Direct ethanol fuel cells with higher ethanol-tolerant nonprecious metal cathode catalysts for oxygen reduction reaction

Direct ethanol fuel cells (DEFCs), which use ethanol as a fuel, have attracted considerable attention due to their relatively high energy density, the non-toxicity of ethanol. However, since the cross-over of ethanol as a fuel in DEFCs can deteriorate the cell performance due to the oxidation of ethanol (EtOH) at the cathode during oxygen reduction reaction (ORR), non-precious metal (NPM) cathode catalysts for ORR have been studied using carbon-based nanostructures as promising alternatives to Pt-based catalysts. Herein, the N-doped carbon nanostructures (Co-N-C) as cathode catalysts were synthesized using Cobalt(II), ۲ MeIm, and Poly-pyrrole as a substrate. Two identical and commercial ۱۰ wt.% Pt/C as the ORR electrocatalyst for the cathode. The anion-exchange membrane (A۲۰۱ Tokuyama), with a thickness of ۲۸ μm is used as an electrolyte. ۲ M of ethanol in a ۲ M KOH solution which was stabled in a ۱۲ ml tank was fed to the anode side and cathode was performed under air-breathing and O۲ bleeding modes. In this study, the performance of these two DEFCs was compared to each other. The cell performances with the cathode of Co-N-C and Pt/C with air-breathing are ۱۵.۵۹ mW cm-۲ and ۷.۶۲ mW cm-۲ and with O۲-breathing are ۲۰.۹۸ mW cm-۲ and ۱۴.۹۱ mW cm-۲ respectively (fig. a). the better performance with the O۲-breathing state is that the mentioned, the difference between the cells is these cathodes, so Co-N-C has better ORR activity than Pt/C (fig. b). The excellent ORR activity of Co-N-C for the DEFC can be attributed to ethanol tolerance in the ORR and low ethanol adsorption energy of the active sites for the ORR of Co-N-C and it’s clearly shown in fig. d that Co-N-C didn't have any responses to ethanol implying the maintained ORR activity in the presence of EtOH. but Pt/C exhibited the sudden current drop in the direction of the oxidation of EtOH plot indicates that Co-N-C has small arcs in both air/O۲-breathing which is confirmed to low charge transfer (fig. c).with the insertion of EtOH. The Nyquistconcentration of Fig. (a) Polarization curves, (b) Anode and cathode polarization curves and (c) Nyquist plots and the corsponding equivalent circuit at voltage of ۰.۵ V of the air/O۲-breathing DEFCs with Co-N-C and ۱۰ wt.% Pt/C as cathode catalysts and ۶۰ wt.% Pt/C as an anode catalyst supplied with ۲ M EtOH. (d) Chronoamperometric curves of Co-N-C and ۱۰ wt.% Pt/C measured at ۰.۵۶ VRHE for ORR in O۲-saturated ۰.۱ M KOH. The ۲ M EtOH (۱۲ mL) solution was instantaneously injected during the ORR processoxygen is more than the air-breathing state. As it’scells are fabricated using the same anodes and Co-N-C

Keywords:

DEFC , Ethanol tolerance , Non-precious metal catalyst , Oxygen reduction reaction