The layered manganese dioxide (δ-type MnO2) film electrodeposited on carbon cloth (CC) functioned as a cathode in aqueous zinc-ion batteries. Battery performance was notably improved by doping MnO2 layers with cobalt and the CC surface with nitrogen. The δ-MnO2 interlayer accommodated Zn2+ ions in the as-deposited state and thus could act as an intercalation host during the discharging process. The Co-doped MnO2 film on the nitrogen-doped CC delivered a discharge capacity as high as 280 mA h g–1 at a specific current of 1.2 A g–1 for 600 charge/discharge cycles, while the discharge capacity did not exceed 30 mA h g–1 even at a specific current as high as 10.5 A g–1. These values are superior to those observed in the absence of doping, demonstrating the positive impact of Co- and N-doping into the MnO2 layers and the CC substrate on the cycling stability and rate capability.

We fabricated a thin film of layered MnO2 whose interlayer space was occupied by hydrated Ni2+ and Cu2+ ions. The process consisted of electrodeposition of layered MnO2 intercalated with tetrabutylammonium cations (TBA+) by anodic oxidation of aqueous Mn2+ ions in the presence of TBA+, followed by ion exchange of the initially incorporated bulkier TBA+ with the denser transition metals in solution. The resulting layered MnO2 co-intercalated with Ni2+ and Cu2+ ions (NiCu/MnO2) catalyzed the ammonia oxidation reaction (AOR) in an alkaline electrolyte with a much lower overpotential than its Ni2+- and Cu2+-intercalated single-cation counterparts. Surprisingly, the NiCu/MnO2 electrode achieved a faradic efficiency as high as nearly 100% (97.4%) for nitrogen evolution at a constant potential of +0.6 V vs Hg/HgO. This can be ascribed to the occurrence of the AOR in the potential region where water is stable and dimerization of the partially dehydrogenated ammonia species is preferred, thereby forming an N–N bond, rather than to be further oxidized into NO x species.