The influence of electrolyte identity upon the electro-reduction of CO2

The influence of supporting electrolyte cations on the voltammetric behaviour and product distribution in N-methylpyrrolidone-based carbon dioxide electroreduction systems is investigated. The reduction potentials associated with TBABF 4 (0.1 M) and corresponding alkali metal (M + ) electrolytes; LiBF 4 , NaBF 4 and RbBF 4 (focussing mainly on the reduction of the widely employed Li + species) were established in both the presence and absence of CO 2 at polycrystalline noble metal working electrodes. In situ and ex situ Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and qualitative element identification via flame testing were used to aid the assignment of reduction processes. It was established that CO 2 reduction products in the metal cationic systems were formed at a much less negative potential than those found with the non-metal cation (−1.5 V vs. Ferrocene, c.f. −2.2 V), however the resultant alteration of the surface environment was found to deactivate the electrode to further CO 2 reduction. The presence of CO 2 in solution was found to affect the potential required for the bulk deposition of metal from the electrolyte through the same process. Where TBA + and M + were employed simultaneously in the system, the resultant voltammetry shared the majority of features with the pure M + system with CO 2 reduction suppressed at more negative potentials therefore supporting the conclusion that any ‘catalytic effect’ associated with TBA + is in fact a lack of deactivation given by the M + system, rather than any enhancement offered by the former.