Shaofeng Li

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 20u2006000 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.

Starch Derived Porous Carbon Nanosheets for High-Performance Photovoltaic Capacitive Deionization

Capacitive deionization (CDI) is an emerging technology that uniquely integrates energy storage and desalination. In this work, porous carbon nanosheets (PCNSs) with an ultrahigh specific surface area of 2853 m2/g were fabricated by the simple carbonization of starch followed by KOH activation for the electrode material of photovoltaic CDI. The CDI cell consisting of PCNSs electrodes exhibited a high salt adsorption capacity (SAC) of 15.6 mg/g at ∼1.1 V in 500 mg/L NaCl as well as high charge efficiency and low energy consumption. KOH activation played a key role in the excellent CDI performance as it not only created abundant pores on the surface of PCNSs but also made it fluffy and improved its graphitization degree, which are beneficial to the transport of ions and electrons. PCNSs are supposed to be a promising candidate for CDI electrode materials. The combination of solar cells and CDI may provide a new approach to reduce the energy cost of CDI and boost its commercial competitiveness.

Microporous MOFs Engaged in the Formation of Nitrogen‐Doped Mesoporous Carbon Nanosheets for High‐Rate Supercapacitors

Nitrogen-doped mesoporous carbon nanosheets (NMCS) have been fabricated from zinc-based microporous metal-organic frameworks (ZIF-8) by pyrolysis in a molten salt medium. The as-prepared NMCS exhibit significantly improved specific capacitance (NMCS-8: 232u2005Fu2009g-1 at 0.5u2005Au2009g-1 ) and capacitance retention ratio (75.9u2009% at 50u2005Au2009g-1 ) compared with the micropore-dominant nitrogen-doped porous carbon polyhedrons (NPCP-5: 178u2005Fu2009g-1 at 0.5u2005Au2009g-1 , 15.9u2009% at 20u2005Au2009g-1 ) obtained by direct pyrolysis of nanocrystalline ZIF-8. The excellent capacitive performance and high rate performance of the NMCS can be attributed to their unique combination of structure and composition, that is, the two-dimensional and hierarchically porous structure provides a short ion-transport pathway and facilitates the supply of electrolyte ions, and the nitrogen-doped polar surface improves the interface wettability when used as an electrode.

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 asymmetric capacitive mixing with oppositely charged carbon electrodes for energy production from salinity differences

Capacitive mixing (CapMix) is an emerging technique that uses supercapacitors for harvesting salinity gradient energy. Here, positively charged quaternized poly(4-vinylpyridine) coated activated carbon and negatively charged nitric acid oxidized activated carbon are employed as electrodes for asymmetric CapMix (Asy-CapMix), enabling the production of electricity via four-step or two-step energy generation cycles without using an external power source and selective membranes. The voltage rise of this capacitor is 150.0 mV, and the average power density can reach as high as 65.0 mW m−2. Both values are higher than those of CapMix using symmetric electrodes and an external power source or selective membranes and better than those of previous Asy-CapMix, including those with external power supplies. Such superior performance can be attributed to the high surface charge density and the good conductivity of the chemically modified activated carbon electrodes, which may give insight into the design of electrodes for high performance Asy-CapMix.

Ultrahigh-Capacity and Long-Life Lithium-Metal Batteries Enabled by Engineering Carbon Nanofiber-Stabilized Graphene Aerogel Film Host

A safe, high-capacity, and long-life Li metal anode is highly desired due to recent developments in high-energy-density Li-metal batteries. However, there are still rigorous challenges associated with the undesirable formation of Li dendrites, lack of suitable host materials, and unstable chemical interfaces. Herein, a carbon nanofiber-stabilized graphene aerogel film (G-CNF film), inspired by constructional engineering, is constructed. As the host material for Li deposition, the G-CNF film features a large surface area, porous structure, and a robust skeleton that can render low local current density. This allows for dendrite-free Li deposition and mitigation of problems associated with large volume change. Importantly, the G-CNF film can keep high Li plating/stripping efficiency at nearly 99% for over 700 h with an areal capacity of 10 mA h cm-2 (the specific capacity up to 2588 mA h g-1 based on the total mass of carbon host and Li metal). The symmetric cells can stably run for more than 1000 h with low voltage hysteresis. The full cell with the LiFePO4 cathode also delivers enhanced capacity and lowered overpotential. As two-in-one host materials for both cathodes and anodes in Li-O2 batteries, the battery exhibits a capacity of 1.2 mA h cm-2 .