Huawei Huang

Electroactive edge site-enriched nickel–cobalt sulfide into graphene frameworks for high-performance asymmetric supercapacitors

Tailor-made edge site-enriched inorganics coupled graphene hybrids hold a promising platform material for high-performance supercapacitors. Herein, we report a simple strategy for fabricating edge site-enriched nickel–cobalt sulfide (Ni–Co–S) nanoparticles decorated on graphene frameworks to form integrated hybrid architectures (Ni–Co–S/G) via an in situ chemically converted method. The Kirkendall effect-involved anion exchange reaction, e.g. the etching-like effort of the S2− ions, plays a crucial role for the formation of the edge site-enriched nanostructure. Density functional theory (DFT) calculations reveal that the Ni–Co–S edge sites have a high electrochemical activity and strong affinity for OH− in the electrolyte, which are responsible for the enhanced electrochemical performance. Benefiting from the integrated structures of Ni–Co–S nanoparticles and conductive graphene substrates, the resultant Ni–Co–S/G hybrid electrodes exhibit a high specific capacitance of 1492 F g−1 at the current density of 1 A g−1, a superior rate capability of 96% when the current density is increased to 50 A g−1, and excellent electrochemical stabilities. An asymmetric supercapacitor fabricated using the edge site-enriched Ni–Co–S/G hybrids as the positive electrode and porous carbon nanosheets (PCNS) as negative electrodes shows a high energy density of 43.3 W h kg−1 at a power density of 0.8 kW kg−1, and an energy density of 28.4 W h kg−1 can be retained even at a high power density of 22.1 kW kg−1.

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.

Towards efficient electrocatalysts for oxygen reduction by doping cobalt into graphene-supported graphitic carbon nitride

A highly efficient electrocatalyst is developed by chemical coordination of cobalt species with g-C3N4 layers which are homogeneously supported on reduced graphene oxide. The formation of Co-Nx complex active sites greatly enhances the electrocatalytic activity and durability towards the oxygen reduction reaction.

Ultrahigh Rate and Long‐Life Sodium‐Ion Batteries Enabled by Engineered Surface and Near‐Surface Reactions

To achieve the high-power sodium-ion batteries, the solid-state ion diffusion in the electrode materials is a highly concerned issue and needs to be solved. In this study, a simple and effective strategy is reported to weaken and degrade this process by engineering the intensified surface and near-surface reactions, which is realized by making use of a sandwich-type nanoarchitecture composed of graphene as electron channels and few-layered MoS2 with expanded interlayer spacing. The unique 2D sheet-shaped hierarchical structure is capable of shortening the ion diffusion length, while the few-layered MoS2 with expanded interlayer spacing has more accessible surface area and the decreased ion diffusion resistance, evidenced by the smaller energy barriers revealed by the density functional theory calculations. Benefiting from the shortened ion diffusion distance and enhanced electron transfer capability, a high ratio of surface or near-surface reactions is dominated at a high discharge/charge rate. As such, the composites exhibit the high capacities of 152 and 93 mA h g-1 at 30 and 50 A g-1 , respectively. Moreover, a high reversible capacity of 684 mA h g-1 and an excellent cycling stability up to 4500 cycles can be delivered. The outstanding performance is attributed to the engineered structure with increased contribution of surface or near-surface reactions.

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.

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.