Oxygen Reduction Properties of Bifunctional α-Manganese Oxide Electrocatalysts in Aqueous and Organic Electrolytes

Abstract

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.

Enhanced Oxygen Reduction Reaction Activity with Electrodeposited Ag on Manganese Oxide–Graphene Supported Electrocatalyst

“…Among the numerous non-Pt catalyst candidates toward the ORR, such as other precious metals and their alloys [6,7], metal macrocycles [8,9], N-containing high-area carbon [10][11][12][13][14][15][16][17], and different transition metal oxides, especially manganese oxides intercalated to carbon-based composites demonstrated itself as promising cathode materials for fuel cells [18][19][20][21][22][23][24]. Manganese oxide (MnO x ) is one of the most promising alternatives with considerable catalytic activity toward the ORR with up-and-coming advantages, such as wide natural abundance, low cost, and environmental friendliness [25][26][27][28]. Surface morphology of MnO x -based catalysts is an important influential factor to their electrochemical properties [29].…”

Practical Challenges Associated with Catalyst Development for the Commercialization of Li-air Batteries

“…120) Therefore, there are good grounds for the implementation of carbon-based nanomaterials; e.g., carbon nanotubes and graphene as support materials [114][115][116] to accommodate a larger amount of Li oxide. 117,118) Regarding metal nanoparticles they are good candidates as well because their catalytic properties can be considerably higher than that of bulk metals. However, it has been suggested that when the sizes of catalyst particles are within the nanometer range, specific catalyst activity does not always follow the above rationale.…”

Manganese-cobalt mixed oxide film as a bifunctional catalyst for rechargeable zinc-air batteries

“…Given this background, MnO x is presently being considered as one of the most promising nonprecious metal ORR electrocatalysts in alkaline solutions due to its high stability against corrosion and relatively high catalytic activity [24][25][26]. Additionally, Co-oxides and hydroxides have been widely studied as electrocatalysts for OER [27][28][29].…”