Direct Ethanol Fuel Cells with Superior 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 nontoxicity of ethanol, and the abundance of ethanol sources. However, since the crossover 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), nonprecious metal (NPM) cathode catalysts for ORR have been studied using carbon-based nanostructures as promising alternatives to Pt-based catalysts. Herein, the doped carbon nanostructures (C/Fe-TMPP and C/Fe-Pc) as cathode catalysts were synthesized using a template method with iron(III) 5,10,15,20-(tetra-4-methoxyphenyl) porphyrin chloride (Fe-TMPP) and iron(II) phthalocyanine (Fe-Pc). In the half-cell test, C/Fe-TMPP exhibited an enhanced ORR activity in 0.5 M H2SO4 (i.e., high half-wave potential and specific current density) and maintained ORR performance in the presence of crossover ethanol, compared to a commercial Pt/C. Moreover, C/Fe-TMPP exhibited high performance in the DEFC supplied with high-concentrated EtOH as a fuel at the cathode. The excellent ORR activity of C/Fe-TMPP 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 C/Fe-TMPP.