to ethanol over Co3ZnC/NC catalyst was explored.The results showed that the unpassivated Co3ZnC/NC catalyst has a better activity than the oxidized and reduced samples.Under this optimized condition with a reaction temperature of 30 ?,the current of 10 mA/cm2,4.5 h,pH of electrolyte solution of 11.5,stirring speed of 600 rpm,and 12.5 mg/cm2 loading of the catalysts,the methanol reaction rate,ethanol selectivity and faraday efficiency are 257.0 g·m-2·h-1,95.1%and 12.5%,respectively.XRD patterns reveals the existence of the(111)and(200)lattices of cubic Co3ZnC in the catalysts.According to TEM images,the particle size of the catalyst is 10.73 nm.The amount of low-valent Co species decreases in the following sequence:reduced Co3ZnC/NC>unpassivated Co3ZnC/NC>oxidized Co3ZnC/NC,which were obtained from XPS.And ESR spectra presented the amount of carbon vacancies with an order of unpassivated Co3ZnC/NC>reduced Co3ZnC/NC>oxidized Co3ZnC/NC>ZIF-8-C.Raman results showed the existence of carbon vacancies in the catalysts.Combined with the characterization and experimental results,it can be found that the ethanol yield is positively correlated with the contents of low-valent Co species and carbon vacancies,which indicates that the synergy between Co3ZnC or Co and carbon vacancies indeed dominates electrocatalytic performances for direct methanol to ethanol.And the results of LSV,Tafel slope,ESR spin trapping indicated the reaction mechanism:hydroxymethyl and methyl radicals are formed on the electropositive low-valent metal sites and electronegative carbon vacancies,respectively,and then combined with each other to form ethanol at the metal/carbon interface.Furthermore,the appropriate participation of water,as a by-product from methanol electrocatalysis,in hydrogen evolution reaction(HER)facilitates electrocatalytic reaction of methanol.Based on the previous research,the electrocatalytic performance of Co/NC catalysts was studied.The Co/NC catalysts were characterized by XRD,BET,elemental analysis,ICP,TEM and other characterization methods.Combined with the results,under the condition of the same metal content,the surface area and particle size of catalysts play an important role in the electrocatalysis,that is,Co/NC-30 catalyst with a surface area of 195.20 m2/g and a particle size of 5.10 nm exhibits the best activity.Moreover,the modified Co/NC-30 catalysts with a different molar ratio of template P123 and F127 were prepared for methanol electrocatalysis to ethanol.Results showed that the optimal catalyst was 3:2-Co/NC-30 with a methanol reaction rate and ethanol selectivity of 341.7 g·m-2·h-1 and 91.9%,respectively.