Metal–air batteries: from oxygen reduction electrochemistry to cathode catalysts

Abstract

Because of the remarkably high theoretical energy output, metal-air batteries represent one class of promising power sources for applications in next-generation electronics, electrified transportation and energy storage of smart grids. The most prominent feature of a metal-air battery is the combination of a metal anode with high energy density and an air electrode with open structure to draw cathode active materials (i.e., oxygen) from air. In this critical review, we present the fundamentals and recent advances related to the fields of metal-air batteries, with a focus on the electrochemistry and materials chemistry of air electrodes. The battery electrochemistry and catalytic mechanism of oxygen reduction reactions are discussed on the basis of aqueous and organic electrolytes. Four groups of extensively studied catalysts for the cathode oxygen reduction/evolution are selectively surveyed from materials chemistry to electrode properties and battery application: Pt and Pt-based alloys (e.g., PtAu nanoparticles), carbonaceous materials (e.g., graphene nanosheets), transition-metal oxides (e.g., Mn-based spinels and perovskites), and inorganic-organic composites (e.g., metal macrocycle derivatives). The design and optimization of air-electrode structure are also outlined. Furthermore, remarks on the challenges and perspectives of research directions are proposed for further development of metal-air batteries (219 references).

Biocompatible Ionic Liquid–Biopolymer Electrolyte-Enabled Thin and Compact Magnesium–Air Batteries

“…Magnesium or its alloys present an appealing anode material due to its elemental abundance, overall benign nature, high theoretical specific charge capacity (2.2 Ah g -1 ) and a considerably negative electrode potential (-2.3 V versus SHE). 14,15 The rapid corrosion (degradation) of pure magnesium in aqueous solution limits use as an anode. The use of Mg alloy, AZ31 can deliver much better discharge characteristics due to its greatly improved corrosion resistance after the incorporation of Al and Zn elements.…”

Hierarchical urchin-shaped α-MnO2 on graphene-coated carbon microfibers: a binder-free electrode for rechargeable aqueous Na–air battery

“…1,10 The crystal structure of α-MnO 2 consists of 2 × 2 tunnels formed by edge-sharing MnO 6 and corner sharing MnO 6 octahedra. 1 Owing to the tunnel size and the requirement to balance the negative charge, α-MnO 2 can accommodate positive ions in the tunnel cavities, thereby providing high feasibility for bidentate O 2 adsorption sites not only on the surface but also in the bulk material.…”

“…3 Although noble metals such as Pt, Pd, Ru, Au and Ag display good catalytic activity towards the ORR and OER, their low abundance and high cost impede their scalability for practical applications. [4][5][6] In recent years, economically favorable transition metal oxide catalysts (such as MnO 2 , Co 3 O 4 , Fe 3 O 4 and their composites) 1,[6][7][8][9][10] and carbon-based materials (such as carbon black, graphene and carbon nanotubes) 3,[11][12][13] have attracted great attention as electrocatalysts for metal-air batteries. Among the transition metal oxides, MnO 2 has drawn particular attention as an electrocatalyst owing to its low cost, high abundance and excellent ORR and OER catalytic activities in alkaline media.…”

Li‐Ion Batteries and Beyond: Future Design Challenges

“…The overall electrochemical reaction depends on the anode material and the type of electrolyte such as aqueous, non-aqueous, or solid-state type and their combinations. [1,13,[131][132][133] Because metal anodes react excessively with H 2 O, protective layers such as ionically conductive ceramics or glass, e.g. LiSICON or NaSICON type ionic conductors must cover the surface of the metal anode in an aqueous electrolyte.…”