Electrocatalytic hydrogenation of pyrolysis bio-oil: Effect of pulsed electrolysis on the conversion of carbohydrate-derived oxygenates

The electrochemical upgrading of bio-oil presents an attractive route to produce green chemicals; however, achieving high product selectivity within these complex mixtures remains a challenge. While previous studies have focused on qualitative trends, this work provides a quantitative investigation of the electrochemical behaviour of oxygenates within the water-soluble fraction of a commercial bio-oil. The electrocatalytic hydrogenation of bio-oil components, including 5-hydroxymethylfurfural (5-HMF), pentoses, hexoses, and levoglucosan, was tracked as a function of charge passed (up to 7313C/g). At 2438C/g, 5-HMF was completely converted, while pentoses reached conversions of 70-80%. In contrast, hexose conversion remained below 60%, while levoglucosan achieved only 30% conversion. To compare the apparent electrochemical responsiveness, a new empirical parameter termed the apparent electrochemical response (P i ) was developed. Under constant current, P i followed the order: 5-HMF (0.7) > pentoses (0.4) > hexoses (0.2) > levoglucosan (0.1), suggesting that molecular structure influences the responsiveness. Furthermore, to our knowledge, this is the first study to investigate the introduction of periodic oxidative pulses. Pulsing decreased the conversion of strongly adsorbing 5-HMF by 20% but increased sugar conversion up to 30%. More importantly, it improved selectivity towards sugar alcohols, resulting in a twofold increase in their partial Faradaic efficiency. These findings are consistent with the hypothesis that oxidative pulses periodically regenerate electrode sites by mitigating surface blocking from strongly adsorbing species, promoting hydrogenation for less surface-active compounds. This work provides new insight into the electrochemical behaviour of bio-oil oxygenates and demonstrates pulsing as a promising strategy for improving selectivity.