Multilayered Molybdate Microflowers Fabricated by One-Pot Reaction for Efficient Water Splitting

The development of high-performance, low-cost and rapid-production bifunctional electrocatalysts towards overall water splitting still poses huge challenges. Herein, the authors utilize a facile hydrothermal method to synthesize a novel structure of Co-doped ammonium lanthanum molybdate on Ni foams (Co-ALMO@NF) as self-supported electrocatalysts. Owing to large active surfaces, lattice defect and conductive channel for rapid charge transport, Co-ALMO@NF exhibits good electrocatalytic performances which requires only 349/341 mV to achieve a high current density of 600 mA cm^-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Besides, a low cell voltage of 1.52 V is required to reach the current density of 10 mA cm^-2 in alkaline medium along with an excellent long-term stability for two-electrode configurations. Density functional theory calculations are performed to reveal the reaction mechanism on Co-ALMO@NF, which shows that the Mo site is the most favorable ones for HER, while the introduction of Co is beneficial to reduce the adsorption intensity on the surface of Co-ALMO@NF, thus accelerating OER process. This work highlighted the importance of the structural design for self-supporting electrocatalysts.

Defects enriched cobalt molybdate induced by carbon dots for a high rate Li-ion battery anode

A defects-enriched CoMoO₄/carbon dot (CD) with CoMoO₄around 37 nm is achieved via hydrothermal reaction by introducing CDs to buffer large volume changes of CoMoO₄during lithiation-delithiation and enhance rate performance. The phase, morphology, microstructure, as well as the interface of the CoMoO₄/CD composites were investigated by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy. When employed as Li-ion battery anode, the CoMoO₄/CD exhibits a reversible capacity of ∼531 mAh g^-1after 400 cycles at a current density of 2.0 A g^-1. Under the scan rate at 2 mV s^-1, the CoMoO₄/CD shows accounts for 81.1% pseudocapacitance. It may attribute to the CoMoO₄with surface defects given more reaction sites to facilitate electrons and lithium ions transfer at high current densities. Through galvanostatic intermittent titration technique, the average lithium ion diffusion coefficient calculated is an order of magnitude larger than that of bulk CoMoO₄, indicating that the CoMoO₄/CD possesses promising electrons and lithium ions transportation performance as anode material.

Porous nanotube networks of SnO2/MoO3@Graphene as anodes for rechargeable lithium-ion batteries

We successfully fabricated composite porous nanotube networks of SnO₂/MoO₃@Graphene through electrospinning and used it as lithium-ion battery anodes. When the ratio of SnO₂ to MoO₃ is 1:1, the composite of SnO₂/MoO₃ delivers a high capacity of 560 mAh g^-1 at 1 A g^-1 after 300 cycles. The excellent electrochemical performance was attributed to the unique 3D porous nanotube network structure which could provide more transmission channels for Li⁺ ions and electrons, and provide more electrochemical reaction sites. The hybrid nanostructure can also weaken local stress and relieve volume expansion which contributes to the attractive cycling stability. Moreover, we added a small amount of graphene in the composite to improve the electrical conductivity, and the SnO₂/MoO₃@Graphene composite showed favorable electrochemical performance (798 mAh g^-1 at 1 A g^-1 after 300 cycles). Finally, electrospinning technology is a simple and efficient synthesis strategy, which can promote the preparation of different types of metal oxide composite materials and has good application prospects.

Hierarchical 0D-2D Co/Mo Selenides as Superior Bifunctional Electrocatalysts for Overall Water Splitting

Development of efficient electrocatalysts combining the features of low cost and high performance for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) still remains a critical challenge. Here, we proposed a facile strategy to construct in situ a novel hierarchical heterostructure composed of 0D−2D CoSe₂/MoSe₂ by the selenization of CoMoO₄ nanosheets grafted on a carbon cloth (CC). In such integrated structure, CoSe₂ nanoparticles dispersed well and tightly bonded with MoSe₂ nanosheets, which can not only enhance kinetics due to the synergetic effects, thus promoting the electrocatalytic activity, but also effectively improve the structural stability. Benefiting from its unique architecture, the designed CoSe₂/MoSe₂ catalyst exhibits superior OER and HER performance. Specifically, a small overpotential of 280 mV is acquired at a current density of 10 mA·cm⁻² for OER with a small Tafel slope of 86.8 mV·dec⁻¹, and the overpotential is 90 mV at a current density of 10 mA·cm⁻² for HER with a Tafel slope of 84.8 mV·dec⁻¹ in 1 M KOH. Furthermore, the symmetrical electrolyzer assembled with the CoSe₂/MoSe₂ catalysts depicts a small cell voltage of 1.63 V at 10 mA·cm⁻² toward overall water splitting.

Structural and electrochemical behavior of a NiMnO3/Mn2O3 nanocomposite as an anode for high rate and long cycle lithium ion batteries

In this work, first time a pre-designed NiMnO₃/Mn₂O₃ nanocomposite is synthesized via a facile urea-assisted auto-combustion synthesis with the phase fraction ratio of ∼89% and ∼11%, respectively as an anode material for lithium-ion batteries.

Doping β-CoMoO4 Nanoplates with Phosphorus for Efficient Hydrogen Evolution Reaction in Alkaline Media

Mass production of hydrogen by electrolysis of water largely hinges on the development of highly efficient and economical electrocatalysts for hydrogen evolution reaction (HER). Though having the merits of high earth abundance, easy availability, and tunable composition, transition-metal oxides are usually deemed as poor electrocatalysts for HER. Herein, we demonstrate that doping β-CoMoO₄ nanoplates with phosphorus can turn them into active electrocatalysts for HER. Theoretical calculation and experimental studies unravel that enhanced electrical conductivity and optimized hydrogen adsorption free energy are major causes for the improvement of intrinsic activity. As a result, only an overpotential of 138 mV is required to drive hydrogen evolving at a current density of 10 mA cm^-2 in 1 M KOH for P-doped β-CoMoO₄, which outstrips many recently reported transition-metal oxides and is just slightly inferior to commercial Pt/C. This work opens a new route to tune the HER performance of transition-metal oxides.

High Areal Capacity Li-Ion Storage of Binder-Free Metal Vanadate/Carbon Hybrid Anode by Ion-Exchange Reaction

Storing more energy in a limited device area is very challenging but crucial for the applications of flexible and wearable electronics. Metal vanadates have been regarded as a fascinating group of materials in many areas, especially in lithium-ion storage. However, there has not been a versatile strategy to synthesize flexible metal vanadate hybrid nanostructures as binder-free anodes for Li-ion batteries so far. A convenient and versatile synthesis of M_x V_y O_x+2.5y @carbon cloth (M = Mn, Co, Ni, Cu) composites is proposed here based on a two-step hydrothermal route. As-synthesized products demonstrate hierarchical proliferous structure, ranging from nanoparticles (0D), and nanobelts (1D) to a 3D interconnected network. The metal vanadate/carbon hybrid nanostructures exhibit excellent lithium storage capability, with a high areal specific capacity up to 5.9 mAh cm^-2 (which equals to 1676.8 mAh g^-1 ) at a current density of 200 mA g^-1 . Moreover, the nature of good flexibility, mixed valence states, and ultrahigh mass loading density (over 3.5 mg cm^-2 ) all guarantee their great potential in compact energy storage for future wearable devices and other related applications.

Electrochemical Performance and Storage Mechanism of Ag2 Mo2 O7 Micro-rods as the Anode Material for Lithium-Ion Batteries

Ag₂ Mo₂ O₇ micro-rods are prepared by one-step hydrothermal method and their lithium electrochemical properties, as the anode for lithium-ion batteries, are comprehensively studied in terms of galvanostatic charge-discharge cycling, cyclic voltammetry, and rate performance measurements. The electrode delivers a high reversible capacity of 825 mAh g^-1 at a current density of 100 mA g^-1 and a superior rate capability with a discharge capacity of 263 mAh g^-1 under the high current density of 2 Ag^-1 . The structural transition and phase evolution of Ag₂ Mo₂ O₇ were investigated by using ex situ XRD and TEM. The Ag₂ Mo₂ O₇ electrode is likely to be decomposed into amorphous molybdenum, Li₂ O, and metallic silver based on the conversion reaction. Silver nanoparticles are not involved in the subsequent electrochemical cycles to form a homogeneous conducting network. Such in situ decomposition behavior provides an insight into the mechanism of the electrochemical reaction for the anode materials and would contribute to the design of new electrode materials in future.

Synthesis of porous CoMoO4 nanorods as a bifunctional cathode catalyst for a Li-O2 battery and superior anode for a Li-ion battery

We report the synthesis of porous CoMoO₄ nanorods and their applications in lithium oxygen (Li-O₂) and lithium ion (Li-ion) batteries. The unique porous structures of CoMoO₄ nanorods can promote the permeation of electrolyte and benefit the transport of lithium ion. When employed as the cathode catalyst for a Li-O₂ battery, CoMoO₄ nanorods deliver an improved discharge capacity (4680 mA h g^-1), lower charge potential and better cycle stability (41 cycles at 500 mA h g^-1 capacity limit) compared with the bare carbon. When employed as an anode in Li-ion batteries, CoMoO₄ nanorods can retain a capacity of 603 mA h g^-1 after 300 cycles (400 mA g^-1) and exhibit excellent rate capability.

Efficient MMoO4 (M = Co, Ni) carbon cloth electrodes for water oxidation

Cobalt/nickel molybdate hierarchical microflowers on conductive carbon cloth (MMoO₄-CC, M = Co, Ni) as three-dimensional self-supported electrodes exhibit an excellent OER.

Graphene foam supported multilevel network-like NiCo2S4 nanoarchitectures for robust lithium storage and efficient ORR catalysis

Interconnected mesoporous ultrathin nanosheets are assembled to form NiCo₂S₄ nanowall arrays, which are grown on 3D graphene foams to fabricate multilevel network-like composites.

Hollow SnO2@carbon core–shell spheres stabilized on reduced graphene oxide for high-performance sodium-ion batteries

Graphene exhibits superior performance in sodium-ion batteries when it is hybridized with hollow carbon encapsulated SnO₂.

Construction of hollow Co3O4cubes as a high-performance anode for lithium ion batteries

We report on hollow Co₃O₄cubes synthesizedviaa self-sacrificing template method and their application as an anode material for reversible electrochemical lithium storage.

Synthesis of graphene wrapped porous CoMoO4 nanospheres as high-performance anodes for rechargeable lithium-ion batteries

Herein, we described a facile method to synthesise porous CoMoO₄ nanospheres wrapped with graphene (CoMoO₄@G).

Facile synthesis of MgFe2O4/C composites as anode materials for lithium-ion batteries with excellent cycling and rate performance

A MgFe₂O₄/C material is synthesized via a facile method and the MgFe₂O₄/C electrode shows excellent cycling and rate capability.