Accelerated Durability Tests for Pt-Nanoclusters Modified Carbide Derived Carbons Catalysts in Acidic Solution
Authors: Vaarmets Kersti , Sepp Silver , Nerut Jaak , Lust Enn 
Published: February 2020

Pt-nanoparticles activated porous carbon composite catalysts are widely used in PEMFC applications. The instability of these catalysts in harsh fuel cell working conditions is the main problem hindering the large-scale application of the fuel cell technology in commercial and energy recuperation systems [1].

Hierarchical microporous-mesoporous carbon supports C(Mo2C) were prepared from molybdenum carbide using high temperature chlorination method at different synthesis temperatures from 600 °C to 1000 °C. The Pt-nanoparticles were deposited onto the carbon support using the NaHB4method [2,3]. The X-ray diffraction, low temperature nitrogen sorption, thermogravimetric analysis (TGA) and high-resolution scanning electron microscopy (HRSEM) methods were used to characterize the catalysts materials. The medium size of the Pt-nanoparticles deposited was 4.5±0.6 nm.

Corrosion of the Pt-C(Mo2C) catalysts were evaluated using an accelerated durability test (ADT) method (in oxygen (99.999%, AGA) saturated 0.5 M H2SO4 aqueous solution, from 0.58 V to 0.98 V vs SHE, at potential scan rate 50 mV s−1) [4]. The oxygen electroreduction reaction kinetics and the value of electrochemically active surface area (ECA) of the catalysts were determined after 10, 100, 1000, 3000, 10 000, 20 000 and 30 000 cycles.

Electrochemical impedance spectra were obtained at 0.9 V vs SHE within ac frequencies from 0.01 to 10 000 Hz to determine the changes of the electrolyte resistance and capacitance values during the ADT. The results show that only 20% decrease in electrode capacitance and 15% increases in series resistance takes place during 30,000 potential cycles.

The values of ECA were estimated in the solution saturated with nitrogen (99.999%, AGA) using the cyclic voltammetry at different potential scan rates from 30 to 1000 mV s−1. The rotating disc electrode method was used to evaluate the oxygen electroreduction kinetics in solution saturated with oxygen at rotation rate 1600 rev min−1 and at potential scan rate 20 mV s−1within the region of potentials from 1.03 V to 0.03 V vs SHE. Based on the cyclic voltammetry and rotating disk electrode data the main decrease in ECA took place during the first 1000 cycles and thereafter the ECA value stabilized. The half wave potential values depend weakly on the number of cycles (up to 30,000) measured.

The content of Pt in the catalyst was determined before and after the ADT using the electrochemical dissolution of platinum from the electrode in 6 M HCl solution. The average weight percentage of Pt in different catalyst materials was 71.8±1.7. The content of Pt in the catalysts before the ADT was in a good agreement with the TGA data.

References

[1] B.C.H. Steele, A. Heinzel, Nature 414 (2001) 345–352.

[2] K. Vaarmets, J. Nerut, E. Härk, E. Lust, Electrochimica Acta 104 (2013) 216–227.

[3] E. Lust, K. Vaarmets, J. Nerut, I. Tallo, P. Valk, S. Sepp, E. Härk, Electrochimica Acta 140 (2014) 294–303.

[4] U.S Department of Energy, Office of Energy Efficiency and Renewable Energy, Rotating Disk-Electrode Aqueous Electrolyte Accelerated Stress Tests for PGM Electrocatalyst/Support Durability Evaluation (2011).

Acknowledgements

This work was supported by Estonian target research project IUT20-13, Personal Research Grant PUT55, Estonian Centre of Excellence Projects No. 2014-2020.4.01.15-0011 and 3.20101.11-0030.