Electrochemical reduction of CO₂ (CO₂ER) into value-added chemical feedstocks and liquid fuels using renewable energy is a promising route for CO₂ recycling.[1] The major challenges are the large overpotential for CO₂ activation and the competitive H₂ evolution in aqueous mediums.[2] Although some nanostructured noble metal catalysts have demonstrated impressive electrocatalytic activity and selectivity for CO or formate production over CO₂ER, the low abundance and high cost limit their large-scale applications.[3] Efficient and cost-effective electrocatalysts with high energy efficiency and product selectivity are highly desirable to drive the development of CO₂ER.

In our study, we developed a low-cost Sn particle modified N-doped carbon nanofiber hybrid catalyst via a straightforward electrospinning technique coupled with a pyrolysis process.[4] Its electrocatalytic performance was tuned by the coverage of Sn nanoparticles and the structure of N species on the nanofiber surface. The pyridinic-N supported Sn nanodots drove efficient formate formation with a high current density of 11 mA cm^-2 and a faradaic efficiency of 62% at a moderate overpotential of 690 mV. After a simple acidic leaching treatment, only atomically dispersed Sn species remained on the surface of pyridinic-N-doped carbon nanofibers. This catalyst dominantly promoted the CO₂-to-CO conversion with a high faradaic efficiency of 91% at a low overpotential of 490 mV.

The change of product selectivity was attributed to the difference in local chemical and electronic environment (Sn-Sn or Sn-N) surrounding the Sn active sites, which facilitated different intermediate stabilization and reaction pathway. The abundance of Sn nanodots and the strong electronic interaction between Sn and pyridinic-N-doped carbon may promote the formate formation, while the efficient CO production over the Sn atoms modified nanofibers may arise from the intrinsically high activity and selectivity of the formed Sn-N moieties.

References

[1] J. Qiao, Y. Liu, F. Hong and J. Zhang, Chem. Soc. Rev., 631-675 (43) 2014.
[2] E. E. Benson, C. P. Kubiak, A. J. Sathrum, J. M. Smieja , Chem. Soc. Rev. 89-99(38) 2009.
[3] Q. Lu, Jonathan Rosen, F. Jiao, ChemCatChem, 38-47 (7) 2015.
[4] Y. Zhao, J.J. Liang, C.Y. Wang, J.M. Ma, G.G. Wallace, Tunable and efficient tin modified nitrogen-doped carbon nanofibers for electrochemical reduction of aqueous carbon dioxide, Adv. Energy Mater., accepted on 16/10/2017.