A highly efficient multidirectional N-doped porous carbon network with plenty of graphitic N-species has been explored as cathode catalysts in fuel cells.
In the bottom-up synthesis strategy performed in this study, the Co-catalyzed pyrolysis of chelate-complex and activated carbon black at high temperatures triggers the graphitization reaction which introduces Co particles in the N-doped graphitic carbon matrix and immobilizes N-modified active sites for the oxygen reduction reaction (ORR) on the carbon surface. In this study, the Co particles encapsulated within the N-doped graphitic carbon shell diffuse up to the Pt surface under the polymer protective layer and forms a chemically ordered face-centered tetragonal (fct) Pt-Co catalyst PtCo/CCCS catalyst as evidenced by structural and compositional studies. The fct-structured PtCo/CCCS at low-Pt loading (0.1 mg cm) shows 6% higher power density than that of the state-of-the-art commercial Pt/C catalyst. After the MEA durability test of 30 000 potential cycles, the performance loss of the catalyst is negligible. The electrochemical surface area loss is less than 40%, while that of commercial Pt/C is nearly 80%. After the accelerated stress test, the uniform catalyst distribution is retained and the mean particle size increases approximate 1 nm. The results obtained in this study indicated that highly stable compositional and structural properties of chemically ordered PtCo/CCCS catalyst contribute to its exceptional catalyst durability.
Carbon composite catalyst (CCC) and activated carbon composite catalyst (A-CCC), both containing active catalytic sites for oxygen reduction reaction (ORR), were synthesized and used as supports to develop hybrid cathode catalysts (HCCs). HCCs are a combination of CCC or A-CCC supports and Pt or Co-doped Pt catalysts. Uniform Pt deposition on these supports was accomplished through surface modification and modified polyol processes. The Co-doped Pt was synthesized at 800°C in the presence of polyaniline protective coating. The HCCs, namely Pt/A-CCC, Co-doped Pt/CCC, and L-Co-doped Pt/CCC catalysts showed peak power densities of 944, 857, and 1050 mW cm−2, respectively, which are much higher than the commercial Pt/C (746 mW cm−2). Furthermore, the Pt/C showed very high power density loss (63%) when compared to HCCs (16–26% loss) after 30,000 potential cycles (0.6–1.0 V). The Pt/A-CCC catalyst showed excellent support stability when subjected to potential holding at 1.2 V for 400 h (27 mV loss at 800 mA cm−2) and 5,000 potential cycles between 1.0 and 1.5 V (25 mV loss at 1500 mA cm−2) which are less than that of 2017 US DOE targets (≤30 mV loss). The durability studies indicated that the HCCs are promising cathode catalysts for transportation applications.
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