Laiquan Li

Binary metal oxide: advanced energy storage materials in supercapacitors

Binary transition metal oxides (BTMOs) possess higher reversible capacity, better structural stability and electronic conductivity, and have been widely studied to be novel electrode materials for supercapacitors. In this review, we present an extensive description of BTMO materials and the most commonly used synthetic methods. Furthermore, we review several notable BTMOs and their composites in application of supercapacitors. With the increasing attention for energy storage, more and more exciting results about BTMO materials will be reported in the future.

On the effects of moisture in a polyurethane shape memory polymer

It was observed that the polyurethane shape memory polymer (SMP) loses its shape fixing capability after being exposed in the air at room temperature for several days. A significant indication for this change is the continuous decrease of the glass transition temperature (Tg) of polyurethane. Accompanying the decrease of Tg, the uniaxial tensile behaviour also changes. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were carried out to find the cause behind this phenomenon. Moisture was concluded as the main reason. A mathematical expression was obtained for the relationship between Tg and the moisture. Moreover, the polyurethane shape memory polymer can fully regain its original properties after being heated at temperatures above 180 °C, which is the melting temperature of this SMP.

Graphene and cobalt phosphide nanowire composite as an anode material for high performance lithium-ion batteries

The synthesis of a composite of cobalt phosphide nanowires and reduced graphene oxide (denoted CoP/RGO) via a facile hydrothermal method combined with a subsequent annealing step is reported. The resulting composite presents large specific surface area and enhanced conductivity, which can effectively facilitate charge transport and accommodates variations in volume during the lithiation/de-lithiation processes. As a result, the CoP/RGO nanocomposite manifests a high reversible specific capacity of 960 mA·h·g–1 over 200 cycles at a current density of 0.2 A·g–1 (297 mA·h·g–1 over 10,000 cycles at a current density of 20 A·g–1) and excellent rate capability (424 mA·h·g–1 at a current density of 10 A·g–1).

ZIF-8 derived carbon (C-ZIF) as a bifunctional electron acceptor and HER cocatalyst for g-C3N4: construction of a metal-free, all carbon-based photocatalytic system for efficient hydrogen evolution

A ZIF-8 derived carbon (C-ZIF)/g-C3N4 composite was constructed for the first time through facile thermal condensation of a zeolitic imidazolate framework (ZIF-8) and melamine. The obtained C-ZIF/g-C3N4 composite exhibited an obviously enhanced photocatalytic H2 production rate compared to pure g-C3N4 under visible light irradiation. The 1 wt% C-ZIF/g-C3N4 composite without loading the Pt co-catalyst showed 36.2 times higher H2 evolution rate than that of pure g-C3N4, which is even 2.8 times higher than that of Pt/g-C3N4 (the state-of-the-art g-C3N4-based photocatalyst). It was revealed by photoluminescence spectroscopy, time-resolved fluorescence spectroscopy and electrochemical impedance spectroscopy that the formed C-ZIF and g-C3N4 junction could promote quick charge carrier separation and transfer. The C-ZIF not only acted as an effective electron acceptor, but also functioned as an efficient hydrogen evolution reaction (HER) cocatalyst to promote photocatalytic hydrogen evolution. Our work provides an effective way for the development of metal-free, all carbon-based photocatalysts for H2 evolution.

Hierarchical carbon@Ni3S2@MoS2 double core–shell nanorods for high-performance supercapacitors

Hierarchical carbon@Ni3S2@MoS2 (C@Ni3S2@MoS2) double core–shell nanorods have been synthesized by a facile hydrothermal method using highly conductive carbon/Ni (C/Ni) nanorods as both the precursor and template. As supercapacitor electrodes, the C@Ni3S2@MoS2 nanorods deliver a specific capacitance as high as 1544 F g−1 at a current density of 2 A g−1 with excellent cycling stability (retaining 92.8% of the capacitance after 2000 cycles at a current density of 20 A g−1). The C/Ni nanorods as the backbone played crucial roles in enhancing the rate performance of the device, in the meanwhile, interconnected MoS2 nanosheets on the shell provided numerous accessible surfaces and contacts with the electrolyte. Our work demonstrated an effective design of robust hierarchical double core/shell nanostructures, which could provide a general and promising approach to fabricate high-performance materials for energy storage applications.

Nanowires assembled from MnCo2O4@C nanoparticles for water splitting and all-solid-state supercapacitor

The rational design of earth-abundant catalysts with excellent water splitting activities is important to obtain clean fuels for sustainable energy devices. In this study, mixed transition metal oxide nanoparticles encapsulated in nitrogendoped carbon (denoted as AB2O4@NC) were developed using a one-pot protocol, wherein a metal–organic complex was adopted as the precursor. As a proof of concept, MnCo2O4@NC was used as an electrocatalyst for water oxidation, and demonstrated an outstanding electrocatalytic activity with low overpotential to achieve a current density of 10 mA·cm−1 (η10 = 287 mV), small Tafel slope (55 mV·dec−1), and high stability (96% retention after 20 h). The excellent electrochemical performance benefited from the synergistic effects of the MnCo2O4 nanoparticles and nitrogen-doped carbon, as well as the assembled mesoporous nanowire structure. Finally, a highly stable all-solid-state supercapacitor based on MnCo2O4@NC was demonstrated (1.5% decay after 10,000 cycles).

Carbon@NiCo2S4 nanorods: an excellent electrode material for supercapacitors

Carbon@NiCo2S4 nanorods were synthesized through a facile in situ hydrothermal approach using carbon supported nickel (Ni/C) nanorods as both the template and nickel source. The morphology and electrochemical properties of NiCo2S4 can be effectively tuned with carbon nanorods as well as the addition of hydrogen peroxide (H2O2) during the hydrothermal process. The carbon nanorod endows NiCo2S4 with rod-like morphology and good electrochemical stability during active reversible redox reactions. Moreover, the addition of H2O2 creates the porous structure of NiCo2S4, improving its electrochemically active surface area greatly, which is beneficial for efficient charge and ion transport in electrodes. Electrochemical measurements indicate that the H2O2 treated carbon@NiCo2S4 (labeled as C@NiCo2S4–H) nanorods present high specific capacitance (1455 F g−1 at the current density of 1 A g−1) and excellent cycling stability (83% retention after 2000 cycles). It is believed that other carbon-based composites with superior electrochemical behavior for supercapacitor applications can also be synthesized using the proposed method in this study.