Electrochemical Redox Reactions Research Articles

Enhancing selective ammonium transport in membrane electrochemical systems

Recovering ammonia nitrogen from wastewater is a sustainable strategy that simultaneously addresses both nitrogen removal and fertilizer production. Membrane electrochemical system (MES), which utilizes electrochemical redox reactions to transport ammonium ions through cation exchange membranes, has been considered as an effective technology for ammonia recovery from wastewater. In this study, we develop a mathematical model to systematically investigate the impact of co-existing ions on the transport of ammonium (NH4+) ions in MES. Our analysis elucidates the importance of pH values on both the NH4+ transport and inert ion (Na+) transport. We further comprehensively assess the system performance by varying the concentration of Na+ in the system. We find that while the inert cation in the initial anode compartment competes with NH4+ transport, NH4+ dominates the cation transport in most cases. The transport number of Na+ surpasses NH4+ only if the fraction of Na+ to total cation is extremely high (>88.5%). Importantly, introducing Na+ ions into the cathode compartment significantly enhances the ammonia transport due to the Donnan dialysis. The analysis of selective ion transport provides valuable insights into optimizing both selectivity and efficiency in ammonia recovery from wastewater.

3D hierarchical flowerball-like CoSe2/MnSe nanosheet arrays as a novel electrode for electrochemical sensing of hydrazine

Hydrazine (N2H4) is considered to be a highly toxic substance harmful to human body and environment, and has received much attention in the field of electrochemical detection in recent years. In this study, 3D hierarchical flowerball-like CoSe2/MnSe nanosheet arrays (CoSe2/MnSe FNSAs) were obtained using CoMn-LDH as precursor and cobalt glycerate spheres as the sacrificial template by simple hydrothermal reaction and selenization method. Bimetal selenides have more active electrochemical activity and more abundant electrochemical redox reactions. The unique hierarchical flowerball-like nanosheet array heterostructure can accelerate ionic diffusion kinetics and improve electron transfer. As a hydrazine electrochemical sensor, CoSe2/MnSe FNSAs exhibits excellent electrocatalytic performance with a wide detection range of 0.001–7.45 mM and a low detection limit of 0.4 μM. This strategy provides a new choice for the detection of environmental organic pollutants.

Cost-effective layered double hydroxides/conductive polymer nanocomposites for electrochemical detection of wastewater pollutants

There is an urgent need to develop multifunctional cost-effective nanomaterials and nanocomposites that can be used in numerous applications while showing high efficiency and cheaper implementation compared to conventional techniques and/or materials. In this work, zinc/iron layered double hydroxide (LDH) and polyaniline (PANI) were synthesized as a model LDH/conductive polymer nanocomposite, which is a promising family of cheap multifunctional materials. This electrochemical properties of this nanocomposite was investigated for detection of heavy metal (HM) ions in water streams, using lead as a model HM. In the present work, zinc/iron LDH and PANI was assigned as carbon paste electrode modifier. The composite was fully characterized using various characterization techniques including X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform InfraRed (FTIR). The electrochemical redox reactions of lead (II) ions at the modified electrode interface were investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), Accordingly, a linear relation of Pb2+ ions was achieved in the concentration range 1–80 µM with limit of detection (LOD) was 167.8 nM and limit of quantification (LOQ) was 559.4 nM. Furthermore, the cost of using such material for lead removal using a typical adsorption study was compared to using conventional inductively coupled plasma (ICP) or atomic absorption spectrometry (AAS) equipment for tracking HM removal during the adsorption process. Cost analysis revealed that the final overall cost of the modified carbon paste electrode is estimated as 1.25 USD. This cost represents less than 0.1% of the total cost required to conduct the same adsorption study using a typical ICP or AAS equipment. This composite can pave the road towards portable measurements for onsite detection of wastewater pollutants using cheap disposable-electrodes as compared to massive expensive off site equipment such as ICP and AAS.

A High‐Capacity and High‐Voltage Aqueous Zn‐Polymer Battery with Self‐Charging Function

AbstractOrganic electrodes in aqueous batteries rely on electrochemical redox reactions for charge and discharge. The organic cathode at a discharged state can be spontaneously oxidized when exposed to air, which facilitates the development of air‐charging batteries. However, polymer cathodes in aqueous rechargeable Zn‐ion batteries (ARZIBs) generally show low discharge median voltage below 1 V. Herein, a new polymer cathode is reported that is prepared by electrodepositing poly(4‐hydroxydiphenylamine, HDPA) onto mesoporous activated carbon and shows a relatively high discharge voltage plateau at ≈1.1 V when coupled with a Zn anode. Its self‐charging performances at different conditions are investigated. Also, a high areal capacity of 3.8 mAh cm−2 of the cathode is achieved. The poly(4‐HDPA) contains both amino and carbonyl groups, and the carbonyl group is found to be fully responsible for redox reaction. Further investigation suggests that both Zn2+ and H+ in the ZnSO4 electrolyte participate in the charge storage process, and the H+ plays a dominant role. The air‐charging mechanism of this polymer cathode is elucidated both experimentally and theoretically. To demonstrate the practical applications, prototypes of box‐shaped battery pack are air‐charged to either drive a mini electric fan or light up LEDs.

Understanding the influence of sulfur configuration on the electrochemical reaction pathway for lithium storage in molybdenum sulfides

Molybdenum sulfides are highly regarded as conversion-type electrodes with exceptional performance potential in lithium-ion batteries (LIBs). However, elucidating their lithium (Li) storage behavior has proven challenging due to the intricate sulfur (S) coordination with molybdenum atoms, which has impeded the realization of high energy densities in future Li storage systems. In this study, we investigate the electrochemical redox reaction pathways of molybdenum sulfide, specifically exploring the impact of various S configurations, including terminal, bridging, and apical S. We employ a comprehensive approach, involving extensive electrochemical measurements and depth X-ray photoelectron spectroscopy (XPS) profiling. In contrast to the multi-step conversion reactions observed in MoS2, sulfur-enriched molybdenum sulfides exhibit a unique single-step Li-ion storage mechanism. As a consequence of the pronounced effect of S configuration on the activation energy barrier during charging and discharging, the redox reaction voltage with Li ions exhibits variations. This versatility verifies that molybdenum sulfides have the potential to serve as both anode and cathode materials in lithium-ion batteries. Furthermore, we propose the incorporation of reduced graphene oxide (rGO) composites to address inherent limitations of molybdenum sulfides, including low electrical conductivity and irreversible reactions. The robust interaction between molybdenum sulfides and oxygen functional groups in rGO enhances rate capability and ensures a stable cycling lifespan. Through this systematic investigation, we suggest a comprehensive insight into the electrochemical reaction pathways governing Li storage behavior in molybdenum sulfides with distinct S configurations. This contributes to the fundamental understanding of these materials and their potential applications in advanced energy storage systems.

Enhancing Electrochemical Non-Enzymatic Dopamine Sensing Based on Bimetallic Nickel/Cobalt Phosphide Nanosheets.

In this study, the successful synthesis of bimetallic nickel/cobalt phosphide nanosheets (Ni-Co-P NSs) via the hydrothermal method and the subsequent high-temperature phosphorization process were both confirmed. Ni-Co-P NSs exhibited excellent electrocatalytic activity for the electrochemical non-enzymatic DA sensing. The surface morphologies and physicochemical properties of Ni-Co-P NSs were characterized by atomic force microscopy (AFM), field-emission scanning (FESEM), field-emission transmission electron microscopy (FETEM), and X-ray diffraction (XRD). Further, the electrochemical performance was evaluated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The metallic nature of phosphide and the synergistic effect of Ni/Co atoms in Ni-Co-P NSs provided abundant catalytic active sites for the electrochemical redox reaction of DA, which exhibited a remarkable consequence with a wide linear range from 0.3~50 μM, a high sensitivity of 2.033 µA µM-1 cm-2, a low limit of detection of 0.016 µM, and anti-interference ability. As a result, the proposed Ni-Co-P NSs can be considered an ideal electrode material for the electrochemical non-enzymatic DA sensing.

Electrochemical oxidative dehydrogenative annulation of 1-(2-aminophenyl)pyrroles with cleavage of ethers to synthesize pyrrolo[1,2-a]quinoxaline derivatives.

An array of pyrrolo[1,2-a]quinoxaline derivatives were achieved with moderate to good yields via the electrochemical redox reaction, which includes the functionalization of C(sp3)-H bonds and the construction of C-C and C-N bonds. In this atom economic reaction, THF was used as both a reactant and a solvent, and H2 was the sole by-product.

Electrochemical coupling in subnanometer pores/channels for rechargeable batteries.

Subnanometer pores/channels (SNPCs) play crucial roles in regulating electrochemical redox reactions for rechargeable batteries. The delicately designed and tailored porous structure of SNPCs not only provides ample space for ion storage but also facilitates efficient ion diffusion within the electrodes in batteries, which can greatly improve the electrochemical performance. However, due to current technological limitations, it is challenging to synthesize and control the quality, storage, and transport of nanopores at the subnanometer scale, as well as to understand the relationship between SNPCs and performances. In this review, we systematically classify and summarize materials with SNPCs from a structural perspective, dividing them into one-dimensional (1D) SNPCs, two-dimensional (2D) SNPCs, and three-dimensional (3D) SNPCs. We also unveil the unique physicochemical properties of SNPCs and analyse electrochemical couplings in SNPCs for rechargeable batteries, including cathodes, anodes, electrolytes, and functional materials. Finally, we discuss the challenges that SNPCs may face in electrochemical reactions in batteries and propose future research directions.

Electrically Triggered Color‐Changing Materials: Mechanisms, Performances, and Applications

AbstractElectrically triggered color‐changing materials, termed as electrochromic materials, offer precise and programmable color transistions through the manipulation of electric field frequency and amplitude. They are used as displays, sensors, military camouflage, wearable devices, and anticounterfeiting materials. Their future advancements depend on clear understanding of the color change mechanisms and pros/cons between different electrochromic materials. To this end, we starts by categorizing electrochromism into two classes according to color production mechanism: chemical color‐based and physical color‐based. Within the former, color emerges from chemical molecules selectively absorbing specific wavelengths of light and color changes stem from electrochemical redox reactions. The latter, meanwhile, hinges upon electrically induced alterations in the geometries, dimensions, or arrangements of nano/micro structures, such as photonic crystals and plasmonic nanostructures. The principles of color changes in both categories are detailed, and compare their differences in terms of response time, operating voltage, degree of color change, and stability. At the end, their applications will be discussed spanning from smart windows to color display, dynamic camouflage, energy storage, and thermal management. This critical review is aimed to provide multidisciplinary insights that will benefit both novices and seasoned experts engaged in fundamental exploration or practical investigations of electrochromic materials.

Graphene nanosheet-supported ultrafine RuO2 quantum dots as electrochemical energy materials

Ruthenium oxide (RuO2) shows great promise as an electrode material for supercapacitors, which are energy storage devices that have large power densities. However, RuO2 materials suffer low surface area, poor electrical conductivity and a tendency to aggregate after reactions, limiting their rate capability and cycle stability and can lead to inadequate redox reactions with electrolytes. To address these problems, this work synthesized homogeneous ultrafine-RuO2 quantum dots (QDs) materials with a size of around 2 nm on the surface of graphene nanosheets (GNS) via a facile hydrothermal method. The small size and uniform distribution of RuO2 QDs in the composite electrode material allowed for a high concentration of active adsorption sites for ions in the electrolyte while also facilitating efficient electrochemical redox reactions. The resulting RuO2/GNS composite exhibited a large specific area of 177.34 m2g‐1 and demonstrated an excellent capacitance performance of 1138.5 Fg‐1 at a current density of 0.5 Ag‐1. Additionally, a retention rate of 91.4 % when applying current densities from 0.5 to 10 Ag‐1 and cycling stability with 94.5 % retention after 20000 cycles, demonstrates the occurrence of a rapid and reversible faradaic redox reaction on the electrode surface. The symmetrical supercapacitor configuration with two identical RuO2/GNS electrodes was fabricated and demonstrated a high capacity (309.16 Fg‐1 at a current density of 0.5 Ag‐1) and an outstanding retention rate of 91.2 % at a current density of 10 A g−1). A device operated within a 1.8 V potential window showed high energy density from 126 Whkg‐1 to 139.2 Whkg‐1 and a power density from 440.1 Wkg‐1 to 8494.4 Wkg‐1 at current densities ranging from 0.5 Ag‐1 to 10 Ag‐1, respectively. This ultrafine-RuO2 quantum dots composite is a potentially promising advanced functional electrode material for electrochemical applications beyond supercapacitors and may be suitable for a broader range of energy storage and conversion applications.

On-demand engineerable visible spectrum by fine control of electrochemical reactions.

Tunability of optical performance is one of the key technologies for adaptive optoelectronic applications, such as camouflage clothing, displays, and infrared shielding. High-precision spectral tunability is of great importance for some special applications with on-demand adaptability but remains challenging. Here we demonstrate a galvanostatic control strategy to achieve this goal, relying on the finding of the quantitative correlation between optical properties and electrochemical reactions within materials. An electrochromic electro-optical efficiency index is established to optically fingerprint and precisely identify electrochemical redox reactions in the electrochromic device. Consequently, the charge-transfer process during galvanostatic electrochemical reaction can be quantitatively regulated, permitting precise control over the final optical performance and on-demand adaptability of electrochromic devices as evidenced by an ultralow deviation of <3.0%. These findings not only provide opportunities for future adaptive optoelectronic applications with strict demand on precise spectral tunability but also will promote in situ quantitative research in a wide range of spectroelectrochemistry, electrochemical energy storage, electrocatalysis, and material chemistry.

Manganese(I) Diimine(tricarbonyl) Complexes with a Redox-active Free Catechol Unit: Redox-induced Molecular Conversion of Catechol to Quinone by Electrochemical Redox Reactions on the Complex

Manganese(I) Diimine(tricarbonyl) Complexes with a Redox-active Free Catechol Unit: Redox-induced Molecular Conversion of Catechol to Quinone by Electrochemical Redox Reactions on the Complex

NiS2 nanoparticles decorated hierarchical porous carbon for high-performance lithium-selenium batteries

lithium–selenium (Li–Se) batteries are recognized as an attractive candidate for energy storage owing to its high volumetric capacity (3253 mA h cm−3). However, the sluggish electrochemical redox reaction and the accompanying enormous volume fluctuation greatly impede the application of Li–Se batteries. Herein, a catalyst of nickel disulfide (NiS2) nanoparticles decorated hierarchical porous carbon (HPC) has been fabricated and applied as the cathode for Li-Se batteries. The porous structure offers large amount of viod to buffer the volume change during charge/discharge. At the same time, the NiS2 nanoparticles exhibit strong adsorption capabilities towards lithium polyselenides and aslo promote the conversion of these intermediates. As a consequence, the NiS2-HPC cathode delivers a superior rate capacity (569 mAh g−1 at 0.5 C and 549 mAh g−1 at 1 C) and good cycling stability (289 mAh g−1 after 1000 cycles at 2 C with a Coulombic efficiency of ∼100%). This work demonstrates the viability of employing metal sulfide-anchored porous carbon materials for high-performance lithium-selenium batteries.

Elucidating the Role of Mass Transfer in Electrochemical Redox Reactions on Electrospun Fibers

Mass transfer can tune the surface concentration of reactants and products and subsequently influence the catalytic performance. The morphology of nanomaterials plays an important role in the mass transfer of reaction microdomains, but related studies are lacking. Herein, a facile electrospinning technique utilizing cellulose was employed to fabricate a series of carbon nanofibers with different diameters, which exhibited excellent electrochemical nitrate reduction reaction and oxygen evolution reaction activities. Furthermore, the microstructure of electrocatalysts could influence the gas–liquid–solid interfacial mass transfer, resulting in different electrochemical performances.Graphical abstract

Application of TiS2 as an Active Material for Aqueous Calcium-Ion Batteries: Electrochemical Calcium Intercalation into TiS2 from Aqueous Solutions

This study explores the potential of titanium disulfide (TiS2) as an active material for aqueous calcium-ion batteries (CIBs). We investigate the electrochemical redox reactions of calcium ions within TiS2 and assess its suitability for use in aqueous CIBs. Additionally, we examine the impact of varying electrolyte concentrations, ranging from 1.0 to 8.0 mol dm−3, on TiS2 electrode reactions. Our findings reveal that TiS2 exhibits distinct charge–discharge behaviors in various aqueous calcium-ion electrolytes. Notably, at higher electrolyte concentrations, TiS2 effectively suppresses the hydrogen generation reaction caused by water decomposition. In situ X-ray diffraction analysis confirms the intercalation of Ca2+ ions between the TiS2 layers during charging, which is a groundbreaking discovery, signifying TiS2’s applicability in aqueous CIBs. X-ray photoelectron spectroscopy analysis further supports the formation of a solid electrolyte interphase (SEI) on the TiS2 electrode surface, contributing to the suppression of electrolyte decomposition reactions. Furthermore, we investigate the influence of anions in the electrolyte on charge–discharge behavior. Our findings suggest that the choice of anion coordinated with Ca2+ ions affects the SEI formation and cycling performance. Understanding the role of anions in SEI formation is crucial for optimizing aqueous CIBs. In conclusion, this research underscores TiS2’s potential as an active material for aqueous calcium-ion batteries and emphasizes the importance of the electrolyte composition in influencing SEI formation and battery performance, contributing to sustainable and efficient energy storage technologies.

Iron-cobalt-nickel-copper-zinc (FeCoNiCuZn) high entropy alloy as positive electrode for high specific capacitance supercapacitor

High entropy alloys (HEAs) are new-generation supercapacitive materials providing multiple active sites for enhanced electrochemical redox reactions. In this regard, we have successfully synthesized HEA comprising of Iron-Cobalt-Nickel-Copper-Zinc (Fe-Co-Ni-Cu-Zn) using induction melting and reduced its dimensions via ball milling. The ball-milled Fe-Co-Ni-Cu-Zn sample is throughly characterized by using basic structural and morphological techniques. A positive electrode is fabricated for supercapacitor application. This quinary HEA shows the highest gravimetric capacitance of 325.17 F g − 1 at 1 A g − 1 (3 M potassium hydroxide, aqueous electrolyte) in single electrode system. The asymmetric device also demonstrates energy density of 23.82 Wh kg−1 by consuming a power density of 325 W kg−1. Additionally, theoretical studies (DFT) shows that the electronic distribution of quinary Fe-Co-Ni-Cu-Zn elements in the alloy enhances chemical stability which is the reason for higher specific capacitance.

Cu-substituted Prussian white with low crystal defects as high-energy cathode materials for sodium-ion batteries

Prussian white (PW) has emerged as a promising cathode material for high-energy sodium-ion batteries owing to its high working voltage, high specific capacity, and cost-effectiveness. Nonetheless, its practical utilization is impeded by challenges related to insufficient cycling stability, primarily stemming from poor structural stability due to large defects in the lattice structures and irreversible phase transitions. In this study, we propose a novel strategy to overcome these challenges by substituting the manganese sites of PW with 10 mol% copper. During the synthesis process, substitution with Cu enabled the formation of fewer defects and interstitial water. Cu has no electrochemical redox reactions during the charge-discharge process; so, it showed an initial lower capacity(120 mAh g-1 at 0.1C). However, Cu substitution resulted in a significant improvement in the long-term cycling stability(67.6% at 10C after 500 cycles) by relieving structural stress due to the reversible rhombohedral-to-cubic phase transition. Moreover, the pouch cell (PW-Cu10/hard carbon) exhibits a discharge capacity of 85.4 mAh g−1 and stable cycling retention of 80% at 1.0C after 250 cycles. This work demonstrates a feasible strategy for designing practical Prussian white cathode materials for sodium-ion batteries.

A braided flexible Zn–MnO2 yarn battery based on cobweb-like carbonized polypyrrole modified carbon fiber electrodes

Flexible zinc ion batteries (ZIBs) are promising candidates for energy storage devices because of high safety and low cost. Carbon fibers (CFs) are ideal current collectors for ZIBs due to their good flexibility, electrical conductivity and corrosion resistance. Herein, a novel CFs-based current collector is proposed. At first, the inertness and non-polarity of CFs were significantly modified by activating and etching to obtain a multi-layered porous structure. Thereafter, carbonized polypyrrole (CPPy) nanowire conductive networks were built up on etched carbon fibers (ECFs) by electrochemical in situ growth and carbonization. Based on the CPPy network, MnO2 nanoflowers were grown firmly by the hydrothermal method to construct multi-layer MnO2@CPPy@ECFs composite electrode. The multi-layered 3D CPPy conductive network is rooted in MnO2, providing a dedicated transmission path for both electrons and ions during electrochemical redox reactions. The MnO2@CPPy@ECFs electrode had an initial capacity of 346.1 mA h·g−1 at 0.1 A g−1 and 252.8 mA h·g−1 after 800 cycles. In addition, the integrated flexible Zn–MnO2 2D fabric battery with MnO2@CPPy@ECFs fabric cathode shows a specific capacity of 254.7 mA h·g−1 at 0.1 A g−1. Finally, a flexible Zn–MnO2 yarn battery with high flexibility, shape adaptability, structural integrity and good mechanical stability was fabricated by the 2D braid method. The initial specific capacity of the flexible Zn–MnO2 yarn battery is 111.7 mA h·g−1 at 0.1C, which also presents a remarkable volumetric energy density of 30.5 mW h cm−3. This work opens up a new pathway for the rational design of flexible electrodes for wearable ZIBs.

Electrochemical determination of cadmium ions in biological and environmental samples using a newly developed sensing platform made of nickel tungstate-doped multi-walled carbon nanotubes

Simple and rapid analysis of cadmium ion in environmental and biological samples is of great importance due to the severe toxicity caused by this heavy metal. In the present work, nickel tungstate (NiWO4) dispersion was mixed with multi-walled carbon nanotubes (MWCNTs) to obtain a homogenous composite of (NiWO4/MWCNTs) which was assigned as carbon paste electrode modifier. The composite was fully characterized using various characterization techniques including X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Thermo-Gravimetric Analysis (TGA) and Fourier Transform InfraRed (FTIR). The electrochemical redox reactions of cadmium (II) ions at the modified electrode interface were investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and linear sweep voltammetry (LSV). Effective parameters on the electro-analysis assay performance including the electrode composition, types of electrolyte, scan rate and pH were tested to achieve the best effective optimum conditions. Accordingly, a linear relation of cadmium ions was achieved in the concentration range 50–450 µM with limit of detection of 0.12 µM. Besides, the proposed electrode was successfully used to monitor trace amounts of cadmium ions in various real samples.Graphical abstractSchematic illustration of synthesis process of NiWO4/MWCN nanocomposite and its application as high-performance cadmium ion sensors

Hierarchically porous N-doped carbon nanosheet aerogel cathodes for Zn-ion hybrid supercapacitors with superhigh energy density

Carbon nanomaterials with large specific surface area and high electronic conductivity, have been widely used as capacitive cathode materials for Zn-ion hybrid supercapacitors. Doping of heteroatoms and regulation of pore structure are crucial for boosting the energy storage performances of the carbon-based cathodes. We propose a N-doped carbon nanosheet aerogel (N-CNAG) with high active N content and hierarchically porous structure, which can be prepared by the bubble-templated polymerization of Py and the carbonization of the PPy nanosheet hydrogel (PPyNHG). The high active N content of N-CNAG can produce high pseudocapacitance through the N-dependent electrochemical redox reactions. The hierarchically porous structure of N-CNAG can facilitate fast electrolyte ion diffusion. Based on the Zn anode and the N-CNAG cathode, the Zn-ion hybrid supercapacitor can provide a remarkable specific capacitance of 706 F g−1 at 1 A g−1 and the rate capability of 50 % from 1 A g−1 to 5 A g−1, mainly attributed to the high active N content and the hierarchically porous structure of N-CNAG. Additionally, this Zn-ion hybrid supercapacitor provides the superhigh energy density of 392 Wh kg−1 at 1 kW kg−1 and the cycling stability of 87.4 % after 10,000 cycles, holding great potential for developing high-energy-density Zn-ion hybrid supercapacitors.