Glucose is an environmentally friendly and sustainable carbohydrate that is actually a cyclized aldehyde in aqueous solution i.e. a hemiacetal. Its selective oxidation by the anomeric carbon in C1-position without any function protection is of great interest for cogeneration because the electrochemical process enables converting this highly functionalized organic molecule into electricity, heat and added-value chemicals. For this objective, we decided to synthesize effective nanomaterials towards glucose conversion at the anode and the oxygen reduction reaction (ORR) in the cathodic side of a fuel cell. The physical characterizations of the prepared materials and their electrochemical analysis at each half-cell, permitted to optimize the activity of the electrodes according to their elemental composition and structure. Furthermore, a constructed direct glucose fuel cell (DGFC) delivered an open-circuit voltage of 1.1 V in 0.5 mol L^‒1 NaOH and an outstanding output power of 2 mW cm^‒2 in 0.5 M KOH (Figure 1a). Complementary analytical techniques were employed to quantify the reaction processes involved in each compartment, to determine the reaction products resulted from the glucose transformation and thereby, to understand reaction mechanisms of the glucose oxidation and the ORR over the synthesized electrode materials used in alkaline medium. As results, the identification of gluconate as the sole reaction product in the anodic side showed a selective 2-electron conversion of glucose (Figure 1b), while the ORR proceeded through a 4-electron pathway over the designed cathode catalyst (Figure 1c).

Figure 1: (a) Fuel cell polarization curves for different concentrations of glucose in a single fuel cell. Anode: 20 wt.% Au/C (0.18 mg_Au cm^‒2); cathode 20 wt.% Pt/C (0.17 mg_Pt cm^‒2); Fumatech AEM. Anode: 0.5 mol L^‒1 KOH + glucose (deoxygenated by N₂); cathode: 0.5 mol L^‒1 KOH + O₂. (b) LC–MS negative ionization mass spectrum (M-1) of the product. (c) Electrochemical durability tests: Comparison of the ORR polarization curves (at 5 mV s⁻¹) before (black) and after 1000 CVs (red); insets show the normalized specific electrochemical active surface area (SECSA) decay over the 1000 cycles from 0.05 to 1.1 V vs. RHE at 50 mV s⁻¹.

Acknowledgments

The authors gratefully acknowledge financial support from the French National Research Agency ANR-ChemBio-Energy

 

References

1. Y. Holade et al., ChemSusChem, 9, 252 (2016).