Theoretical Study On The Mechanism Of Decomposition And Oxidation Of Methanol On Fe/g-C₃N₄

Considering the environmental energy problem and sustainable development strategy,people's demand for clean energy is increasing.In recent years,fuel cells have been a good choice.Among them,direct methanol fuel cell?DMFC?is favored by many researchers because of its excellent characteristics.Fuel sources are extremely abundant,the start-up temperature of the generator is relatively low,the products produced by the reaction have little pollution to the environment and high energy density,so it is an efficient renewable energy source.In the anode of direct methanol fuel cell,the oxidation and decomposition of methanol is a very important step,and the speed of the anode reaction depends on the choice of anode catalyst,so we must find an anode catalyst with high efficiency,low cost and stable properties.Platinum catalyst has always been the first choice for anodic catalytic materials,but its low reserves and high production cost limit the commercial application of methanol fuel cells.Moreover,CO,the by-product of the reaction,is stable on the surface of the catalyst,occupying the active site first,it is difficult to continue other reactions on the surface of the catalyst,which will reduce the catalytic efficiency.Therefore,we are trying to find substitutes for pure platinum atoms,For example,palladium,gold,iridium,silver and other precious metals and copper,cobalt,nickel and other non-precious metals.Monoatom catalysts have been widely used in catalytic field.Monoatom catalysts have shown remarkable differences in activity,selectivity and stability from traditional nano-catalysts in many redox reactions,including thermal,electro-catalytic and photocatalytic reactions.In recent years,monoatomic catalysis has rapidly become a research frontier in the field of catalysis.When atoms are dispersed on carriers,they will bring many characteristics,such as the increase of surface free energy,quantum size effect,unsaturated coordination environment between metals and carriers.Atom-loaded carriers are usually metal oxides,graphene,nanotubes and so on.After many years of research,we have found that graphene-like structures have great potential in the field of catalysis.In this paper,we designed a new type of anodic catalyst Fe/g-C₃N₄ with graphite carbonitride?g-C₃N₄?as carrier and transition metal iron atom as monoatomic catalyst.On the anode catalytic layer of the battery device,methanol fuel reacts with water to produce carbon dioxide,protons and electrons.The reaction formula is CH₃OH+H₂O+CO₂+6H+6e^-.In this paper,the decomposition and oxidation mechanism of methanol on Fe/g-C₃N₄ is studied by density functional theory.By analyzing the bond breaking mode of methanol,the reaction energy barriers of O-H bond and C-H bond breaking are calculated respectively.The first step of methanol decomposition is more prone to O-H bond breaking.The whole decomposition process is mainly methanol decomposition dehydrogenation to produce CO,followed by the decomposition of intermediates generated by water decomposition hydroxyl oxidation to produce CO₂.During the calculation,we discussed the stable adsorption structure,the adsorption energy of methanol and its intermediates on Fe/g-C₃N₄,the energy barrier needed for the reaction,the electron transfer between methanol and the substrate,and the potential energy surface of the whole reaction.Through the analysis of geometrical structure,we found that the optimized structure of Fe/g-C₃N₄ is very stable.When the reaction takes place,both methanol and water molecules preempt the active site of Fe atom,and O atom forms coordination bond with Fe atom,thus adsorbing on Fe/g-C₃N₄ stably.Through the analysis of relevant data,the catalytic cycle reaction energy of the whole reaction is reduced,which is conducive to the reaction.Compared with the decomposition and oxidation of methanol on pure Pt and defective graphene,the energy barrier of Fe/g-C₃N₄ for methanol decomposition is slightly lower,and the reaction barrier of the intermediate formed by methanol dehydrogenation is lower in the oxidation process.The results show that Fe/g-C₃N₄ has good catalytic performance for the decomposition and oxidation of methanol.It realizes the gradual decomposition of methanol molecule on the catalyst,oxidizes the decomposition products and finally produces CO₂,which improves the catalytic efficiency of the anode.It provides theoretical basis for the experimental study of methanol in Fe/g-C₃N₄,and provides new ideas for the development and Application of the anode catalyst of methanol fuel cell.