Structure-dependent electrochemical properties of cobalt (II) carbonate hydroxide nanocrystals in supercapacitors

In this work, we report the structure-dependent electrochemical performance of cobalt carbonate hydroxide (Co₂(OH)₂CO₃) nanocrystals by experimental investigation and theoretical simulation. Different Co₂(OH)₂CO₃ nanostructures including two-dimensional (2D) nanosheets (NSs) and one-dimensional (1D) nanowires (NWs), were synthesized on self-supported carbon cloth substrates by a facile hydrothermal method. Compared to 1D NWs, 2D Co₂(OH)₂CO₃ NSs provided a short ion transfer path, and low electron transfer resistance during the electrochemical reaction. At the current density of 2 mA cm^-2, 2D Co₂(OH)₂CO₃ NSs exhibited a higher area capacitance of 2.15F cm^-2 and better cycling performance (96.2% retention after 10,000 cycles) than that of 1D NWs (1.15F cm^-2 and 90.1% retention). First-principles density functional theory (DFT) calculations revealed that the band gap of the (120) facet in 2D NSs was 0.2 eV, far less than of the (200) facet in 1D NWs (1.04 eV). Electrochemical impedance spectroscopy (EIS) measurements further indicated that the electron transfer and reaction kinetics were more efficient in 2D NSs. This work can provide an important insight in understanding the mechanism of electrochemical energy storage.