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Binary metal sulfides have been considered as promising electrode materials for supercapacitors with excellent performance. Herein, we demonstrate a simple two-step hydrothermal method to grow the interconnected Co9S8/NiCo2S4 nanosheet arrays (denoted as Ni-Co sulfide NSAs) on nickel foam with robust adhesion for high performance supercapacitors. Remarkably, the as-synthesized Ni-Co sulfide binder-free electrode exhibits an ultrahigh areal capacitance of 7.4 F cm−2 for supercapacitors, which is about five times higher than 1.5 F cm−2 of the Ni-Co oxide electrode at the current density of 5 mA cm−2. The Ni-Co sulfide binder-free electrode also exhibits a good cycling stability, which still displays a high capacitance retention of 90.7% after 2000 cycles even at a high current density of 40 mA cm−2. The good electrochemical performance could be ascribed to the high electrical conductivity and porous nanosheet structure of the Ni-Co sulfide nanosheets, as well as the robust adhesion with the current collector. These electrochemical results suggest that such Ni-Co sulfide NSA binder-free electrode might hold some potential for electrochemical energy applications.

Graphene and metal oxide nanocomposites have been demonstrated as promising electrode materials for high-performance lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). In this work, ultrafine CoMn2O4 nanoparticles uniformly anchored on reduced graphene oxide (rGO) sheets have been synthesized through a facile and effective two-step strategy. Owing to the rational combination of merits from both ternary CoMn2O4 and graphene sheets, the as-synthesized rGO/CoMn2O4 nanocomposite exhibits remarkable Li-battery performance with high reversible capacity, good cycling stability and excellent rate performance. Remarkably, the rGO/CoMn2O4 nanocomposite displays high reversible capacities of 1102.1 and 811.1 mA h g−1 at the current densities of 200 and 500 mA g−1 after 60 cycles, respectively. The discharge capacities of the rGO/CoMn2O4 nanocomposite are as high as 851.1, 835.3, 795.2, 755.9, 694.0, and 563.6 mA h g−1 at the current densities of 100, 200, 500, 1000, 2000 and 5000 mA g−1, respectively. These electrochemical results suggest the rGO/CoMn2O4 nanocomposite could be a promising anode material for high-performance LIBs. Besides, the rGO/CoMn2O4 nanocomposite also exhibits comparably promising electrochemical performance as an anode material for SIBs. Our study also highlights the importance of rational synthesis of graphene-based nanocomposite materials for high-performance LIBs and SIBs.

Construction of metal oxide/sulfide and carbon-based material nanocomposites is an effective strategy to obtain high-performance electrode materials for supercapacitors. In the present work, graphene oxide nanofibers (GONFs) are selected as the support materials, and the nanocomposite of reduced graphene oxide nanofiber and cobalt sulfide (rGONF/CoS2) is synthesized via a simple and facile method. As an electrode material for pseudocapacitors, the rGONF/CoS2 nanocomposite exhibits a high specific capacitance of 635.8 F g-1 at a current density of 1 A g-1 measured in 6 M KOH electrolyte, which is much higher than that of bare cobalt sulfide. Furthermore, the rGONF/CoS2 nanocomposite has also shown excellent cycling performance with 95.4% capacitance retention over 2000 cycles. In addition, the assembled asymmetric supercapacitor (ASC) device using rGONF/CoS2 nanocomposite as cathode material and activated carbon (AC) as anode material can work at a high operating voltage of 1.65 V and show a maximum energy density of 13.8 W h kg−1 at a power density of 824.6 W kg−1.

Defect-mediated engineering has been proven as a novel and effective strategy to integrate two individual materials into a nanocomposite to boost the performance. In the present work, nanocomposite of partially-unzipped stacked-cup carbon nanofibers (PUSCNFs) decorated with platinum nanoparticles (Pt NPs) have been successfully synthesized through the defect-mediated formation method. Owing to the introduction of abundant structural defects during the chemical oxidation process, Pt NPs with an average diameter of 2–3 nm were uniformly anchored on the PUSCNFs without any surfactant involved. As comparison, the Pt NPs grown on the stacked-cup carbon nanofibers (SCNFs) possessed markedly larger nanoparticle size and trended to aggregate. The electrochemical properties of the nanocomposite-modified electrodes for biosensing were examined. Our results showed the Pt-PUSCNFs nanocomposite possessed optimal electrocatalytic activities and biosensing performance for detection of biomolecules, which could be attributed to a synergistic effect between the PUSCNFs and Pt NPs on electron transport and catalytic properties. We anticipate that the PUSCNFs may be a potential support material for construction of nanocomposites with good performance.

In this work, N-doped carbon nanotubes (NCNTS) have been easily unzipped using a chemical oxidation method to obtain porous and multi-defective partially unzipped N-doped carbon nanotubes (PU-NCNTs), which are promising as negative electrode materials for supercapacitors and are also suitable substrate materials for the efficient loading of ultrathin manganese dioxide (MnO 2 ) nanosheets. Herein, the PU-NCNT/MnO 2 composite was synthesized through a simple microwave irradiation method. Moreover, we have fabricated an asymmetric supercapacitor (ASC) using PU-NCNT/MnO 2 composite as cathode, PU-NCNTs as anode and neutral aqueous Na 2 SO 4 as electrolyte. Because of the synergistic effects of the PU-NCNTs electrode and the high capacitance as well as good rate performance of PU-NCNT/MnO 2 composite, the asymmetric cell exhibited good electrochemical performance. The optimized ASC can be worked stably in the voltage window of 0–1.8 V and exhibited a maximum energy density of 14.76 Wh kg −1 at the current density of 1 A g −1 . Additionally, the PU-NCNT/MnO 2 //PU-NCNT ASC exhibited long cycling stability with 80.5% specific capacitance retained after 1000 cycles at a current density of 1 A g −1 . These encouraging results show that PU-NCNT/MnO 2 could be promising materials for commercial use of supercapacitors.

Transition metal oxides (TMOs) with high capacity have been extensively studied as promising anode candidates for lithium-ion batteries (LIBs). However, the intrinsic low electrical conductivity, sluggish reaction kinetics and dramatic volume expansion greatly restrict their practical applications. In the present work, we delicate design and synthesis of an advanced composite consisting of multi-component CoO/MoO2/CoMoO4 hierarchical hollow nanocages anchored on reduced graphene oxide (named as Co–Mo–O NCs/rGO composite) with strong interfacial interaction. The hierarchical hollow structure is beneficial for large electrode/electrolyte contact area and fast ion diffusion. Meanwhile, graphene can provide rapid electron transport pathway and buffer the volume change. As a result, the Co–Mo–O NCs/rGO composite exhibits excellent lithium storage performance in aspects of high reversible specific capacity (964 mA h g−1 at 0.1 A g−1), good rate capability (333 mA h g−1 at 5 A g−1) and long-term cycling performance (731 mA h g−1 at 1 A g−1 after 400 cycles). Moreover, electrode kinetics analysis further reveals the capacitive-controlled lithium ion storage mechanism in the Co–Mo–O NCs/rGO composite. The present work would demonstrate the importance of integrating multi-component TMOs hierarchical hollow structures and graphene into one intriguing architecture to boost the electrochemical performance.