No abstract

The construction of advanced electrode materials with well-connected channels and a satisfactory specific surface area for energy storage techniques, such as supercapacitors, is promising but still challenging. Herein, applying the copper Prussian blue analogue (CuFe-PBA) as the precursor, a polygonal prism-like CuS was synthesized through a grinding method at ambient temperature. The reaction between CuFe-PBA and Na2S led to the substitution of S2– for [Fe­(CN)6]3–, and then, CuS was obtained. Benefitting from the porous precursor, the increased electrochemically active surface area enabled CuS to fully expose the electrochemically active sites and facilitated the effective contact between them and the electrolyte. Moreover, the energy storage mechanism was investigated based on ex situ X-ray photoelectron spectroscopy. The results demonstrated that both the copper and sulfur in CuS are electrochemically active sites, contributing to the distinguished specific capacitance. When used as a negative electrode, the as-fabricated CuS showed the excellent specific capacitance of 1850 F g–1 at 1 A g–1. Then, a quasi-solid-state asymmetry supercapacitor was assembled with CuS as the negative electrode and CuFe-PBA as the positive electrode, possessing an energy density of 56.01 W h kg–1 at a power density of 250.05 W kg–1. Furthermore, the capacitance retention of the asymmetry supercapacitor after 5000 cycles is 83.3%, showing good cycle stability. This work provides an effective strategy toward the design of CuS negative electrode materials with continuously connected channels and outstanding electrochemical properties for energy storage applications.

Heterostructure construction and heteroatom modification are considered as effective approaches to modulate the electronic structure and boost the energy storage activity of electrode materials. Herein, oxygen-modified CuS/Mn 3 O 4 (O-CuS/Mn 3 O 4 ) heterogeneous nanoflakes with abundant defects are fabricated by solid-state grinding followed by NaBH 4 treatment (NBHT) at room temperature using MnCu Prussian blue analogue (MnCu-PBA) as the precursor. During the NBHT, a portion of the sulfur atoms in CuS is removed, and the remaining sites in the lattice are occupied by oxygen in the water, resulting in an oxygen modification. Experimental results and theoretical calculations confirm that heterojunction, defect, and oxygen modification not only greatly facilitate the adsorption of OH − on the surface of the electrode material but also endow improved electrical conductivity, wettability, specific surface area, and active sites. Benefiting from these advantages, O-CuS/Mn 3 O 4 exhibits an excellent specific capacitance of 1307 F g −1 at 1 A g −1 . Moreover, the solid-state asymmetric supercapacitor with O-CuS/Mn 3 O 4 and MnO 2 (O-CuS/Mn 3 O 4 //MnO 2 ) shows an outstanding energy density of 34.4 Wh kg −1 at 800.1 W•kg −1 and cyclic stability with 85.7% capacitance retention after 5000 cycles at 6 A g −1 . Our work highlights the integration of heterojunction and oxygen modification to fabricate and optimize the energy storage electrode materials.

In our work, a Cu9S5/Fe2O3 composite with nanosphere morphology is prepared by an efficient one-pot solvothermal selective sulfurization. The structure investigation confirms that there is uneven charge distribution at the interfaces of Cu9S5 and Fe2O3. Furthermore, the corresponding electrochemical measurements reveal the detailed redox kinetics process about Cu2+/Cu+, Fe3+/Fe2+, and (S2)−/S2–. When the obtained Cu9S5/Fe2O3 composite is used as a negative electrode, it exhibits a high specific capacity (348.2 mA h g–1 at 1 A g–1) with good rate capability. Moreover, a hybrid capacitor (HCP) assembled with Cu9S5/Fe2O3 as negative and Ni–Co hydroxide/Cu­(OH)2/CF as positive electrodes, respectively, shows a high energy density with a corresponding high power density (64.54 W h kg–1 at 757.81 W kg–1) and a high specific capacitance (47 mA h g–1 at 1 A g–1) with a capacity retention of 45.68% (21.5 mA h g–1) even at 20 A g–1 in a solid-state gel electrolyte. Thus, a facial fabricated anode material with outstanding electrochemical properties for HCPs is provided.