Experimental design of the electrocatalytic CO2 reduction of single-atom electrocatalysts based on the first-principle calculation
[Objective]The problems of excessive CO2 emission,the greenhouse effect,and energy shortage have been widely discussed among countries worldwide.Electrocatalytic CO2 reduction reaction(ECO2RR)can realize the conversion of CO2 into value-added chemical fuel under mild conditions and the storage of renewable electricity,which is an effective way to promote China's aim of carbon peak and carbon neutrality.To pursue higher catalytic activity and product selectivity,researchers are committed to developing highly efficient ECO2RR electrocatalysts.In this paper,we designed Mo2CO2 MXene-based single-atom catalysts(SACs)(TM@Mo2CO2-Ov,TM = Fe,Co,Ni)according to the needs of ECO2RR,focusing on their electronic structure,catalytic performance,as well as reaction mechanism through theoretical simulation of the electrocatalytic process.[Methods]In this work,the CIF file of the Mo2CO2 MXene structure downloaded from the crystal structure database was first imported into the Materials Studio software.Then,the(110)crystal plane was cleaved,and a vacuum layer of 15 Å was created.Afterward,a 3×3 supercell treatment was applied to the system.Next,the VASP software was utilized to perform structure optimization.After the Mo2CO2 structure was optimized,a vacancy site for an oxygen atom on the surface was constructed.Subsequently,the Fe,Co,and Ni metal atoms were introduced into the respective vacancy sites to create the Fe@Mo2CO2-Ov,Co@Mo2CO2-Ov,and Ni@Mo2CO2-Ov catalyst models,respectively.Finally,the VASP software was employed to optimize the catalyst structures and the adsorption structures of the reaction intermediates.The performance evaluation of ECO2RR on different SACs was obtained by studying the reaction mechanism of the production of C1 products(CO,HCOOH,CH3OH,and CH4).The free energy of ECO2RR was calculated using the computational hydrogen electrode mode,wherein the energy of(H+ + e-)remained equivalent to that of 1/2H2 at normal pressure and temperature.[Results]The calculated results showed the following:1)In the Mo2CO2-Ov framework,single Fe,Co,and Ni atoms replaced the Mo atom at the center of the O defect.After structural optimization,it was found that these three structures did not change significantly,and the bond lengths only changed slightly.2)The CO2 molecule was stably adsorbed on Fe@Mo2CO2-Ov,Co@Mo2CO2-Ov,and Ni@Mo2CO2-Ov via chemisorption.The structures of CO2 were significantly bent after adsorption,and the calculated absolute values of the interaction exceeded four.The DOS analysis showed that the occupation of d orbitals of Ni,Co,and Fe led to the adsorption difference.The d orbitals of Co and Fe were hybridized with the πg and πM* orbitals of CO2,which promoted the adsorption and activation of CO2.3)The ECO2RR free energy diagram and reaction path analysis showed that Co@Mo2CO2-Ov had higher ECO2RR activity and better CH4 selectivity and was a better electrocatalyst for the formation of C1 products from ECO2RR than Fe@Mo2CO2-Ov and Ni@Mo2CO2-Ov.[Conclusions]By integrating the geometrical analysis,DOS calculation,and free energy analysis,Co@Mo2CO2-Ov was established as the ideal ECO2RR catalyst.The work can achieve the expected goal of significantly enhancing the ECO2RR performance and improving students'scientific research literacy to explore micromechanisms and processes through the extension of the experimental process.
electrocatalytic CO2 reductionfirst-principle calculationsingle-atom catalyst
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