We report an ordered Pd3Fe intermetallic catalyst that exhibits significantly enhanced activity and durability for the oxygen reduction reaction under alkaline conditions. Ordered Pd3Fe enables a hybrid Li-air battery to exhibit the best reported full-cell cycling performance (220 cycles, 880 h).

Polymer binders in battery electrodes may be either active or passive. This distinction depends on whether the polymer influences charge or mass transport in the electrode. Although it is desirable to understand how to tailor the macromolecular design of a polymer to play a passive or active role, design rules are still lacking, as is a framework to assess the divergence in such behaviors. Here, we reveal the molecular-level underpinnings that distinguish an active polyelectrolyte binder designed for lithium–sulfur batteries from a passive alternative. The binder, a cationic polyelectrolyte, is shown to both facilitate lithium-ion transport through its reconfigurable network of mobile anions and restrict polysulfide diffusion from mesoporous carbon hosts by anion metathesis, which we show is selective for higher oligomers. These attributes allow cells to be operated for >100 cycles with excellent rate capability using cathodes with areal sulfur loadings up to 8.1 mg cm–2.

Lithium‐air (Li‐air) batteries have become attractive because of their extremely high theoretical energy density. However, conventional Li‐air cells operating with non‐aqueous electrolytes suffer from poor cycle life and low practical energy density due to the clogging of the porous air cathode by insoluble discharge products, contamination of the organic electrolyte and lithium metal anode by moist air, and decomposition of the electrolyte during cycling. These difficulties may be overcome by adopting a cell configuration that consists of a lithium‐metal anode protected from air by a Li+‐ion solid electrolyte and an air electrode in an aqueous catholyte. In this type of configuration, a Li+‐ion conducting “buffer” layer between the lithium‐metal anode and the solid electrolyte is often necessary due to the instability of many solid electrolytes in contact with lithium metal. Based on the type of buffer layer, two different battery configurations are possible: “hybrid” Li‐air batteries and “aqueous” Li‐air batteries. The hybrid and aqueous Li‐air batteries utilize the same battery chemistry and face similar challenges that limit the cell performance. Here, an overview of recent developments in hybrid and aqueous Li‐air batteries is provided and the factors that influence their performance and impede their practical applications, followed by future directions are discussed.

Hybrid Li-air batteries fabricated with mesoporous NiCo 2 O 4 nanoflakes directly grown onto nickel foam and N-doped mesoporous carbon loaded onto a hydrophobic carbon paper, respectively, as the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts are found to exhibit the best reported cycle life.

electrolyte, which can be operated at room temperature, has rarely been reported. [ 11 ] The rechargeability of ZABs requires bifunctional catalytic activity of the air cathode: ORR and OER. The requirements for the active sites and electrochemical environment for ORR and OER are so different that it is very diffi cult to achieve high activity for both reactions within one material. For example, ORR prefers hydrophobic sites, which form a three-phase (solid catalyst, liquid electrolyte, and air) interface. In contrast, OER prefers hydrophilic sites to maximize the contact between the catalyst and the electrolyte. Recently, a "decoupled" design of bifunctional air electrodes has attracted much attention. [ 12 ] By dividing the ORR and OER functions into two different electrodes, which are optimized for ORR and OER respectively, high cell effi ciency as well as long cycle life could be achieved. However, the decoupled design has mainly been pursued with alkaline metal-air batteries, and no such design has been reported for acidic metal-air batteries.We report here AZABs with decoupled air electrodes, which is promising to eliminate the problems of conventional Zn-air batteries. The prototype AZABs are composed of a Zn-metal anode, an alkaline anode electrolyte, a NASICON-type Li-ion solid electrolyte (LTAP), an acidic phosphate buffer catholyte, and a decoupled IrO 2 thin fi lms grown onto a Ti mesh (IrO 2 @Ti) for OER and a commercial Pt/C catalyst on a gas diffusion layer (GDL) for ORR. The Li-ion solid electrolyte LTAP separates the alkaline anode electrolyte and the acidic catholyte and provides ionic channels. LTAP does not serve as a direct Zn 2+ -ion conductor, but as a Li + -ion "messenger" to achieve the charge balance on both sides of an AZAB. [ 13 ] The decoupled OER electrode is carbon-free and binder-free, ensuring good mechanical integrity in the high-voltage oxidizing environment. The decoupled ORR electrode is isolated during the high-voltage charge process, minimizing the problem of catalyst dissolution and oxidation. [ 14 ] During cell operation, a high discharge voltage close to 2.0 V could be achieved at a low current density. The acidic catholyte also eliminates the persistence problem of CO 2 ingression associated with alkaline electrolytes. In addition, the solid electrolyte provides the possibility of blocking Zn dendrite from reaching the cathode, greatly improving the battery safety. Moreover, although the soluble discharge product zincate will still form on the anode side, the solid electrolyte will keep the zincate in the anode chamber, decreasing the mass transport barrier and facilitating zincate reduction upon charge. The assembled AZABs achieve a high voltaic effi ciency of ≈81% at 0.1 mA cm −2 . The cell could also be cycled for hundreds of hours in the ambient air environment without signifi cant degradation. Figure 1 shows the discharge and charge mechanism of an AZAB based on an alkaline anode electrolyte and an acidic catholyte. During discharge, oxygen (O 2 ) from air diff...

No abstract

Placement of amidoxime functionalities within the pores of microporous polymer membranes yields a new family of selective membranes for aqueous electrochemical cells-which we call AquaPIMs. At high pH, where amidoximes are ionized, AquaPIM membranes feature concomitantly high conductivity and transport selectivity when compared to other membranes, including Nafion. Design rules are laid out, tying membrane architecture and pore chemistry to membrane stability, conductivity, and transport selectivity in aqueous electrolytes over a broad range of pH. These attributes dictate whether it is possible to operate aqueous electrochemical cells without the influence of active-material crossover.

Inexpensive hierarchical oxygen reduction and oxygen evolution reaction (ORR/OER) catalysts offer higher cell efficiency and much longer cycle life than Pt/C + IrO2 bifunctional catalysts in metal–air batteries.