To provide further insights to this hypothesis, Raman spectroscopy was used to investigate the dynamics of the Co Terpy-RF catalyst. A particular point of interest was pyridine units that typically feature a pKa below the neutral pH of the electrolyte. 39 Thus, we concentrated on the band around 1020 cm -1 that corresponds to a ring breathing mode and is sensitive to both the hydrogen bonding environment and protonation of the pyridine unit (Fig. ). First, using Co Terpy-OH as a starting point, we noted that the dried molecule has only one band, centered at 1029 cm -1 . Dissolved in DI water, the same molecule features two bands, at 1029 and 1017 cm -1 , corresponding to non-protonated and protonated pyridine, respectively. In aqueous solution, this molecule is known to exist in a quinoid tautomeric form with a protonated pyridine. Adding acid to the solution increases the protonated pyridine band at 1017 cm -1 while adding base instead results in only the non-protonated pyridine at 1029 cm -1 being visible. For Co Terpy-RF, a dried film shows a single band at 1024 cm -1 we attribute to a pyridine coordinated to Co. With an acid solution overtop of the film, the band shifts to 1033 cm -1 which likely indicates a degree of a protonation to the pyridine, while with a basic solution overtop of the film, the band shifts to 1024 cm -1 as there is no more protonated pyridine. Interestingly, under CO2R conditions using a GDEbased spectroelectrochemical cell, the band splits into two -a main band at 1019 cm -1 and a shoulder at 1033 cm -1 . We take this to signify that the terpyridine unit of Co Terpy-RF is partially protonated in these conditions. In particular, in the Co(I) oxidation state, binding to 6 pyridine N atoms is no longer favorable and one pyridine unit will dissociate, further promoting its protonation as well as leaving the Co site open for catalysis. As pyridine units have facilitated proton conductivity in previous studies, and proton shuttles in CO2 reduction 44 it is not unreasonable to think that they can be playing a similar role within the self-assembled films. This is also evident in the weak proton conductivity of Co Terpy-RF films (Fig. ).