# Experimental and Modeling Study for the Solar-Driven CO2 Electrochemical Reduction to CO
## 2 Materials and Methods  
### Electrochemical Cell  
The system comprises a batch cell reactor for the CO\({}_{2}\)RR and a module of 6 DSSCs connected in series for energy harvesting. The electrochemical system is based on a commercial electrochemical reactor (ElectroCell, Ringkoebing-Skjern, Denmark) equipped with ethylene-propylene-diene monomer (EPDM) gaskets to establish separate anodic and cathodic compartments. A Nafion N117 proton-exchange membrane (supplied by Ion Power, New Castle, DE, USA) acts as the separator, ensuring ionic conductivity while preventing the physical mixing of the compartments. The electrolyte is a 0.1 M potassium bicarbonate (KHCO\({}_{3}\)) solution, prepared using KHCO\({}_{3}\) with 99.7% purity (Sigma Aldrich, St. Louis, MO, USA) and dissolved in distilled water. This electrolyte is continuously recirculated between the electrochemical cell and external reservoirs using a peristaltic pump (MCP ISM404B, Ismatec, Glattbrugg, Switzerland) operating at a controlled flow rate of 1.547 mL/min. CO\({}_{2}\) is supplied directly into the electrochemical cell through two mass flow controllers (from Bronkhorst, Ruurlo, The Netherlands), each calibrated to maintain a constant flow rate of 15 mL/min, ensuring a steady supply of CO\({}_{2}\) to the cathodic compartment. The electrodes are configured to facilitate the targeted electrochemical reactions. For the anode, a commercial platinum foil (Pt) with a geometric area of 9.9 cm\({}^{2}\) (GoodFellow, Huntingdon, UK) is used to drive the oxygen evolution reaction (OER). The cathode features silver nanoparticles deposited onto a carbon paper substrate (28 BC from SGL Carbon, Wiesbaden, Germany) using a physical sputtering technique. During the deposition process, a current of 50 mA (I\({}_{\text{dep}}\)) is applied for 300 s (T\({}_{\text{dep}}\)) to achieve uniform nanoparticle coverage. Due to slight variations in the preparation process, the cathodic geometric area ranges between 1.2 and 1.9 cm\({}^{2}\) across the experiments. To mitigate the accumulation of gas bubbles in the electrolyte, plastic meshes are inserted into both the anodic and cathodic compartments. Electrochemical experiments are performed using chronoamperometry with aVSP potentiostat (supplied by BioLogic, Seyssinet-Pariset, France). A two-electrode configuration is employed, wherein a controlled voltage is applied across the electrodes, and the current response is recorded over time, typically for a duration of approximately one hour for each applied voltage point. The gaseous products generated at the cathode are analyzed using a Micro Gas Chromatograph (supplied by Inficon Fusion, Bad Ragaz, Switzerland) equipped with two analytical modules: an Rt-Molsieve 5A column and an Rt-Q-Bond column. Each module is coupled with a microthermal conductivity detector to ensure the accurate quantification of gaseous species. To assess the potential formation of liquid products, high-performance liquid chromatography (HPLC) is employed using a Shimadzu (Kyoto, Japan) system with a ReproGel column (300 \(\times\) 8 mm) and an ultraviolet-visible (UV-Vis) detector set to 210 nm. The mobile phase consists of 9.0 mM H\({}_{2}\)SO\({}_{4}\). The faradaic efficiency (\(FE\)) for the different products is calculated through the following formula:  
\[FE\ =\ \frac{2 NF}{Q} \tag{1}\]  
where **N** is the amount of a product detected (number of moles), 2 is the number of electrons required to obtain 1 molecule of this product (CO, HCOOH, or H\({}_{2}\) formation), \(F\) is the Faraday constant, and \(Q\) is the total charge passed through the system recorded during electrolysis.