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.