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 (CO 2 RRs) to produce fuels and chemicals. CO 2 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/SnO 2 –CN x ) composite was prepared for the electrochemical CO 2 reduction reaction. The catalyst shows formate as the major product with a small amount of carbon monoxide (CO) and hydrogen (H 2 ). The heterostructured (Sn/SnO 2 ) 15 -CN x electrode showed 83.5 ± 2.3% faradaic efficiency and 16.7 mA/cm 2 partial current density for formate production at 20 mA/cm 2 applied current density in an H-type cell, which are better than those of bare SnO 2 and bare Sn/SnO 2 composites. The catalyst also shows good durability during CO 2 RR. To comprehend the experimental mechanism, density functional theory is used to compute the free energy profile of CO 2 -to-formate transformation on the Sn(200), SnO 2 (110) surface, and Sn/SnO 2 model, suggesting that the Sn/SnO 2 model requires a low energy barrier compared to Sn and SnO 2 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 CO 2 reaction.