Oxygen reduction activity of binary PtMn/C, ternary PtMnX/C (X = Fe, Co, Ni, Cu, Mo and, Sn) and quaternary PtMnCuX/C (X = Fe, Co, Ni, and Sn) and PtMnMoX/C (X = Fe, Co, Ni, Cu and Sn) alloy catalysts

In this study, we evaluated the activity of binary PtMn/C, ternary PtMnX/C (X = Fe, Co, Ni, Cu, Mo and, Sn) and quaternary PtMnCuX/C (X = Fe, Co, Ni, and Sn) and PtMnMoX/C (X = Fe, Co, Ni, Cu and Sn) alloy catalysts towards the oxygen reduction reaction (ORR) in acidic solution. Although all catalysts exhibited improved activities towards the ORR if normalized by the mass of Pt; when they are considered per milligram of total metal only a handful of them illustrated improved activities towards the ORR in terms of onset potential and current intensity determined by cyclic voltammetry with respect to pure Pt/C. PtMnCu/C, PtMnCuFe/C and PtMnMoCu/C were found to be the best catalysts for ORR. In order to gain a better understanding of the pathways of ORR, Pt/C, PtMnCu/C, PtMnCuFe/C and PtMnMoCu/C were further studied using a Rotating Disk Electrode (RDE) and Rotating Ring Disk Electrode (RRDE). Tafel plots and Koutecky–Levich analysis of the data revealed that the activity towards the ORR is better with PtMnMoCu/C followed by PtMnCuFe/C and PtMnCu/C. The estimated average number of the electrons transferred during the ORR process was found to be around 4e−. The average percentage of the generated H2O2 reached as high as ∼7.5% with PtMnMoCu/C. All these data point to the fact that the pathways of ORR which produce H2O2 and H2O as final products took place. As a final comparison for this series of catalysts, this study also gives a better selection of the catalysts that may preferably be used at the anode for ethanol oxidation or at the cathode for ORR to yield fuel cells with substantial output voltages.

► Binary alloy PtMn/C is evaluated towards ORR. ► Ternary PtMnX/C (X = Fe, Co, Ni, Cu, Mo and, Sn) alloys were evaluated towards ORR. ► Quaternary PtMnCuX/C (X = Fe, Co, Ni, and Sn) alloys were evaluated towards ORR. ► Quaternary PtMnMoX/C (X = Fe, Co, Ni, Cu and Sn) alloys were evaluated towards ORR. ► PtMnCu/C, PtMnCuFe/C and PtMnMoCu/C were found to be the best catalysts for ORR.