Suppression of Hydrogen Peroxide Formation on Pt Using WO3 as Anode Co-Catalysts
Authors: Hoisang Watcharaporn , Farooq Muhammad , Sugimoto Wataru 
Published: December 2024

Polymer electrolyte fuel cells (PEFCs) are emerging as promising candidates for next-generation energy systems, particularly for hydrogen vehicles and clean energy applications, due to their advanced high-power density production and efficiency. However, the commercialization of PEFCs is hindered by issues related to fuel cell durability, primarily caused by the chemical degradation of proton exchange membranes (PEMs) due to reactive oxygen-related radical attacks, notably generated through the production of hydrogen peroxide (H2O2). Anode catalysts, such as carbon-supported platinum nanoparticles (Pt/C), play a vital role in facilitating the hydrogen oxidation reaction (HOR), which is accompanied by the undesired formation of H2O2 due to oxygen gas (O2) crossover from the cathode. As for the Pt surface, the structure is sensitive to H2O2 production. Hence, minimizing H2O2 generation while maintaining HOR activity by developing anode catalysts is necessary to suppress degradation. Tungsten oxide (WO3) has emerged as an interesting active material due to its stability in acidic solutions and its ability to increase the rate of hydrogen oxidation by facilitating hydrogen spill-over from the Pt surface to WO3 to generate hydrogen tungsten bronze (HxWO3). [1, 2] This process enhances the availability of hydrogen on the Pt surface by effectively transferring hydrogen atoms from Pt to WO3. With more active sites available on the Pt surface, there is a higher likelihood of hydrogen oxidation, reducing the formation of H2O2 as an intermediate product.

This study aims to develop an anode catalyst by incorporating WO3 nanoparticles into the Pt/C to suppress H2O2 production during HOR, particularly in the presence of oxygen. The rotating ring-disk electrode (RRDE) technique was utilized to evaluate catalyst performance and detect H2O2 generation during HOR. HOR activity and H2O2 production rate measurements were conducted in H2-sat. and H2/air-sat. 0.1 M HClO4 electrolyte at different temperatures (25, 40, and 60 ℃). The electrochemical measurements demonstrated that both Pt/C and WO3-Pt/C catalysts exhibited enhanced H2O2 formation rates with increasing temperature. This observation underscores the significance of temperature as a modulator of catalytic performance and suggests the existence of temperature-dependent kinetic mechanisms governing H2O2 generation during HOR. Moreover, the comparative analysis between Pt/C and WO3-Pt/C catalysts reveals distinct temperature-dependent behaviors. While both catalysts exhibit temperature-enhanced H2O2 formation, the WO3-Pt/C catalyst demonstrated significantly reduced H2O2 production at 0 V vs reversible hydrogen electrode (RHE) approximately 40% at 60 ℃ as compared with Pt/C, and it exhibited high HOR mass activity and surface activity across a broad temperature range. This suppression is attributed to the synergistic effect between platinum and tungsten oxide species, which facilitates improved HOR kinetics and H2O2 selectivity.

This study was supported in part by funds for the “R&D of novel anode catalyst” project in the “Collaborative industry-academia-government R&D project for solving common challenges toward dramatically expanded use of fuel cells” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. The authors thank Prof. Hiroyuki Uchida (The University of Yamanashi) for his kind advice.

References:

[1] A.C.C. Tseung, K.Y. Chen, Catal. Today
38, 1997, 439.

[2] J. Shim, C.R. Lee, H.K. Lee, J.S. Lee, E.J. Cairns, J. Power Sources
102, 2001, 172.