Exploring efficient and inexpensive materials for supercapacitors has become a research highlight. In this work, coral-like CoFeS2 nanomaterials were synthesized by an organic solvothermal method and applied to supercapacitors. Due to their large specific surface area and unique coral structure, the CoFeS2 electrode materials exhibited high specific capacity (1457.1 F g−1 at 2 A g−1) and rate performance in a 2M KOH aqueous electrolyte. An asymmetric CoFeS2‖AC supercapacitor delivers a high energy density of 66.4 W h kg−1 at a power density of 790 W kg−1, and the retention rate of specific capacitance is 97.6% after 10 000 cycles at a current density of 10 A g−1, showing good cycling stability. The electrode material of CoFeS2 was assembled into a button battery that can light up an LED or turn on a motor fan. In order to evaluate the feasibility of wearable flexible asymmetric energy storage devices, flexible all-solid-state asymmetric supercapacitors were investigated, which showed a high energy density of 47.2 W h kg−1 at a power density of 525 W kg−1, and the retention rate of specific capacitance was 87.8% after 8000 cycles at a current density of 5 A g−1. This study provides the possibility of applying them in future practical applications, and the synthesis strategy can be extended to synthesize other transition metal sulfide materials with excellent supercapacitor performance.
Jingjing Cai,Huijun Liu,Yulin Luo,Yuqing Xiong,Lizhu Zhang,Sheng Wang,Kang Xiao,Zhao-Qing Liu
Bimetallic sulfides, integrating the merits of individual components, are ideal structures for efficient electrocatalysis. However, for bimetallic sulfides including metal sulfide heterojunctions (MSH) and single-phase bimetallic sulfides (SBS), it is still unclear about which one has better catalytic activity toward reversible oxygen catalysis and its difference on catalytic mechanism. In this work, we demonstrate a bimetallic sulfide electrocatalyst that could transform from metal sulfide heterojunction (CoS/FeS) to single-phase bimetallic sulfide (CoFeS 2 ) through a facile temperature control strategy. The single-phase bimetallic sulfide (CoFeS 2 ) affords high intrinsic activity, fast reaction kinetics and superior durability toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Density functional theory (DFT) simulations reveal that the (CoFeS 2 ) has homogeneous electron distribution of the CoFeS 2 structure, improves the central energy level of d band, and optimizes the O* and OOH* intermediate and efficiently reduces the energy barrier of the reaction rate-determining step (RDS). The assembled rechargeable zinc-air battery is more stable than the Pt/C and IrO 2 assemblies due to the excellent electrocatalytic activity and stability of CoFeS 2 /NC, suggesting that it has potential for use in practical applications.
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