Changtai Zhao

A superhydrophilic “nanoglue” for stabilizing metal hydroxides onto carbon materials for high-energy and ultralong-life asymmetric supercapacitors

Coupling electroactive species with carbon supports to fabricate hybrid electrodes holds promise for high-performance supercapacitors. Nevertheless, the poor compatibility and weak bonding between carbon substrates and electroactive species remain a bottleneck to be tackled. Herein, we present a superhydrophilic “nanoglue” strategy for stabilizing NiCo-layered double hydroxide (NiCo-LDH) nanosheets on inert carbon cloth (CC) by employing a nitrogen-doped (N-doped) carbon layer as the structure/interface coupling bridge to make hybrids (denoted as CC–NC-LDH) for supercapacitors. Such a “nanoglue” on a CC substrate results in the formation of a superhydrophilic surface/interface, which is favorable for the robust and uniform growth of NiCo-LDH on the CC, and helps effectively tune the electronic structural states and results in a strong coupling interaction between the CC and NiCo-LDH nanosheets. Benefiting from these integrated merits, asymmetric supercapacitors fabricated with the CC–NC-LDH hybrids as the positive electrode and typical activated carbon as the negative electrode deliver a high energy density of 69.7 W h kg−1 at a power density of 0.8 kW kg−1, with an ultra-low average capacitance fade rate of ∼0.00065% per cycle within 20 000 cycles at a current density of 10 A g−1. This superhydrophilic “nanoglue” strategy can also be extended to assemble other kinds of active species on different inert substrates, and holds the potential for creating efficient and robust electrode materials for energy-related devices.

Ultrasmall diiron phosphide nanodots anchored on graphene sheets with enhanced electrocatalytic activity for hydrogen production via high-efficiency water splitting

Transition metal phosphides (TMP) have been one of the excellent candidates as low-cost and high-efficiency catalysts for the sustainable hydrogen evolution reaction (HER). Nevertheless, construction of TMP with abundant exposed active sites is of urgent concern and highly desirable for the HER. Herein, we report a novel strategy to configure integrated active site-enriched architectures (Fe2P-ND/FG) composed of diiron phosphide (Fe2P) nanodots with a diameter of ∼2.5 nm uniformly anchored on porous and fluffy graphene sheets (FG). The interconnected conductive networks within porous FG favor the formation of uniformly and highly dispersed Fe2P nanodots, finally helping the promotion of fast electrolyte ion and electron transfer during the electrochemical process. Compared with bulk Fe2P, these ultrasmall Fe2P nanodots lead to abundant exposed edges and atoms. Benefiting from the highly exposed active sites derived from Fe2P nanodots and superior electrical conductivity stemming from an interconnected graphene matrix, the as-made Fe2P-ND/FG hybrids exhibit outstanding HER catalytic activity and stability. Overpotentials as low as 44 and 91 mV are required to achieve current densities of 2 and 10 mA cm−2, respectively. The present strategy provides a novel approach for configuring electrode materials with highly exposed active sites for high-efficiency energy storage/conversion devices.

High‐Stacking‐Density, Superior‐Roughness LDH Bridged with Vertically Aligned Graphene for High‐Performance Asymmetric Supercapacitors

The high-performance electrode materials with tuned surface and interface structure and functionalities are highly demanded for advanced supercapacitors. A novel strategy is presented to conFigure high-stacking-density, superior-roughness nickel manganese layered double hydroxide (LDH) bridged by vertically aligned graphene (VG) with nickel foam (NF) as the conductive collector, yielding the LDH-NF@VG hybrids for asymmetric supercapacitors. The VG nanosheets provide numerous electron transfer channels for quick redox reactions, and well-developed open structure for fast mass transport. Moreover, the high-stacking-density LDH grown and assembled on VG nanosheets result in a superior hydrophilicity derived from the tuned nano/microstructures, especially microroughness. Such a high stacking density with abundant active sites and superior wettability can be easily accessed by aqueous electrolytes. Benefitting from the above features, the LDH-NF@VG can deliver a high capacitance of 2920 F g-1 at a current density of 2 A g-1 , and the asymmetric supercapacitor with the LDH-NF@VG as positive electrode and activated carbon as negative electrode can deliver a high energy density of 56.8 Wh kg-1 at a power density of 260 W kg-1 , with a high specific capacitance retention rate of 87% even after 10 000 cycles.

Tailor-made graphene aerogels with inbuilt baffle plates by charge-induced template-directed assembly for high-performance Li–S batteries

Graphene as a host material has attracted intense interest to accommodate the sulfur for lithium–sulfur (Li–S) batteries. Nevertheless, there is still a major challenge on how to modulate the nanostructure of graphene architectures to further enhance the electrochemical performance. Herein, self-closure graphene aerogels with inbuilt baffle plates (SGA) were prepared by a combined strategy involving electrostatic assembly, hydrothermal fixing, polydopamine (PDA) coating, and annealing. The electrostatic assembly between graphene oxide (GO) and polystyrene sphere@polydopamine (PS@PDA) is the key factor to form the self-closure aerogels and the graphene sheets wrapped onto the PS@PDAs are responsible for the formation of the baffle plates. When employed as the host material for Li–S batteries, the as-made SGA can contribute to promotion of the transport of electrons, increasing the sulfur loading, confining the dissolution and diffusion of lithium polysulfides, and accommodating the volume expansion. As a result, the as-made SGA–sulfur composite can deliver an outstanding cycling stability of 509 mA h g−1 after 400 cycles at 1C. The present work will provide a simple and effective approach to tuning the assembly of graphene and further configuring the tailor-made host materials for high-performance Li–S batteries.

Nitrogen-doped tubular/porous carbon channels implanted on graphene frameworks for multiple confinement of sulfur and polysulfides

Graphene has excellent potential as a sulfur host in a lithium–sulfur (Li–S) battery owing to its outstanding electrical conductivity and robust mechanical properties. However, graphene itself cannot effectively confine sulfur and suppress polysulfide diffusion, leading to severely fast capacity decay. Herein, nitrogen-doped tubular/porous carbon channels were implanted on graphene sheets (NTPC–G) via a double-template method, with graphene sheets as the shape-directed agents and NiCo–carbonate hydroxide nanowires as the guides of tubular channels. The resultant one-dimensional hollow tubular carbon and two-dimensional graphene nanosheets were wrapped by nitrogen-doped porous carbon layers to construct the unique three-dimensional sandwich-type architectures. The adopted graphene sheets functioned as conductive networks and robust frameworks; moreover, the nitrogen-doped tubular/porous carbon channels comprising hollow tubular carbon and porous carbon coating layers implanted on graphene frameworks served as the sulfur-confined space and polysulfide reservoirs. On integrating these fascinating benefits into one electrode material, sulfur and NTPC–G composites (S@NTPC–G) delivered high rate capability (563 mA h g−1 at 6 C) and good cycle stability up to 600 cycles. This rational construction of tubular/porous carbon channels on nanosheet materials with comprehensive advantages could be promising and applicable in rechargeable Li–S batteries and other advanced energy storage devices.

Hierarchically porous carbon architectures embedded with hollow nanocapsules for high-performance lithium storage

One of the great challenges in the development of lithium ion batteries (LIBs) is to achieve the design and synthesis of electrode materials with a large capacity and a high rate capability. Here, we report a novel hierarchical pore architecture material composed of a micro-sized porous carbon sphere matrix embedded with hollow nanocapsules (HNs-HPCS) as a promising anode material for large capacity and ultra-high rate capability in LIBs. Such a hierarchical porous structure delivers a very high capacity of 805 mA h g−1 at a current density of 0.1 A g−1, and the capacity of ca. 210 mA h g−1 can be kept at 20 A g−1 (ca. 38 s to fully charge). We believe that the hollow nanocapsules embedded within the carbon interior would store large amounts of Li ions, while hierarchical pores are favorable for the fast transportation of Li ions in the electrolyte to a great degree, and thus mean that the micro-sized material has great potential for the fabrication of high-performance LIBs.

An electrocatalyst with anti-oxidized capability for overall water splitting

An anti-oxidized NiS2 electrocatalyst with improved catalytic activity was developed using a Fe-induced conversion strategy. X-ray photoelectron spectroscopy reveals that betatopic Ni species with high valence states are present within the Fe-NiS2 matrix and relatively less oxidized layers exist on the catalyst’s surface, indicating its greatly enhanced anti-oxidized capability. Density functional theory calculations reveal that the Ni and Fe sites on the Fe-NiS2 catalyst surface possess strong adsorption capacity toward hydroxyl ions compared with the Ni sites on NiS2. Benefiting from its unique microstructure and modulated electronic structure due to the effects of iron species, the Fe-NiS2 catalyst prepared on carbon fiber delivers a remarkably enhanced catalytic activity and superior long-life durability for overall water splitting. The present results provide an efficient strategy for the design and configuration of anti-oxidation catalysts, especially for energy storage and catalysis.

High performance concentration capacitors with graphene hydrogel electrodes for harvesting salinity gradient energy

Salinity gradient energy (SGE) is the energy available from the salinity difference between freshwater and saltwater. Herein, we propose a concentration capacitor as a novel capacitive mixing (CapMix) technique to harvest SGE. The concentration capacitor comprises identical electrodes and a membrane that separates concentrated and diluted solutions that alternately flow through the capacitor. Graphene hydrogel (GH) electrodes and a filtration membrane (FM) or an anion exchange membrane (AEM) are used to construct GH//FM//GH and GH//AEM//GH concentration capacitors. These concentration capacitors show excellent performance in harvesting SGE, particularly the GH//AEM//GH concentration capacitor, whose voltage rise and average power density can reach 288.5 mV and 482.4 mW m−2, respectively, which are higher than those obtained with other CapMix techniques. The outstanding performance is associated with the double-channel construction, the membrane potential, and the macroporous structure and abundant negative charge of the GH electrodes. Our results show that the concentration capacitor is a promising approach for efficiently extracting SGE.

Template-free synthesis of interconnected carbon nanosheets via cross-linking coupled with annealing for high-efficiency triiodide reduction

Counter electrodes (CEs) play critical roles in the reduction and regeneration of triiodide/iodide redox couple in dye-sensitized solar cells (DSSCs). Compared to commercial Pt, cost-efficient CEs with excellent electrocatalytic activity and superior electrochemical stability are highly desired. Herein, we report a facile, template- and active agents-free fabrication strategy for the synthesis of carbon nanosheets (CNSs) via annealing of small molecular precursors. This process was achieved by a combined strategy, including a low-temperature solid-phase cross-linking reaction and a subsequent high temperature annealing. When employed as metal-free CEs for DSSCs, the as-obtained CNSs demonstrated an annealing temperature-dependent electrochemical behavior. Owing to the superior electrical conductivity and electrocatalytic activity, the CNSs obtained by annealing at 1200 °C exhibit the best electrochemical performance with a power conversion efficiency of 8.71%, which is superior to that of Pt CE (7.24%), thus being attractive alternatives to precious metal Pt CEs. This study presents a simple and effective strategy to configure nanostructured carbonaceous materials for high-performance energy storage and conversion.