As the demand for electric vehicles, grid energy storage, and portable devices continues to grow, there is an increasing need for low-cost and efficient energy storage systems. Electrochemical energy conversion and storage technologies, such as fuel cells, water splitting, supercapacitors, and ion batteries, are at the forefront of renewable and green energy solutions. Supercapacitors stand out among various energy storage devices for their high-power density, fast charging capabilities, and long cycle lifespan. Designing high-specific capacitance materials with excellent rate performance remains a critical challenge in the supercapacitor field. Transition metal oxides with multiple valence states are highly regarded for enhancing pseudo-capacitance through multi-step redox reactions. Co3O4 has attracted attention because of its high theoretical specific capacitance (3560 F/g), excellent reversibility, and low cost. Nevertheless, the inherent poor intrinsic conductivity of transition metal oxides and the nano-limited domain effect severely limit the full utilization of the theoretical specific capacitance. The controllable modulation of morphological structures has been a hot research topic. Realizing the activity of the reaction sites on the structure of the specific surface area is the key that needs to be solved urgently. Additionally, various preparation methods can produce Co3O4 nanostructures with different morphologies and sizes or adjust the ratio of high-valence to low-valence cobalt ions to regulate oxygen vacancies, thereby optimizing charge storage and ion transfer rates 

    Dealloying selectively dissolves one or more components from the original material. During the dealloying process, as specific elements dissolve, the remaining components migrate along the metal-medium interface and reorganize. Dealloying techniques include but are not limited to chemical dealloying, electrochemical dealloying, liquid metal dealloying, solid-state dealloying, and vapour-phase dealloying. In the dealloying process, designing suitable dealloying precursors is one of the critical steps, as the choice of precursor directly affects the final microstructure, chemical composition and electrochemical performance of the product. Ideal precursors should have uniform single phases and a significant electrochemical potential difference between their components. Currently, precursors for dealloying are primarily obtained through methods requiring harsh preparation conditions and high energy consumption, involving expensive costs, such as arc melting or induction melting. 

    In this study, a rapid TE method was successfully employed to synthesize porous CoAl IMC precursors for dealloying, and the impact of solid diffusion on the intermediate phases was investigated. A one-step synthesis method combining chemical and electrochemical dealloying techniques was developed to fabricate Co3O4(OV) self-supported materials featuring rod-like, nanoflower, and honeycomb nanostructures that were synthesized in one step. The as-synthesized samples can be directly used as electrode materials for supercapacitors without relying on binders and conductive agents to enhance mechanical stability and conductivity. Electrochemical testing revealed that the nanoflower-structured Co3O4(OV) exhibited exceptional pseudocapacitive performance at high current densities, including high specific capacitance and excellent cycle stability. Moreover, the efficient charge storage capacity is primarily attributed to the synergistic effects of oxygen vacancies and high specific surface area. Oxygen vacancies drastically shorten the band gap structure of the material, accelerate the electrochemical response rate, and enhance the reactivity of the reactive sites, thus exhibiting high energy storage properties. The research results provide new insights and experimental evidence for designing and fabricating structurally-functional integrated porous materials.

Fig. 1. XPS spectra of the samples (a-c) DC-1, (d-f) DC-2 and (g-i) DC-3

Fig. 2. Three-electrodes system measurement (a) GCD curves of DC-1, DC-2 and DC-3 at 10 mA/cm2 current density, (b-d) GCD of each sample under different current densities, (e-g) area capacitance at different current densities of DC-1, DC-2 and DC-3, (h) EIS of DC-1, DC-2 and DC-3, (i) 2000 cycles lifespan test of DC-1, DC-2 and DC-3 at 20 mA/cm2

Fig. 3.  (a, b) Static charge maps of Co3O4 and Co3O4(O_V) on the (311) crystal surface and adsorption energies, (c, e) calculated differential charges map at the adsorbed OH- of Co3O4 and Co3O4(OV), (d, f) plane-averaged electron density differences of the Co3O4 and Co3O4(OV) in the Z-axis direction

Title: Rapid fabrication of morphology-controlled nano-flower Co₃O₄(O_V) from CoAl intermetallic via thermal explosion combined with dealloying for self-supported supercapacitor electrodes

Authors: Zhichao Shang¹, Man Zhang¹,  Jingjing Qu, Sanjith Udayakumar, Xintan Bai, Xiaohong Wang, Baojing Zhang**, Jianzhong Wang,  Farshid Pahlevani,  Peizhong Feng* 

Link: https://www.sciencedirect.com/science/article/pii/S0925838824034364

DOI: https://doi.org/10.1016/j.jallcom.2024.176849

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