Post-synthesis isomorphous substitution of layered Co-Mn hydroxide nanocones with graphene oxide as high-performance supercapacitor electrodes.

Layered metal hydroxides are promising materials for electrochemical energy conversion and storage. Generally, compared with layered monometallic hydroxides, layered bimetallic hydroxides have more excellent electrochemical performance due to abundant redox reactions. Unfortunately, layered bimetallic hydroxides cannot be usually achieved through coprecipitation and/or homogeneous precipitation. Herein, we demonstrate that layered Co-Mn hydroxide nanocones (NCs) can be successfully fabricated via post-synthesis isomorphous substitution under mild conditions. In particular, the specific capacity and cycling stability of layered Co-Mn hydroxide NCs are remarkably enhanced in comparison with those of layered Co hydroxide NCs. Furthermore, the resulting layered Co-Mn hydroxide NCs and graphene oxide (GO) composite (GO/Co-Mn NCs) exhibits a high specific capacity of 677 C g-1 at 3 A g-1 and an excellent capacity retention of 95% after 2000 cycles. Asymmetric supercapacitor cells employing GO/Co-Mn NCs as the positive electrode and activated carbon (AC) as the negative electrode can achieve a high specific capacity of 189 C g-1 at 3 A g-1. This method provides a viable protocol for constructing efficient electrodes of layered bimetallic hydroxides for sustainable electrochemical energy storage.