The biodiesel production method via the transesterification of biomass-derived triglycerides is considered a renewable, eco-friendly, and non-toxic alternative for traditional diesel oil [1]. Nevertheless, biodiesel production generates large amounts of glycerol (10% by weight byproduct). This exceeds the current demand for glycerol and therefore limits the price of biodiesel. The utility of the glycerol byproduct can be significantly increased through oxidative processes since almost every product of glycerol oxidation is more valuable than glycerol itself [2]. Structurally, glycerol contains three alcohol functional groups, and selectively oxidizing one of these very similar functional groups while preventing further oxidation can be complicated.

In this sense, electrochemical glycerol oxidation has recently received a great deal of attention as it can be coupled to renewable sources of electricity and employ water as the reaction medium [3]. Ni-based electrocatalysts have been extensively investigated [4]. It is known that the active layer for these electrocatalysts is nickel oxide hydroxide, which can oxidize primary alcohols to the corresponding carboxylic acids. Catalytic oxidation of glycerol is a very promising way to produce a variety of value-added products. The oxidation products of glycerol mainly include C2 and C3 organic compounds. Considering that C─C bond is broken during the catalytic process, C2 compound products are the main products, including oxalic acid (OA), tartronic acid (TA), glyceric acid (GLA), glycolic acid (GCA), and formic acid (FA) [5].

In this work we initially studied the glycerol electrooxidation reaction in a conventional three electrode cell using a Ni foil working electrode with 0.1 M LiOH/water as electrolyte solution. Later, to improve the mass transfer and selectivity of the system we focused our research on glycerol electrooxidation using an electrochemical two electrodes flow cell. Running the reactions in a continuous flow system allowed us to mimic reactions and develop them in a setting that is more like industry. In this way, several experimental setups were studied. By mean of chronopotentiometry technique, the current densities were varied from 1 to 5 mA/cm² while also controlling the flow rate (1 to 20 mL/min) and the experimental time. The Faradaic efficiency (FE), and the products distribution were analyzed and compared with the electrooxidation reactions performed in the conventional cell. The results showed that in batch mode the highest FE (99 %) was found by applying 1 mA/cm² for 45 min, meanwhile the highest FE for the flow system was obtained during the first 15 min of reaction and then decreases. Furthermore, at current densities of 3 mA/cm² and flow rates of 10 and 20 mL/min, the FE reached values close to 100%, obtaining OA, TA, GLA, GCA, and FA as majority products.