Résumé
Biosourced polyols such as ethylene glycol (EG) and glycerol (GL) have very high theoretical H2 storage capacity, of 8.15 wt% and 6.15 wt%, respectively. Moreover, both loaded and unloaded molecules display no or much lower toxicity, higher safety and are more environmentally-friendly (being also biodegradable), as well as cheaper than the classical LOHCs. Therefore, they could be excellent candidates as biosourced LOHCs, minimizing the risk during transportation. In addition, thermodynamic data indicate that these molecules can theoretically be oxidized from the very low potentials of ca. 0.11 V vs. RHE and ca. 0.27 V vs. RHE for GL and EG, respectively, with the release of hydrogen with electrical energy consumptions of ca. 20 kJ molH2−1 and ca. 53 kJ molH2−1, respectively, values lower or equivalent to that for classical LOHC. Then, several PtM/C and PdM/C catalysts were synthesized by a water-in-oil microemulsion method and characterized. Their behavior towards the GL and EG electrooxidation was followed by cyclic voltammetry, in situ infrared spectroscopy, and chronoamperometry with analysis of products by HPLC. The Pt9Bi1/C catalysts displayed the best activity and selectivity towards the formation of C3 and C2 oxidized compounds for GL and EG oxidation, respectively. For cell voltage ≤ 0.60 V vs. RHE, GL oxidation leads mainly to glyceraldehyde, then glyceric acid, tartronic acid and a small amount of formic acid. EG electrooxidation allows the formation of glycolic acid as main product, oxalic acid and an unidentified intermediate that is consumed when increasing the electrolysis time, but no formic acid. For these reasons, EG appears as the best candidate as LOHC.