Self-assembled Electrode Research Articles

Two birds with one stone: Bimetallic ZnCo2S4 polyhedral nanoparticles decorated porous N-doped carbon nanofiber membranes for free-standing flexible anodes and microwave absorption

Cost-efficient material with an ingenious design is important in the engineering applications of flexible energy storage and electromagnetic (EM) protection. In this study, bimetallic ZnCo2S4 (ZCS) polyhedral nanoparticles homogenously embedded in the surface of porous N-doped carbon nanofiber membranes (ZCS@PCNFM) have been fabricated by electrospinning technique combined with carbonization and hydrothermal processes. As a self-assembled electrode for lithium-ion batteries (LIBs), the bimetallic ZCS nanoparticles possess rich redox reactions, good electrical conductivity, and pseudocapacitive properties, while the three-dimensional (3D) multiaperture architecture of the nanofiber film not only shortens the transfer spacing of lithium ions and electrons but also effectively tolerates the volume variation during lithiation and delithiation cycles. Benefiting from the above merits, the ZCS@PCNFM electrode exhibits good cycle performance (662.3 mA h/g at 100 mA/g after 100 cycles), superior rate capacity (401.3 mA h/g at 1 A/g) and an extremely high initial specific capacity of 1152.2 mAh/g at 100 mA/g. Meanwhile, depending on the hierarchical nanostructure and multi-component heterogeneous interface effects constructed by 3D inlaid architecture, the ZCS@PCNFM nanocomposite exhibits fascinating microwave absorption (MA) characteristics with a superhigh reflection loss (RL) of –49.7 dB at a filling content of only 20 wt% and corresponding effective absorption bandwidth (EAB, RL<–10 dB) of 5.2 GHz ranging from 12.8 to 18.0 GHz at 2.2 mm.

Refining Mn(III) Active Sites in MnO2-Based Self-Assembled Electrodes Via Oxygen Vacancy Induction to Enhance Oxygen Reaction Performance in Zinc-Air Batteries

Rechargeable zinc-air batteries are considered as a promising candidate for next-generation electrochemical energy conversion devices due to their safety, low cost, and high theoretical capacity/ energy density. Over the past few decades, α-MnO2-based electrodes have demonstrated their excellent performance and competitiveness in oxygen catalytic reactions. (1) According to eg filling theory, Mn(III) (t2g3eg1) sites in [MnO6] octahedral unit deliver superior bifunctional activity compared to Mn(II) (t2g3eg2) and Mn(IV) (t2g3eg0) sites.(2) However, the presence of unpaired single electrons of the Mn(III) site leads to low thermodynamic stability. Introducing oxygen vacancies to promote the electron rearrangement of the [MnO6] unit is a promising approach for enhancing the durability of Mn(III) active sites. Herein, we construct an oxygen-vacancy-enhanced MnO2-based electrode via a self-assembly process (NiCo2O4-MnO2@Ni foam). The intrinsic oxygen catalytic activity of NiCo2O4-MnO2@Ni foam is significantly improved by forming abundant highly stable Mn(III) active sites, which accelerate the mass transfer ability. As expected, the NiCo2O4-MnO2@Ni foam shows good bifunctional activity with a low overpotential of 0.69 V. The zinc-air battery assembled by NiCo2O4-MnO2@Ni foam exhibits a high peak power density of 576 mW cm-2, surpassing that of the Pt/C-Ir/C electrode. Additionally, benefiting from its stable flower-shaped hierarchical structure, the self-assembled electrode demonstrates long-term charge-discharge cycling stability, which lasts over 800 hours. This work provides innovative insights into enhancing MnO2-based electrodes by oxygen vacancy introduction.References N. Xu, Q. Nie, L. Luo, C. Z. Yao, Q. Gong, Y. Liu, X. Zhou, and J. Qiao, ACS applied materials & interfaces (2018).Z. Yin, R. He, H. Xue, J.-M. Chen, Y. Wang, X. Ye, N. Xu, J. Qiao and H. Huang, Energy Materials (2022).

Multifunctional-regions integrated with Mn-Co-Ni ternary hydroxides as self-assembled electrodes for high-performance hybrid supercapacitors

High-performance supercapacitors require elaborate design for electroactive materials with hierarchical structure and multiple components. In the present work, hierarchical nanoarrays composed of MnCoNi LDH@CoNi LDH (MCNL@CNL) with enoki-mushroom-like structure were constructed by integrating the structural regions with complementary functions. The self-assembled electrodes were fabricated upon MCNL@CNL with MnCo LDH@ZIF-67 as precursor and nickel foam as supporter, which achieved a specific capacitance of 2126.7 F/g at 0.5 A/g. The assembled hybrid supercapacitor exhibited the maximum energy density and power density of 51.4 Wh/kg and 7500 W/kg within the voltage range of 0–1.5 V, respectively, and it provided cycling stability with high capacitance retention (104.1%) and Coulombic efficiency (101.1%) after 10,000 cycles. Based on the characterizations results, MCNL@CNL electrode endowed with fast mass transfer, high conductivity and rich electroactive sites was produced, and its induced synergy effect facilitated charge transfer and promoted specific capacitance. Moreover, the hierarchical structure and rough surface of the fabricated MCNL@CNL accelerated the ions/electrons diffusion, and the cross-growing nanosheets on the surface enhanced the affinity. This work provides a novel approach to designing and fabricating self-assembled electrodes with high-performance and lifetime for supercapacitors.

RGO-Induced Flower-like Ni-MOF In Situ Self-Assembled Electrodes for High-Performance Hybrid Supercapacitors.

Currently, the primary bottlenecks that hinder the widespread application of supercapacitors are low energy density and narrow potential windows. Herein, the hybrid supercapacitor with high energy density and wide potential window is constructed via an in situ self-assembly method employing RGO-induced flower-like MOF(Ni). Benefiting from the synergistic effect between RGO and MOF(Ni), the interfacial interactions are effectively improved, and the contact area with the electrolyte is enhanced, which increases the ion transfer kinetics and overall electrochemical performance. The MOF(Ni)@RGO electrode exhibits a specific capacitance of 1267.73 F g-1 at a current density of 1 A g-1. Crucially, the assembled MOF(Ni)@RGO//BC with a broad potential window and good stability employing a MOF(Ni)@RGO anode and biomass carbon cathode, combined with a 2 M PVA-KOH gel-electrolyte, achieves a maximum energy density of 70.16 Wh kg-1 at a power density of 2200.09 W kg-1, outperforming most reported supercapacitors. This hybrid supercapacitor exhibits excellent stability and high energy density, providing a novel strategy for further large-scale applications.

Biaxial Stretching Array Based on High-Energy-Efficient MXene-Based Al-Ion Micro-supercapacitor Island and Editable Stretchable Bridge.

Employment of multivalent charge carriers with higher charge density to replace frequently used univalent ones can effectively increase the areal capacitance of micro-supercapacitors utilizing few-layered MXene self-assembled electrodes. However, their larger charge density and ionic size usually lead to a sluggish extraction/insertion dynamic between MXene interlayers with limited free space, greatly offsetting the benefits. Herein, we show how to facilitate de-/intercalation of high-valence charge carriers (Al3+) by using polypyrrole-coated bacterial cellulose (BC@PPy) nanospacers to expand MXene interlayer space. Together with the longitudinal electron transport path between interlayers synchronously constructed by the conductive PPy shell, a significant 496% areal capacitance enhancement (232.79 mF cm-2) is realized in the fabricated symmetric Al3+-ion micro-supercapacitors (AMSCs) with the obtained MXene/BC@PPy hybrid film electrodes employing polyacrylamide/1 M AlCl3·6H2O hydrogel electrolyte relative to the cell with pure MXene film electrodes (39.02 mF cm-2). Further benefiting from a high output voltage of 1.2 V, the AMSCs acquire an areal energy density up to 45.3 μW h cm-2. As a device demonstration, we further fabricate a biaxially stretchable AMSC array, simulate its spatial strain distribution during biaxial stretching, and characterize its electrochemical and mechanical properties up to an extreme areal strain of 300%. The proposed rational fabrication paradigm achieves a new level of combined energy density, stretch performance, and architectural simplicity, which presents a route toward a commercially viable stretchable micro energy-storage system with high energy efficiencies.

Sensitive, Highly Stable, and Anti-Fouling Electrode with Hexanethiol and Poly-A Modification for Exosomal microRNA Detection

It remains a huge challenge to integrate the sensitivity, stability, reproducibility, and anti-fouling ability of electrochemical biosensors for practical applications. Herein, we propose a self-assembled electrode combining hexanethiol (HT), poly-adenine (poly-A), and cholesteryl-modified DNA to meet this challenge. HT can tightly pack at the electrode interface to form a hydrophobic self-assembled monolayer (SAM), effectively improving the stability and signal-to-noise ratio (SNR) of electrochemical detection. Cholesteryl-modified DNA was immobilized at the electrode through the hydrophobic interaction with HT to avoid the competition between the SAM and the DNA probe on the gold site. Thus, the assembly efficiency and uniformity of the DNA probe as well as the detection reproducibility were increased remarkedly. Poly-A was added on the HT assembled electrode to occupy the unreacted sites of gold to further enhance the anti-fouling ability. The combination of HT and poly-A allows the electrode to ensure favorable anti-fouling ability without sacrificing the detection performance. On this basis, we proposed a dual-signal amplification electrochemical biosensor for the detection of exosomal microRNAs, which showed excellent sensitivity with a detection limit down to 1.46 aM. Importantly, this method has been successfully applied to detect exosomal microRNA-21 in cells and human serum samples, proving its potential utility in cancer diagnosis.

Self-assembled microtubular electrodes for on-chip low-voltage electrophoretic manipulation of charged particles and macromolecules

On-chip manipulation of charged particles using electrophoresis or electroosmosis is widely used for many applications, including optofluidic sensing, bioanalysis and macromolecular data storage. We hereby demonstrate a technique for the capture, localization, and release of charged particles and DNA molecules in an aqueous solution using tubular structures enabled by a strain-induced self-rolled-up nanomembrane (S-RuM) platform. Cuffed-in 3D electrodes that are embedded in cylindrical S-RuM structures and biased by a constant DC voltage are used to provide a uniform electrical field inside the microtubular devices. Efficient charged-particle manipulation is achieved at a bias voltage of <2–4 V, which is ~3 orders of magnitude lower than the required potential in traditional DC electrophoretic devices. Furthermore, Poisson–Boltzmann multiphysics simulation validates the feasibility and advantage of our microtubular charge manipulation devices over planar and other 3D variations of microfluidic devices. This work lays the foundation for on-chip DNA manipulation for data storage applications.

Symmetrically Controlled Design of Twin Alumina-Co Composite Thin Films

Self-assembled dual-working electrode electrolytic cells were designed to produce twin alumina-Co composite films with highly symmetrical microstructures using a deflected electric field-assisted alternating current electrodeposition method. The results show that the deposition current density, microstructure, and optical and magnetic properties of the twin composite films exhibit a high degree of symmetry. The distribution of magnetic Co particles in the alumina nanopores can be changed by adjusting the magnitude of the deflected electric field, resulting in a synchronous symmetrical change in the microstructure of the composite films, which enables the fine-tuning of the magneto-optical properties of the twin alumina-Co composite films at the microscopic scale. The current density distribution on the surface of the twin composite films along the direction of the deflected electric field was quantitatively analyzed by theoretical calculations and numerical simulations. The results show that the deposition current density gradually increases from 0.024 A/m2 in region C to 0.056 A/m2 in region A at 6 V deflection voltage. The saturation magnetization intensity gradually increases along the radial direction, which is 118, 130, and 150 kA/m, respectively

Self-assembled electrodes based on polyaniline grafted with reduced graphene oxide and polystyrene sulfonate

In this work, composites based on polyaniline (PAni) grafted with reduced graphene oxide (rGO) were obtained by the in situ chemical polymerization of aniline with rGO (mass ratio of 1 and 2.5%) dispersed into the monomer solutions. PAni and its PAni-rGO composites were used to prepare self-assembled (SA) films by depositing them onto indium tin oxide (ITO) substrates with alternating layers of polystyrene sulfonate (PSS). The structure and morphology of the materials were characterized by Fourier-transform infrared spectroscopy (FT-IR), RAMAN spectroscopy, and scanning electron microscopy (SEM). The oxidation states of PAni and its PAni-rGO composites were characterized by cyclic voltammetry (CV) and UV-Vis spectroscopy during the SA procedure. The electrochemical behavior of the obtained SA films was also characterized by electrochemical impedance spectroscopy (EIS). The EIS results showed a significant decrease in the polarization resistance (Rp), from 1020 to 302 Ω, for the film with 1% of rGO (PAni-1%rGO/PSS) when compared with its unmodified counterpart (PAni/PSS). The synergic effects observed for the PAni-1%rGO/PSS film showed that controlling the rGO mass ratio plays an important role in the improvement of the charge transfer processes, and that this electrode has potential for electrochemical applications, such as sensors and charge storage devices.

Hydrogen Peroxide Sensor Based on a Polymeric Self-assembled Nanoparticles-Modified Screen-Printed Electrode

Hydrogen Peroxide Sensor Based on a Polymeric Self-assembled Nanoparticles-Modified Screen-Printed Electrode

Self-assembly of graphene-based planar micro-supercapacitor with selective laser etching-induced superhydrophobic/superhydrophilic pattern

Facile production of graphene-based in-plane interdigital electrode is critical for microscale supercapacitors but remains a great challenge (time consuming, expensive equipment needed, etc). The preparation of fine interdigital electrode planar micro-supercapacitors (MSCs) by selective laser etching of ceramic substrate is proposed, which provides an alternative method for rapid fabrication of planar MSCs. The formation of self-assembled electrode of graphene ink via the laser etching-induced heterogeneous surface wettability was firstly investigated, and then an all-solid-state MSCs microdevice was obtained by adding a polyvinyl alcohol–sulfuric acid gel electrolyte to the interdigital electrode region. The results of cyclic voltammetry test showed that the micro-supercapacitor device could offer an area capacitance of 5.5 mF cm−2 at a potential scan rate of 5 mV s−1 and the capacitance retention of 88.5% after 4500 cycles.

Effect of surface amphiphilic property of azobenzene self-assembled electrode materials on properties of supercapacitors

In this report, novel azobenzene self-assembled complexes (azo-Cn, n = 8, 12, 16) were used as an electrode material for pseudo-capacitors. The as-prepared azo-Cn exhibited a good reversible redox process and possessed a specific capacitance as high as 221.0 F g−1 at 10 mV s−1. However, with the value n increased from 8 to 16, the specific capacitances of azo-Cn electrode materials decreased. In order to study the reasons, the effect of surface amphiphilic property of azobenzene self-assembled electrode materials on the properties of supercapacitors was studied and the results showed that the capacitive behaviors of azo-Cn could be greatly improved by better surface hydrophilic properties and azo-C8 with good supercapacitive characteristics could be the potential ideal electrode materials for low-cost and high-efficiency electrochemical supercapacitors.

Self-Assembly of Hybrid Nanorods for Enhanced Volumetric Performance of Nanoparticles in Li-Ion Batteries.

The benefits of nanosize active particles in Li-ion batteries are currently ambiguous. They are acclaimed for enhancing the cyclability of certain electrode materials and for improving rate performance. However, at the same time, nanoparticles are criticized for causing side reactions as well as for their low packing density and, therefore, poor volumetric battery performance. This paper demonstrates for the first time that self-assembly can be used to pack nanoparticles into dense battery electrodes with up to 4-fold higher volumetric capacities. Furthermore, despite the dense packing of the self-assembled electrodes, they retain a higher volumetric capacity than randomly dispersed nanoparticles up to rates of 5 C. Finally, we did not observe substential degradation in capacity after 1000 cycles, and post-mortem analysis indicates that the self-assembled structures are maintained during cycling. Therefore, the proposed self-assembled electrodes profit from the advantages of nanostructured battery materials without compromising the volumetric performance.

Photo-assisted acid-base machine: Battery ensemble to perform work from neutralization reactions

This study proposes a power source that operates between acidic and basic reservoirs under sunlight to treat acidic wastewater sustainably. We present a strategy that harvests energy from an ionic gradient associated with acidic solution neutralization and water photo-oxidation under UV light. In contrast to neutralization batteries, these photo-assisted acid-base machines operate with an interconnected battery ensemble comprising (A) a photo-assisted acid battery composed of photo-anode (TiO2) for water photo-oxidation and a selective self-assembled cathode consisting of poly(3,4-ethylenedioxythiophene) and phosphomolybdic acid for proton insertion; (B) a proton-alkali ion battery composed of the self-assembled electrode for proton deinsertion and a cathode made of copper hexacyanoferrate for potassium ion electro-insertion, which can be used as portable or stationary power source; (C) an alkali ion-air battery composed of the polycyanometalate for potassium ion deinsertion and a platinum cathode for the oxygen reduction reaction (ORR). This ensemble avoids reverse water splitting reactions and dismisses the need for external electrical power sources, which increases machine efficiency. Experiments demonstrate that acidic solution neutralization from pH = 1.3 to pH = 6.0 can harvest 102.6 kJ per mol of electro-inserted proton: this process converts energy from sunlight and from ionic gradient into electrical work. Therefore, the strategy presented here may contribute to environmental preservation and sustainable growth.

自己組織化単分子膜修飾電極を有する有機トランジスタ型化学センサの基盤研究

有機トランジスタは柔軟性や簡便な製造プロセスの適用が可能であるなど，化学センサのプラットフォームとして魅力的な電子デバイスである．筆者は，水系媒質中での標的化学種の検出を指向し，自己組織化単分子膜を活用した分子認識材料(抗体・酵素・人工レセプタ)の固定化と，それにより認識能が賦与された有機トランジスタ型化学センサの構築を試みてきた．これまでに，カチオン・アニオン・中性低分子種からタンパク質に至るまで，水溶液中に含まれる生体関連化学種および環境汚染物質の検出に取り組んでおり，有機トランジスタによる認識情報の電気的読み出しに成功している．有機トランジスタと自己組織化単分子膜修飾電極を組合せた当該デバイスによる本成果は，超分子化学・分析化学・有機デバイス工学の視点から見て興味深いものであり，有機分子エレクトロニクスおよび分子認識材料の新たな可能性を切り拓くものである．

Simultaneous electrochemical detection of dopamine and epinephrine in the presence of ascorbic acid and uric acid using a AgNPs–penicillamine–Au electrode

A silver nanoparticle immobilized penicillamine self-assembled electrode, AgNPs–PCA–Au, can simultaneously sense dopamine, epinephrine, ascorbic acid and uric acid at neutral pH.

High-performance infrared light trapping in nano-needle structured p⁺ SnOx (x ≤ 1)/thin film n-Ge photodiodes on Si.

We report nano-needle structured conductive SnOx (x≤1) as a self-assembled electrode for high-efficiency light trapping in thin-film infrared (IR) photonic devices, benefiting from the high scattering efficiency, high density, and low IR loss of the nano-needles. We demonstrate a 2.2× responsivity enhancement for a 1.5-μm-thick Ge absorber in a nano-needled p(+) SnOx/n-Ge photodiode on Si at λ=1580 nm, in good agreement with theoretical calculation of 2.3× enhancement assuming no IR loss in the nano-needles. Such low-loss light trapping can potentially enable 15-30× absorption enhancement at λ=1600-1650 nm in the Ge layer when integrated with a perfect rear reflector.

Electrochemical performance and durability of carbon supported Pt catalyst in contact with aqueous and polymeric proton conductors.

Significant differences in catalyst performance and durability are often observed between the use of a liquid electrolyte (e.g., sulfuric acid), and a solid polymer electrolyte (e.g., Nafion). To understand this phenomenon, we studied the electrochemical behavior of a commercially available carbon supported platinum catalyst in four different electrode structures: catalyst powder (CP), catalyst ionomer electrode (CIE), half membrane electrode assembly (HMEA), and full membrane electrode assembly (FMEA) in both ex situ and in situ experiments under a simulated start/stop cycle. We found that the catalyst performance and stability are very much influenced by the presence of the Nafion ionomers. The proton conducting phase provided by the ionomer and the self-assembled electrode structure render the catalysts a higher utilization and better stability. This is probably due to an enhanced dispersion, an improved proton-catalyst interface, the restriction of catalyst particle aggregation, and the improved stability of the ionomer phase especially after the lamination. Therefore, an innovative electrode HMEA design for ex-situ catalyst characterization is proposed. The electrode structure is identical to the one used in a real fuel cell, where the protons transport takes place solely through solid state proton conducting phase.

Self assembled silver nanowire mesh as top electrode for organic–inorganic hybrid solar cell

We prepare transparent, selfassembled polygonal silver nanowire (AgNW) mesh by bubble template and use as top electrode for a poly (3,4ethylenedioxythiophene):poly(stylenesulfonate) (PEDOT:PSS)/n-Si hybrid solar cell. Devices were fabricated by pressing the self-assembled AgNW and ITO electrodes onto the surface of the PEDOT:PSS and device performances were compared. In identical transmittances of ITO and self-assembled AgNW (i.e., 87% transmittance at wavelength of 550 nm), the self-assembled AgNW mesh electrodes shows lower sheet resistance (8 Ω/square) with enhanced transparency in the ultraviolet and infrared regions. As a result, a device performance with an efficiency of 9.60% was obtained with the self-assembled electrode compared to 9.07% efficiency from the indium–tin oxide (ITO) electrode under 100 mW/cm2 of AM 1.5 illumination. This study suggests the potential application of a self-assembled AgNW electrode as the transparent conducting electrode for future optoelectronic devices.

Flexible polymer electrode using self-assembled porous polyaniline

The soft portable electronic equipment, such as rollup displays and wearable devices, requires the development of flexible energy sources. Among them, a bendable battery needs soft electrode materials. Polyaniline (PANI) has been examined as an electrode material, on the basis of reversible doping behaviour, inexpensive cost, and low self-discharge rate. However, PANI has some shortcomings of poor processability and performance. Then in this study, self-assembled porous PANI electrode was prepared by emulsion polymerisation of aniline and polyvinyl alcohol (PVA). PVA was chosen as a supporting material to make porous structure and increases the flexibility. And the characterisations of the polymer electrode were carried out by means of 4-point probe, UV-vis spectra, scanning electron microscopy (SEM), and X-ray diffraction (XRD), etc. Also, the electric conductivity of self-assembled porous PANI electrode was intensively investigated.