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

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 SnOx layer of Sn nanoparticles (100 nm), while the selectivity towards the formation of CO and formate exhibited a strong relationship with the initial SnOx thickness. Electrodes with a native SnOx layer of similar to 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 degrees C for 6 hours. The electrodes with a native SnOx layer displayed the highest overall selectivity towards CO2 reduction. The decrease of the selectivity towards CO2 reduction with increasing the thickness of the SnOx layer can be attributed to the enhancement of hydrogen evolution on the Sn clusters with a low-coordination number derived from the reduction of SnOx. The Faradaic efficiency towards hydrogen production was observed to increase with increasing the thickness of the SnOx 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.