Critical roles of molybdate anions in enhancing capacitive and oxygen evolution behaviors of LDH@PANI nanohybrids

Ce-4f as an electron-modulation reservoir weakening Fe-O bond to induce iron vacancies in CeFevNi hydroxide for enhancing oxygen evolution reaction

Designing novel rare-earth-transition metal composites is at the forefront of electrocatalyst research. However, the modulation of transition metal electronic structures by rare earths to induce vacancy defects and enhance electrochemical performance has rarely been reported. In this study, we systematically investigate the mechanism by which Ce-4f electron modulation weakens the Fe-O bond, thereby altering the electronic structure in CeFevNi hydroxide to improve oxygen evolution reaction (OER) performance. Theoretical calculations and experimental characterizations reveal that Ce-4f orbitals function as electron-modulation reservoirs, capable not only of retaining or donating electrons but also of influencing the material's electronic structure. Moreover, Ce-4f bands optimize the Fe lower Hubbard bands (LHB) and O-2p bands, leading to weakened Fe-O bonds and the formation of cationic vacancies. This change results in the upshift of the d-band center at the active sites, favoring the reaction energy barrier for oxygen intermediates in the OER process. The synthesized catalyst demonstrated an overpotential of 201 mV at 10 mA cm-2 and a lifetime exceeding 200 h at 100 mA cm-2 under alkaline conditions. This work offers a proof-of-concept for the application of the mechanism of rare earth-induced transition metal vacancy defects, providing a general guideline for the design and development of novel highly efficient catalysts.

High-performance aqueous rechargeable NiCo//Zn battery with molybdate anion intercalated CoNi-LDH@CP bilayered cathode

Seeking cathode materials with high areal capacity and excellent cycling tolerance is a key step to develop aqueous rechargeable zinc-based alkaline batteries with high energy density, power density and excellent stability. Here, the bilayered cathode composite (MCN-LDH@CP) of molybdate intercalated cobalt-nickel layered hydroxide nanosheets (MCN-LDH) grown on cobalt phosphate octahydrate microsheet (CP) was prepared by a two-step hydrothermal process. Molybdate intercalation significantly reduces the thickness of cobalt-nickel layered hydroxide, greatly increases its specific surface area, regulates its pore distribution, increases the crystal plane spacing, promotes the diffusion rate of hydroxide in it, and increases its specific capacity. Meanwhile, the bilayered MCN-LDH@CP electrode significantly improved the areal energy density (2.89 mWh/cm2) and peak power density (111.22 mW/cm2) and cycle stability (97.8 % after 7000 cycles) of the CoNi//Zn battery. The excellent stability is mainly due to the fact that the MCN-LDH overlay inhibits the loss of P element of CP and improves the structural stability of the sample. The quasi-solid-state MCN-LDH@CP//Zn battery can still charge a mobile phone even when hammered and pierced, showing excellent safety and reliability. This work opens a new avenue to develop CoNi//Zn batteries with high energy density, power density and excellent tolerance.

Design and fabrication of MoO42--intercalated LDH nanosheets coated on Co9S8 nanotubes with enhanced cycling stability for high-performance supercapacitors

Transition metal sulfides are promising electrode materials for supercapacitors due to their excellent electrochemical performance and high conductivity. Unfortunately, the low rate performance and poor cycling stability limited their progress towards commercial applications. Herein, the core-shell structure of MoO42--intercalated LDHs coated on Co9S8 nanotubes was rationally designed and prepared to improve their electrochemical performance and cycling stability by adjusting the composition of LDHs. Compared to NiMo-LDH@Co9S8 and CoMo-LDH@Co9S8, the optimized NiCoMo-LDH@Co9S8 electrode exhibits excellent areal specific capacitance (11 F cm-2 at 3 mA cm-2) and excellent cycling stability (94.4% after 5000 cycles). In addition, asymmetric supercapacitor devices were assembled with NiCoMo-LDH@Co9S8 and activated carbon (AC), which delivered a high energy density of 0.94 mWh cm-2, at a power density of 1.70 mW cm-2, and good cycling stability (89.4% after 5000 cycles). These results indicate that the introduction of MoO42- can enhance the synergistic effect of multiple metals and the synthesized NiCoMo-LDH@Co9S8 core-shell composite has great potential in the development of high-performance electrode materials for supercapacitors.

Advances in layered double hydroxide based labels for signal amplification in ultrasensitive electrochemical and optical affinity biosensors of glucose

Since the development of enzyme electrodes, the research area of glucose biosensing has seen outstanding progress and improvement. Numerous sensing platforms have been developed based on different immobilization techniques and improved electron transfer between the enzyme and electrode. Interestingly, these platforms have consistently used innovative nanostructures and nanocomposites. In recent years, layered double hydroxides (LDHs) have become key tools in the field of analytical chemistry owing to their outstanding features and benefits, such as facile synthesis, cost-effectiveness, substantial surface area, excellent catalytic performance, and biocompatibility. LDHs are often synthesized as nanomaterial composites or manufactured with specific three-dimensional structures. The purpose of this review is to illustrate the biosensing prospects of LDH-based glucose sensors and the need for improvement. First, various clinical and conventional approaches for glucose determination are discussed. The definitions, types, and various synthetic methodologies of LDHs are then explained. Subsequently, we discuss the various research studies regarding LDH-based electrochemical and optical assays, focusing on modified systems, improved electron transfers pathways (through developments in surface science), and different sensing designs based on nanomaterials. Finally, a summary of the current limitations and future challenges in glucose analysis is described, which may facilitate further development and applications.

An efficient electrolyte additive of tetramethylammonium sulfate hydrate for Dendritic-Free zinc anode for aqueous Zinc-ion batteries

Recently, zinc metal has been considered as a promising metal anode for aqueous rechargeable metal ion batteries due to its low electrochemical potential and high theoretical capacity. However, zinc metal suffers from hydrogen evolution reaction (HER) and dendrite growth during plating/stripping. Here, we propose a low-cost, effective and non-toxic electrolyte additive, tetramethylammonium sulfate hydrate (TMA₂SO₄), as a simple cationic surfactant additive for zinc-ion batteries, to trigger the smooth Zn deposition during charging and discharging process. It is found that TMA₂SO₄ enable the realization of the deposition of Zn ions along the surface of zinc foil laterally without stacking and thus dendrite growth and side reactions are greatly mitigated by the electrolyte additive of TMA₂SO₄ even when the amount of the additive is as low as 0.25 mM. As a result, the TMA₂SO₄ additive induces excellent cycling stability over 1800 h at the current density of 0.5 mA cm^-2 with the limited capacity of 0.5 mAh cm^-2 for the Zn-Zn symmetrical cell. Moreover, the electrolyte with TMA₂SO₄ can well match with MnO₂ cathode, which achieves the high initial capacity of 181.3 mAh g^-1 at 0.2 A g^-1 and long-term cycling stability with the capacity retention of 98.72 % after 200 cycles for the Zn/MnO₂ full cell. This work provides a general electrolyte design strategy to suppress zinc dendrite growth and side reactions to achieve long-lifespan zinc metal anodes for aqueous zinc ion batteries by electrostatic shielding effect.

Electrolyte Additives for Improving the High-Temperature Storage Performance of Li-Ion Battery NCM523∥Graphite with Overcharge Protection

The overcharge safety performance of lithium-ion batteries has been the major bottleneck in the widespread deployment of this promising technology. Pushing the limitations further may jeopardize cell safety when it is performed at high-temperature storage. On the basis of the lacking systematic research on overcharge protection electrolyte additives with high-temperature storage capacity, we explore the promotion effect of overcharge additives on electrolyte decomposition at 60 °C. Specifically, the addition of tris(trimethylsily) phosphite (TMSP) and lithium difluoro(oxalato)borate (LiDFOB) in the electrolyte can not only form the robust cathode electrolyte interface/solid electrolyte interphase (CEI/SEI) but also improve the thermal stability of the electrolyte. Therefore, we promote the electrolyte system to realize the 18,650 LIB storage at 60 °C for 50 days by optimizing the formula in the electrolyte containing biphenyl (BP) and cyclohexylbenzene (CHB) overcharge protection additives, and the capacity retention rate can reach more than 90% with overcharge safety. Further, the optimized electrolyte system has also been implemented to commercial 18,650 LIBs and demonstrates the widening of the route to the widespread application of the electrolyte under extreme conditions.

High-capacity CoP-Mn3P nanoclusters heterostructures derived by Co2MnO4 as advanced electrodes for supercapacitors

Although transition metal oxides (TMOs) have attracted enormous attention owing to their high performance in supercapacitors, it still remains challenging issues in terms of the poor electrical conductivity, sluggish redox kinetics and insufficient electrochemical active sites. Herein, the high-capacity CoP-Mn₃P nanoclusters featuring the heterogeneous interfaces have been successfully synthesized through hydrothermal method followed by annealing. The heterojunction formed between CoP and Mn₃P redistributes the charge at the interface between them, generating the built-in electric field to accelerate electron transfer, and thus the conductivity of the electrode is enhanced. Moreover, the unique morphology of nanoclusters composed of flake structures is beneficial to provide more electrochemical active sites. Consequently, the resultant CoP-Mn₃P nanoclusters electrode delivers an exceptional gravimetric specific capacity (2714 F g^-1 at 1 A g^-1) as well as a long cycle lifespan (83.1% of capacitance retention after 10,000 cycles). An asymmetric supercapacitor (ASC) device assembling with employing CoP/Mn₃P electrode presents an ultrahigh energy density value of 46.4 Wh kg^-1 at a power density of 800.0 W kg^-1 and a super capacitance retention of 86.2% after 30,000 cycles. This work paves an effective way for the investigation on the charge transfer kinetics of electrode materials.

Carbonate doped NiCo-LDH modified with PANI for high performance asymmetric supercapacitors

The as-prepared PANI-NCLDH/CO32− composite has two forms: linear and clustered. The good combination style makes the prepared composite electrode and the assembled device have excellent electrochemical performance.

Synergistic coupling of FeOOH with Mo-incorporated NiCo LDH towards enhancing the oxygen evolution reaction

FeOOH-modified NiCoMo LDH/NF with excellent OER activity and stability was successfully prepared using a hydrothermal method combined with electrodeposition.

Facile Synthesis of MoP-RuP2 with Abundant Interfaces to Boost Hydrogen Evolution Reactions in Alkaline Media

Exploiting efficient electrocatalysts for hydrogen evolution reactions (HERs) is important for boosting the large-scale applications of hydrogen energy. Herein, MoP-RuP₂ encapsulated in N,P-codoped carbon (MoP-RuP₂@NPC) with abundant interfaces were prepared via a facile avenue with the low-toxic melamine phosphate as the phosphorous resource. Moreover, the obtained electrocatalyst possessed a porous nanostructure, had abundant exposed active sites and improved the mass transport during the electrocatalytic process. Due to the above merits, the prepared MoP-RuP₂@NPC delivered a greater electrocatalytic performance for HERs (50 mV@10 mA cm⁻²) relative to RuP₂@NPC (120 mV) and MoP@NPC (195 mV) in 1 M KOH. Moreover, an ultralow potential of 1.6 V was required to deliver a current density of 10 mA cm⁻² in the two-electrode configuration for overall water splitting. For practical applications, intermittent solar energy, wind energy and thermal energy were utilized to drive the electrolyzer to generate hydrogen gas. This work provides a novel and facile strategy for designing highly efficient and stable nanomaterials toward hydrogen production.

Enhancing electrochemical performance of electrode material via combining defect and heterojunction engineering for supercapacitors

The poor conductivity and deficient active sites of transition metal oxides lead to low energy density of supercapacitors, which limits their wide application. In this work, double transition metal oxide heterojunctions with oxygen vacancy (V_o-ZnO/CoO) nanowires are prepared by effective hydrothermal and thermal treatments. The formation of the heterojunction results in the redistribution of interface charge between ZnO and CoO, generating an internal electric field to accelerate the electron transport. Meanwhile, oxygen vacancies can enhance the redox reaction activity to further improve the electrochemical kinetics of the electrode material. Therefore, the prepared V_o-ZnO/CoO can provide a superior specific capacity of 845 C g^-1 (1 A g^-1). An asymmetric supercapacitor with the V_o-ZnO/CoO as positive electrode shows a higher energy density of 51.6 Wh kg^-1 when the power density reaches 799.9 W kg^-1. This work proposes a synergistic combination of defect and heterojunction engineering to improve the electrochemical properties of materials, providing an important guidance for material design in energy-storage field.

Rational design of flower-like Co-Zn LDH@Co(H2PO4)2 heterojunctions as advanced electrode materials for supercapacitors

Layered double hydroxides (LDHs) with high theoretical specific capacity have been considered as one of the most promising candidates for high-performance supercapacitors. However, the low electronic conductivity and insufficient active sites hinder the further large-scale application of bulk LDHs. Here, we successfully synthesized heterostructured Co-Zn LDH@Co(H₂PO₄)₂ nanoflowers by a simple hydrothermal method. As the amount of Co(H₂PO₄)₂ in the whole heterostructure increases, the nanosheets steadily evolve into nanoflowers with a high surface area, providing more electrochemically active sites. Moreover, the built-in electric field formed between Co-Zn LDH and Co(H₂PO₄)₂ improves the conductivity of the composite electrode. As a result, the as-prepared Co-Zn LDH@Co(H₂PO₄)₂ shows a high specific capacity of 919 C g^-1 at a current density of 1 A g^-1. A hybrid supercapacitor (HSC) with activated carbon (AC) as the negative electrode and Co-Zn LDH@Co(H₂PO₄)₂ as the positive electrode delivers an energy density of 30.4 W h kg^-1 at a power density of 400 W kg^-1, and 95.3% of the initial capacity is retained after 5000 cycles. This study provides a novel synthesis strategy for constructing heterojunctions to enhance the energy storage properties of LDH-based materials.

Core-shell nanostructured Zn-Co-O@CoS arrays for high-performance hybrid supercapacitors

Although zinc oxide (ZnO) with wide distribution is one of the most attractive energy storage materials, the low electronic conductivity and insufficient active sites of bulk ZnO increase the internal resistance and reduce the capacity of electrodes for supercapacitors. Herein, CoS nanosheets are coated on the surface of heterostructured ZnO/Co₃O₄ nanowires to synthesize a core-shell Zn-Co-O@CoS electrode by a three-step method. The built-in electric field formed between ZnO and Co₃O₄ can enhance the conductivity of the composite electrode. The coating of amorphous CoS can also provide sufficient active sites and improve the chemical stability of ZnO/Co₃O₄ nanowires. As a result, the as-prepared Zn-Co-O@CoS electrode delivers a high specific capacity of 1190 C g^-1, which is 7 times higher than that of the pristine ZnO electrode. Besides, a hybrid supercapacitor (HSC) with the Zn-Co-O@CoS electrode exhibits a high energy density of 56.8 W h kg^-1 at a power density of 771.6 W kg^-1. Furthermore, we assembled a solar-charging power system by combining the HSC and monocrystalline silicon plates to prove the practicability of the device, which can power a toy electric fan successfully. This study provides an effective idea and strategy for preparing Zn-based supercapacitor electrodes with low cost and deep discharge.