Spectroscopic investigations of the electrolytic CO${}_2$ reduction

The electrolytic reduction of CO${}_2$ in solution is recognized as an approach to combat anthropogenic driven global warming as it provides a method to produce CO${}_2$ neutral energy carriers. The product of the electrolysis reaction varies with the electrode metal where carbon monoxide is yielded at silver electrocatalysts. The study of the CO${}_2$ reduction reaction can be divided into investigations of the processes at the electrocatalyst surface and the processes in the electrolyte solution. This PhD thesis aims to contribute to both of these subjects. In the first part, a post test Raman study on the degradation mechanism of silver based gas diffusion electrodes (GDEs) was performed. No evidence for the deactivation of the catalyst by carbon deposition was found. Instead, it was shown that silver nanoparticles are formed, which enable surface enhanced Raman scattering (SERS). In the second part of the thesis an in operando NMR study of the electrolytic CO${}_2$ reduction in aqueous media was performed. First, an in operando electrolysis setup was developed compatible to high-field NMR spectrometers and liquid state probe heads. Interactions with the magnetic fields used in NMR were overcome by minimizing the amounts of metallic components and applying extensive shielding. In the second step an in operando electrolysis setup was employed to study the chemistry and processes in the aqueous bicarbonate electrolyte during electrolysis. It was found that the electrolyte exists as both, free ions and solvent-shared or solvent-separated ion pairs in solution. The exchange rate between both forms is impacted by the applied potential during electrolysis. The exchange between free ions and ion pairs affects the dynamic equilibrium between solvated CO${}_2$ and bicarbonate in solution which could provide an approach to resupply CO${}_2$ during the electrolysis reaction.