The Theoretical Simulation Of Carbon Dioxide Electrocatalytic Reduction By Boron-doped Diamond

According to available and accurate data,the carbon dioxide emissions are increasing year by year,and the greenhouse effect caused by it is self-evident.Evidence shows that relying solely on photosynthesis of plants to consume large amounts of carbon dioxide globally is far from reaching its goal.The United Nations calls on all countries to carry out energy reforms and strive to control the global temperature rise within the range of 1.5℃to ensure the normal circulation of the global ecosystem.As China is the largest carbon dioxide emission country,it must not only shoulder the responsibility of reducing emissions,but also face the pressure of economic growth.Therefore,carbon dioxide should be effectively captured and converted into fuel or fine chemicals through advantageous electrochemical methods.That is a very promising solution.When it comes to formaldehyde,everyone associates it with air pollution,but in fact,the use of formaldehyde is very extensive,such as in the wood industry for the production of urea-formaldehyde resin and phenolic resin.In the production of textiles,the addition of formaldehyde can prevent the fabric from wrinkling,prevent it from shrinking and block its burning.Of course,it can also make the coloring more lasting and smoother.Formaldehyde is also used for antiseptic and sterilization in medicine.Therefore,the topic of electrocatalytic reduction of carbon dioxide to formaldehyde is not only interesting but also valuable.The high activity,excellent durability,and outstanding selectivity of doped carbon materials when reducing carbon dioxide have made it attract much attention and have great prospects.Based on previous experiments,electrocatalysis on boron-doped diamond（BDD）electrodes,the reduction of carbon dioxide to formaldehyde has a high Faraday efficiency,but as far as the author of this paper knows,no one has discussed the reaction mechanism of forming formaldehyde on this kind of material.In this paper,starting from density functional theory（DFT）,the simulation calculation is performed by using VASP to determine the best reaction path.Four parts form the core content of this work:1.Optimizing the diamond（111）reconstruction and unreconstructed surface models,exploring the adsorption of CO₂ on undoped surfaces to determine that unreconstructed surfaces are more suitable for reducing CO₂.2.Performing boron doping in the ways of doped with single boron and multiple borons,to explore the effect of doping sites and continuous doping on the electrochemical properties of the catalyst.Through the results density of state analysis（DOS）,geometric structure analysis,charge analysis,formation energy,etc.,and the final determination of a single boron in（1×1）,it is determined that the doping of the surface layer and the second layer of C（111）are the two surface models of the subsequent reaction,respectively,and whether the boron doped on the surface layer bonds with carbon or oxygen in the adsorbent is another discussion target.3.Studying the adsorption states of each intermediate and the final product formaldehyde on different doped surfaces in the three reaction pathways.4.Calculating the change of free energy in the three possible reaction paths to finally determine the best route to formaldehyde.Since the free energy of*CO₂→*OCHO was caculated to decrease by 1.16 e V,the best response path was*CO₂→*OCHO→*HCOOH→*HC（OH）₂→*CH₂（OH）₂→*HCHO.