Controlled distribution of both Pt nanoparticles and ionomer in self-supported nanoporous carbon scaffolds significantly enhances oxygen reduction kinetics and stability

Marwa Atwa; Shicheng Xu; Xiaoan Li; Samuel Dull; Zhaoxuan Wang; Haoyang Yu; Rui Tang; Timothy Goh; Yunha Jung; Mehrdad Kiani; Markus Lid; Hirotomo Nishihara; Fritz B. Prinz; Viola Birss

doi:10.1039/D5TA04830C

Controlled distribution of both Pt nanoparticles and ionomer in self-supported nanoporous carbon scaffolds significantly enhances oxygen reduction kinetics and stability

Marwa Atwa,

^abc Shicheng Xu,^c Xiaoan Li,^a Samuel Dull,^d Zhaoxuan Wang,^e Haoyang Yu,^f Rui Tang,^g Timothy Goh,^e Yunha Jung,^e Mehrdad Kiani,^e Markus Lid,^ch Hirotomo Nishihara,

^g Fritz B. Prinz^ceh and Viola Birss

*^a

Author affiliations

* Corresponding authors

^a Department of Chemistry, University of Calgary, 2500 University Dr NW, Calgary, AB, Canada
E-mail: birss@ucalgary.ca

^b Department of Chemistry, Suez Canal University, El Salam District, Ismailia, Egypt

^c Department of Mechanical Engineering, Stanford University, Building 530, 440 Escondido Mall, Stanford, CA, USA

^d Department of Chemical Engineering, Stanford University, 443 Via Ortega, Stanford, CA, USA

^e Department of Material Science and Engineering, Stanford University, 496 Lomita Mall, Stanford, CA, USA

^f NanoFAB Centre, University of Alberta, Edmonton, AB, Canada

^g Advanced Institute for Materials Research (WPI-AIMR)/Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Japan

^h Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology, Høgskoleringen 1, Trondheim, Norway

Abstract

We have developed a family of binder-free, bimodal, ball-and-stick carbon scaffolds (BCS) to overcome the poisoning of Pt nanoparticles (NPs) by Nafion ionomer in polymer exchange membrane (PEM) fuel cell cathodes. The BCS design features sub-micron-sized spheres containing 3D interconnected mesopores (∼12 nm) that house only the Pt NPs. Nafion resides only on the outer sphere surfaces, size-screened out from direct contact with the NPs, as verified by the unique hydrogen adsorption (HUPD) profile observed. Proton transport is facilitated along wet hydrophilic mesopore surfaces at 100% relative humidity (RH), enabled by a rich density of oxygen-functionalities, confirmed by temperature-programmed desorption and the RH dependence of the Pt electrochemically active surface area (ECSA). Notably, an exceptionally high ECSA of Pt NPs (∼100 m² g_Pt⁻¹) is achieved in a membrane-electrode assembly (MEA), even without any Nafion in the cathode. The Pt/BCS catalyst layers exhibit enhanced oxygen reduction reaction (ORR) kinetics, achieving very high activity (0.58 ± 0.1 A mg_Pt⁻¹) and durability in MEAs. These results establish a direct link between ionomer poisoning of Pt and ORR activity while also demonstrating the effectiveness of combining tailored carbon scaffolds and oxygen-rich surfaces to achieve ultra-high electrocatalytic performance.

Journal of Materials Chemistry A

Controlled distribution of both Pt nanoparticles and ionomer in self-supported nanoporous carbon scaffolds significantly enhances oxygen reduction kinetics and stability

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Controlled distribution of both Pt nanoparticles and ionomer in self-supported nanoporous carbon scaffolds significantly enhances oxygen reduction kinetics and stability

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