Preparation of N-Containing Shell on Carbon Via Polymer-Coating and Application for Pt Supporting Materials
Authors: Kim Chaerin , Fang Xinying , Fujigaya Tsuyohiko 
Published: December 2024

It is challenging to synthesize Pt nanoparticles supported on carbon materials (Pt/C) that are highly durable, efficient and affordable for use in proton exchange membrane fuel cells (PEMFC). The leading electrocatalysts consist of Pt supported on conductive carbon materials but existing carbon supports are prone to corrosion during repetitive start-stop cycles, leading to performance degradation [1]. Thus, stability of carbon supports used as an electron conductive Pt supporting material is also essential to improve Pt stability since carbon corrosion catalyzed by Pt also takes place at a high potential which triggers the detachment of Pt and subsequent agglomeration. The use of durable carbon supports against the oxidation is crucial to increase the PEMFC durability [2].

To address this challenge, over the past decade we have developed that PEMFC Pt catalyst having poly[2,2'-(pyridine-2,6-diyl)bibenzimidazole-5,5'-diyl](PyPBI)-coated carbon as a carbon support showed excellent durability upon fuel cell accelerated durability test [3].

PyPBI are selected as the N-containing precursor because PBIs having phenyl-linked and pyridyl-linked structures are used to explore the effect of N-content and the Pt metal binding affinity of PBls toward the oxygen reduction reaction (ORR) activity.

In this study, we have developed a strategy to introduce a facile synthesis method for forming N-containing carbon support based on a PyPBI physisorption approach, followed by calcination. The work aimed to identify the influence of the N-containing carbon support on the resulting structure of the Pt electrocatalyst and the direction of the ORR durability.

In previous study, we reported the fabrication of a metal free N-containing carbon around multi-walled carbon nanotubes and single-walled carbon nanotubes by calcination of carbon nanotube coated with metal-coordinated PyPBI [4].

In this study, we applied this method to carbon balck (CB) to fabricate CB wrapped with the N-containing CB (denote N-CB) as a catalyst support with Pt. First, carbon wrapped with PyPBI were prepared according to our previous method [5]. After coordination of the composite with cobalt(Il) in methanol, the obtained complex was calcined at 600 °C for 60 min under N2 to provide the N-CB that cobalt(Il) ions served as the catalyst to promote the formation of the catalytic sites. As synthesized N-CB was subjected to the Pt depositions using H2PtCI6·6H20 and ethylene glycol as a Pt source and reducing agent, respectively, to fabricate Pt/N-CB. All investigated calcination conditions resulted in the formation of carbon structures containing nitrogen atoms. Electronic structure of Pt confirmed by X-ray photon-electron spectroscopy and the amounts of Pt in the catalysts were estimated by thermogravimetric analysis. From the transmission electron microscope, homogeneous dispersion of the Pt nanoparticles for Pt/N-C was observed. The electrochemical measurements were performed with potentiostat connected in a three-electrode configuration at room temperature using a Pt wire and an Ag/AgCl as the counter and reference electrodes, respectively. All rotating disk electrode measurements were conducted in 0.1 M HCIO4 solution. We demonstrate here that, the N-C electrocatalyst with Pt exhibits comparable ORR catalytic activity to commercial Pt/C counterpart.

References

[1] Mittermeier,T.,Weiß,A., Hasch,F., Hubner,G., Hubert, A.&Gasteiger, J. Electrochem. Soc, 164 (2) F127-F137 (2017) [2] Sharma,S.& Pollet,B., J. Power Sources. 208, 96–119208 (2012) [3] Fujigaya, T. & Nakashima, Adv. Mater. 25, 1666–1681 (2013) [4] Fujigaya, T., Okamoto, M. & Nakashima, N, Carbon. 47, 3227–3232 (2009) [5] Fujigaya, T., Morita, J. & Nakashima, N., ChemCatChem. 6, 3169 – 3173 (2014)