Growth of nickel silicate nanoplates on reduced graphene oxide as layered nanocomposites for highly reversible lithium storage

Structure engineering of nickel silicate/carbon composite with boosted electrochemical performances for hybrid supercapacitors

In the wake of the carbon-neutral era, the exploration of innovative materials for energy storage and conversion has garnered increasing attention. While nickel silicates have been a focal point in energy storage research, their application in supercapacitors (SCs) has been relatively underreported due to poor conductivity. A newly designed architecture, designated as rGO@NiSiO@NiO/C (abbreviated for reduced graphene oxide (rGO), nickel silicate (NiSiO), nickel oxide/carbon (NiO/C)), has been developed to enhance the electrochemical performance of NiSiO. The incorporation of inner rGO provides structural support for NiSiO, enhancing conductivity, while the outer NiO/C layer not only boosts conductivity but also safeguards NiSiO from structural degradation and electrolyte dissolution. This architecture eliminates multi-phase mixtures, facilitating rapid electron/mass transfer kinetics and accelerating electrochemical reactions, resulting in exceptional electrochemical properties. The rGO@NiSiO@NiO/C architecture achieves a specific capacitance of 324F·g-1 at 0.5 A·g-1, with a superb cycle performance of ∼ 91 % after 10,000 cycles, surpassing state-of-the-art nickel silicates. Furthermore, the hybrid supercapacitor (HSC) device incorporating the rGO@NiSiO@NiO/C electrode attains an areal capacitance of 159 mF·cm-2 at 2.5 mA·cm-2, a retention ratio of ∼ 98 % after 10,000 cycles, and an energy density of 0.68 Wh·m-2 (26.7 Wh·kg-1) at 3.4 W·m-2 (343.8 W·kg-1). This study presents a layer-by-layer approach for constructing transition metal silicates/C architectures to enhance their electrochemical performance.

Achieving High Lithium Storage Capacity and Long-Term Cyclability of Novel Cobalt Germanate Hydroxide/Reduced Graphene Oxide Anodes with Regulated Electrochemical Catalytic Conversion Process of Hydroxyl Groups

To develop ternary transition-metal germanate anodes with superior lithium storage performances for lithium-ion batteries, a novel capacity counterbalance approach in one compound is designed by introducing an electrocatalytic conversion-type component with a positive cycling trend to compensate the negative cycling trend of the GeO₂ component. Novel cobalt germanate hydroxide (CGH) nanoplates chemically bonded on reduced graphene oxide (RGO) sheets are thus synthesized with a mild one-pot hydrothermal approach, constructing maximal face-to-face contact interfaces with interfacial bonds to boost the electrochemical conversion reactions. Furthermore, the hydroxyl groups (Co-OH) of CGH nanoplates are regulated by thermal annealing treatments, thus controlling the capacity contribution resulting from the electrocatalytic conversion reaction of LiOH to exactly offset the capacity fading of GeO₂. The results on the CGH electrodes at different cycling potentials confirm the stepwise electrochemical reactions of Co, GeO₂, and LiOH. The equilibrium of these electrochemical reactions ensures a stable cycling capacity without obvious fluctuations. Consequently, the optimal CGH/RGO hybrid anode delivers a reversible capacity as high as 1136 mA h g^-1 at 0.1 A g^-1 until 100 cycles. It also exhibits a long cyclability with a retained capacity of 560 mA h g^-1 at 1 A g^-1 until 1000 cycles. This work demonstrates a general and efficient capacity counterbalance method to highly boost lithium storage performances in terms of high capacity and long-term cyclability.

Si and Ge-Based Anode Materials for Li-, Na-, and K-Ion Batteries: A Perspective from Structure to Electrochemical Mechanism

Silicon and germanium are among the most promising candidates as anodes for Li-ion batteries, meanwhile their potential application in sodium- and potassium-ion batteries is emerging. The access of their entire potential requires a comprehensive understanding of their electrochemical mechanism. This Review highlights the processes taking place during the alloying reaction of Si and Ge with the alkali ions. Several associated challenges, including the volumetric expansion, particle pulverization, and uncontrolled formation of solid electrolyte interphase layer must be surmounted and different strategies, such as nanostructures and electrode formulation, have been implemented. Additionally, a new approach based on the use of layered Si and Ge-based Zintl phases is presented. The versatility of this new family permits the tuning of their physical and chemical properties for specific applications. For batteries in particular, the layered structure buffers the volume expansion and exhibits an enhanced electronic conductivity, allowing high power applications.

Cobalt Hydroxide Carbonate/Reduced Graphene Oxide Anodes Enabled by a Confined Step-by-Step Electrochemical Catalytic Conversion Process for High Lithium Storage Capacity and Excellent Cyclability with a Low Variance Coefficient

Transition metal carbonates/hydroxides have attracted much attention as appealing anode materials due to their considerable reversible electrochemical catalytic conversion capacity. However, their serious positive or negative trends with cycles caused by the electrochemical catalytic conversion seriously affect their practical applications. Herein, novel one-dimensional cobalt hydroxide carbonate (CHC) nanomaterials are tightly anchored on reduced graphene oxide (RGO) sheets via a facile one-pot hydrothermal synthesis, forming surface-confined domains to further restrict the electrochemical catalytic conversion process. The analysis on the cycled electrodes at varied potentials confirms that the added capacity of CHC arises from the step-by-step reversible reactions of Li₂CO₃ and LiOH under the electrochemical catalysis of Co metal generated by the conversion reaction of CHC. The reversible reaction of Li₂CO₃ is followed closely by that of LiOH in the discharge process, while the order is opposite in the charge process. Such a step-by-step electrochemical catalytic conversion process could confine each other to accommodate the volume change and avoid side reactions. The confined effect is further enhanced by limiting the width and length of the CHC, which are determined by regulating the nucleation and growth of CHC on the surface of RGO, leading to an extraordinary cyclability. The optimized CHC/RGO hybrid maintains a high reversible capacity of 1110 mA h g^-1 after 100 cycles at 0.1 A g^-1, which is much higher than the theoretical value of CHC (506 mA h g^-1) on the basis of the recognized conversion reaction. Furthermore, it keeps high reversible capacities of 755 and 506 mA h g^-1 after 200 cycles at 1 and 2 A g^-1, respectively, exhibiting a high-rate cyclability with the lowest coefficient of variance of 9.4% among the reported ones. The confined step-by-step electrochemical catalytic conversion process facilitates high lithium storage capacity and satisfactory cyclability with a pretty low variance coefficient.

Hierarchical mesoporous cobalt silicate architectures as high-performance sulfate-radical-based advanced oxidization catalysts

Self-sacrificial biomass-derived silica is a rising and promising approach to fabricate large metal silicates, which are practical water treatment agents ascribed for easy sedimentation and separation. However, the original biomass architecture is difficult to be maintained and utilized. Furthermore, sufficient ion diffusion pathways need to be created to satisfy massive mass transport in large bulk materials. Herein, a series of metal silicates, including cobalt silicate (CoSiO_x), copper silicate, nickel silicate, iron silicate, and magnesium silicate, are synthesized from Indocalamus tessellatus leaf as the biomass-derived silica source and investigated as catalysts in sulfate-radical-based advanced oxidization processes (SR-AOPs) for the first time. Among them, CoSiO_x presents an analogical sandwich structure as a leaf-derived template of micron-level size. More importantly, the interior hollow nanotubes assembled by small nanosheets provide numerous pathways for ion diffusion and remarkably promote the mass transport in such large bulk materials. Owing to the combination of the unique structure with the high reactivity of Co (II) toward peroxymonosulfate, CoSiO_x exhibits excellent catalytic performance with 0.242 and 0.153 min^-1 rate constants for the removal of methylene blue and phenol, respectively, which outperforms/is comparable to that of the reported nanomaterials toward organic contaminants in SR-AOPs.

Synthesis of urchin-like Ni3Si2O5(OH)4 hierarchical hollow spheres/GO composite with enhanced electrochemical properties for high-performance hybrid supercapacitors

Urchin-like Ni₃Si₂O₅(OH)₄ hierarchical hollow sphere/GO composites were synthesized, which showed an enhanced electrochemical performance of 165 F g⁻¹ at 0.5 A g⁻¹ and 84% capacity retention after 5000 cycles.

Efficient conversion of CO2 to methane using thin-layer SiOx matrix anchored nickel catalysts

Thin-layer SiO_x matrix anchored nickel catalysts with high specific surface area and a unique electronic/geometric structure were fabricated for efficient CO₂ methanation.

Enhanced lithium storage performances of novel layered nickel germanate anodes inspired by the spatial arrangement of lotus leaves

The rapid capacity degradation of Ge-based materials hinders their practical application for next generation lithium ion batteries, which could be solved by synthesizing Ge-containing ternary oxides, with new structures and hybridizing with carbon nanomaterials. Herein, novel Ni3Ge2O5(OH)4 nanosheets were synthesized and distributed in situ on reduced graphene oxide (RGO) sheets, with both flat-lying and vertically-grown spatial distributions to imitate the growth of lotus leaves. These two types of Ni3Ge2O5(OH)4 nanosheets enhance their efficient contact with RGO, and increase the mass loading of active materials. Furthermore, the interfacial bonds between RGO sheets and Ni3Ge2O5(OH)4 nanosheets are introduced to improve the diffusion rate of lithium ions. The RGO sheets act as a buffer matrix to sustain the volume change and prevent the nanosheets from aggregation. Consequently, the chemically bonded Ni3Ge2O5(OH)4/RGO hybrid delivers a high specific capacity of 863 mA h g-1 over 75 cycles, which is much higher than those for neat Ni3Ge2O5(OH)4 nanosheets or the hybrid without the interfacial bonding. This study provides a novel perspective for designing high-performance Ge-based anode materials for advanced lithium ion batteries.

High Lithium Storage Capacity and Long Cycling Life Fe3S4 Anodes with Reversible Solid Electrolyte Interface Films and Sandwiched Reduced Graphene Oxide Shells

Increasing demands for lithium-ion batteries (LIBs) with high energy density and high power density require highly reversible electrochemical reactions to enhance the cyclability and capacities of electrodes. As the reversible formation/decomposition of the solid electrolyte interface (SEI) film during the lithiation/delithiation process of Fe₃S₄ could bring about a higher capacity than its theoretical value, in the present work, synthesized Fe₃S₄ nanoparticles are sandwich-wrapped with reduced graphene oxide (RGO) to fabricate highly reversible and long cycling life anode materials for high-performance LIBs. The micron-sized long slit between sandwiched RGO sheets effectively prevents the aggregation of intermediate phases during the discharge/charge process and thus increases cycling capacity because of the reversible formation/decomposition of the SEI film driven by Fe nanoparticles. Furthermore, the RGO sheets interconnect with each other by a face-to-face mode to construct a more efficiently conductive network, and the maximum interfacial oxygen bridge bonds benefit the fast electron hopping from RGO to Fe₃S₄, improving the depth of the electrochemical reactions and facilitating the highly reversible lithiation/delithiation of Fe₃S₄. Thus, the resultant Fe₃S₄/RGO hybrid shows a highly reversible charge capacity of 1324 mA h g^-1 over 275 cycles at a current density of 100 mA g^-1, even retains 480 mA h g^-1 over 500 cycles at 1000 mA g^-1, which are much higher than reported values.

Self-templated Synthesis of Nickel Silicate Hydroxide/Reduced Graphene Oxide Composite Hollow Microspheres as Highly Stable Supercapacitor Electrode Material

Nickel silicate hydroxide/reduced graphene oxide (Ni₃Si₂O₅(OH)₄/RGO) composite hollow microspheres were one-pot hydrothermally synthesized by employing graphene oxide (GO)-wrapped SiO₂ microspheres as the template and silicon source, which were prepared through sonication-assisted interfacial self-assembly of tiny GO sheets on positively charged SiO₂ substrate microspheres. The composition, morphology, structure, and phase of Ni₃Si₂O₅(OH)₄/RGO microspheres as well as their electrochemical properties were carefully studied. It was found that Ni₃Si₂O₅(OH)₄/RGO microspheres featured distinct hierarchical porous morphology with hollow architecture and a large specific surface area as high as 67.6 m² g^-1. When utilized as a supercapacitor electrode material, Ni₃Si₂O₅(OH)₄/RGO hollow microspheres released a maximum specific capacitance of 178.9 F g^-1 at the current density of 1 A g^-1, which was much higher than that of the contrastive bare Ni₃Si₂O₅(OH)₄ hollow microspheres and bare RGO material developed in this work, displaying enhanced supercapacitive behavior. Impressively, the Ni₃Si₂O₅(OH)₄/RGO microsphere electrode exhibited outstanding rate capability and long-term cycling stability and durability with 97.6% retention of the initial capacitance after continuous charging/discharging for up to 5000 cycles at the current density of 6 A g^-1, which is superior or comparable to that of most of other reported nickel-based electrode materials, hence showing promising application potential in the energy storage area.

Facile preparation of hexagonal tin sulfide nanoplates anchored on graphene nanosheets for highly efficient sodium storage

Tin sulfide/graphene nanocomposite with hexagonal tin sulfide (SnS₂) nanoplates anchored on reduced graphene oxide (RGO) nanosheets was easily synthesized by one-step controllable hydrothermal growth followed by mild reduction. The SnS₂ hexagonal-plates distributed tightly and uniformly on the RGO support in a more favorable face-to-face (FTF) manner. The formation of SnS₂ nanoplates with hexagonal morphology may result from the accelerating growth of six energetically equivalent high-index (1 1 0) crystal planes and prohibiting growth of the (0 0 1) crystal plane on graphene. The FTF architecture is beneficial for the optimal electric contact efficiency of SnS₂ nanoplates with RGO matrix, thus leading to the greatly enhanced electrochemical performance of SnS₂/RGO composite than bare SnS₂. The graphene-constructed two-dimensional integrated conductive networks minimize the transport paths of electrons and Na ions between electrode and electrolyte as well as accommodate the mechanical strain during long term cyclic. The SnS₂/RGO composite exhibits great application potential as an anode for sodium ion batteries with the advantages of unique structure and superior sodium storage performance.

Na-ion Storage Performances of FeSe(x) and Fe2O3 Hollow Nanoparticles-Decorated Reduced Graphene Oxide Balls prepared by Nanoscale Kirkendall Diffusion Process

Uniquely structured FeSe(x)-reduced graphene oxide (rGO) composite powders, in which hollow FeSe(x) nanoparticles are uniformly distributed throughout the rGO matrix, were prepared by spray pyrolysis applying the nanoscale Kirkendall diffusion process. Iron oxide-rGO composite powders were transformed into FeSe(x)-rGO composite powders by a two-step post-treatment process. Metallic Fe nanocrystals formed during the first-step post-treatment process were transformed into hollow FeSe(x) nanoparticles during the selenization process. The FeSe(x)-rGO composite powders had mixed crystal structures of FeSe and FeSe2 phases. A rGO content of 33% was estimated from the TG analysis of the FeSe(x)-rGO composite powders. The FeSe(x)-rGO composite powders had superior sodium-ion storage properties compared to those of the Fe2O3-rGO composite powders with similar morphological characteristics. The discharge capacities of the FeSe(x)- and Fe2O3-rGO composite powders for the 200(th) cycle at a constant current density of 0.3 A g(-1) were 434 and 174 mA h g(-1), respectively. The FeSe(x)-rGO composite powders had a high discharge capacity of 311 mA h g(-1) for the 1000(th) cycle at a high current density of 1 A g(-1).

Hollow Nanostructured Metal Silicates with Tunable Properties for Lithium Ion Battery Anodes

Hollow nanostructured materials have attracted considerable interest as lithium ion battery electrodes because of their good electrochemical properties. In this study, we developed a general procedure for the synthesis of hollow nanostructured metal silicates via a hydrothermal process using silica nanoparticles as templates. The morphology and composition of hollow nanostructured metal silicates could be controlled by changing the metal precursor. The as-prepared hierarchical hollow nanostructures with diameters of ∼100-200 nm were composed of variously shaped primary particles such as hollow nanospheres, solid nanoparticles, and thin nanosheets. Furthermore, different primary nanoparticles could be combined to form hybrid hierarchical hollow nanostructures. When hollow nanostructured metal silicates were applied as anode materials for lithium ion batteries, all samples exhibited good cyclic stability during 300 cycles, as well as tunable electrochemical properties.