Using Metal Cation to Control the Microstructure of Cobalt Oxide in Energy Conversion and Storage Applications

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Abstract
Herein, a facile and efficient synthesis of microstructured Co3O4 for both supercapacitor and water‐splitting applications is reported. Metal cations (Fe3+, Cu2+) serve as structure‐directing agents regulating the structure of Co compounds, which are subsequently annealed to yield Co3O4. Detailed characterizations and density functional theory (DFT) calculations reveal that the in situ Cl‐doping introduces oxygen defects and provides abundant electroactive sites, and narrows the bandgap, which enhances the electron excitation of the as‐formed Co3O4. The as‐prepared Cl‐doped Co3O4 hierarchical nanospheres (Cl‐Co3O4‐h) display a high specific capacitance of 1629 F g−1 at 1 A g−1 as an electrode for supercapacitors, with excellent rate capability and cyclability. The Cl‐Co3O4‐h//activated carbon (AC) asymmetric supercapacitor (ASC) electrode achieves a specific capacitance of 237 F g−1 at 1 A g−1, with an energy density of 74 Wh kg−1 at a power density of 807 W kg−1 and even maintains 47 Wh kg−1 at the higher‐power density of 24.2 kW kg−1. An integrated electrolyzer for water‐splitting with Cl‐Co3O4‐h as both cathode and anode can be driven by Cl‐Co3O4‐h//AC ASC. The electrolyzer provides a high current density of 35 mA cm–2 at a cell voltage of 1.6 V, with good current density retention over 50 h.
Funding Information
  • Imperial College London
  • China Scholarship Council
  • Imperial College London

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