Pd/carbon paper electrodes modified with polyaniline as co-support for sustainable energy conversion of bioethanol from Salicornia bigelovii

Abstract

The production of sustainable and renewable fuels for energy conversion is vital for designing green technologies to supply the energy needs of the population. In this work, bioethanol was obtained from Salicornia bigelovii as a salt-tolerant plant watered with seawater, converting it in an interesting sustainable energy source for clean and renewable technologies, such as fuel cells. Thus, Bioethanol (BioEOR) and ethanol (EOR) electro-oxidation reactions were evaluated using polyaniline (PANI) as a co-support in Pd/carbon paper electrodes in alkaline medium (0.3 M KOH). PANI was growth electrochemically on carbon paper (PANI-T) for the further electrodeposition of Pd on both, carbon paper (T) and PANI-T. Physicochemical characterization by XRD, TEM, EDX mapping, and XPS indicated that PANI promoted differences in the properties of Pd/PANI-T compared to Pd/T as the reference material. It decreased crystallite and particle sizes to 8.29 nm and 15 ± 3 nm. PANI improved particle homogeneity and prevented the formation of microsized Pd agglomerates. PANI promoted shifts in binding energies of Pd due to their metal/support interaction. Electrocatalytic evaluation of Pd/PANI-T for EOR resulted in a maximum current density of 295.88 mA cm−2, and an oxidation potential of −0.41 V vs. NHE at 5 M ethanol. This current was 110 mA cm−2 higher to that achieved by Pd/T. In addition, Pd/PANI-T presented higher current density for BioEOR (146.41 mA cm−2 at 3 M bioethanol) than Pd/T. However, this current density was lower to that found for EOR due to the presence of impurities like toluene. According to a spectroelectrochemical analysis by surface-enhanced Raman spectroscopy, the differences in activity for BioEOR of Pd/PANI-T and Pd/T were associated with changes in the reaction pathway: Pd/PANI-T promoted the formation of formates and carbonates (12e−), while Pd/T formed mainly acetates (4e−). Thus, Pd/PANI-T enabled a higher electron transfer per bioethanol molecule.