Evaluation of Platinum‐Based Catalysts for Methanol Electro‐oxidation in Phosphoric Acid Electrolyte

Abstract

Carbon‐supported catalysts of Pt, Pt/Ru, Pt/Ru/W, and Pt/Ru/Pd were evaluated for the electro‐oxidation of methanol in phosphoric acid at 180°C. These catalysts were characterized using cyclic voltammetry and x‐ray diffraction. Addition of Ru to a 0.5 mg/cm2 Pt catalyst (1:1 atomic ratio) caused a large reduction in polarization. The open‐circuit voltage was reduced by 100 mV and polarization at 400 mA/cm2 was reduced by 180 mV. A Pt/Ru (5:2) catalyst with the same Pt content lowered the open‐circuit voltage 70 mV. Additions of W to form Pt/Ru/W (1:1:1, atomic ratio) and Pd to form Pt/Ru/Pd (2:2:1), all with the same platinum loading, gave the same performance as Pt/Ru (1:1) without the additions. All of the catalysts showed two Tafel slopes, 140 mV/dec at lower polarizations and 100 to 120 mV/dec at higher polarizations, indicating that the reaction mechanisms are the same for all of the catalysts. Methanol oxidation is greatly enhanced at 180°C in phosphoric acid compared to the lower operating temperatures of a perfluorosulfonic acid electrolyte. The exchange current density for methanol oxidation is higher than that for O2 reduction. Ru metal dissolves from catalysts at high potentials. Hydrogen oxidation in the presence of 1 mole percent carbon monoxide showed carbon monoxide tolerance in the order: Pt/Ru/Pd > Pt/Ru > Pt.

The effect of methanol and ethanol cross-over on the performance of PtRu/C-based anode DAFCs

“…As a typical example, the over-potential of ethanol electro-oxidation is about 0.72 V (versus DHE) in comparison with about 0.56 V (versus DHE) of methanol electro-oxidation at a current density of 100 mA/cm 2 . This is due to the fact that PtRu/C is a well-known effective catalyst for methanol electro-oxidation [23], but not for ethanol electro-oxidation [24]. This is also the reason that there is a more rapid decrease in the DEFC voltage in the activation-controlled region with respect to the corresponding value of DMFC.…”

Kinetics of CH3OH oxidation on PtRu/C studied by impedance and CO stripping voltammetry

“…Binary PtRu/C is a promising anode catalyst for use in the direct-methanol fuel cell (DMFC) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”

Systematic Study of Pt-Ru/C Catalysts Prepared by Chemical Deposition for Direct Methanol Fuel Cells

“…The Debye-Scherrer equation was used to calculate the average crystallite size in all the samples from the XRD diffraction curves [15]. The Pt(111) and Pt(220) peaks are used to calculate the average crystallite sizes indicated in Table 1.…”