Electronic structure engineering on electrode materials could bring in a new mechanism to achieve high energy and high power densities in sodium ion batteries. Herein, we design and create Co ...vacancies at the interface of atomically thin CoSe2/graphene heterostructure and obtain Co1−xSe2/graphene heterostructure electrode materials that facilitate significant Na+ intercalation pseudocapacitance. Density functional theory (DFT) calculation suggests that the Na+ adsorption energy is dramatically increased, and the Na+ diffusion barrier is remarkably reduced due to the introduction of Co vacancy. The optimized electrode delivers a superior capacity of 673.6 mAh g−1 at 0.1 C, excellent rate capability of 576.5 mAh g−1 at 2.0 C and ultra‐long life up to 2000 cycles. Kinetics analysis indicates that the enhanced Na+ storage is mainly attributed to the intercalation pseudocapacitance induced by Co vacancies. This work suggests that the creation of cation vacancy could bestow heterostructured electrode materials with pseudocapacitive Na+ intercalation for high‐capacity and high‐rate energy storage.
The Co vacancies (VCo) at the interface of Co1−xSe2/graphene (GE) afford strong adsorption of Na+ and a low Na+ diffusion energy barrier to facilitate rapid intercalation/deintercalation of Na+ ions giving remarkable pseudocapacitance. The as‐prepared Co1−xSe2/GE‐based sodium ion batteries deliver high specific/rate capacity performance and exceptional cycling performance.
Developing cost-efficient electrocatalysts for oxygen evolution is vital for the viability of H2 energy generated via electrolytic water. Engineering favorable defects on the electrocatalysts to ...provide accessible active sites can boost the sluggish reaction thermodynamics or kinetics. Herein, Col_xS nanosheets were designed and grown on reduced graphene oxide （rGO） by controlling the successive two-step hydrothermal reaction. A belt-like cobalt-based precursor was first formed with the assistance of ammonia and rGO, which were then sulfurized into Col_xS by L-cysteine at a higher hydrothermal temperature. Because of the non-stoichiometric defects and ultrathin sheet-like structure, additional cobalt vacancies （V~o） were formed/exposed on the catalyst surface, which expedited the charge diffusion and increased the electroactive surface in contact with the electrolyte. The resulting Col_xS/rGO hybrids exhibited an overpotential as low as 310 mV at 10 mA.cm-2 in an alkaline electrolyte for the oxygen evolution reaction （OER）. Density functional theory calculations indicated that the Vco on the Col_xS/rGO hybrid functioned as catalytic sites for enhanced OER. They also reduced the energy barrier for the transformation of intermediate oxygenated species, promoting the OER thermodynamics.
Nanocomposites made of magnetic spinel oxide Co1+yAl2-yO4 nanoparticles (NPs) with y = 0.93, 1.20 and 1.34 dispersed in an amorphous SiO2 matrix were prepared by a sol-gel method. The average ...crystallite size DXRD of about 25 nm determined by X-ray diffraction (XRD) agrees well with the average particle size observed in transmission electron microscopy (TEM). Dynamic magnetic susceptibility measurements indicate a spin-glass-like behavior of the nanoparticles below the spin-glass (SG) transition temperature TC < 10 K. Field dependent magnetization exhibits weak ferromagnetism and shift of the magnetic hysteresis loop. On the basis of the observed magnetic properties, we propose a model of the core-shell structure of the Co1+yAl2-yO4 nanoparticles with the spin-glass phase in the core and weak ferromagnetism in the shell. The exchange bias field disappears above the spin-glass transition temperature TC, whereas the weak ferromagnetism persists also at temperatures above TC. The component of weak ferromagnetism is associated with the presence of Co vacancies in the nanoparticle spinel crystal lattice.
•Co1+yAl2-yO4 nanoparticles (NPs) exhibit spin-glass (SG) behavior below TC < 10 K.•Hysteresis loop recorded at T > TC reveals the existence of weak ferromagnetism (FM).•Weak FM is associated with the presence of Co vacancies in the NPs spinel lattice.•Horizontal shift of the hysteresis loop at T < TC is attributed to exchange bias effect.•A model of the NPs structure is proposed with SG in the core and weak FM in the shell.
The introduction of defect sites has been widely reported to enhance electrocatalysts’ abilities by increasing their affinity for reaction intermediates. Many different defect types, such as cation ...and anion vacancies, can exist in nano-materials. The different defect sites can make different contributions to the electrochemical ability. Therefore, a constructed defect should be accurate and specific, which makes it easy to identify the optimal defect type to facilitate electrochemical reactions. In this work, we used cobalt vacancies in Co
3
O
4
as an example and synthesized Co
3
O
4
with bivalent cobalt vacancies (Co
3
O
4
-VCo(II)) and trivalent cobalt vacancies (Co
3
O
4
-VCo(III)). Electrochemical results demonstrate that introducing cobalt vacancies considerably enhances the electrocatalytic activity of Co
3
O
4
. Furthermore, Co
3
O
4
-VCo(II) exhibits the most outstanding oxygen evolution ability with the fastest reaction kinetic rate. Quasi-
operando
X-ray photoelectron microscopy spectrum analysis results indicate that the presence of VCo(II) can accelerate CoOOH active site formation during the oxygen evolution reaction process. Density functional theory calculations reveal that introducing cobalt vacancies can endow Co
3
O
4
with metal-like conductivity. The O p-band center can be moved near the Fermi level, and the free energy barrier can be the lowest with the presence of VCo(II), resulting in a fast kinetics rate of oxygen exchange at the electrocatalyst surface and optimal adsorption energy to reaction intermediates to display excellent electrochemical ability. This work provides substantial guidance for designing efficient defect-rich electrocatalysts.
Electronic structure engineering on electrode materials could bring in a new mechanism to achieve high energy and high power densities in sodium ion batteries. Herein, we design and create Co ...vacancies at the interface of atomically thin CoSe2/graphene heterostructure and obtain Co1−xSe2/graphene heterostructure electrode materials that facilitate significant Na+ intercalation pseudocapacitance. Density functional theory (DFT) calculation suggests that the Na+ adsorption energy is dramatically increased, and the Na+ diffusion barrier is remarkably reduced due to the introduction of Co vacancy. The optimized electrode delivers a superior capacity of 673.6 mAh g−1 at 0.1 C, excellent rate capability of 576.5 mAh g−1 at 2.0 C and ultra‐long life up to 2000 cycles. Kinetics analysis indicates that the enhanced Na+ storage is mainly attributed to the intercalation pseudocapacitance induced by Co vacancies. This work suggests that the creation of cation vacancy could bestow heterostructured electrode materials with pseudocapacitive Na+ intercalation for high‐capacity and high‐rate energy storage.
The Co vacancies (VCo) at the interface of Co1−xSe2/graphene (GE) afford strong adsorption of Na+ and a low Na+ diffusion energy barrier to facilitate rapid intercalation/deintercalation of Na+ ions giving remarkable pseudocapacitance. The as‐prepared Co1−xSe2/GE‐based sodium ion batteries deliver high specific/rate capacity performance and exceptional cycling performance.
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Electronic structural engineering plays a key role in the design of high-efficiency catalysts. Here, to achieve optimal electronic states, introduction of exotic Fe dopant and Co ...vacancy into CoSe2 nanosheet (denoted as Fe-CoSe2-VCo) is presented. The obtained Fe-CoSe2-VCo demonstrates excellent catalytic activity as compared to CoSe2. Experimental results and density functional theory (DFT) calculations confirm that Fe dopant and Co defects cause significant electron delocalization, which reduces the adsorption energy of LiO2 intermediate on the catalyst surface, thereby obviously improving the electrocatalytic activity of Fe-CoSe2-VCo towards oxygen redox reactions. Moreover, the synergistic effect between Co vacancy and Fe dopant is able to optimize the microscopic electronic structure of Co ion, further reducing the energy barrier of oxygen electrode reactions on Fe-CoSe2-VCo. And the lithium-oxygen batteries (LOBs) based on Fe-CoSe2-VCo electrodes demonstrate a high Coulombic efficiency (CE) of about 72.66%, a large discharge capacity of about 13723 mA h g−1, and an excellent cycling life of about 1338 h. In general, the electronic structure modulation strategy with the reasonable introduction of vacancy and dopant is expected to inspire the design of highly efficient catalysts for various electrochemical systems.
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•A ultra-facile technique is reported for synthesis of cobalt deficient Co(OH)2 nanosheets.•Vco-Co(OH)2 had large surface area, low impedance, high heterogeneous rate constant than ...that of defect-free Co(OH)2.•Vco-Co(OH)2-based disposable sensor shows excellent electrochemical sensing performance for Glucose and l-Cysteine.
Engineering of nanomaterials with atomic defects has becoming an effective way to boost the sensitivity of the electrochemical biosensors but challenging. Herein, a rational, facile and in-situ strategy has been reported to obtain cobalt hydroxide nanosheets (VCo-Co(OH)2) with abundant cobalt vacancies. The cobalt defects greatly enriched electroactive sites and charge transfer rates, thereby delivered excellent electrocatalytic oxidation performance towards glucose and l-cysteine. The dynamic range and low limit of detection of glucose at VCo-Co(OH)2 electrodes were found as 0.4 μM–8.23 mM and 295 nM respectively. Besides, VCo-Co(OH)2 electrodes accurately sensed the l-cysteine with lowest detection limit (76.5 nM), and broad linear sensing range (200 nM-1.94 mM), which are better than the performance of defect-free Co(OH)2 electrodes, evidence that construction of cobalt vacancy significantly boosted the electrocatalysis. Importantly, fabricated sensors had excellent interference immunity against the many biomolecules, owns good stability and reproducibility. Present work not only proposed a novel and simplistic approach to prepare the metal hydroxides with copious metal cation vacancies for electrocatalysis but also provides economical, precise, high-sensitive and disposable biosensors for clinical analysis glucose and l-cysteine.
Hydrogen generated by electrochemical water splitting is an attractive alternative to fossil fuels. Herein, we developed hollow-like Co2N nanoarrays that serve as electrocatalysts for the hydrogen ...evolution reaction (HER) with surface engineering by argon plasma. The argon plasma-engraved Co2N nanoarrays (Ar-Co2N/CC) represent a dramatic catalytic performance for the HER with an overpotential of 34 mV at a current density of 10 mA cm–2 in an alkaline electrolyte, as well as outstanding durability of 240 h. Characterization experiments and density functional theory (DFT) calculations suggest that the enhanced HER activity is due to the rational coordination environment of Co, which can be tuned by Ar plasma engraving. Based on our research, one new view for conducting exceptional catalyst surface modification engineering via plasma engraving might be established.
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•Co-vacancy rich Co3O4 is synthesized by using layered cobalt glycerate as a precursor.•Vco-Co3O4 exhibits outstanding catalytic activity for the hydrolysis of ammonia ...borane.•Vco-Co3O4 yields a high hydrogen production rate of 934 mL min−1 gCat-1.•Vco-Co3O4 shows a low activation energy of 32.65 kJ mol−1 for catalytic hydrolysis.
Development of efficient and economical non-precious metal catalysts for dehydrogenation of ammonia borane is an important way to store and release hydrogen. Vacancy-engineered defective catalysts with modulated electronic structure allow ideal adsorption and dissociation of reactant molecules for the optimized catalytic activity. In this study, we report a facile synthesis of cobalt-defective Co3O4 (VCo-Co3O4) nanocatalyst by the calcination of layered cobalt glycerate as a key precursor. The stacked cobalt-oxygen sheets and interlayer bound glycerate anions in a layered structure are favorable for introducing cation vacancy during calcination process. The obtained Vco-Co3O4 exhibits outstanding catalytic activity for the hydrolysis of ammonia borane, along with a high hydrogen production rate of 934 mL min−1 gCat-1 and a low activation energy of 32.65 kJ mol−1. The catalytic performance of the VCo-Co3O4 catalyst can be well maintained for consecutive five cycles. The current study establishes a new example of cation vacancy strategy to facilitate the hydrolysis of ammonia borane for hydrogen generation.
•The introduction of copper into CoTe induces the formation of cobalt vacancies.•The electrode shows excellent performance in both half- and full-cell systems.•The proposed cobalt vacancy synthesis ...strategy can be extended to CoSe2 anode.•Cobalt vacancy can effectively reduce ∆GH* and improve charge transfer efficiency.
Designing novel electrode materials with unique structures is of great significance for improving the performance of lithium ion batteries (LIBs). Herein, copper-doped Co1-xTe@nitrogen-doped carbon hollow nanoboxes (Cu-Co1-xTe@NC HNBs) have been fabricated by chemical etching of CuCo-ZIF nanoboxes, followed by a successive high-temperature tellurization process. The as-synthesized Cu-Co1-xTe@NC HNBs composite demonstrated faster ionic and electronic diffusion kinetics than the pristine CoTe@NC HNBs electrode. The existence of Co-vacancy promotes the reduction of Gibbs free energy change (∆GH*) and effectively improves the Li+diffusion coefficient. XPS and theoretical calculations show that performance improvement is ascribed to the electronic interactions between Cu-Co1-xTe and nitrogen-doped carbon (NC) that trigger the shift of the p-band towards facilitation of interfacial charge transfer, which in turn helps boost up the lithium storage property. Besides, the proposed Cu-doping-induced Co-vacancy strategy can also be extended to other conversion-type cobalt-based material (CoSe2) in addition to as-obtained Cu-Co1-xSe2@NC HNBs anodes for long-life and high-capacity LIBs. More importantly, the fabricated LiCoO2//Cu-Co1-xTe@NC HNBs full cell exhibits a high energy density of 403 Wh kg−1 and a power density of 6000 W kg−1. We show that the energy/power density reported herein is higher than that of previously studied cobalt-based anodes, indicating the potential application of Cu-Co1-xTe@NC HNBs as a superior electrode material for LIBs.
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