Temperature promotes selectivity during electrochemical CO 2 reduction on NiO:SnO 2 nanofibers.

Electrolyzers operate over a range of temperatures; hence, it is crucial to design electrocatalysts that do not compromise the product distribution unless temperature can promote selectivity. This work reports a synthetic approach based on electrospinning to produce NiO:SnO 2 nanofibers (NFs) for selectively reducing CO 2 to formate above room temperature. The NFs comprise compact but disjoined NiO and SnO 2 nanocrystals identified with STEM. The results are attributed to the segregation of NiO and SnO 2 confirmed with XRD. The NFs are evaluated for the CO 2 reduction reaction (CO 2 RR) over various temperatures (25, 30, 35, and 40 °C). The highest faradaic efficiencies to formate (FE HCOO - ) are reached by NiO:SnO 2 NFs containing 50% of NiO and 50% SnO 2 (NiOSnO50NF), and 25% of NiO and 75% SnO 2 (NiOSnO75NF), at an electroreduction temperature of 40 °C. At 40 °C, product distribution is assessed with in situ differential electrochemical mass spectrometry (DEMS), recognizing methane and other species, like formate, hydrogen, and carbon monoxide, identified in an electrochemical flow cell. XPS and EELS unveiled the FE HCOO - variations due to a synergistic effect between Ni and Sn. DFT-based calculations reveal the superior thermodynamic stability of Ni-containing SnO 2 systems towards CO 2 RR over the pure oxide systems. Furthermore, computational surface Pourbaix diagrams showed that the presence of Ni as a surface dopant increases the reduction of the SnO 2 surface and enables the production of formate. Our results highlight the synergy between NiO and SnO 2 , which can promote the electroreduction of CO 2 at temperatures above room temperature.