Enhanced Charge Density Research Articles

Enhancement of high-efficiency potassium ion hybrid supercapacitors utilizing oxygen-deficient Co2NiO4@nitrogen-doped carbon nanoflower

Transition metal oxides represent a promising category of pseudocapacitive materials for potassium-ion hybrid supercapacitors (PIHCs) characterized by high energy density. Nevertheless, their utility is hindered by intrinsic low conductivity, restricted electrochemical sites, and notable volume expansion, all of which directly contribute to the degradation of their electrochemical performance, thereby limiting their practical applicability in supercapacitor systems. In this study, we present a facile synthesis approach to fabricate nitrogen-doped carbon-supported oxygen vacancy-rich Co2NiO4 nanoflowers (Ov-Co2NiO4/NC NFs) featuring tunable surface layering and electron distribution. The nanoflower structure augments the contact area between the material and the electrolyte. Density functional theory (DFT) calculations reveal oxygen vacancies could bring an enhanced charge density across the entire Fermi level in Co2NiO4 and expand the interatomic distances between adjacent cobalt and nickel atoms to 3.370 Å. N-doped carbon carriers further accelerate charge transfer, increase the electrostatic energy storage and inhibit the structural collapse of Co2NiO4. These structural modifications serve to improve electrochemical reaction kinetics, augment the binding energy of K+ (−2.87 eV), and mitigate structural variations during K+ storage. In a 6 M KOH electrolyte, Ov-Co2NiO4/NC NF exhibits a specific capacitance of 1104 F g−1 at a current density of 0.5 A g−1, with a remarkable capacitance retention rate of 91.48 % after 6500 cycles. Furthermore, the assembled PIHCs demonstrate an energy density of 47.8 Wh kg−1 and an ultra-high power density of 376 W kg−1, alongside notable cycle stability, retaining 90.13 % of its capacitance after 8000 cycles in a 6 M KOH electrolyte.

Biopolymer and Biomimetic Techniques for Triboelectric Nanogenerators (TENGs).

Triboelectric nanogenerators (TENGs) play a crucial role in attaining sustainable energy for various wearable devices. Polymer materials are essential components of TENGs. Biopolymers are suitable materials for TENGs because of their degradability, natural sourcing, and cost-effectiveness. Herein, the latest progress in commonly used biopolymers and well-designed biomimetic techniques for TENG is summarized. The applications of natural rubber, polysaccharides, protein-based biopolymers, and other common synthetic biopolymers in TENG technology are summarized in detail. Each biopolymer is discussed based on its electrification capability, polarity variations, and specific functionalities as active and functional layers of TENGs. Important biomimetic strategies and related applications of specific biopolymers are also summarized to guide the structural and functional design of TENG. In the future, the study of triboelectric biopolymers may focus on exploring alternative candidates, enhancing charge density, and expanding functionality. Various possible applications of biopolymer-based TENGs are proposed in this review. By applying biopolymers and related biomimetic methods to TENG devices, the applications of TENG in the fields of healthcare, environmental monitoring, and wearable/implantable electronics can be further promoted.

Biomimetic MOFs/GO membranes with enhanced charge density for osmotic power generation

Osmotic power generation is a renewable energy technology that harnesses energy from the natural mixing of freshwater and saltwater, offering a promising solution for sustainable energy. However, it is still a challenge to achieve high energy output without compromising scalability and stability. Herein, inspired by the nano-constrained dynamics of neuronal cell transmembrane transport, an anodic oxidation electrodeposition method is employed to fabricate metal organic frameworks (MOFs) within 2D graphene oxide (GO) layers. The in-situ integration of high-density charges within nanometer pore with 0.34 nm entrance of MOFs facilitates rapid and selective cation transport, which significantly increases the diffusion voltage (363.8 mV, 106 fold concentration gradient). Our device demonstrates a maximum output power of 6.82 μW under a 10 fold concentration gradient at a load resistance of 5000 Ω, possessing an energy conversion efficiency of 48.8% at an effective area of 12.56 mm2, which substantially surpasses the performance reported before. More importantly, the device performs exceptionally well, showing robust and stable performance. This is proven by its ability to power various electronic devices. These findings underscore the potential of biomimetic ion channel membranes in sustainable energy applications, offering a promising avenue for the broader field of energy harvesting technologies.

Copper-doped nickel–iron metal/metal oxide electrode with improved performance by promoting synergistic effects in the oxygen evolution reaction

Advancing the performance of NiFe catalytic systems for oxygen evolution reaction (OER) is challenging, notably upon incorporating a third transition metal to create a trimetallic configuration. This study introduces a Cu-doped NiFe electrocatalyst, synthesized via a streamlined redeposition technique. The catalyst exhibits a Tafel slope of 38 mV dec−1 and a low overpotential of 248 mV at a current density of 100 mA cm−2, plus a 2.5-fold boost in intrinsic activity. Density Functional Theory (DFT) and spectroscopic analyses demonstrate that Cu doping refines the electronic structure, enhancing charge density around the Fermi level and multiplying active OER sites. The Cu1Fe6Ni18 catalyst features robust Cu–O and Fe–O bond interactions, enhancing charge transport and OER kinetics. Our research elucidates the synergistic effects of Cu and Fe in a trimetallic system, offering an impactful approach to elevate trimetallic catalyst performance.

Magnéli Ti4O7 nanowire induces locally enhanced electric field and electrocatalytic activity for rapid and efficient water disinfection via synergistic electroporation and electrochlorination

Waterborne pathogens in drinking water remains a prominent cause of morbidity and mortality in developing rural areas. Electrochlorination offers a promising alternative for decentralized water disinfection, but its efficiency was strongly restrained by the low Cl- concentrations in natural waters. Herein, we proposed a Magnéli Ti4O7 nanowire-assisted electrochemical approach via forming locally enhanced electric field over nanowire tips for reinforcing electroporation, and via forming locally enhanced charge density for promoting Cl- enrichment and subsequent electrochlorination on anodic nanowire tips. Ti4O7 nanowires induced the enhancement of electric field by 4 orders of magnitude and Cl- concentration by ∼3 orders of magnitude at nanowire tips, and promoted ∼3 times more active chlorine generation at a voltage of 3.0 V compared with non-nanostructured one. Synergistic electroporation and electrochlorination on nanowires enabled rapid and efficient disinfection with hydraulic retention time of ∼36 s and energy consumption below ∼5 J/L/log for inactivation of various gram-positive/negative bacteria and phage MS2. Analyses of cell morphology and membrane integrity revealed that electroporation-induced cell pores provided diffusion channels of reactive chlorine species for oxidative damage of cell structures, resulting in ∼1.5–4.5 times lower energy consumption than the thin-film, nanoparticle, and nanorod ones. The excellent operation stability for tap water with significant bacterial inactivation and active chlorine generation demonstrated its great application potential for decentralized water disinfection.

Stabilizing Lattice Oxygen through Mn Doping in NiCo2O4-δ Spinel Electrocatalysts for Efficient and Durable Acid Oxygen Evolution.

Design the electrocatalysts without noble metal is still a challenge for oxygen evolution reaction (OER) in acid media. Herein, we reported the manganese (Mn) doping method to decrease the concentration of oxygen vacancy (VO) and form the Mn-O structure adjacent octahedral sites in spinel NiCo2O4-δ (NiMn1.5Co3O4-δ), which highly enhanced the activity and stability of spinel NiCo2O4-δ with a low overpotential (η) of 280 mV at j=10 mA cm-2 and long-term stability of 80 h in acid media. The isotopic labelling experiment based on differential electrochemical mass spectrometry (DEMS) clearly demonstrated the lattice oxygen in NiMn1.5Co3O4-δ is more stable due to strong Mn-O bond and shows synergetic adsorbate evolution mechanism (SAEM) for acid OER. Density functional theory (DFT) calculations reveal highly increased oxygen vacancy formation energy (EVO) of NiCo2O4-δ after Mn doping. More importantly, the highly hydrogen bonding between Mn-O and *OOH adsorbed on adjacent Co octahedral sites promote the formation of *OO from *OOH due to the greatly enhanced charge density of O in Mn substituted sites.

Stabilizing Lattice Oxygen through Mn Doping in NiCo2O4−d Spinel Electrocatalysts for Efficient and Durable Acid Oxygen Evolution

Design the electrocatalysts without noble metal is still a challenge for oxygen evolution reaction (OER) in acid media. Herein, we reported the manganese doping method to decrease the concentration of oxygen vacancy (Vo) and form the Mn−O structure adjacent octahedral sites in spinel NiCo2O4−δ (NiMn1.5Co3O4−δ), which highly enhanced the activity and stability of spinel NiCo2O4−δ with a low overpotential (η) of 280 mV at j = 10 mA cm−2 and long‐term stability of 80 h in acid media. The isotopic labelling experiment based on differential electrochemical mass spectrometry (DEMS) clearly demonstrated the lattice oxygen in NiMn1.5Co3O4−δ is more stable due to strong Mn‐O bond and synergetic adsorbate evolution mechanism (SAEM) for acid OER. Density functional theory (DFT) calculations reveal highly increased oxygen vacancy formation energy (EVO) of NiCo2O4−δ after Mn doping. More importantly, the highly hydrogen bonding between Mn−O and *OOH adsorbed on adjacent Co octahedral sites promote the formation of *OO from *OOH due to the greatly enhanced charge density of O in Mn substituted sites.

Synergistic Densification in Hybrid Organic‐Inorganic MXenes for Optimized Photothermal Conversion

AbstractOptimizin the efficient light‐trapping in the photothermal conversion by enhancing localized surface plasmon resonance (LSPR) is crucial in improving light‐heat‐conversion efficiency of Ti3C2Tx MXene. However, its susceptibility to oxidation makes it prone to oxides formation, diminishing its metallic properties and significantly reducing the LSPR effect. This work synthesizes a kind of air‐stable hybrid Ti3C2Tx MXenes by a synergistic densification strategy that incorporates sulfhydryl‐bonding between organic and inorganic parts by reacting Ti3C2Tx MXene with thiocarboxylic acids. The resultant shortening of electron transport pathways, enhanced charge density, and the generation of additional electronic states around the Fermi level collectively contribute to an augmented LSPR effect. Additionally, the hybrid Ti3C2Tx MXenes also demonstrate high‐temperature resistance and reduced water interactions. These combined effects substantially elevate photothermal conversion efficiency through thiocarboxylic acids modification, reaching a photothermal evaporation rate of 1.77 kg m−2 h−1 with 94.56% efficiency in hybrid Ti3C2Tx MXenes. The approach paves the way for the design and development of a three‐in‐one strategy for photothermal conversion.

Nanowire-assisted electrochemical perforation of graphene oxide nanosheets for molecular separation

Two-dimensional nanosheets, e.g., graphene oxide (GO), have been widely used to fabricate efficient membranes for molecular separation. However, because of poor transport across nanosheets and high width-to-thickness ratio, the permeation pathway length and tortuosity of these membranes are extremely large, which limit their separation performance. Here we report a facile, scalable, and controllable nanowire electrochemical concept for perforating and modifying nanosheets to shorten permeation pathway and adjust transport property. It is found that confinement effects with locally enhanced charge density, electric field, and hydroxyl radical generation over nanowire tips on anode can be executed under low voltage, thereby inducing confined direct electron loss and indirect oxidation to reform configuration and composition of GO nanosheets. We demonstrate that the porous GO nanosheets with a lot of holes are suitable for assembling separation membranes with tuned accessibility, tortuosity, interlayer space, electronegativity, and hydrophilicity. For molecular separation, the prepared membranes exhibit quadruple water permeance and higher rejections for salts (>91%) and small molecules (>96%) as/than original ones. This nanowire electrochemical perforation concept offers a feasible strategy to reconstruct two-dimensional materials and tune their transport property for separation.

Modulating the electronic structure of VS2via Ru decoration for an efficient pH-universal electrocatalytic hydrogen evolution reaction.

High-efficiency water electrolysis over a broad pH range is desirable but challenging. Herein, Ru-decorated VS2 on carbon cloth (Ru-VS2/CC) has been in situ synthesized, which features the regulated electronic structure of VS2 by introducing Ru. It is remarkable that the optimal Ru-VS2/CC displays excellent electrocatalytic hydrogen evolution activity with overpotentials of 89 and 87 mV at -10 mA cm-2 in 0.5 M H2SO4 and 1.0 M KOH, respectively. Theoretical calculations and electrocatalytic measurements have demonstrated that introducing Ru induces an enhanced charge density around the Fermi level, facilitating charge transfer and speeding up the electrocatalytic HER kinetics. The Gibbs free energy of the hydrogen intermediate (ΔGH*) of Ru-VS2/CC (0.23 eV) is much closer to zero than that of pure VS2 (0.51 eV) and Ru (-0.37 eV), demonstrating an easier hydrogen adsorption and desorption process for Ru-VS2/CC. The more favorable ΔGH*, differential charge density and the d-band center endow Ru-VS2 with enhanced intrinsic electrocatalytic activity. This study presents a feasible strategy for enhancing electrocatalytic HER activity by the regulation of the electronic structure and the rational integration of dual active components.

Stretchable and biodegradable triboelectric nanogenerator based on elastomeric nanocomposites

Biologically benign, dissolvable materials-based triboelectric nanogenerators hold significant potential as a sustainable power source for bioresorbable, transient electronic systems; however poor options in materials and engineering approaches are major obstacles to the desired electrical, physical, and mechanical properties, particularly when considering operations under restrictive, demanding conditions or environments. Here, we present an elastomeric composites-based triboelectric nanogenerator with a package of completely degradable materials. Assembly of inorganic nanoparticles with high charge affinity/permittivity and micro-pyramid structures with high surface area produces enhanced charge density and power outputs over those of existing elements. Study on mechanical and biochemical characteristics validates the capability of maintaining stable, long-life electrical outputs under cyclic tests and aqueous solutions. Demonstrations of energy harvesting at an artificial knee and self-powered motion sensing at a finger joint suggest the practical feasibility in versatile areas of biomedical and eco-resorbable electronics.

Remarkably Enhanced Charge Density of Inorganic Material Via Regulating Contact Barrier Difference and Charge Trapping for Triboelectric Nanogenerator

AbstractCurrently, the research on improving charge density of charge‐excitation triboelectric nanogenerators (CE‐TENG) mainly focuses on surface modification and thinning of organic polymer materials. However, to increase durability and output, the exploration of high permittivity and high‐thickness inorganic materials is important for extensive applications. Meanwhile, the physical mechanism of air ionization caused by air breakdown during secondary self‐charge excitation (SSCE) needs to be explored. Herein, this study proposes a new strategy for CE‐TENG based on inorganic materials by de‐trapping reverse charge and increasing the contact barrier difference to obtain high charge density and achieve secondary self‐charge excitation. SSCE of three types of films with different leakage currents are evaluated according to their trapping and de‐trapping reverse charges. It is found that the trap distribution of dielectric films with larger leakage currents are mostly shallow‐level traps, whose de‐trapping ability becomes stronger after reverse charge injection. By regulating the contact barrier difference with thin organic polymer on thick inorganic high permittivity material, this study has achieved a high charge density of 1310 µC m−2 with a fast start‐up time of SSCE, which is a new record for the charge density of inorganic materials. This study promotes TENG of inorganic materials toward high‐energy output applications.

Strongly enhanced charge density via gradient nano-doping for high performance elastic-material-based triboelectric nanogenerators

Elastic-material-based triboelectric nanogenerators (EMB-TENGs) are most effective to harvest random (low frequency, low amplitude) and distributed mechanical energy. However, the low output of EMB-TENGs caused by drastic charge attenuation and low sensitivity limits its applications. Here, we propose a gradient nano-doping strategy to boost the charge density and sensitivity of triboelectric sponge materials via the gradient electrical field caused by the inhomogeneous concentration field of polytetrafluoroethylene nanoparticles. The triboelectric charge density (537 μC·m−3) and the peak power density (732.6 mW·m−3) is increased by 1.2 times and 1.8 times. A sensitivity of 1.851 kPa−1 is successfully realized at 50% compressive strain. From this, a self-powered smart boxing bag with functions of both the force analysis and real-time counting statistic was developed at the large strain. This work presents a new method for design and development of triboelectric materials, as well as expanding the functionalities and applications of self-powered system combining with the EMB-TENGs.

Regulating the charge density of Cu(I) single sites enriched on the surface of N3c Vacancies-engineered g-C3N4 for efficient Fenton-like reactions

The construction of highly accessible copper active sites with enhanced charge density is essential for the performance of Cu-based Fenton catalysts. Herein, we report the preparation of a catalyst comprising Cu(I) atoms anchored on the surface of N3c vacancies-engineered g-C3N4 (Cu/Nv-CN) and its enhanced Fenton-like performance. The surface-enrichment of single Cu(I) atoms maximizes the exposure of active sites and reduces the mass transfer limitation for short-lived hydroxyl radicals. The N3c vacancies, meanwhile, facilitate electron donation from N2c to Cu sites, greatly increasing the number of single Cu(I) sites. These two strategies synergistically enhance the hydroxyl radical production rate in the Fenton-like process and endow Cu/Nv-CN with not only excellent performance in degrading various contaminants (such as phenolic compounds, endocrine disruptors, antibiotics, and dyes), both in purified and real water samples matrixes, but also superior bactericidal properties for Escherichia coli. Compared to bulk Cu-doped g-C3N4 without N3c vacancies (CO-Cu/CN), Cu/Nv-CN shows a more than 14-fold increase in phenol degradation and an enhancement of approximately 4 log10 CFU/mL in bacterial inactivation. Our strategy of increasing the number of Cu(I) single atoms through surface enrichment and enhanced electron donation opens up a new route for the design of efficient Fenton-like catalysts for environmental remediation.

Enhanced charge density wave with mobile superconducting vortices in La1.885Sr0.115CuO4

Superconductivity in the cuprates is found to be intertwined with charge and spin density waves. Determining the interactions between the different types of order is crucial for understanding these important materials. Here, we elucidate the role of the charge density wave (CDW) in the prototypical cuprate La1.885Sr0.115CuO4, by studying the effects of large magnetic fields (H) up to 24 Tesla. At low temperatures (T), the observed CDW peaks reveal two distinct regions in the material: a majority phase with short-range CDW coexisting with superconductivity, and a minority phase with longer-range CDW coexisting with static spin density wave (SDW). With increasing magnetic field, the CDW first grows smoothly in a manner similar to the SDW. However, at high fields we discover a sudden increase in the CDW amplitude upon entering the vortex-liquid state. Our results signify strong coupling of the CDW to mobile superconducting vortices and link enhanced CDW amplitude with local superconducting pairing across the H − T phase diagram.

In-situ scanning tunneling microscopy observation of thickness-dependent air-sensitive layered materials and heterodevices

Quasi-two-dimensional (Quasi-2D) van der Waals (vdW) materials can be mechanically or chemically exfoliated down to monolayer because of their strong intralayer bonding and the weak interlayer vdW interaction. Thanks to this unique property, one can often find exotic thickness-dependent electronic properties from these quasi-2D vdW materials, which can lead to bandgap opening, emerging superconductivity, or enhanced charge density waves with decreasing thickness. Surface-sensitive scanning tunneling microscopy (STM) can provide direct observation of structural and electronic characteristics of such layered materials with atomic precision in real space. However, it is very challenging to preserve the intrinsic surfaces of air-sensitive quasi-2D materials between preparation and measurement. In addition, vdW 2D crystals after exfoliation are extremely hard to explore with a typical STM setup due to their small size (≤ 10 μm). Here, we present a straightforward method compatible with any STM setup having optical access: (1) exfoliating and/or stacking layered materials in a glove box, (2) transferring them to an ultra-high vacuum STM chamber using a suitcase without exposure to air, and (3) navigating surface to locate exfoliated vdW 2D flakes with different thicknesses. We successfully demonstrated that the clean surfaces of the air-sensitive $$\hbox {Fe}_3\hbox {GeTe}_2$$ can be effectively protected from unwanted oxidation during transfer. Furthermore, our method provides a simple but useful way to access a specific tiny stack of layered materials without any ex-situ fabrication processes for STM navigation. Our experimental improvement will open up a new way to investigate air-sensitive layered vdW materials with various thicknesses via surface-sensitive techniques including STM.

Band splitting and enhanced charge density wave modulation in Mn-implanted CsV3Sb5.

Kagome metal CsV3Sb5 has attracted unprecedented attention due to the charge density wave (CDW), Z2 topological surface states and unconventional superconductivity. However, how the paramagnetic bulk CsV3Sb5 interacts with magnetic doping is rarely explored. Here we report a Mn-doped CsV3Sb5 single crystal successfully achieved by ion implantation, which exhibits obvious band splitting and enhanced CDW modulation via angle-resolved photoemission spectroscopy (ARPES). The band splitting is anisotropic and occurs in the entire Brillouin region. We observed a Dirac cone gap at the K point but it closed at 135 K ± 5 K, much higher than the bulk value of ∼94 K, suggesting enhanced CDW modulation. According to the facts of the transferred spectral weight to the Fermi level and weak antiferromagnetic order at low temperature, we ascribe the enhanced CDW to the polariton excitation and Kondo shielding effect. Our study not only offers a simple method to realize deep doping in bulk materials, but also provides an ideal platform to explore the coupling between exotic quantum states in CsV3Sb5.

Improving the Performance of the Lamellar Reduced Graphene Oxide/Molybdenum Sulfide Nanofiltration Membrane through Accelerated Water-Transport Channels and Capacitively Enhanced Charge Density.

Graphene is promising in the construction of next-generation nanofiltration membranes for wastewater treatment and water purification. However, the application of graphene-based membranes has still been prohibited by their deficiencies in permeability and ion rejection. Herein, regulating the 2D channel and enhancing the charge density are co-adopted for simultaneous enhancement of the water flux and salt rejection of reduced graphene oxide (rGO) membranes through the intercalation of molybdenum sulfide (MoS2) nanosheets and external electrical assistance. The fabricated rGO/MoS2 membranes possess expanded nanochannels with less friction and a higher water molecule transport velocity gradient (from 8.57 to 14.07 s-1) than those of rGO membranes. Consequently, their water permeance increases from 0.92 to 34.9 L m-2 h-1 bar-1. Meanwhile, benefiting from the high capacitance and negative potential of -1.1 V versus the saturated calomel electrode given to the membranes, their rejection rates toward NaCl reach 87.2% and those toward Na2SO4 reach 93.7%. The Donnan steric pore model analysis indicates that the capacitively and electrically increased surface charge density make great contributions to the higher ion rejection rate. This work gives new insights into membrane design for high water flux and salt rejection efficiency.

Computational Mechanism Investigation of C=C Bond Hydrogenation Catalyzed by Rhodium Hydride.

The hydrogenation of unsaturated carbons is a commonly used synthetic tool in pharmaceutical and industrial production. Recently, the Norton group realized highly selective hydrogenation of C=C bonds catalyzed by a rhodium hydride. Despite the great efforts made by experimentalists, details regarding the mechanism remained unclear. In this work, detailed DFT calculations were carried out to elucidate the principal features of this transformation. For enones we find that two possible competing mechanisms proposed by the experimental groups are computationally excluded, our proposed alternative mechanism with a total barrier of 20.0 kcal mol-1 is theoretically feasible, solvent methanol to also plays a crucial role in assisting β-hydrogenation in addition to being the hydrogen source for α-hydrogenation, and the cross-polarization of the substrate enone-conjugated system to result in an enhanced charge density of the α-carbon, which favors being hydrogenated first. For isolated alkenes, neither of the two possible competing mechanisms can be excluded computationally and which carbon atom is first hydrogenated depends on the electronic properties of the substrate itself. The combination of rhodium and C=C bonds changes the electronic properties of H on the rhodium hydride and enhances its hydrogenation activity.

Simple enhanced charge density of chitosan film by the embedded ion method for the flexible triboelectric nanogenerator

This research proposed a simple ionic embedded method to improve electrical output performance by adding surface charges of cationic chitosan (CS) biopolymer for compatible utilization of the triboelectric nanogenerator (TENG). By simply embedding cationic salts, the TENG performance was enhanced by over four times more than that with pristine CS. Moreover, by modifying roughness on the film surface, the optimized condition of R-CS/3 %CaCl2 reached the highest VOC and ISC of ~149 V and ~15 μA, respectively, thus exceeding the output from pristine R-CS TENG by four- and three times of ⁓38 V and ⁓5.1 μA. The maximum power output of 400 μW/cm2 can be observed at the 10 MΩ external load resistance. Finally, by integrating an automatic self-charge pumping (ASCP) module, the ASCP/CS-TENG provided highly efficient VOC and ISC output power by over 1.3 times more than the R-CS/3 %CaCl2 TENG and could light up 72 light emitting diodes (LEDs) easily.