Oxygen Reduction Catalytic Activity of Hollandite-Type Manganese Oxides

Takuya Kenko; Tatsuya Takakuwa; Morihiro Saito; Hideo Daimon; Akimasa Tasaka; Minoru Inaba; Yoshihiro Kadoma; Naoaki Kumagai; Hidenobu Shiroishi; Takeo Hatai; Jun Kuwano

doi:10.4028/www.scientific.net/KEM.566.253

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Oxygen Reduction Catalytic Activity of Hollandite-Type Manganese Oxides

Abstract:

Hollandite-type Mn oxides were synthesized by a co-precipitation (CP) and a hydrothermal (HT) method as the cathode catalysts for anion-exchange membrane fuel cells (AEMFCs), and their oxygen reduction reaction (ORR) activities and AEMFC single cell performances were evaluated. In this study, we prepared two kinds of hollandite oxides K_0.14MnO₂·0.12H₂O(KMO-CP) and K_0.12MnO₂·0.06H₂O(KMO-HT) and their partially Co-substituted ones K_0.11(Mn_0.88 Co_0.12)O₂・0.16H₂O(KMC_0.12-CP) and K_0.11(Mn_0.88Co_0.12)O₂· 0.08H₂O(KMC_0.12-HT), and examined the ORR activities with a rotating ring-disk electrode (RRDE) in 0.1 M KOH at 50°C. All the samples showed high onset potentials of ORR, ca. 0.9 V vs. reversible hydrogen electrode (RHE), and relatively high ORR currents at 0.75 V and high efficiencies for 4-electron reduction (Eff₄) of around 90% were obtained for the HT samples owing to higher crystallinity and higher specific surface area than those of the CP ones. The AEMFC single cells prepared with KMO-HT and KMC_0.12-HT cathode catalysts were operated stably and exhibited the maximum power densities of ca. 49 and 42 mW cm^-2, respectively, which were comparable to that of the single cell using a conventional 50 wt% Ag/C catalyst.