Suppression of H2O2 Formation and Durability of Various H2-Anode Catalysts for Long-Life PEFCs
Authors: Imran Muhammad , Farooq Muhammad , Sugimoto Wataru , Chisaka Mitsuharu , Nagano Waka , Takeguchi Tatsuya , Ozawa Nobuki , Kubo Momoji , Nishino Hanako , Uchida Hiroyuki 
Published: December 2024

Chemical decomposition of polymer electrolyte membranes (PEMs) by a radical attack is a significant issue affecting long-term durability of PEMs.1 Hydroxyl radicals (·OH) are generated via the reaction of H2O2 with impurities (such as Fe2+ and Cu2+ ions) present in the PEM. Hydrogen peroxide is produced when oxygen (crossover through PEM from the cathode) reacts with adsorbed hydrogen (Had) at Pt nanoparticles (NPs) supported on carbon (Pt/C) used for the hydrogen oxidation reaction (HOR) at the anode.2

In the present work, we examined the H2O2 production rates j(H2O2) and HOR activities on various anode catalysts developed in the NEDO (New Energy and Industrial Technology Development Organization of Japan) project. The catalysts examined are PtCo/CHT (PtCo NPs supported on acetylene black, followed by heat-treatment),3 Pt/Ti4O7-C (Pt NPs supported on Magnèli-phase Ti4O7, plus amorphous carbon),4 and commercial Pt/CB (c-Pt/CB, Pt NPs supported on carbon black) with addition of WO3
5 or IrO2 nanosheet.6 The values of j(H2O2), electrochemically active surface area (ECSA), kinetically-controlled mass activity MA
k and specific activity j
k for the HOR on Nafion-coated anode catalysts were measured by use of 0.1 M HClO4 electrolyte solution in a half-cell (channel flow double electrode cell technique) at 80 °C.3 An accelerated stress test (AST) for start/stop cycles7 was also examined.

The initial values of j(H2O2) at E = 0.02 V vs. RHE (practical anode potential for the HOR) and HOR activities on various catalysts are summarized in Table I. All the developed catalysts exhibited an excellent initial property of lower j(H2O2) than that of c-Pt/CB. Among them, the PtCo/CHT catalyst exhibited the lowest j(H2O2), i.e., nearly 1/5 that of c-Pt/CB. It was also found that the value of j
k for the HOR at PtCo/CHT was ca. 1.3 times higher than that at c-Pt/CB. For the case of Ptskin‒PtCo/C, it was clarified that both low j(H2O2) and high j
k for the HOR was ascribed to the weakened adsorption of Had, which might be caused by the modified electronic properties of the Pt-skin surface due to the presence of underlying Co.3, 7 Studies on the change in the adsorption energy of Had at the PtCo/CHT catalyst are under progress.

The Pt/Ti4O7-C catalyst also exhibited lower j(H2O2) together with higher j
k for the HOR than those of c-Pt/CB. The electronic state of Pt was found to be modified by the Ti4O7 support.4 Such a modified electronic state of Pt could contribute to suppress the H2O2 production, similar to the case of Ptskin‒PtCo/C.

It was found that a physical mixture of WO3 NPs or IrO2(ns) with c-Pt/CB also suppressed H2O2 production. The role of WO3 can be a promotion of Had spillover from the Pt surface to form HxWO3, while the j
k for the HOR was not so affected. It is also envisioned that H2O2 production might be suppressed by the addition of IrO2 nanosheets and WO3 via formation of a complex with H2O2 due to their interaction, similar to the case of silica NPs.8

The lowest j(H2O2) on PtCo/CHT was maintained during the AST (potential sweep cycles between 0.02 V and 1.0 V) of 6000 cycles. The analysis of degradation behavior of every catalyst is under progress, taking all properties (j(H2O2), MA
k, j
k, and ECSA) into account.

This work was supported by funds for the “R&D of novel anode catalyst project” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

References

B. LaConti, M. Hamdan and R. C. McDonald, Handbook of Fuel Cells, ed. W. Vielstich, A. Lamm, and H. Gasteiger (Wiley, Chichester, England), 3
, p. 647 (2003).

Zatoń, J. Rozière, and D. J. Jones, Sustain. Energy Fuels, 1, 409 (2017).

Shi, D. A. Tryk, T. Iwataki, H. Yano, M. Uchida, A. Iiyama and H. Uchida, J. Mater. Chem.
A, 8, 1091 (2020).

Chisaka, W. Nagano, B. Delgertsetseg, and T. Takeguchi, Chem. Commun., 57, 12772 (2021).

P-Yves Olu, T. Ohnishi, Y. Ayato, D. Mochizuki, W. Sugimoto, Commun., 71, 69 (2016).

Takimoto, K. Fukuda, S. Miyasaka, T. Ishida, Y. Ayato, D. Mochizuki, W. Shimizu, and W. Sugimoto, Electrocatalysis, 8, 144 (2017).

Shi, H. Yano, D. A. Tryk, A. Iiyama, and H. Uchida, ACS Catal., 7, 267 (2017).

M. R. Berber, M. Imran, H. Nishino, and H. Uchida, ACS Appl. Mater. Interfaces, 15, 13219 (2023).

Figure 1