Polythiophene, Polypyrrole and Carbon Nanotube-Based Catalyst for Alkaline Membrane Fuel Cell Cathode
Authors: Mooste Marek , Sokka Andri , Marandi Margus , Käärik Maike , Kozlova Jekaterina , Kikas Arvo , Kisand Vambola , Treshchalov Alexey , Tamm Aile , Leis Jaan , Holdcroft Steven , Tammeveski Kaido 
Published: November 2022

The transformation from hydrocarbons to a cleaner and sustainable H2 economy is considered a favorable approach to meet the increasing energy demand. Among different H2 technologies, fuel cell technology is a viable option for environmentally clean energy conversion (1). Anion-exchange membrane fuel cell (AEMFC) is one of the suitable candidates to meet this demand as they could be more cost-effective than their widely used acidic counterpart, proton-exchange membrane fuel cell. For providing an affordable AEMFC, the non-precious metal catalyst (NPMC) for oxygen reduction reaction (ORR) at the cathode is needed (2).

Co-doping (e.g. with N, S and Fe) of the nanocarbon material has been found to be more beneficial for the preparation of highly active ORR electrocatalysts compared to the application of just one dopant atom (e.g. N) (3). Therefore, we have prepared the polypyrrole (PPy), polythiophene (TPh), and multi-walled carbon nanotubes (MWCNT) based composite material that has been further pyrolysed and subjected to the acid treatment procedure to prepare the NPMC for the AEMFC cathode. Versatile optimization procedures were performed to finally obtain the nanocarbon material with the high ORR activity (A-PPy/PTh/MWCNT) (4).

According to the scanning electron microscopy images, the composite catalyst exhibited mainly tubular morphology with PPy and PTh wrapped around the MWCNT. The physical characterization of A-PPy/PTh/MWCNT revealed the BET surface area of 379 m2 g−1 and micro-mesoporous tubular structure. The surface composition of the catalyst was found to contain S, C, N, O and Fe, while the latter originates from the FeCl3 polymerization catalyst. The ORR studies with A-PPy/PTh/MWCNT electrocatalyst in 0.1 M KOH showed the ORR half-wave potential of 0.85 V vs. RHE. According to the Koutecky-Levich analysis, the NPMC catalyzed a preferred 4-electron oxygen reduction pathway (4).

A single-cell AEMFC experiment with A-PPy/PTh/MWCNT cathode catalyst showed the maximum power density (P
max) of 284 mW cm−2, while the P
max value of 328 mW cm−2 was recorded for commercial Pt/C in similar AEMFC conditions (Figure 1). The obtained data show that the three-component (PPy, PTh and MWCNT) composite prepared herein is a promising route for the development of AEMFC cathode catalyst (4).

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Figure 1