Kun Rui

2D Black Phosphorus for Energy Storage and Thermoelectric Applications

Recent progress in the currently available methods of producing black phosphorus bulk and phosphorene are presented. The effective passivation approaches toward improving the air stability of phosphorene are also discussed. Furthermore, the research efforts on the phosphorene and phosphorene-based materials for potential applications in lithium ion batteries, sodium ion batteries, and thermoelectric devices are summarized and highlighted. Finally, the outlook including challenges and opportunities in these research fields are discussed.

Ultrathin and large-sized vanadium oxide nanosheets mildly prepared at room temperature for high performance fiber-based supercapacitors

Ultrathin vanadium oxide (V2O5) nanosheets with lateral sizes of up to tens of micrometers were synthesized, and then incorporated into multi-walled carbon nanotube (MWCNT) fibers. The solid-state supercapacitor based on such hybrid fibers exhibited an improved volumetric capacitance of 31 F cm−3 at 1.0 A cm−3, and a volumetric energy density of 2.1 mW h cm−3 at 1.5 W cm−3.

Self‐Templated Formation of Uniform F‐CuO Hollow Octahedra for Lithium Ion Batteries

Novel F-CuO and FeOOH hollow octahedra are developed through a facile structure-evolution reaction. The formation of interior voids within the hierarchical octahedra is motivated by the Cl- ions based etching, under a precise control over reaction agents and conditions. Owing to the synergistic effect of unique structural features and favorable composition, the hollow octahedra exhibit superior lithium-storage properties.

Carbon Necklace Incorporated Electroactive Reservoir Constructing Flexible Papers for Advanced Lithium–Ion Batteries

Metal-organic frameworks (MOFs) and their derivatives with well-defined structures and compositions show great potential for wide applications such as sensors, catalysis, energy storage, and conversion, etc. However, poor electric conductivity and large volume expansion are main obstacles for their utilization in energy storage, e.g., lithium-ion batteries and supercapacitors. Herein, a facile strategy is proposed for embedding the MOFs, e.g., ZIF-67 and MIL-88 into polyacrylonitrile fibers, which is further used as a template to build a 3D interconnected conductive carbon necklace paper. Owing to the unique structure features of good electric conductivity, interconnected frameworks, electroactive reservoir, and dual dopants, the obtained flexible electrodes with no additives exhibit high specific capacities, good rate capability, and prolonged cycling stability. The hollow dodecahedral ZIF-67 derived carbon necklace paper delivers a high specific capacity of 1200 mAh g-1 and superior stability of more than 400 cycles without capacity decay. Moreover, the spindle-like MIL-88 derived carbon necklace paper shows a high reversible capacity of 980 mAh g-1 . Their unique 3D interconnected structure and outstanding electrochemical performance pave the way for extending the MOF-based interweaving materials toward potential applications in portable and wearable electronic devices.

Interlayer-Expanded Metal Sulfides on Graphene Triggered by a Molecularly Self-Promoting Process for Enhanced Lithium Ion Storage

A general synthetic approach has been demonstrated to fabricate three-dimensional (3D) structured metal sulfides@graphene, employing few-layered sulfide nanostructures with expanded interlayer spacing of the (002) plane (e.g., 0.98 nm for MoS2 nanoclusters and 0.65 nm for VS4 nanoribbons) and electrically conductive graphene as ideal building blocks. Here, small molecules (thioacetamide) acting as both the sulfur source and, more importantly, the structure-directing agent adjusting the interlayer spacing are wisely selected, further contributing to a sufficient space for ultrafast Li+ ion intercalation. The appealing features of a mechanically robust backbone, ultrathin thickness, abundant exposure of interlayer edges, and good electrical conductivity in such 3D architectures are favorable for providing easy access for the electrolyte to the structures and offering a shortened diffusion length of Li+ when utilized for energy storage. As a proof of concept, the electrochemical behavior of the resulting 3D structured metal sulfides@graphene as an anode material of lithium ion batteries (LIBs) is systematically investigated. As a consequence, high specific capacities, long lifespans, and superior rate capabilities have been realized in such well-designed architectures, e.g. maintaining a specific capacity as high as 965 mAh g-1 for 120 cycles for VS4@graphene and 1100 mAh g-1 for 150 cycles for MoS2@graphene.

Dual-Function Metal–Organic Framework-Based Wearable Fibers for Gas Probing and Energy Storage

Metal-organic frameworks (MOFs) coupled with multiwalled carbon nanotubes (MWCNTs) have been developed with an ultrahigh sensitivity for hazardous gas monitoring. Both the MOF/MWCNT and as-derived metal oxides (MOs)/MWCNTs hybrid fibers deliver an ultralow detection limit for NO2 down to 0.1 ppm without external heating, and they can be further bent into different angles without loss of sensing performance. Also, a high specific capacitance of 110 F cm-3 can also be obtained for MO/MWCNT hybrid fibers, demonstrating promising application for integrated wearable devices.

Epitaxial growth of Ni(OH)2 nanoclusters on MoS2 nanosheets for enhanced alkaline hydrogen evolution reaction

Constructing heterostructures is an effective strategy for designing efficient electrocatalysts. MoS2 is a star catalyst for hydrogen evolution reaction (HER) in acidic media; however, the alkaline HER activity is deficient due to the sluggish water dissociation process. Herein, Ni(OH)2/MoS2 heterostructures with Ni(OH)2 nanoclusters epitaxially decorated on the surface of MoS2 are synthesized towards the alkaline HER. As compared with MoS2, the epitaxial Ni(OH)2/MoS2 heterostructures show significantly enhanced HER activity in 1 M KOH, and the overpotential is decreased by nearly 150 mV to reach a current density of 10 mA cm-2. The substantial increase in turnover frequency (TOF) demonstrates that the intrinsic activity is greatly improved after the incorporation of Ni(OH)2 nanoclusters. The presence of Ni(OH)2 nanoclusters would provide additional water dissociation sites while MoS2 is ready for the adsorption and combination of the generated H*, and this so-called synergistic effect eventually induces significantly enhanced alkaline HER kinetics. Besides, the electron transfer from Ni(OH)2 to MoS2 increases the proton affinity of MoS2. The present results describe an interesting case of an atomic-scale electrochemically inert material promoted HER process, and would open a new avenue into designing efficient hetero-nanostructures towards electrocatalytic applications.

CoSe2/MoSe2 Heterostructures with Enriched Water Adsorption/Dissociation Sites towards Enhanced Alkaline Hydrogen Evolution Reaction

Transition-metal dichalcogenides (TMDs) are promising electrocatalysts toward the hydrogen evolution reaction (HER) in acid media, but they show significantly inferior activity in alkaline media due to the extremely sluggish water dissociation kinetics. Herein, CoSe2 /MoSe2 heterostructures with CoSe2 quantum dots anchored on MoSe2 nanosheets are synthesized towards enhanced alkaline HER catalytic activity. The incorporation of CoSe2 is intended to construct additional water adsorption sites on the basal planes of MoSe2 to promote water dissociation. The CoSe2 /MoSe2 heterostructures show substantially enhanced activity over MoSe2 and CoSe2 in 1u2009m KOH. The optimal overpotential required to reach a current density of 10u2005mAu2009cm-2 is merely 218u2005mV, which is more than 100u2005mV greater than that of MoSe2 , which is by far the best performance demonstrated for precious-metal-free catalysts. Detailed analyses based on electrochemical testing demonstrate that the water adsorption and subsequent dissociation process is accelerated by CoSe2 species with rich edge sites; meanwhile, MoSe2 species provide sufficient active sites for the adsorption and combination of adsorbed hydrogen (H. ). These results provide an effective strategy for developing earth-abundant catalysts with high activity for the alkaline HER, and are of great significance to promote the practical application of alkaline water electrolysis.

Iron-doped nickel molybdate with enhanced oxygen evolution kinetics

Electrochemical water splitting is one of the potential approaches for making renewable energy production and storage viable. The oxygen evolution reaction (OER), as a sluggish four-electron electrochemical reaction, has to overcome high overpotential to accomplish overall water splitting. Therefore, developing low-cost and highly active OER catalysts is the key for achieving efficient and economical water electrolysis. In this work, Fe-doped NiMoO4 was synthesized and evaluated as the OER catalyst in alkaline medium. Fe3+ doping helps to regulate the electronic structure of Ni centers in NiMoO4 , which consequently promotes the catalytic activity of NiMoO4 . The overpotential to reach a current density of 10u2005mAu2009cm-2 is 299u2005mV in 1u2009m KOH for the optimal Ni0.9 Fe0.1 MoO4 , which is 65u2005mV lower than that for NiMoO4 . Further, the catalyst also shows exceptional performance stability during a 2u2005h chronopotentiometry testing. Moreover, the real catalytically active center of Ni0.9 Fe0.1 MoO4 is also unraveled based on the exu2005situ characterizations. These results provide new alternatives for precious-metal-free catalysts for alkaline OER and also expand the Fe-doping-induced synergistic effect towards performance enhancement to new catalyst systems.

Recent progress of nickel-based oxide/(oxy)hydroxide electrocatalysts for oxygen evolution reaction

Developing clean and sustainable energies as alternatives to fossil fuels is in strong demand within modern society. The oxygen evolution reaction (OER) is the efficiency-limiting process in plenty of key renewable energy systems, such as electrochemical water splitting and rechargeable metal-air batteries. In this regard, ongoing efforts have been devoted to seeking high-performance electrocatalysts for enhanced energy conversion efficiency. Apart from traditional precious-metal-based catalysts, nickel-based compounds are the most promising earth-abundant OER catalysts, attracting ever-increasing interest due to high activity and stability. In this review, the recent progress on nickel-based oxide and (oxy)hydroxide composites for water oxidation catalysis in terms of materials design/synthesis and electrochemical performance is summarized. Some underlying mechanisms to profoundly understand the catalytic active sites are also highlighted. In addition, the future research trends and perspectives on the development of Ni-based OER electrocatalysts are discussed.