Investigation on High Stable Ordered Ptｍ (M=Fe, Co, Ni, Cu) Catalysts Via
Operando X-Ray Absorption Spectroscopy Analysis
Authors: Pei Chunlin , Gao Yunfei , Kumar Mukesh , Thakur Neha , Watanabe Toshiki , Sato Ryota , Teranishi Toshiharu , Imai Hideto , Sakurai Yoshiharu , Uchimoto Yoshiharu 
Published: December 2024

In the development of society, energy stands as the cornerstone for human survival and progress. Historically, traditional fossil fuels served as the primary energy source; however, the widespread utilization of fossil fuels exacerbates issues like climate change and environmental pollution and necessitates the development of new, clean, and efficient energy alternatives to supplant conventional fossil fuels. Hydrogen, with its high energy density and emission-free properties, emerges as a promising alternative energy carrier, particularly in fuel cell technology. 1 However, the widespread adoption of fuel cells is hindered by challenges, notably the high cost associated with platinum catalysts used in oxygen reduction reactions (ORR). Addressing this challenge requires innovative approaches to enhance catalytic performance while reducing cost concern. 2 This has led to the exploration of alloying Pt with non-noble metals (Fe, Co, Ni, Cu), which improves the ORR activity than benchmark Pt/C and simultaneously solves the high catalyst cost issues. 3 Previous analyses of these alloys show that the significant improvement in ORR activity is due to optimized Pt 5d orbital vacancy, which shortens the Pt-Pt bond distance and weakens the binding of intermediates. The Pt-Pt bond distance has been widely regarded as a crucial factor in analyzing the structure-activity relationship.

This research aimed to explore the relationship between catalytic performance and Pt-Pt bond distance, combining electrochemical performance with the operando X-ray absorption spectroscopy analysis during ORR conditions. In this study, various ordered PtM (M=Fe, Co, Ni, Cu) alloys were synthesized by thermal treatment under NH3 atmosphere using mesoporous carbon supports, which restrict particle growth during thermal treatment. The morphological attributes analyzed by TEM images clearly show that Pt-M alloys is located inside the pores of the mesoporous carbon layer. The detailed electrochemical investigation by Cyclic voltammetry (CV) and Linear sweep voltammetry (LSV), shows three times superior activity than benchmark Pt/C. The Operando HERFD-XAS analysis, conventional EXAFS combined with electrochemical investigations shows a positive correlation between specific activity and the Pt-Pt bond, which indicated that contracted lattice structure would contribute to less formation of the Pt oxide species and ultimately results in superior ORR activity and durability. Therefore, our results demonstrate the importance of the Pt-Pt bond length in assessing ORR activity and validate that structural changes during operation can be a key enabling factor in predicting catalytic performance and durability.

Acknowledgment

This work is supported by the PEFC and the NEDO FC-Platform commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Reference:

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C. Kim, F. Dionigi, V. Beermann, X. Wang, T. Moeller and P. Strasser, Adv. Mater., 2019, 31, 1805617.

Figure 1