Several different preparation and morphologies of α-manganese oxide catalysts were synthesized, and their physical properties were characterized. These catalysts were also characterized by electrochemical means (RDV and CV) for oxygen reduction in both aqueous and organic electrolytes. The solvent-free preparation yielded catalysts with ideal physical properties: low average oxidation state (3.73) of manganese, small crystallite size (8.1 nm), small particle size (d = 10 nm, l = 30–100 nm), high surface area (144 m2 g–1), and pore volume (0.470 cm3/g). This catalyst displayed the highest activity in both aqueous (i L = 3.66 ± 0.12 mA cm–2, i 0 = 1.0 × 10–5 mA cm–2) and organic electrolytes (i L = 2.25 ± 0.15 mA cm–2, αn = 0.51). Doping the solvent-free preparation with Ni2+ slightly improved its oxygen reduction capabilities in aqueous (i L = 3.78 ± 0.15 mA cm–2, i 0 = 2.3 × 10–5 mA cm–2) and organic electrolytes (i L = 2.43 ± 0.17 mA cm–2, αn = 0.47). A large increase in the ability of the catalysts to decompose hydrogen peroxide was observed (2.7 ± 0.26 vs 0.53 ± 0.03 s–1 g–1), which is a good indicator of enhanced bifunctionality for application in secondary lithium air batteries. Stability tests in the presence of Li2O2 at elevated temperatures (100 °C) indicate a decrease in catalyst crystallinity as exposure time is increased.

Manganese oxides were fabricated by hydrothermal reactions of KMnO4 and MnSO4 solutions. Crystal structures and morphologies of samples were characterized by X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller (BET) measurements, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The combined effects of temperature, additives of H2SO4, and tetrabutylammonium bromide (TBAB) on manganese oxide crystal structures were investigated. The key factors affecting catalytic activity and electrochemical performance of manganese oxides were studied using oxidation of benzyl alcohol and cyclic voltammetry, respectively. The results indicated that pyrolusite (OMS-7) was formed in 0.1 mol·L–1 MnSO4 solution with KMnO4/MnSO4 molar ratios of 7:18 and 8:17 at 120 °C, respectively. A mixture of OMS-7 and cryptomelane (OMS-2) was prepared when the molar ratio increased. Potassium ion plays an important role in the formation of OMS-2. Steric effects arose from complexation reactions of TBAB and MnSO4 solutions and facilitated the formation of OMS-2. K-OMS-2 and H-K-OMS-2 were formed by adding 0.1 mol·L–1 TBAB and 0.2 mol·L–1 H2SO4 to 0.1 mol·L–1 MnSO4 solution with a KMnO4/MnSO4 molar ratio of 11:14 at 120 °C, respectively. The catalytic oxidation activity was found to follow this trend: H-K-OMS-2 > K-OMS-2 > OMS-7 likely because of the larger amount of acid sites in H-K-OMS-2 . However, the exchangeable active oxygen and specific surface area had a greater impact on the electrochemical performance of manganese oxides. The electrocatalytic activity of synthesized manganese oxides for oxygen reduction increased in the order: OMS-7 < H-K-OMS-2 < K-OMS-2. Supercapacitor performance was compared, and the capacitance also increased in the sequence: OMS-7 < H-K-OMS-2 < K-OMS-2.

Metal flux synthesis in a low-melting eutectic mixture of lanthanum and nickel has produced a family of complex intermetallic carbide phases. La(21)Fe(8)M(7)C(12) (M = Sn, Bi, Sb, Te, Ge) has a new cubic structure featuring tetrahedra of iron atoms capped with carbon on each edge. These tetrahedra are surrounded by a La/M framework and are therefore isolated from each other. The antiferromagnetic coupling of the iron atoms is frustrated by their ideal tetrahedral arrangement; this is evidenced by magnetic susceptibility measurements on the La(21)Fe(8)Sn(7)C(12) analogue. Deviations from Curie-Weiss behavior begin at 100 K; variation in field-cooled vs zero-field-cooled behavior is seen at 5 K indicative of magnetic ordering. AC susceptibility data indicate that the temperature of this transition is frequency-dependent, behavior characteristic of spin glass systems.

Crystals of La 21-δ Mn 8 M 7 C 12 (M = main group elements Ge/Al, Sn, Sb, Te, Bi) were synthesized in La/Ni eutectic flux. The structure features tetrahedral manganese clusters edge-capped by carbon atoms, Mn 4 C 6 , embedded into a nonmagnetic La/M network. The structures were determined from single-crystal X-ray diffraction (La 21 Mn 8 -Ge 6.2 Al 0.8 C 12 , Fm3m; a = 16.2259(3) Å; Z = 4; R 1 = 0.022). While most of the La 21 Mn 8 M 7 C 12 analogues are completely ordered, the M = Te compound features partial occupancy of one of the La sites, and the M = Ge analogue exhibits mixed Ge/Al occupancy on one of the M sites. La 21-δ Mn 8 M 7 C 12 with M = Sn, Sb, Te, Bi are paramagnets, but the susceptibility of La 21 Mn 8 Ge 6.2 Al 0.8 C 12 exhibits ZFC-FC divergence at T 1 ≈ 6 K and an additional feature at T 2 ≈ 3 K. Such behavior is indicative of frustration of antiferromagnetically coupled manganese magnetic moments within the Mn 4 tetrahedra. AC susceptibility measurements confirm the presence of two cusps at T 1 and T 2 ; however, no frequency dependence of cusp maxima was found. This differentiates La 21 Mn 8 Ge 6.2 Al 0.8 C 12 from the Fe analogue, La 21 Fe 8 Sn 7 C 12 , where frequency dependence indicates spin-glass behavior. Electronic calculations on La 21-δ Mn 8 M 7 C 12 confirm that the vacancy on one of the La sites in the La 20 Mn 8 Te 7 C 12 analogue stabilizes the phase by shifting the Fermi level to a pseudogap in the density of states. 57 Fe and 119 Sn M€ ossbauer spectroscopy of spin-glass compound La 21 Fe 8 Sn 7 C 12 and paramagnetic La 21 Mn 8 Sn 7 C 12 supports the presence of spin glass behavior in the Fe analogue and not in the Mn analogue.

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