Sn/SnO2 Nanocomposite Encapsulated on Nitrogen-Doped Carbon as a Highly Efficient Catalyst for the Electrochemical Reduction of CO2 to Formate

The development of an inexpensive, highly active catalyst is important for electrochemical carbon dioxide reduction reactions (CO2RRs) to produce fuels and chemicals. CO2 can be converted into formate electrochemically using tin-based composites. Due to the synergistic effects induced by interfaces between metallic and oxide phases, tin species with different oxidation states may enhance the catalytic activity. Therefore, synthesizing hybrid catalysts with heterogeneous active interfaces is desirable yet difficult. Herein, a heterointerface-rich tin/tin oxide encapsulated on a nitrogen-doped carbon (Sn/SnO2–CNx) composite was prepared for the electrochemical CO2 reduction reaction. The catalyst shows formate as the major product with a small amount of carbon monoxide (CO) and hydrogen (H2). The heterostructured (Sn/SnO2)15-CNx electrode showed 83.5 ± 2.3% faradaic efficiency and 16.7 mA/cm2 partial current density for formate production at 20 mA/cm2 applied current density in an H-type cell, which are better than those of bare SnO2 and bare Sn/SnO2 composites. The catalyst also shows good durability during CO2RR. To comprehend the experimental mechanism, density functional theory is used to compute the free energy profile of CO2-to-formate transformation on the Sn(200), SnO2 (110) surface, and Sn/SnO2 model, suggesting that the Sn/SnO2 model requires a low energy barrier compared to Sn and SnO2 to give the formate product. The high performance of the catalyst may be attributed to the presence of a heterointerface, porous configuration, high electrochemical surface area, and synergistic interaction between the catalyst and support. This work suggests that interface engineering could play a key role in the development of high-performance electrocatalysts for the CO2 reaction.