The intrinsically sluggish kinetics of the oxygen reduction reaction (ORR) and overuse of expensive and unstable Pt-based catalysts have severely hampered the development of clean energy technologies. Herein, a type of non-noble metal nanozyme as an ORR electrocatalyst, with Fe–Cu dual atomic sites embedded in three-dimensional porous N-doped carbon (FeCu-DA/NC), is fabricated by mimicking both the constituents of active centers and enzymatic microenvironment of Cytochrome c oxidase (CcO). The atomically dispersed Fe–Cu single atom sites are clearly identified by direct aberration-corrected transmission electron microscopy imaging, systematic X-ray absorption fine structure (XAFS) analyses, and density functional theory (DFT) calculations. FeCu-DA/NC exhibits a superior ORR activity, with about 30 mV more positive half-wave potential (E_1/2) than that of commercial Pt/C catalysts in a base, and moreover with only an E_1/2 gap of 20 mV to Pt/C in an acid. Importantly, FeCu-DA/NC displays an excellent durability under both acidic and basic conditions, which is much superior to that of Pt/C. DFT calculations further demonstrate that the enhanced performance can be attributed to the unique synergistic effect between Cu and Fe single atoms in which Cu–N₄ serves as the electron donor to increase the electron density of the active centers of Fe–N₄ and thus to facilitate O₂ activation.

The demand for high rate energy storage systems is continuously increasing driven by portable electronics, hybrid/electric vehicles and the need for balancing the smart grid. Accordingly, Nb₂O₅ based materials have gained great attention because of their fast cation intercalation faradaic charge storage that endows them with high rate energy storage performance. In this review, we describe the crystalline features of the five main phases of Nb₂O₅ and analyze their specific electrochemical characteristics with an emphasis on the intrinsic ion intercalation pseudocapacitive behavior of T-Nb₂O₅. The charge storage mechanisms, electrochemical performance and state-of-the-art characterization techniques for Nb₂O₅ anodes are summarized. Next, we review recent progress in developing various types of Nb₂O₅ based fast charging electrode materials, including Nb₂O₅ based mixed metal oxides and composites. Finally, we highlight the major challenges for Nb₂O₅ based materials in the realm of high rate rechargeable energy storage and provide perspectives for future research.