Electrothermally Driven Nucleation Energy Control of Defective Carbon and Nickel–Cobalt Oxide-Based Electrodes

Abstract

Multielement metal/metal oxides/carbon-based support hybrids are promising candidates for high-performance electrodes. However, conventional solid-state synthesis utilizing slow heating-cooling rates is limited by discrepancies in their phase transition temperatures. Herein, we report a rational strategy to control the nucleation energy of defective carbon fibers (DCFs) and Ni-Co-oxide-based electrodes capable of electrochemical activation using electrothermal waves (ETWs). The ETWs, triggered by Joule heating passing through CFs and Ni-Co precursors, induce programmable high-temperature processes via adjustable input powers and durations. The first ETW (∼1500 °C) fabricates the presculpted DCFs, while the second ETW (∼600 °C) directly synthesizes NiCo₂O₄ spinel nanoparticles on the DCFs. Predesigning DCFs through the Gibbs free energy theory enables tunable control of nucleation energy and solution compatibility with Ni-Co precursors, allowing the morphological and compositional design of the optimal NiCo₂O₄@DCFs hybrids. Furthermore, they are electrochemically activated to change the morphologies and oxidation states of Ni-Co to more stable wrinkled structures strongly anchored to carbon supports and Ni-Co cations with low oxidation numbers. The activated NiCo₂O₄@DCFs electrodes exhibit outstanding specific capacitance and long-term cyclic stability (∼1925 F g^-1 and ∼115-123% for 20 000 cycles). The ETWs offer a facile yet precise method to predesign carbon supports and subsequently synthesize hybrid electrodes.