In-situ formed hierarchical transition metal oxide nanoarrays with rich antisite defects and oxygen vacancies for high-rate energy storage devices

Developing transition metal oxides (TMOs) with high energy, power, and long cycle lifetime for electric energy storage devices remains a critical challenge to date. Herein, we demonstrate a facile method that enables in-situ transformation of nickel cobalt oxide nanowire arrays (NiCoO NWA) into hierarchical nanowire-nanosheet arrays (ac-NiCoO NWSA) for enhanced energy storage properties. More specifically, the method leads to formation of atomically thin nanosheets (only 2.0 nm) and creates abundant antisite defects and oxygen vacancies. Owing to these merits, the as-prepared ac-NiCoO NWSA electrode exhibits over five-fold higher specific capacity, superior rate capability (up to 100 A/g), and excellent cycling stability of 10,000 cycles at 50 A/g in alkaline electrolyte compared to pristine NiCoO NWA. Density functional theory (DFT) simulations elucidate the electrochemical activity enhancement mechanism of the TMOs. Moreover, our method triggers similar structural reconstruction phenomenon on other TMOs including ZnCo-, CoMn- and ZnNiCo-oxides, proving the universality of the method. Our findings provide a general method towards simultaneously manipulating the micro-morphologies and defects of TMOs for advanced energy storage devices.