Sputtered Ag electrodes with different thickness and on different substrates were deposited. To distinguish between the electrodes, the notation AgX will be used, where X denotes the Ag thickness in nanometers. If the sample was plasma-treated, the letter "P" follows and a number as subscript corresponding to the duration of the plasma treatment in seconds. The Ag mass loading of the electrode was experimentally determined by weighing the substrate before and after sputtering. With this method, the mass loading for 100, 200 and 500 nm of Ag was 0.078, 0.180 and 0.380 mg/cm 2 , respectively. These are in good agreement with calculated values, using the bulk Ag density of 10.5 g/cm . The target was to reduce the Ag loading as much as possible, but still to have a film which will allow the plasma modification of its surface, without completely depleting it (as the O2 plasma treatment removes part of the Ag). For the Ag200, this compromise could be best achieved, and therefore this thickness was used for most of the subsequent characterizations and experiments. increasing the RMS roughness to above 17 nm. Some of the material is removed by O2 plasma, as the mass loading was decreased from 0.180 to 0.130 mg/cm 2 after 36 secs of plasma. The obvious modifications of the surface morphology by the plasma, are accompanied by the oxidation of the Ag surface, as shown by the XRD investigation in 2. After the deposition, the Ag film is polycrystalline with the cubic structure and dominant (111) peak reflection at 2θ=38.11. After the plasma treatment, a reflection stemming from the Ag2O is clearly visible. To electrochemically evaluate the catalysts, the double-layer capacitance Cdl of the samples was extracted from cyclic voltammetry measurements. Firstly, in the CV plot, the potential range was identified where no faradaic processes occur, so the current in this region is due to the charging/discharging of the electric double layer. This potential region was between -300 mV and -200 mV vs. Ag/AgCl. Then CV measurements were realized at various potential scan rates from 10 mV/s to 500 mV/s. The CVs for all samples are shown in Fig. . For each sample and scan rate, at the potential of -250 mV, the absolute values of the anodic and cathodic current densities were averaged, yielding jav. The jav was then plotted against the scan rate, as shown in Fig. (a) for the samples with 200 nm Ag, un-treated and subjected to 12 and 36 sec of plasma treatment (i.e. Ag200, Ag200P12 and Ag200P36). The relationship between the current and the scan rate is linear in the non-faradaic region, with the slope being the double-layer capacitance per area. From the linear fits in Fig. , a clear increase of the slope is obtained with increasing plasma duration, with the Cdl being 0.13, 0.16, and 0.24 mF/cm 2 for the electrodes with 0, 12 and 36 secs of plasma treatment, respectively. For longer plasma duration (48 s) the Ag mass loss is too significant, and the electrode is barely conductive. This is the reason why the maximum plasma treatment for the 200 nm-thick electrode was 36 s. Since the Cdl is proportional to the ECSA, the conclusion can be drawn that the plasma treatment enhances the electrochemical active area of the electrode. The electrocatalytic activity was evaluated via linear sweep voltammetry (LSV) curves for the Ag200P36 electrode in the presence of He and CO2, shown in Fig. . In these experiments, the anolyte, catholyte and He or CO2 were fed to the 3-compartment cell for several minutes to ensure the compartments were filled and then the flows were stopped for the duration of the voltammetry. A catalytic wave at an onset potential of -0.53 V vs. RHE was observed only in the presence of CO2, thus assigned to the CO2RR. In the presence of inert gas, the catalytic wave is shifted to more cathodic potentials (-0.87 VRHE) but still present and likely due to the proton reduction from the aqueous-based electrolyte. A slightly lower onset potential is obtained for the Ag200P36 , in line with previous reports. The Ag200 and Ag200P36 curves are crossing at high cathodic potential (~1.25 V), beyond which the Ag200 reaches higher current density. This can be attributed to the higher conductivity of this sample due to the higher Ag loading. An overpotential of only 650 mV was estimated based on an equilibrium potential of -530 mV for the CO2 + 2H + +2e -= CO + H2O reaction and the potential of -1.18V vs. RHE used in this study.