Aerophilic Co-Embedded N-Doped Carbon Nanotube Arrays as Highly Efficient Cathodes for Aluminum-Air Batteries.

Abstract

Recently, aluminum-air batteries have attracted great interest owing to their high output energy density, low cost, and feasibility to store and transport Al metal. However, the commercial application is still hindered by the lack of a high-performance air cathode, where the oxygen reduction reaction (ORR) happens, requiring fast charge transfer and mass transport at the catalyst-electrolyte-air interface. Herein, we report an aerophilic air cathode featuring both high intrinsic catalytic activity and large three-phase interface to facilitate air transport, which is prepared by growing cobalt-embedded and nitrogen-doped carbon nanotube (CoNCNT) arrays on carbon fiber paper and then modifying surface wettability with polytetrafluoroethylene solution. The optimized air electrode during the ORR shows a high onset potential of 0.95 V and fast current increase of 342.96 mA cm-2 V-1, which is comparable to the commercial 20 wt % Pt/C, and has even better stability under the same conditions. Moreover, the aluminum-air battery with the aerophilic air electrode is superior to the battery with a commercial Pt/C electrode or aerophobic electrode in terms of maximum power density and long discharging durability. Bubble behavior measurement shows that aerobic wettability plays an important role in gas transport, thus controlling ORR efficiency of the air electrode. The concept of the gas-wettable electrode proves to be effective in the enhancement of oxygen reduction kinetics and would be also adapted in other gas-involved electrodes for energy-related applications.