Electrochemical reduction of carbon dioxide III. The role of oxide layer thickness on the performance of Sn electrode in a full electrochemical cell

Abstract

A full electrochemical cell was employed to investigate the role of the surface oxide thickness on the activity of Sn-based electrodes for the electrochemical conversion of CO₂. The current density showed a negligible dependence on the thickness of the surface SnO_x layer of Sn nanoparticles (100 nm), while the selectivity towards the formation of CO and formate exhibited a strong relationship with the initial SnO_x thickness. Electrodes with a native SnO_x layer of ∼3.5 nm exhibited the highest Faradaic efficiency (64%) towards formate formation at -1.2 V. The Faradaic efficiency towards CO production reached a maximum (35%) for the electrode with an oxide thickness of 7.0 nm, formed by annealing the Sn nanoparticles at 180 °C for 6 hours. The electrodes with a native SnO_x layer displayed the highest overall selectivity towards CO₂ reduction. The decrease of the selectivity towards CO₂ reduction with increasing the thickness of the SnO_x layer can be attributed to the enhancement of hydrogen evolution on the Sn clusters with a low-coordination number derived from the reduction of SnO_x. The Faradaic efficiency towards hydrogen production was observed to increase with increasing the thickness of the SnO_x layer. Our results suggest the importance of the underlying surface structure on the selectivity and activity of the Sn electrode for CO₂ reduction and provide an insight into the development of efficient catalysts.