Novel electrochemical strategies for the conversion of CO2 emissions into sustainable energy vectors using Sn-based materials

Abstract

Nowadays, the CO₂ electroreduction reaction (CO₂RR) is regarded as a highly attractive approach to convert CO₂ into value-added feedstocks and renewable energy carriers. However, its practical application is strongly limited by two main challenges: the poor selectivity towards carbon-based products and the high overpotentials required to activate the CO₂ molecule. One promising strategy to address these issues is the development of catalysts that efficiently promote CO₂ reduction while simultaneously suppressing hydrogen evolution (HER), the main competing side reaction. In this context, Sn stands out due to its high selectivity for formate (HCOOH) and its strong ability to suppress HER.

In this thesis, an extensive study of Sn-based catalysts has been carried out with the aim of finding new strategies to lower the overpotential, tune the selectivity, and enhance overall CO₂RR performance. Mg–Sn alloys were investigated to evaluate the influence of Mg on catalytic activity and its potential role in reducing the overpotential needed to activate CO₂. Another strategy explored was the use of chiral oxides, such as SnO₂ and CuOₓ, to assess the impact of nanostructured chiral surfaces on selectivity and possible catalytic enhancement. Furthermore, the role of Sn oxidation states and the incorporation of chalcogen elements were also examined with the same objectives.

The catalytic performance was first screened using linear sweep voltammetry (LSV) to identify the most active materials. Chronoamperometry (CA) experiments were then performed in a three-electrode H-cell coupled with gas chromatography (GC) to analyze gaseous products and determine Faradaic efficiencies (FE). Additionally, ion chromatography (IC) was employed to quantify liquid products.

In most cases, a surface evolution was observed during CO₂RR, often leading to improved catalytic activity over time. Chiral nanostructured materials showed only modest improvements, although further experiments are required to better understand their behavior. The incorporation of sulfur as an additive was found to significantly increase selectivity and strongly suppress HER, yielding the best performance with a FE of 80% to formate.