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Abstract
Tantalum (Ta) modified TiO2 was synthesized using a sol-gel procedure and evaluated for use as an electrocatalyst support. Platinum nanoparticles were deposited on this support via the incipient wetness method. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray energy dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS) and nitrogen desorption were used to investigate their microstructure. Of the formulations studied, Ta0.3Ti0.7O2 possessed an adequate powder electronic conductivity of 0.2 S/cm. The capacitance of this Ta0.3Ti0.7O2 support changed by only 12% whereas the pseudocapacitance of a carbon benchmark changed by over 100% over 10,000 support stability test cycles (support stability test protocol: 1.0-1.5 V vs. RHE at a scan rate of 500 mV/s in a 0.1 M HClO4 electrolyte at 25°C) under identical test conditions. The stability of 20% Pt/Ta0.3Ti0.7O2, 20% Pt/C, and 46% Pt/C (commercial, TKK) catalysts were evaluated by monitoring the evolution of the electrochemical surface area (ECSA) under load cycling (load cycling protocol: 0.6-0.95 V vs. RHE with a dwell time of 3 s at either potentials in a 0.1 M HClO4 electrolyte at 25°C). The loss in ECSA in 20% Pt/Ta0.3Ti0.7O2 was found to be 35% compared to 44-47% for 20% Pt/C and 46% Pt/C over 10,000 load cycles. 20% Pt/Ta0.3Ti0.7O2 yielded the following performance-related metrics: the ECSA of this electrocatalyst was 41 m2/g, the mass activity and area-specific activities for the oxygen reduction reaction (ORR) determined at 0.9 V vs. RHE in a 0.1 M HClO4 electrolyte at 25°C were 62 mA/mgPt and 151 μA/cm2Pt, respectively. Koutecky-Levich analysis carried out to evaluate ORR kinetics suggested that all 3 catalysts (20% Pt/Ta0.3Ti0.7O2, 20% Pt/C and 46% Pt/C) demonstrated similar ORR mechanisms. We propose that Ta0.3Ti0.7O2 shows outstanding promise as a corrosion-resistant alternative to carbon as an electrocatalyst support in polymer electrolyte fuel cells.
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