Towards a sustainable technology for H2 production: Direct lignin electrolysis in a continuous-flow Polymer Electrolyte Membrane reactor

We have performed, for the very first time in literature, the production of pure H-2 via electrolysis of lignin solutions in continuous-flow mode in a Polymer Electrolyte Membrane (PEM) reactor. A Pt-Ru//Fumapem (OH- conductor)//Pt/C (Anode//Anion Exchange membrane//Cathode) electrochemical cell was used. Under the explored conditions, we have demonstrated that lignin can be electrolyzed at much lower electrical potentials (from similar to 0.45 V) compared to that of water electrolysis (thermodynamically favored from similar to 1.2 V). In addition, we observed that increasing the reaction temperature gives rise to an enhanced activity towards the electrolysis of lignin, increasing therefore the production of pure H-2. Finally, in-situ cyclic voltammetry experiments were performed in the PEM cell to demonstrate that lignin electro-oxidation takes place at potentials lower than that for O-2 evolution. These experiments also showed that the whole system did not suffer a significant deactivation during the electrolysis experiments, which pointed out the promising stability and reproducibility of the proposed technology. Further studies should be performed to identify the products of the lignin electro-oxidation at the anode. This study establishes a very important step-forward towards the direct electrochemical valorization of lignin (usually considered as a biomass residue) for a sustainable production of pure H-2 using renewable sources.