An important bottleneck to commercializing CO₂ electrolysis is the high cell voltage under operating conditions (often U_cell ≥ 3V), partly due to the oxygen evolution reaction (OER), which is typically employed as the anode process. Replacing the OER with alternative anode processes, such as the oxidation of small organic molecules, could decrease the cell voltage while enabling the formation of valuable products. Glycerol is an attractive candidate for this purpose, since it is widely available in a relatively pure form as the byproduct of biodiesel production.

In this presentation, I will discuss our results on several glycerol oxidation (GOR) catalysts from the perspective of electrocatalytic GOR activity, selectivity, and (long-term) stability. Two sets of catalysts were investigated in continuous-flow electrolyzer cells: first, mono-, and bimetallic noble metal catalysts such as Au, Pt, Pd, PdAu, and PdPt. Secondly, non-noble metal-containing systems were also scrutinized, including Ni, Fe, and FeNi as single-atom catalysts anchored on an N-doped carbon support. In all cases, CO2RR was driven at the cathode (Ag nanoparticles) of the electrolyzer cell. While a considerable decrease in cell voltage was achieved in the case of noble metals, always a mixture of C1-C3 GOR products formed along with a considerable amount of CO₂ (20-40 % of the passed charge). As opposed to noble metals, formate was the primary GOR product in the case of the non-noble alternatives; however, the measured cell voltages remained only a bit lower than those measured if OER was the anode process. An additional advantage of the non-noble electrocatalysts is the marginal influence of glycerol on their long-term stability, in opposition to what was observed with noble metals.

The majority of published studies on paired CO2RR/GOR electrolysis have been conducted at the laboratory scale (e.g., cell and electrode sizes, duration of the experiment, etc.). In the second half of my talk, I will discuss the main obstacles hampering the scale-up of paired CO2RR/GOR electrolysis. These will be showcased by presenting results demonstrating how cell design, electrode support selection, and various operating conditions (temperature, glycerol concentration, flow rates, transmission of electrolyte, etc.) influence the performance of the paired CO2RR/GOR electrolyzer cell.