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Alkali metal ion batteries (AMIBs) are playing an irreplaceable part in the energy revolution, due to their intrinsic advantages of large capacity/power density and abundance of alkali metal ions in the earth’s crust. Despite their great promise, the inborn deficiencies of commercial graphite and other anodes being researched so far call for the quest of better alternatives that exhibit all-round performance with the balance of energy/power density and cycling stability. Gallium-based materials, with impressive capacity utilization and self-healing ability, provide an anticipated solution to this conundrum. In this review, an overview on the recent progress of gallium-based anodes and their storage mechanism is presented. The current strategies used as engineering solutions to meet the scientific challenges ahead are discussed, in addition to the insightful outlook for possible future study.

Metal-sulfur batteries are advanced energy storage systems featuring intriguingly high theoretical capacity and high energy density. Spurred on by the failures in commercializing Li-S and Na-S batteries, K-Q (Q = S, Se, and SexSy) batteries have entered the sights of researchers because of the low redox potential and natural abundance of element K and its synergistic reaction with S or Se. Unfortunately, the current K-Q battery still suffers from several drawbacks, such as drastic volume change, shuttling phenomenon, relatively low reactivity, and dendrite growth. To help to push forward progress of the K-Q battery, here in this review, we first introduce the operation principle and the fundamental challenges faced by the current K-Q batteries, followed by a comprehensive review of effective strategies that have been developed, including engineering of the electrode structure and optimization of the battery composition. Discussions of the mechanism are also included to deepen the understanding of such battery systems. Finally, we discuss the perspectives and challenges for practical application of K-Q batteries. We hope the insights provided in this review can shed light on this new yet rapidly developing field and offer guidance for the development of future high-performance K-Q batteries.

Aqueous Al-ion batteries (AAIBs) are the subject of great interest due to the inherent safety and high theoretical capacity of aluminum. The high abundancy and easy accessibility of aluminum raw materials further make AAIBs appealing for grid-scale energy storage. However, the passivating oxide film formation and hydrogen side reactions at the aluminum anode as well as limited availability of the cathode lead to low discharge voltage and poor cycling stability. Here, we proposed a new AAIB system consisting of an Al x MnO2 cathode, a zinc substrate-supported Zn-Al alloy anode, and an Al(OTF)3 aqueous electrolyte. Through the in situ electrochemical activation of MnO, the cathode was synthesized to incorporate a two-electron reaction, thus enabling its high theoretical capacity. The anode was realized by a simple deposition process of Al3+ onto Zn foil substrate. The featured alloy interface layer can effectively alleviate the passivation and suppress the dendrite growth, ensuring ultralong-term stable aluminum stripping/plating. The architected cell delivers a record-high discharge voltage plateau near 1.6 V and specific capacity of 460 mAh g-1 for over 80 cycles. This work provides new opportunities for the development of high-performance and low-cost AAIBs for practical applications. National Research Foundation (NRF) Accepted version

The discovery of novel electrode materials promises to unleash a number of technological advances in lithium-ion batteries. V2O5 is recognized as a high-performance cathode that capitalizes on the rich redox chemistry of vanadium to store lithium. To unlock the full potential of V2O5, nanotechnology solution and rational electrode design are used to imbue V2O5 with high energy and power density by addressing some of their intrinsic disadvantages in macroscopic crystal form. Here, we demonstrate a facile and environmental-friendly method to prepare nanorods-constructed 3D porous V2O5 architectures (3D-V2O5) in large-scale. The 3D porous architecture is found to be responsible for the enhanced charge transfer kinetics and Li-ion diffusion rate of the 3D-V2O5 electrode. As the result, the 3D-V2O5 surpasses the conventional bulk V2O5 by showing enhanced discharge capacity and rate capability (delivering 154 and 127 mAh g−1 at 15 and 20 C, respectively).

In the present study, V3O5 microcrystals that synthesized via vacuum calcination are employed as anodes for lithium‐ion batteries (LIBs) for the first time. Despite the widely observed sluggish reaction kinetics and poor cycling stability in most micro‐sized transition metal oxides, the V3O5 microcrystals exhibit excellent rate capability (specific capacities of 144 and 125 mAh g−1 are achieved at extremely high current densities of 20 and 50 A g−1, respectively) and long‐term cycling performance (specific capacity of 117 mAh g−1 is sustained over 2000 cycles at 50 A g−1). It is ascribed to the three‐dimensional open‐framework structure of the V3O5 microcrystals as a major factor in dictating the fast reaction kinetics (lithium diffusion coefficient: ~10−9 cm2 s−1). In addition, significant insight into the reaction mechanism of the V3O5 microcrystals in concomitant its phase evolution are obtained from ex‐situ XRD study, revealing that the V3O5 microcrystals undergo intercalation reaction with insignificant structural change in response to lithiation/delithiation.

Advanced energy storage systems hold critical significance in satisfying the ever-increasing global demand for energy. And as a viable and effective alternative to lithium-ion batteries that dominate the current energy market, Zn-based batteries [i.e. Zn-ion batteries (ZIBs) and Zn-air batteries (ZABs)] have attracted extensive research efforts. Zn metal possesses many advantages because of its high theoretical capacity, its inexpensiveness and its good safety characteristic, and in recent years, tremendous efforts have been carried out to accelerate the development of ZIBs and ZABs with various electrode materials and electrocatalysts being proposed and investigated. In addition, with advances in characterization techniques, the underlying reaction mechanisms of these materials are also being elucidated. Therefore, this review will provide a comprehensive summary of the latest progress in various electrode materials adopted in the current ZIBs and ZABs along with corresponding mechanisms. Specifically, Mn- and V-containing cathode materials for ZIBs and associated reaction mechanisms will be thoroughly discussed, and emerging cathodes such as Prussian blue analogues, NASICON-type nanostructures and organic compounds will be presented. In terms of ZABs, this review will discuss three major types of electrocatalysts, including noble metals, heteroatom-doped carbons and transition metal oxides/sulphides/phosphides/nitrides. In addition, as a critical factor in the performance of Zn-based batteries, challenges encountered by the current Zn anodes and strategies developed to tackle these issues will be discussed as well. Finally, a short summary including the current progress and future perspectives of ZIBs and ZABs will be provided.

Sodium-ion batteries (SIBs) are considered to be the most promising electrochemical energy storage devices for large-scale grid and electric vehicle applications due to the advantages of resource abundance and cost-effectiveness. The electrochemical performance of SIBs largely relies on the intrinsic chemical properties of the cathodic materials. Among the various cathodes, rhombohedral Na3V2(PO4)3 (NVP), a typical sodium super ionic conductor (NASICON) compound, is very popular owing to its high Na+ mobility and firm structural stability. However, the relatively low electronic conductivity makes the theoretical capacity of NVP cathodes unviable even at low rates, not to mention the high rate of charging/discharging. This is a major drawback of NVPs, limiting their future large-scale applications. Herein, a comprehensive review of the recent progresses made in NVP fabrication has been presented, mainly including the strategies of developing NVP/carbon hybrid materials and elemental doping to improve the electronic conductivity of NVP cathodes and designing 3D porous architectures to enhance Na-ion transportation. Moreover, the application of NVP cathodic materials in Na-ion full batteries is summarized, too. Finally, some remarks are made on the challenges and perspectives for the future development of NVP cathodes.

Silicon-based materials that have higher theoretical specific capacity than other conventional anodes, such as carbon materials, Li2 TiO3 materials and Sn-based materials, become a hot topic in research of lithium-ion battery (LIB). However, the low conductivity and large volume expansion of silicon-based materials hinders the commercialization of silicon-based materials. Until recent years, these issues are alleviated by the combination of carbon-based materials. In this review, the preparation of Si/C materials by different synthetic methods in the past decade is reviewed along with their respective advantages and disadvantages. In addition, Si/C materials formed by silicon and different carbon-based materials is summarized, where the influences of carbons on the electrochemical performance of silicon are emphasized. Lastly, future research direction in the material design and optimization of Si/C materials is proposed to fill the current gap in the development of efficient Si/C anode for LIBs.

In this study, we report an oxygen-doped MoS

A facile pathway of the electrocatalytic nitrogen oxidation reaction (NOR) to nitrate is proposed, and Ru-doped TiO

Highly active oxygen evolution reaction (OER) electrocatalysts are important to effectively transform renewable electricity to fuel and chemicals. In this work, we construct a series of multimetal oxide nanoplate OER electrocatalysts through successive cation exchange followed by electrochemical oxidation, whose electronic structure and diversified metal active sites can be engineered via the mutual synergy among multiple metal species. Among the examined multimetal oxide nanoplates, CoCeNiFeZnCuOx nanoplates exhibit the optimal adsorption energy of OER intermediates. Together with the high electrochemical active surface area, the CoCeNiFeZnCuOx nanoplates manage to deliver a small overpotential of 211 mV at an OER current density of 10 mA cm-2 (η10) with a Tafel slope as low as 21 mV dec-1 in 1 M KOH solution, superior to commercial IrO2 (339 mV at η10, Tafel slope of 55 mV dec-1), which can be stably operated at 10 mA cm-2 (at an overpotential of 211 mV) and 100 mA cm-2 (at an overpotential of 307 mV) for 100 h. Ministry of Education (MOE) National Research Foundation (NRF) The authors gratefully acknowledge the financial support from Singapore MOE AcRF Tier 2 under Grant Nos. 2017-T2-2- 069 and MOE Tier 1 2017-T1-002-009 and 2020-T1-001-031, and National Research Foundation of Singapore (NRF) Investigatorship, Award No. NRF2016NRF-NRFI001-22. We also acknowledge the 111 project (D18023) from Zhengzhou University for their support for this work.

The oxygen evolution reaction (OER) is a key process involved in energy and environment-related technologies. An ideal OER electrocatalyst should show high exposure of active sites and optimal adsorption energies of oxygenated species. However, earth-abundant transition-metal-based OER electrocatalysts still operate with sluggish OER kinetics. Here, a cation-exchange route is reported to fabricate cobalt-vanadium-iron (oxy)hydroxide (CoV-Fe0.28) nanosheets with tunable binding energies for the oxygenated intermediates. The formation of an amorphous/crystalline heterostructure in the CoV-Fe0.28 catalyst boosts the exposure of active sites compared to their crystalline and amorphous counterparts. Furthermore, the synergetic interaction of Co, V, and Fe cations in the CoV-Fe0.28 catalyst subtly regulates the local coordination environment and electronic structure, resulting in the optimal thermodynamic barrier for this elementary reaction step. As a result, the CoV-Fe0.28 catalyst exhibits superior electrocatalytic activity toward the OER. A low overpotential of 215 mV is required to afford a current density of 10 mA cm−2 with a small Tafel slope of 39.1 mV dec−1, which outperforms commercial RuO2 (321 mV and 86.2 mV dec−1, respectively). Ministry of Education (MOE) National Research Foundation (NRF) M.K. and J.Z. contributed equally to this work. The authors gratefully acknowledge the financial support from Singapore Ministry of Education (MOE) AcRF Tier 2 under Grant Nos. 2017-T2-2-069 and 2018-T2-01-010 and National Research Foundation of Singapore (NRF) Investigatorship, Award No. NRF2016NRF-NRFI001-22. The authors would also like to acknowledge 111 project (D18023) from Zhengzhou University for their support for this work.

The rational synthesis of transition metal sulfides with long cycle life and good rate performance is essential for building superior electrochemical energy storage devices. In this work, the MnS nanoparticles/N,S-codoping carbon nanotubes (MnS@N,S-C NTs) with double-layer carbon have been synthesized through a facile in situ transformation method. The synergetic coupling effects benefited from the advantages of double N,S-C layers, and porous structures are effective to allow fast electrons/lithium ions transport and keep good structural integrity during the charging/discharging process. Owing to the large surface area, the MnS@N,S-C NTs electrode is mainly pseudocapacitive in nature during the charge–discharge process, which is beneficial to enhance the electrochemical transfer kinetics. When used as anodes for lithium ion batteries, the MnS@N,S-C NTs exhibit a high specific capacity of 796 mAh g–1 during the 200th cycle at 1.0 A g–1. Even at 10.0 A g–1, the discharge specific capacity of the MnS@N,S-C ...

Oxidation induced irredeemable magnetic loss is of key concern in the high temperature applications of Sm2Co17-type permanent magnets. Herein, the atomic-scale oxidation mechanism of a Sm2Co17 magnet is unveiled using aberration-corrected transmission electron microscopy. Heating at 500 °C in air, the oxidation scale growth and energy product reduction of the magnets undergo a two-stage process. Due to the formation of a transition oxidation zone between the internal oxidation zone (IOZ) and matrix, the stage-I (t 1 1 ¯ 1} pyramidal planes act as the preferential oxygen diffusion pathways at the magnet side and top surfaces, respectively. This results in the non-uniform oxidation, i.e., the oxidation scale at the cylindrical sides of the magnet is 1.4–2 times thicker than that at the top. Oxygen penetration along basal or pyramidal planes firstly induces the oxidation of 1:3R Z-plates and Cu depletion from the 1:5H boundaries in the magnet. Then the 1:5H and 2:17R phases are decomposed into Sm, CoFe and Cu metal lamellae, which finally evolve into the IOZ with nano-oxides, oxygen-enriched CoFe and Cu particles inside. This work sheds light on the atomic-scale oxidation behavior of Sm2Co17-type magnets.

Layered alkali metal oxides have been emerged as an alternative group of low-cost and promising electrocatalysts in water oxidation. The distinct layered configuration may offer some interesting possibilities to tune the intrinsic activity by regulating the intralayer edge-shared CoO6 octahedra and the CoO2 interlayer spacing/strain. In this work, electrochemical desodiation tuning method is explored on intralayer Ag, Cu, Ce-doped Na0.7CoO2 for highly active OER catalysts. It is demonstrated that the ΔGOH* value in the volcano plot is optimized by proper desodiation. Meanwhile, the lattice strain introduced along with the desodiated process modulates the ΔGOH*, according to first principle calculations. It shows that ∼0.157 % compressive strain in the CoO2 layers and ∼1% tensile strain between CoO2 layers are introduced in the desodiated Ag doped Na0.7CoO2. Among these catalysts, the desodiated Ag-Na0.7CoO2 sample exhibits an optimal RuO2-beyond water oxidation (OER) activity with the lowest overpotential of 236 mV@10 mA/cm2, the smallest Tafel slope of 48 mV/dec and the highest mass current density of 227.8 A/g. This work provides an interesting avenues to optimize existing layered materials with inter/intralayer modifications for highly efficient water oxidation electrolysis.

Irredeemable magnetic loss caused by oxidation remains a critical concern for the application of Sm2Co17-type permanent magnets. Herein, oxygen induced decomposition in the early-stage oxidation of a Sm(CobalFe23.5Cu4.9Zr1.7)7.5 magnet is studied using aberration-corrected TEM. Upon oxygen penetration along the 1:3R Z-plates, the 1:5H cell boundaries are decomposed into separate Sm and Co(Fe) lamellae with thicknesses of ~5 nm. Subsequently, the Fe-rich 2:17R cells are decomposed into similar metal lamellae. Besides the normal hexagonal stacking, the Sm lamellae also exhibit a twinned face-centered cubic (FCC) structure. The decomposed Co(Fe) lamellae and Cu particles are FCC-structured. The nano-twinned Cu particles are sparsely distributed. Interestingly, the closely-packed planes of these metal lamellae tend to align with the {0001}2:17R plane. The metal lamellae enriched with oxygen interstitials finally turn into nano-oxides by oxidation. This work offers in-depth insights into the initial oxidation behavior of alloys. This work was conducted within the Rolls-Royce@NTU Corporate Lab with support from the Industry Alignment Fund (IAF) Singapore under the Corp-Lab@University Scheme. We also acknowledge the FACTs@NTU for the usage of SEM and TEMs

Few-layer black phosphorus (BP) is a promising anode material for sodium ion batteries (SIBs) due to its high theoretical capacity and favorable layered structure. However, practical implementation is hindered by sluggish reaction kinetics and large volume change during de/sodiation process. Especially, combining BP with large portion of low-capacity carbonaceous materials is a common strategy to improve the Na storage properties, but leading to reduced specific capacity based on the overall mass of the whole electrode. To address these challenges, nanoscale surface engineering of few-layer BP is herein performed by homogeneously depositing horizontally aligned Poly(3, 4-ethylenedioxythiophene) (PEDOT) nanofibers on specially surface-modified BP nanosheets. Such material design could achieve simultaneously: (1) enhanced charge transfer kinetics and (2) super surface wettability with electrolyte. Benefiting from the unique functionalization, the reaction kinetics are greatly enhanced accordingly for both sodium and lithium storage. Our strategy sheds light on designing advanced electrodes for high-performance rechargeable batteries and other energy storage/conversion devices.

Sodium-ion batteries (SIBs) are considered to be the most promising electrochemical energy storage devices for large-scale grid and electric vehicle applications due to the advantages of resource abundance and cost-effectiveness. The electrochemical performance of SIBs largely relies on the intrinsic chemical properties of the cathodic materials. Among the various cathodes, rhombohedral Na3V2(PO4)3 (NVP), a typical sodium super ionic conductor (NASICON) compound, is very popular owing to its high Na+ mobility and firm structural stability. However, the relatively low electronic conductivity makes the theoretical capacity of NVP cathodes unviable even at low rates, not to mention the high rate of charging/discharging. This is a major drawback of NVPs, limiting their future large-scale applications. Herein, a comprehensive review of the recent progresses made in NVP fabrication has been presented, mainly including the strategies of developing NVP/carbon hybrid materials and elemental doping to improve the electronic conductivity of NVP cathodes and designing 3D porous architectures to enhance Na-ion transportation. Moreover, the application of NVP cathodic materials in Na-ion full batteries is summarized, too. Finally, some remarks are made on the challenges and perspectives for the future development of NVP cathodes.

Aqueous multivalent metal ion batteries (AMMIBs), with their unique strengths of high safety, low cost and the characteristic of multiple electron transfers, have been widely applied in the fields of wearable devices, consumer electronics and electric vehicles. Layer structured materials are regarded as promising electrode materials for AMMIBs owing to their tunable interlayer spacing and the ability to accommodate other guest ions or molecular. However, their large-scale application is impeded by several issues including dissolution, structural instability, low conductivity and poor electrochemical properties. This review highlights various strategies aimed to solve these issues for layer structured materials. It begins with the brief introduction on the fundamental characteristics of the AMMIBs and challenges facing layer structured materials. Subsequently, one section is to elaborate several strategies specific to layer structured materials for AMMIBs in detail with corresponding progress highlighted, which pave the way to high-performance AMMIBs. The last, a brief summary of the strengths and weaknesses of the above strategies are presented and focus is placed on possible direction for further improvements in this field. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This work was financially supported by Singapore MOE AcRF Tier 2 under Grant Nos. 2017-T2-2-069 and 2018-T2-01-010, Tier 1 under grant Nos. 2020-T1-001-031 and 2017-T1-002-009, and National Research Foundation of Singapore (NRF) Investigatorship, award Number NRF2016NRF-NRFI001-22, and the China Scholarship Council (201806370038). We also like to acknowledge 111 project (D18023) from Zhengzhou University for their support.

The fabrication of novel multifunctional nanohybrids of vanadium carbide nanoparticles decorated reduced graphene oxide (RGO) is presented. The resulting composite exhibits large specific surface area and enhanced electrical conductivity, which can effectively increase the number of active sites and facilitate the charge transport. As a result, the V8C7/RGO electrode demonstrates comparable oxygen reduction reaction (ORR) catalytic activity with commercial Pt/C in terms of high electron transfer number, high current density and good durability. In particular, the onset potential of the as-prepared sample is only about 50 mV lower than that of the Pt/C catalyst. When the V8C7/RGO was evaluated as anode material for lithium ion batteries (LIBs), the V8C7/RGO nanocomposite shows a high reversible specific capacity (1st-cycle charge capacity of 995.8 mAh g−1 at 0.1 A g−1), a long cycling life (specific capacity of 349.6 mAh g−1 after 400 cycles at 10 A g−1), and an excellent rate performance (e. g. specific capacity of 277.2 mAh g−1 at 10 A g−1).

A facile and effective approach to prepare Co 3 O 4 /CoFe 2 O 4 hollow cubes with uniform size and complex interior architectures is proposed via annealing of metal-cyanide-bridged hybrid coordination polymers (HCPs). The synergistic effect of the hybrid metal oxides and the rational design of the architecture endow these heterostructures with good lithium storage property and charge carrier transfer kinetics. In the hybrid materials, CoFe 2 O 4 offers high theoretical capacity and Co 3 O 4 provides stability at high current densities, leading to the significant enhancement in lithium storage properties comparing to the pure CoFe 2 O 4 . For example, Co 3 O 4 /CoFe 2 O 4 heterostructures annealed at 800 °C exhibit a high capacity of 511 mA h g −1 at a current density of 8.0 A g −1 and a reversible capacity of 515 mA h g −1 during the 500th cycle at a current density of 5.0 A g −1 .

Large-scale preparation of single-crystalline V 2 O 5 nanobelts is successfully demonstrated with a simple solution treatment process under ambient condition using commercial V 2 O 5 powders as the precursor. Unlike the commonly recognized Ostwald ripening process that involves the dissolution of small crystals and the redeposition of the dissolved species on the more energetically favored large particles, this preparation shows that the reaction mechanism of our method follows a different route, in which the large commercial V 2 O 5 powders (1–4 μm) dissolve in the solution and eventually transform into V 2 O 5 nanobelts with lengths up to several tens of micrometers, widths of 5–50 nm, and thicknesses of only ~5 nm. The density function theory (DFT) calculation indicates that the preferential growth of V 2 O 5 nanobelts along the [010] direction is attributed to the anisotropic bonding of V 2 O 5 layered structure resulting in the fastest nucleation rate at the V 2 O 5 (010) surface. These nanobelts possess a remarkably large surface area, which is about 14 times higher than that of the V 2 O 5 precursor. Binder-free bulky papers can be prepared by the intertwining V 2 O 5 nanobelts with the acid-treated multi-walled carbon nanotubes. When the V 2 O 5 nanobelts are applied as the cathodes in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), such robust and flexible electrodes demonstrate superior lithium and sodium storage performances at fast charge/discharge rates, delivering 144 mA h g −1 at 20 C in LIBs and 61 mA h g −1 at 10 C in SIBs respectively.

Lithium-ion capacitors (LICs) are hybrid energy storage devices that have the potential to bridge the gap between conventional high-energy lithium-ion batteries and high-power capacitors by combining their complementary features. The challenge for LICs has been to improve the energy storage at high charge−discharge rates by circumventing the discrepancy in kinetics between the intercalation anode and capacitive cathode. In this article, the rational design of new nanostructured LIC electrodes that both exhibit a dominating capacitive mechanism (both double layer and pseudocapacitive) with a diminished intercalation process, is reported. Specifically, the electrodes are a 3D interconnected TiC nanoparticle chain anode, synthesized by carbothermal conversion of graphene/TiO2 hybrid aerogels, and a pyridine-derived hierarchical porous nitrogen-doped carbon (PHPNC) cathode. Electrochemical properties of both electrodes are thoroughly characterized which demonstrate their outstanding high-rate capabilities. The fully assembled PHPNC//TiC LIC device delivers an energy density of 101.5 Wh kg−1 and a power density of 67.5 kW kg−1 (achieved at 23.4 Wh kg−1), and a reasonably good cycle stability (≈82% retention after 5000 cycles) within the voltage range of 0.0−4.5 V.

Two-dimensional (2D) graphene oxide/polypyrrole (GO/PPy) hybrid materials derived from in-situ polymerization are used as precursors for constructing functionalized three-dimensional (3D) porous nitrogen-doped carbon nanosheet frameworks (FT-PNCNFs) through a one-step activation strategy. In the formation process of FT-PNCNFs, PPY is directly converted into hierarchical porous nitrogen-doped carbon layers, while GO is simultaneously reduced to become electrically conductive. The complementary functions of individual components endow the FT-PNCNFs with excellent properties for both supercapacitors (SCs) and sodium ion batteries (SIBs) applications. When tested in symmetrical SC, the FT-PNCNFs demonstrate superior energy storage behaviour. At an extremely high scan rate of 3000 mV s −1 , the cyclic voltammetry (CV) curve retains an inspiring quasi-rectangle shape in KOH solution. Meanwhile, high capacitances (∼247 F g −1 at 10 mV s −1 ; ∼146 F g −1 at 3000 mV s −1 ) and good cycling stability (∼95% retention after 8000 cycles) are achieved. In addition, an attractive SIB anode performance could be achieved. The FT-PNCNFs electrode delivers a reversible capacity of 187 mAh g −1 during 160th cycle at 100 mA g −1 . Its reversible capacity retains 144 mAh g −1 after extending the number of cycles to 500 at 500 mA g −1 .

One-dimensional (1D) carbon-supported nanostructured CoP and FeP4 were prepared using fibrous elastin proteins that served as starting materials through an oil-phase method and the as-synthesized products were investigated for their lithium and sodium storage properties. The 1D CoP and FeP4 are composed of nanosized particles decorated on carbon supports. The 1D CoP and FeP4 nanostructures are ∼2 μm in length and 20–50 nm in diameter. The particles on the exterior of the 1D structure are 5–10 nm in diameter. To investigate the as-synthesized 1D TMPs in energy storage applications, the as-synthesized 1D CoP nanostructures are applied as an anode material in half-cells for LIBs and SIBs. For lithium storage performances, the anode delivers a specific capacity as high as ∼740 mAh g−1 at 0.2C and shows good rate performance and capacity retention as well as high rate capability (e.g. a stable specific capacity of ∼365 mAh g−1 for 120 cycles at 3.0C). In SIBs, at 0.2 and 5.0C, the specific capacities of 491.60 and 314.84 mAh g−1 are delivered, respectively. When tested at 1.0, 2.0, and 5.0C, the specific capacities are stable at ∼400, 360, and 300 mAh g−1 over 250, 250, and 1000 cycles, respectively.

The development of 2-dimensional materials has expanded beyond the realm of graphene, and now includes inorganic 2-dimensional transition metal oxides/hydroxides, which show promise for a wide range of applications. As an emerging class of nanoscale materials, they show unprecedented properties that are unattainable in their bulk lamellar systems, which can be attributed to their confined thickness compared to several tens of micrometer lateral dimensions. Such qualities make them viable candidates for battery and supercapacitor applications. There are a few challenges ahead for 2-dimensional transition metal oxides/hydroxides, including the limited types of 2-dimensional parent materials in bulk form, the controlled synthesis of 2-dimensional nanostructures with nonlayered structures, and the ability to control the properties of layers by tuning the chemistry and nanoscopic features. This Focus Review will cover the research landscape of 2-dimensional transition metal oxides/hydroxides, ranging from synthetic approaches, to understanding the properties that emerge at the single-layer scale, to exploiting these properties in both new and existing technologies.

A facile pathway of the electrocatalytic nitrogen oxidation reaction (NOR) to nitrate is proposed, and Ru-doped TiO2 /RuO2 (abbreviated as Ru/TiO2 ) as a proof-of-concept catalyst is employed accordingly. Density functional theory (DFT) calculations suggest that Ruδ + can function as the main active center for the NOR process. Remarkably doping Ru into the TiO2 lattice can induce an upshift of the d-band center of the Ru site, resulting in enhanced activity for accelerating electrochemical conversion of inert N2 to active NO*. Overdoping of Ru ions will lead to the formation of additional RuO2 on the TiO2 surface, which provides oxygen evolution reaction (OER) active sites for promoting the redox transformation of the NO* intermediate to nitrate. However, too much RuO2 in the catalyst is detrimental to both the selectivity of the NOR and the Faradaic efficiency due to the dominant OER process. Experimentally, a considerable nitrate yield rate of 161.9 µmol h-1 gcat -1 (besides, a total nitrate yield of 47.9 µg during 50 h) and a highest nitrate Faradaic efficiency of 26.1% are achieved by the Ru/TiO2 catalyst (with the hybrid composition of Rux Tiy O2 and extra RuO2 by 2.79 wt% Ru addition amount) in 0.1 m Na2 SO4 electrolyte.

In this study, we report an oxygen-doped MoS2 quantum dot (O-MoS2 QD) hybrid electrocatalyst for the hydrogen evolution reaction (HER). The O-MoS2 QDs were prepared with a one-pot microwave method by hydrazine-mediated oxygen-doping. The synthetic method is straightforward, time-saving, and can be applied in large scale preparation. Ultra-small O-MoS2 QDs with the average size of 5.83 nm and 1-4 layers can be uniformly distributed on the surface of reduced graphene oxide (RGO). Benefited from the unique structure and the doping effect of oxygen in the MoS2 QDs and the great number of active sites, the O-MoS2 QD hybrid displayed outstanding electrocatalytic performance toward HER. A low overpotential of 76 mV at 10 mA/cm2 and a Tafel slope of 58 mV/dec were obtained in an acidic solution toward HER. Additionally, the resultant O-MoS2 QD hybrid also exhibited excellent stability and durability toward HER, displaying negligible current density loss after 1000 cycles of cyclic voltammetry. The design and synthesis of the electrocatalyst in this work open up a prospective route to prepare active and stable electrocatalysts toward substituting precious metals for hydrogen generation. Ministry of Education (MOE) Published version The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 21765016) and Singapore MOE Tier 2 (Grant Nos. MOE2017- T2-2-069 and MOE2018-T2-1-010). This work was also supported by Ningxia leading scientific and technological innovation talents Project (Grant No. KJT2018002), the Natural Science Foundation of Ningxia (Grant No. 2018AAC03012), and the First-rate Discipline Construction Project of Ningxia (Grant No. NXYLXK2017A04).

To further increase the energy and power densities of lithium-ion batteries (LIBs), monoclinic Li

A general and simple approach for large-scale synthesis of porous hollow spinel AFe2O4 nanoarchitectures via metal organic framework self-sacrificial template strategy is proposed. By employing this method, we can successfully synthesize uniform NiFe2O4, ZnFe2O4, and CoFe2O4 hollow architectures that are hierarchically assembled by nanoparticles. When these hollow microcubes were tested as anode for lithium ion batteries, good rate capability and long-term cycling stability can be achieved. For example, high specific capacities of 636, 449, and 380 mA h g–1 were depicted by NiFe2O4, ZnFe2O4, and CoFe2O4, respectively, at a high current density of 8.0 A g–1. NiFe2O4 exhibits high specific capacities of 841 and 447 mA h g–1 during the 100th cycle when it was tested at current densities of 1.0 and 5.0 A g–1, respectively. Discharge capacities of 390 and 290 mA h g–1 were delivered by the ZnFe2O4 and CoFe2O4, respectively, during the 100th cycle at 5.0 A g–1. MOE (Min. of Education, S’pore) Published version

Nitrogen and sulfur dual-doped Mo2 C nanosheets provide low operating potential (-86 mV for driving 10 mA cm(-2) of current density). Co-doping of N and S heteroatoms can improve the wetting property of the Mo2C electrocatalyst in aqueous solution and induce synergistic effects via σ-donation and π-back donation with hydronium cation.

In this study, we present a new strategy on controlling the interaction between the Li 2 O 2 -catalyst interfaces through improving the affinity of catalyst surface towards Li 2 O 2 molecules. A seed-mediated growth approach has been developed to synthesize Pt nanosheets on the stainless steel mesh using Fe as the seed. We further grow a uniform layer of metallic Cu nanoparticles on Pt nanosheets surface through electrochemical deposition. The Cu is converted to CuO by exposing it to air under ambient condition. Such strategy has effectively solved the problem of non-uniform deposition of CuO on Pt surface that arises from the poor interaction of oxides on metals. By converting the oxide-on-metal to metal-on-metal system, a relatively uniform of CuO can be successfully deposited on Pt nanosheets. The CuO on Pt provides multiple nucleation sites on the surface of the cathode, which facilitates the formation of Li 2 O 2 thin layer in the discharge cycle. This process plays a crucial role in achieving a high round-trip efficiency of 88%, reversible specific capacity of 1648 mAh g −1 (683 mAh g −1 with respect to the total electrode mass including Li 2 O 2 ) at 100 mA g −1 and maintains capacity retention of 98% during the 60th cycle at a high current density of 1 A g −1 .

Transition metal sulfides gain much attention as electrode materials for supercapacitors due to their rich redox chemistry and high electrical conductivity. Designing hierarchical nanostructures is an efficient approach to fully utilize merits of each component. In this work, amorphous MoS(2) is firstly demonstrated to show specific capacitance 1.6 times as that of the crystalline counterpart. Then, crystalline core@amorphous shell (Ni(3)S(4)@MoS(2)) is prepared by a facile one-pot process. The diameter of the core and the thickness of the shell can be independently tuned. Taking advantages of flexible protection of amorphous shell and high capacitance of the conductive core, Ni(3)S(4) @amorphous MoS(2) nanospheres are tested as supercapacitor electrodes, which exhibit high specific capacitance of 1440.9 F g(-1) at 2 A g(-1) and a good capacitance retention of 90.7% after 3000 cycles at 10 A g(-1). This design of crystalline core@amorphous shell architecture may open up new strategies for synthesizing promising electrode materials for supercapacitors.

Aqueous electrolyte-based asymmetric electrochemical capacitors (AECs) are promising in the field of energy storage because of their wider potential windows compared to the symmetric capacitors and higher ionic conductivity compared to the organic electrolytes. Most of the research works on AECs are directed towards cathode materials, while anode materials have rarely been investigated. Herein, a novel AEC is constructed, in which two highly conductive and lightweight graphitic substrates, graphene framework and graphene foam, are hybridized with Fe3O4@C core–shell nanoparticles (anodes) and mesoporous Co(OH)2 nanosheets arrays (NAs) (cathodes), respectively. The as-assembled AEC device shows extended cell voltage (0.0–1.6 V) and excellent cycle stability (72% retention after 8000 cycles). More importantly, a high specific energy of 75 W h kg−1 is achieved at a specific power of 400 W kg−1. Even at a 10.3 s charge/discharge rate, specific energy as high as 33 W h kg−1 can be retained.

Iron pyrite nanocubes with particle sizes of around 80–120 nm have been synthesized via a facile solvothermal method. Time-dependent characterization found that the iron(II) chloride and sulfur precursors first react to form sheet-like amorphous Fe1−xS, which transforms into pyrite FeS2 nanocubes upon further heating. As an anode material for lithium ion batteries, the as-synthesized pyrite FeS2 nanocubes were found to deliver a reversible discharge capacity of 540 mA h g−1 after cycling for 150 cycles at a current density of 1 A g−1. Even at higher current density of 5 A g−1, the pyrite FeS2 electrode still managed to give a stable discharge capacity of about 220 mA h g−1. The enhanced lithium storage properties are attributed to its higher specific surface area that can provide more lithium ion (Li+) reaction sites, leading to less polarization and better cycling performance.

Although Li-oxygen batteries offer extremely high theoretical specific energy, their practical application still faces critical challenges. One of the main obstacles is the high charge overpotential caused by sluggish kinetics of charge transfer that is closely related to the morphology of discharge products and their distribution on the cathode. Here, a series of noble metal nanoparticles (Pd, Pt, Ru and Au) are encapsulated inside end-opened carbon nanotubes (CNTs) by wet impregnation followed by thermal annealing. The resultant cathode materials exhibit a dramatic reduction of charge overpotentials compared to their counterparts with nanoparticles supported on CNT surface. Notably, the charge overpotential can be as low as 0.3 V when CNT-encapsulated Pd nanoparticles are used on the cathode. The cathode also shows good stability during discharge–charge cycling. Density functional theory (DFT) calculations reveal that encapsulation of “guest” noble metal nanoparticles in “host” CNTs is able to strengthen the electron density on CNT surfaces, and to avoid the regional enrichment of electron density caused by the direct exposure of nanoparticles on CNT surface. These unique properties ensure the uniform coverage of Li2O2 nanocrystals on CNT surfaces instead of localized distribution of Li2O2 aggregation, thus providing efficient charge transfer for the decomposition of Li2O2.

Metallopolymer nanowalls were prepared through a simple wet-chemical process using reduced graphene oxides as heterogeneous nucleation aids, which also help to form conductive electron paths. The nanowalls grow vertically on graphene surface with 100 -200 nm in widths and ∼20 nm in thickness. The Fe-based metallopolymer nanowall-based electrode shows best performance as O2 cathode exhibiting high round-trip efficiencies and stable cycling performance among other transition metal containing metallopolymer counterparts. The electrode delivers discharge–charge capacities of 1000 mAh/g for 40 cycles and maintains round-trip efficiencies >78 % at 50 mA/g. The 1st-cycle round-trip efficiencies are 79%, 72%, and 65% at current densities of 50, 200, and 400 mA/g, respectively. The NMR analysis of the Fe-based metallopolymer based electrode after 40 cycles reveals slow formation of the side products, CH3CO2Li and HCO2Li.

We demonstrate in this paper facile synthesis of CoS2 and NiS2 hollow spheres with various interiors through a solution-based route. The obtained CoS2 microspheres constructed by nanosheets display a three-dimensional architecture with solid, yolk-shell, double-shell, and hollow interiors respectively, with continuous changes in specific surface areas and pore-size distributions. Especially, the CoS2 hollow spheres demonstrate excellent supercapacitive performance including high specific capacitance, good charge/discharge stability and long-term cycling life, owing to the greatly improved faradaic redox reaction and mass transfer. Furthermore, CoS2 hollow spheres exhibit superior electrocatalytic activity for disulfide/thiolate (T2/T−) redox electrolyte in dye-sensitized solar cells (DSCs). Therefore, this work provides a promising approach for the design and synthesis of structure tunable materials with largely enhanced supercapacitor behavior, which can be potentially applied in energy storage devices.

Composite films of platinum and polyaniline (Pt/PANI) with different Pt loadings are prepared by chemical reduction and then a spin-coating process on fluorine-doped tin oxide (FTO) substrates. The obtained Pt/PANI transparent counter electrodes are applied in quasi-solid dye-sensitized solar cells (QDSCs) from front and rear light illuminations, using electrospun poly(vinylidenefluoride-co-hexafluoropropylene)/TiO 2 (PVDF-HFP/TiO 2 ) as the electrolyte. The analytical results show that the 1.8-nm sized Pt nanoparticles are distributed uniformly in the Pt/PANI film when the Pt loading is 1.5 μg cm −2 . Electrocatalytic activity of the Pt/PANI electrode with 1.5 μg cm −2 Pt loading for the I 3 − /I − redox reaction is higher than the conventional sputtered Pt electrode. Furthermore, the mean optical transmittance of the Pt/PANI electrodes is above 60% in the wavelength of 400–800 nm. The optimal QDSC composed of Pt/PANI with 1.5 μg cm −2 Pt loading exhibits power conversion efficiencies of 6.34% and 3.85%, when measured using an AM1.5G solar simulator at 100 mW cm −2 under front and rear light illuminations. The efficiencies are both higher than those of the QDSCs employing the conventional sputtered Pt counter electrode with 8.3 μg cm −2 Pt loading. Moreover, the QDSC exhibits superior long-term stability. These promising results make the potential application of Pt/PANI films as cost-effective, transparent counter electrodes.

In this work, a one-dimensional Co3O4@TiO2 core-shell electrode material with superior electrochemical performance is fabricated by a convenient and controllable route. The approach involves two main steps: the homogeneous deposition of polydopamine and TiO2 layers in sequence on the cobalt coordination polymer and the thermal decomposition of the polymer matrix. The as-prepared electrode material can achieve excellent electrochemical properties and stability as an anode material for lithium ion batteries, such as a high specific capacity of 1279 mA h g(-1), good cycling stability (around 803 mA h g(-1) at a current density of 200 mA g(-1) after 100 cycles), and stable rate performance (around 520 mA h g(-1) at a current density of 1000 mA g(-1)). This dramatic electrochemical performance is mainly attributed to the excellent structural characteristics, which could improve the electrical conductivity and lithium ion mobility, as well as electrolyte permeability and architectural stability during cycling.