Ya Yan

Fe2O3-decorated millimeter-long vertically aligned carbon nanotube arrays as advanced anode materials for asymmetric supercapacitors with high energy and power densities

Construction of high-energy density asymmetric supercapacitors is often hindered by unsatisfactory matching between the anode and cathode. Thus, it is crucial to develop composite anodes with high specific capacitance to match that of cathodes. In this work, a novel anode material with well-dispersed Fe2O3 decorated on vertically aligned carbon nanotubes has been synthesized by a facile two-step method, consisting of supercritical carbon dioxide (SCCO2) assisted impregnation and subsequent thermal annealing. Due to the advantageous nanostructure, the Fe2O3/VACNT composites exhibit a large specific capacitance of 248 F g−1 at 8 A g−1 in 2 M KOH between −1.2 and 0 V versus SCE. An asymmetric supercapacitor operating at 1.8 V is assembled using the Fe2O3/VACNTs as the anode and the NiO/VACNTs as the cathode in a 2 M KOH aqueous electrolyte. The NiO/VACNTs//Fe2O3/VACNT asymmetric supercapacitor achieves an extremely high energy density of 137.3 W h kg−1 at a power density of 2.1 kW kg−1, and still retains 102.2 W h kg−1 at the high power density of 39.3 kW kg−1. Moreover, it also shows an outstanding cycling stability with ∼89.2% capacitance retention after 5000 cycles. The facile and effective synthesis method, as well as the superior electrochemical performance of the Fe2O3/VACNT composites, pave a way for promising applications in high-performance energy storage.

Quasi-Emulsion Confined Synthesis of Edge-Rich Ultrathin MoS2 Nanosheets/Graphene Hybrid for Enhanced Hydrogen Evolution

High-purity hydrogen produced by water splitting is considered as one of the most promising fuels to replace traditional fossil fuels. Developing highly efficient electrocatalysts toward hydrogen evolution is vital for the realization of large-scale H2 generation. Glycerol is used herein in a facile solvothermal process to synthesize edge-rich ultrathin MoS2 /reduced graphene oxide (RGO) composites. The introduction of glycerol plays an important role in the formation of such interesting structures. The MoS2 /RGO electrocatalyst exhibits excellent hydrogen evolution reaction (HER) activity and remarkable stability, owing to the rich active edges and improved electrical conductivity of the catalyst composites. This work provides new insights to engineer the structures of MoSx -based composites and thus achieves more active and efficient electrocatalysts.

Cobalt sulfide supported on nitrogen and sulfur dual-doped reduced graphene oxide for highly active oxygen reduction reaction

Cobalt sulfide nanoparticles grown on nitrogen and sulfur dual-doped reduced graphene oxide sheets (Co–S/NS-rGO) were synthesized as an efficient electrocatalyst for the oxygen reduction reaction (ORR) by a facile one-step annealing process at 400–600 °C. The catalyst synthesized at 500 °C (Co–S/NS-rGO-500) exhibits the best ORR catalytic activity compared to the other samples, together with high four-electron selectivity and excellent stability in alkaline medium. Moreover, the Co–S/NS-rGO-500 composite also manifests good ORR activity and selectivity in acid solution. The facile synthesis approach and superior ORR performance in both alkaline and acid electrolytes make the Co–S/NS-rGO catalysts promising as an alternative to commercial Pt/C catalyst for fuel cells.

Bio-inspired design of hierarchical FeP nanostructure arrays for the hydrogen evolution reaction

Hierarchical FeP nanoarray films composed of FeP nanopetals were successfully synthesized via a bio-inspired hydrothermal route followed by phosphorization. Glycerol, as a crystal growth modifier, plays a significant role in controlling the morphology and structure of the FeO(OH) precursor during the biomineralization process, while the following transfer and pseudomorphic transformation of the FeO(OH) film successfully give rise to the FeP array film. The as-prepared FeP film electrodes exhibit excellent hydrogen evolution reaction (HER) performance over a wide pH range. Theoretical calculations reveal that the mixed P/Fe termination in the FeP film is responsible for the high catalytic activity of the nanostructured electrodes. This new insight will promote further explorations of efficient metal phosphoride-based catalysts for the HER. More importantly, this study bridges the gap between biological and inorganic self-assembling nanosystems and may open up a new avenue for the preparation of functional nanostructures with application in energy devices.

Metal/covalent–organic frameworks-based electrocatalysts for water splitting

Sustainable hydrogen production through water splitting provides an appealing solution for hydrogen energy to achieve a carbon neutral future. However, the realization and scalability of this technology requires efficient electrocatalysts to promote cathodic hydrogen evolution and anodic oxygen evolution. The rapid evolution of the metal/covalent–organic frameworks (MOFs/COFs) family provides new opportunities for the development of water splitting. This review summarizes recent advances of MOF- and COF-based electrocatalysts for water electrolysis and highlights the advantages of these electrocatalysts over those conventionally used. Particular attentions are paid to the design principles, construction strategies, and structure–property relationships for MOF/COF-based electrocatalysts. Finally, current challenges and future perspectives of MOF/COF-based electrocatalysts for water splitting are also presented. We hope this review will provide a timely reference for advancing MOF/COF-based electrode materials towards practicable water splitting and useful insights for future energy technologies beyond water electrolysis.

A two-step approach to synthesis of Co(OH)2/γ-NiOOH/reduced graphene oxide nanocomposite for high performance supercapacitors

A two-step approach was reported to fabricate cobaltous hydroxide/γ- nickel oxide hydroxide/reduced graphene oxide (Co(OH)2/γ-NiOOH/RGO) nanocomposites on nickel foam by combining the reduction of graphene oxide with the help of reflux condensation and the subsequent hydrothermal of Co(OH)2 on RGO. The microstructural, surface morphology and electrochemical properties of the Co(OH)2/γ-NiOOH/RGO nanocomposite were investigated. The results showed that the surface of the first-step fabricated γ-NiOOH/RGO nanocomposites was uniformly coated by Co(OH)2 nanoflakes with lateral size of tens of nm and thickness of several nm. Co(OH)2/γ-NiOOH/RGO nanocomposite demonstrated a high specific capacitance (745 mF/cm2 at 0.5 mA/cm2) and a cycling stability of 69.8% after 1000 cycles at 30 mV/cm2. γ-NiOOH/RGO//Co(OH)2/γ-NiOOH/RGO asymmetric supercapacitor was assembled, and maximum gravimetric energy density of 57.3 W∙h/kg and power density of 66.1 kW/kg were achieved. The synergistic effect between the highly conductive graphene and the nanoflake Co(OH)2 structure was responsible for the high electrochemical performance of the hybrid electrode. It is expected that this research could offer a simple method to prepare graphene-based electrode materials.