Highly Conductive Off-Stoichiometric Zirconium Oxide Nanofibers with Controllable Crystalline Structures and Bandgaps and Improved Electrochemical Activities

The structural and morphological control of durable valve metal oxides with bandgaps over 5 eV (e.g., ZrO2) paves the way for the development of bifunctional electrochemical energy devices with both good stabilities and electronic conductivities. Herein, a tailored synthesis of highly conductive off-stoichiometric ZrO2-x nanofiber materials under a controlled reducing atmosphere is reported. The bandgap and corresponding charge conductivity of ZrO2-x are simultaneously tuned (in the range of visible colors (white, brown, and black)) by generating reduced Zr3+ and oxygen vacancies. The morphological and structural evolution of the ZrO2-x nanofibers obtained under different reducing atmospheres are investigated in detail. Electrochemical kinetics in aqueous and nonaqueous media are promoted by employing a darker ZrO2-x nanofiber electrode. The functionalizing valve metal oxides with a facile charge transfer inspire an advanced design for future electrochemical and electronic devices.