Reversible Redox Research Articles

Modulating Local Oxygen Coordination to Achieve Highly Reversible Anionic Redox and Negligible Voltage Decay in O2‐Type Layered Cathodes for Li‐Ion Batteries

AbstractO2‐type layered oxides have emerged as promising cathode materials for high‐energy lithium‐ion batteries, offering a solution to mitigate voltage decay through reversible transition metal (TM) migration between TM and Li layers during cycling. However, achieving a fully reversible oxygen redox remains a significant challenge. Here, this is addressed by introducing Li─O─Li configurations in the layered structure of Li0.85□0.15[Li0.08□0.04Ni0.22Mn0.66]O2 (O2‐LLNMO), where □ represents vacancies. This adjustment alters the redox‐active oxygen environment and increases the energy gap between the O 2p nonbonding and TM─O antibonding bands. As a result, the contribution of lattice oxygen to capacity is significantly enhanced, improving the reversibility of oxygen redox processes. The O2‐LLNMO cathode demonstrates minimal voltage decay (0.13 mV per cycle) and excellent cycling stability, retaining 95.8% of its capacity after 100 cycles. A novel strategy is presented to design high‐performance layered oxides with stable anionic redox activity, advancing the development of next‐generation lithium‐ion batteries.

Reversible Redox Probes to Determine Band‐Edge Locations and Dopant Concentrations of Nano‐TiO2 Thin‐Films: Settling the Mott‐Schottky Conundrum

Knowing the exact location of the semiconductor band‐edges is key for mechanistic insights into their use for water and CO2 photo/electrocatalysis. In this regard, a reliable strategy for nano‐semiconductors did not exist yet. We demonstrate the use of reversible redox probes on nano‐semiconductor electrodes to determine their band‐edge locations in aqueous solutions. Rectifying current‐potential (i‐U) characteristics with the high work function Fe(CN)63‐/Fe(CN)64‐ redox couple yielded the exact flatband potential at various pH whereas the reversible i‐U characteristics with the low work function Ru(NH3)63+/Ru(NH3)62+ redox couple provided the conduction band‐edge location and dopant concentration for a 30nm thin‐film n‐TiO2. The methodology can be extended to other nano‐semiconductors and serves as an alternative to and goes beyond the capabilities of the Mott‐Schottky procedure for bulk semiconductor electrodes.

Reversible Redox Probes to Determine Band-Edge Locations and Dopant Concentrations of Nano-TiO2 Thin-Films: Settling the Mott-Schottky Conundrum.

Knowing the exact location of the semiconductor band-edges is key for mechanistic insights into their use for water and CO2 photo/electrocatalysis. In this regard, a reliable strategy for nano-semiconductors did not exist yet. We demonstrate the use of reversible redox probes on nano-semiconductor electrodes to determine their band-edge locations in aqueous solutions. Rectifying current-potential (i-U) characteristics with the high work function Fe(CN)63-/Fe(CN)64- redox couple yielded the exact flatband potential at various pH whereas the reversible i-U characteristics with the low work function Ru(NH3)63+/Ru(NH3)62+ redox couple provided the conduction band-edge location and dopant concentration for a 30nm thin-film n-TiO2. The methodology can be extended to other nano-semiconductors and serves as an alternative to and goes beyond the capabilities of the Mott-Schottky procedure for bulk semiconductor electrodes.

Electrochemically Switchable Sulfurized Polyacrylonitrile for Controllable Recovery of Copper in Wastewater Based on Reversible Adsorption/Desorption Regulation.

Within the context of circular economy and industrial ecology, adsorption offers an effective manner for recycling resources from wastewater, but controllable desorption remains a challenge. Inspired by metal-thiol binding and reversible thiol-disulfide redox transformation in biological systems, this study reports the development of a reversible adsorption/desorption (RAD) system for controllable recovery of copper based on electrochemically switchable sulfurized polyacrylonitrile (SPAN). Density functional theory calculations offered theoretical prediction for the formation of S-Cu bonds and reversible weak interaction between S-S bonds and Cu2+. The SPAN anchored onto titanium suboxide ceramic foam (SPAN@TiSO) could regulate Cu2+ adsorption/desorption stimulated by the electrode potential, indicated by the adsorption capacity of 243.3 mg g-1 (30 min) at 0.2 V vs SHE and a desorption efficiency of 98.4% (5 min) at 0.8 V vs SHE. Electrochemical analysis revealed that the reversible redox transformation of S-S/-S- groups in SPAN was responsible for selective adsorption and rapid desorption in response to the electrode potential. This study provides a proof-of-concept demonstration of an electrochemically switchable polymer to build up a reversible RAD system for controllable recovery of heavy metals in wastewater, making value-added resource recovery more efficient, more intelligent, and more sustainable.

Achieving complete solid-solution reaction in layered cathodes with reversible oxygen redox for high-stable sodium-ion batteries

Achieving complete solid-solution reaction in layered cathodes with reversible oxygen redox for high-stable sodium-ion batteries

High-performance α-Fe2O3 nano cubes as anode for supercapacitors

Abundant availability, high theoretical specific capacitance and low cost of transition metal oxides such as iron oxides, make them attractive as electrode materials for energy storage. In order to achieve improved performance, high conductivity, shorter ion-diffusion path, and faster ion accessibility, rational design of morphology of electrode material is highly desirable. We have successfully synthesized mesoporous α-Fe2O3 nanocubes to achieve high specific capacitance and better retention. The as-prepared and annealed α-Fe2O3 nanocubes show high reversible redox activity along with good thermodynamic stability. These nanostructure give rise to high specific capacitance and ~90 % of the capacitance can be retained even after 1000 redox cycles, suggesting good cyclic stability. The electrochemical performance of mesoporous α-Fe2O3 nanocubes is attributed to the morphological features, which results in efficient K+ ion transport into the pores. A two electrode α-Fe2O3//NiO device is fabricated, which shows excellent power and energy density of ∼627 W/kg and ∼23.32 Wh/kg, respectively. Our work demonstrates that 3D nanoporous α-Fe2O3 electrodes forms promising material system as anode for improved charge storage performance.

Advanced label-free electrochemical immunosensor for a minimally invasive detection of proteins in paintings

In recent decades, scientific methodologies applied in theCultural Heritage field have been growing, due to their pivotal role in guiding informed decisions concerning conservation strategies and daily maintenance. To achieve this goal, minimally/non-invasive quantitative and qualitative analyses are needed. However, the non-invasive and selective identification of proteinaceous binders and coatings in artworks represent an open issue in Cultural Heritage science.Herein, a novel miniaturized system is introduced, which consists of a label-free electrochemical immunosensor integrated with biocompatible Gellan gel. This method is intended to selectively and minimally invasively identify ovalbumin (OVA) on-site in paintings. The label-free immunosensor is made up on screen-printed electrodes (SPEs) by functionalizing the working electrode (WE) with a primary antibody (anti-ovalbumin) for the specific recognition of OVA. The presence of OVA produces antigen-antibody reaction, which results in the development of a bulky immunocomplex on the WE. This complex is quantified using square wave voltammetry (SWV) and a reversible redox probe: the current measured is inversely proportional to the OVA concentrations. The developed immunosensors showed good analytical performances when applied directly to painted mock-ups, exhibiting a limit of detection (LOD) of 1.6 ng/mL, a limit of quantification (LOQ) equal to 16 ng mL-1, a working range between 0.01-0.4 μg/mL and selectivity for OVA over other protein components commonly present in painted artworks, including bovine serum albumin (BSA), collagen, and casein.The outcomes highlighted the dependability of the immunosensor in detecting OVA and the efficacy of Gellan gel as a streamlined method for extracting the target protein while preventing residue accumulation on the painting surface. This advancement suggests the potential of Gellan gel-coupled immunosensor systems as viable diagnostic alternatives for artwork management and preservation.

Redox active metallene anchored amino-functionalized cellulose composite for electrochemical capture and conversion of chromium

Considering the ubiquity and high toxicity of Cr(VI) species for destroying a sustainable environment, developing energy-efficient method for capturing and detoxifying chromium [Cr(VI) → Cr(III)] is imperative. Herein, ferrocene (Fc) was combined with carboxymethyl cellulose (CMC) and polyethyleneimine (PEI) for Cr(VI) remediation. Fc species possessed reversible redox behavior and low ionization potential, yet it faced challenges with conductivity and stability. Results revealed that, PEI facilitated the binding of Fc within the CMC through electrostatic interactions or coordination bonds, ensuring the good dispersion and stability of Fc. When applied in the electrochemical adsorption of Cr(VI), the combination created a synergistic effect. The presence of Fc and PEI boosted the electrochemical performance by providing faster electronic and ionic transportation, higher specific capacitance coupled with improved electrode-electrolyte interactions, leading to a higher Cr(VI) adsorption capacity over CMC/PEI/Fc (280.5 mg/g) compared to those over CMC and CMC/PEI. The interactions between the Cr(VI) and electrode included the electrosorption, electrostatic interaction of protonated PEI and oxidized Fc species. When the electric field was reversed, the Cr(VI) was electrostatic repulsed and electrocatalytic reduced to Cr(III) with a reduction rate of 85.4 %. This work promoted the development of effective electrosorption materials suitable for complete Cr(VI) removal and detoxification.

Biomimetic Redox Capacitor To Control the Flow of Electrons.

In biological systems, electrons, energy, and information "flow" through the redox modality, and we ask, does biology have redox capacitor capabilities for storing electrons? We describe emerging evidence indicating that biological phenolic/catecholic materials possess such redox capacitor properties. We further describe results that show biomimetic catecholic materials are reversibly redox-active with redox potentials in the midphysiological range and can repeatedly accept electrons (from various reductants), store electrons, and donate electrons (to various oxidants). Importantly, catechol-containing films that are assembled onto electrode surfaces can enhance the flow of electrons, energy, and information. Further, catechol-containing films can serve as redox-based interactive materials capable of actuating biological responses by turning on gene expression from redox-responsive genetic circuits. Looking forward, we envision that the emerging capabilities for measuring dynamic redox processes and reversible redox states will provide new insights into redox biology and will also catalyze new technological opportunities for information processing and energy harvesting.

Unveiling electrochemical insights of lithium manganese oxide cathodes from manganese ore for enhanced lithium-ion battery performance

Implementing manganese-based electrode materials in lithium-ion batteries (LIBs) faces several challenges due to the low grade of manganese ore, which necessitates multiple purification and transformation steps before acquiring battery-grade electrode materials, increasing costs. At present, most Lithium Manganese Oxide (LMO) materials are synthesized using electrolytic manganese dioxide, and the development of new processes, such as hydrometallurgical processes is important for achieving a cost-effective synthesis of LMO materials. In this work, we develop a full synthesis process of LMO materials from manganese ore, through acid leaching, forming manganese sulfate monohydrate (MnSO4·H2O), an optimized thermal decomposition (at 900, 950 or 1000 °C) producing different Mn3O4 materials and a solid-state reaction, achieving the synthesis of LMO. The latter was used as a cathode material for LIB exhibiting a specific capacity comparable to the state-of-the-art LMO cathode with a remarkable cycling stability of 800 cycles with <20 % in capacity loss. These performances were attributed to the excellent redox reversibility of the LMO cathode, characterized by voltammetry and in operando and in situ characterization by Raman and XRD.

An “Ion Harvester” Battery in Soil Empowered by a Microfluidic Pump and Interlayer Confinement within Micro‐Swiss‐Rolls

AbstractA significant challenge arises in powering distributed tiny sensors that gather high‐resolution soil data are crucial for advancing digital and geospatial technologies in the field. Traditional batteries and solar cells are unsuitable due to size mismatches. Microbial fuel cells lack stability in delivering constant power. Soil naturally contains redox‐active ions, such as Zn2+ and Mn2+, which can be harvested and utilized for electrochemical energy storage. To facilitate access to soluble ions, a microfluidic pump based on micro‐Swiss‐roll structures via micro‐origami is developed. Spontaneous capillary flow allows for efficient liquid extraction. The micro‐Swiss‐roll architecture shows significant improvements in redox reversibility and charge transfer within micrometer‐thick interlayer space. Notably, the interference of Zn0/2+ and Mn(II)/Mn(IV) reactions is suppressed. Consequently, the battery using a micro‐Swiss‐roll electrode shows high voltage and energy efficiency at high currents up to 10 µA, with cycling stability of 300 times. A twin‐micro‐Swiss‐roll architecture of 0.385 ± 0.006 mm2 is used for energy storage in wet soil, yielding over 40 times more energy as compared to soil‐microbial fuel cells. A conceptual demonstration of an integrated irrigation water sensor and micro‐Swiss‐roll battery highlights the potential of microbattery development in addressing the critical challenge of powering tiny sensors in the soil.

Close‐packed One‐dimensional Coordination Polymer Cathode with Fast Kinetics for Sodium‐ion Batteries

Sustainable sodium‐ion batteries (SIBs) have gained tremendous attention; however, the large‐sized Na+ poses serious challenges on the development of inorganic‐based cathodes. To overcome the issues, metal–organic electrode materials are appealing because they combine attractive characteristics of organic redox centers (e.g., flexibility, highly reversible redox properties, fast kinetics (regardless of size and charge of guest ions), structural/redox tunability, and resource abundance) with structural stability arising from metal‐ligand coordination. Herein, a one‐dimensional copper‒benzoquinoid coordination polymer (CP), [CuL(Py)2]n, (LH4 = 1,4‐dicyano‐2,3,5,6‐tetrahydroxybenzene, Py = pyridine) is investigated as cathode for SIBs. As opposed to most CPs reported for SIBs which possess high porosity and surface area, this close‐packed CP can deliver discharge capacity as high as 277 mAh g‒1 at 2C (~523 mA g‒1), and at extremely high rates of 50C and 300C (~13 and 78 A g‒1), reversible capacities of 131 and 74 mAh g‒1 still can be delivered, respectively. The transport kinetics of Na+ in [CuL(Py)2]n is found to be even faster than that of Li+ despite the close‐packed structure. The mechanistic and kinetic studies have been performed. The findings gained in this work undoubtedly unravel a potential design strategy for high‐performance metal–organic electrode materials for emerging post‐Li‐ion batteries.

Nickel-Doped Facet-Selective Copper Nanowires for Activating CO-to-Ethanol Electrosynthesis.

Ethanol isa promising energy vector for closing the anthropogenic carbon cycle through reversible electrochemical redox. Currently, ethanol electrosynthesissuffers from low product selectivity due to the competitive advantage of ethylene in CO2/CO electroreduction. Here, a facet-selective metal-doping strategy is reported, tuning the reaction kinetics of CO reduction paths and thus enhancing the ethanol selectivity. The theoretical calculations reveal that nickel (Ni)doped Cu(100) surface facilitates water dissociation to form adsorbed hydrogen, which promotesselective electrochemical hydrogenation of a key C2 intermediate (*CHCOH) toward ethanol path over ethylene path. Experimentally, a solution-phase synthesis of a Ni-doped {100}-dominated Copper nanowires (Cu NWs) catalyst is reported, enabling an ethanol Faradaic efficiency of 56% and a selectivity ratio of ethanol to ethylene of 2.7, which are ≈4 and 15 times larger than those of undoped Cu NWs, respectively. The operando spectroscopic characterizationsconfirm that Ni-doping in Cu NWs can alter the interfacial water activity and thus regulate the C2 product selectivity. With further electrode engineering, a membrane electrode assembly electrolyzer using Ni-doped Cu NWs catalysts demonstrates an ethanol Faradaic efficiency over 50% at 300mA cm-2 with a full cell voltage of ≈2.7V and operates stably for over 300 h.

A High-Voltage n-type Organic Cathode Materials Enabled by Tetraalkylammonium Complexing Agents for Aqueous Zinc-Ion Batteries.

Tetrabutylammonium (TBA) salt of hexacyano-substituted cyclopropane dianion (Cp(CN)6 2 -) is prepared through a facile two-step synthetic protocol from commercially available materials and fully characterized as a high-voltage n-type organic cathode in rechargeable aqueous zinc-ion batteries (AZIBs). The addition of tetrabutylammonium triflate (TBAOTf)to the electrolyte mitigates dissolution issues, leading to enhanced cycling stability. Remarkably, the Cp(CN)6 2 - cathode demonstrates a high discharge voltage of 1.43V in AZIBs and retains 85% of its capacity after 1000 cycles at a high loading of 10mg cm- 2 and a cycling rate of 10C. These results, combined with spectroscopic analyses, elucidate a reversible two-electron redox process of Cp(CN)6 2 - facilitated by the insertion/de-insertion of TBA cation. These findings underscore the potential of Cp(CN)6 2 - as a conversion-based n-type cathode in energy storage applications.

Highly Reversible Conversion-Type CoSn2 Cathode for Fluoride-Ion Batteries.

An all-solid-state fluoride-ion battery (FIB) is one of the promising candidates for the next-generation battery owing to its high energy density and high safety. For the practical application of FIBs, it is an urgent task to operate FIBs at lower temperatures. However, there are still two major difficulties in conventional conversion-type pure metal cathodes: low F- ion conductivities and poor cycle stabilities. Here, the conversion-type Sn-based intermetallic alloy is proposed as a new cathode that can overcome the above issues. The present CoSn2 cathode retains the discharge capacity of 229 mAh g-1 after 250 cycles, even at 60°C. CoSn2 is decomposed into CoF2 and SnF2 nanocrystals in the charging process, and the nanoscale network structure of SnF2 provides the fast F- ion conduction path throughout the cathode, facilitating the battery operation at lower temperatures. Moreover, the formed CoF2 and SnF2 phases are merged into the original CoSn2 phase in the discharging process, leading to a highly reversible redox reaction and the high cycle stability of CoSn2. These findings should pave the way to enhance the performance of all-solid-state FIBs at lower temperatures.

Phosphorescent cyclometalated Ir(III) complexes with fluoranthene unit and their near-infrared (NIR) OLEDs showing NIR% higher than 99 %

With the aim to design and synthesize cyclometalated Ir(III) complexes with near-infrared (NIR) emission, a series of ppy-type ligands with fluoranthene unit have been synthesized bearing different aromatic nitrogen heterocycles of isoquinoline, quinoline, pyridine and benzo [d]thiazole. With these organic ligands, four [Ir (ppy)2 (acac)] complexes are prepared named as IrFTIQ, IrFTQL, IrFTPY and IrFTBZ. In solution, IrFTIQ can emit NIR phosphorescence at 738 nm, while IrFTQL (ca. 692 nm), IrFTPY (ca. 670 nm) and IrFTBZ (ca. 690 nm) are typical deep-red emitters. It should be noted that all these fluoranthene-based cyclometalated Ir(III) complexes show good electrochemical stability indicated by their reversible redox procedures. When doped in the emission layer of OLEDs, IrFTIQ and IrFTBZ can furnish NIR electroluminescence (EL) at 748 nm and 700 nm, respectively, while the devices with IrFTPY as emitter can furnish deep-red EL. Critically, the optimized OLED doped with IrFTIQ can achieve maximum external quantum efficiency (EQE) as high as 5.01 % and a radiance up to 6284 mW Sr−1 m−2. Critically, the NIR OLEDs based on IrFTIQ can furnish EL with NIR component (NIR%) of a total spectrum > 99 %. All these encouraging results definitely demonstrate the effectiveness of our molecular design strategy for the new-type Ir(III) NIR phosphorescent complexes and the great potential of the fluoranthene group in developing high-performance Ir-based NIR phosphors for OLEDs.

Organometallic Polymer Constructed by Active Fe-C12N8 Centers for Boosting Sodium-Ion Storage.

Organic-metal coordination materials with rich structural diversity are considered as promising electrode materials for rechargeable sodium-ion batteries. However, the electrochemical performance can be constrained by the limited number of active sites and structural instability under the discharge/charge process. Herein, organometallic polymer microspheres (Fe-PDA-220) with a unique d-π conjugated structure was designed and successfully constructed through a simple synchronous polymerization and coordination reactions. Polymerization of phenylenediamine was initiated by Fe3+ and Fe2+ ions generated synchronously during the polymerization integrated with poly-aminoquinone chains to form Fe-C12N8 active centers. Used as electrode materials for sodium-ion batteries, the distinctive Fe-C bond significantly boosts the structural stability, and the π-d conjugation system could facilitate electron transfer. A high reversible capacity of 345 mAh g-1 was delivered at 0.1 A g-1 and a capacity of 106 mAh g-1 was maintained even after discharged/charged at 1.0 A g-1 for 5000 cycles, outperforming most reported coordination materials. Spectroscopic and electronic analyses revealed that a two-electron reaction occurred per active unit, accompanied by the reversible redox evolution of the C=N groups and Fe ions during the sodiation/desodiation. This work provides a promising and efficient strategy for boosting the electrochemical performance of organic electrode materials by the design of organometallic polymers.

Organometallic Polymer Constructed by Active Fe−C12N8 Centers for Boosting Sodium‐Ion Storage

AbstractOrganic‐metal coordination materials with rich structural diversity are considered as promising electrode materials for rechargeable sodium‐ion batteries. However, the electrochemical performance can be constrained by the limited number of active sites and structural instability under the discharge/charge process. Herein, organometallic polymer microspheres (Fe‐PDA‐220) with a unique d‐π conjugated structure was designed and successfully constructed through a simple synchronous polymerization and coordination reactions. Polymerization of phenylenediamine was initiated by Fe3+ and Fe2+ ions generated synchronously during the polymerization integrated with poly‐aminoquinone chains to form Fe−C12N8 active centers. Used as electrode materials for sodium‐ion batteries, the distinctive Fe−C bond significantly boosts the structural stability, and the π‐d conjugation system could facilitate electron transfer. A high reversible capacity of 345 mAh g−1 was delivered at 0.1 A g−1 and a capacity of 106 mAh g−1 was maintained even after discharged/charged at 1.0 A g−1 for 5000 cycles, outperforming most reported coordination materials. Spectroscopic and electronic analyses revealed that a two‐electron reaction occurred per active unit, accompanied by the reversible redox evolution of the C=N groups and Fe ions during the sodiation/desodiation. This work provides a promising and efficient strategy for boosting the electrochemical performance of organic electrode materials by the design of organometallic polymers.

Redox Couple Strategy for Improving the Oxygen Redox Activity and Reversibility of Li- and Mn-Rich Cathode Materials.

The specific capacity of Li- and Mn-rich layered oxide (LMROs) cathodes can be enhanced by the oxidation of lattice oxygen at high voltages. Nevertheless, an irreversible oxygen loss emerges with cycling, which triggers interlocking surface/interface issues and results in the fast deterioration of cycling performance. Herein, we prepare a surface modified LMRO electrode by one step doctor-blade casting and introducing a benzoquinone species DBBQ redox couple. The electrochemical test shows that the DBBQ-modified electrode has a high reversible capacity (>320 mAh g-1) and excellent rate performance, while the cyclic stability has been significantly improved as well. The capacity retention reaches as high as 93.3% after 500 cycles at 1 C. Mechanism analysis shows that DBBQ can not only play a redox couple in LMROs which achieves the adsorption and reduction of surface oxygen gas but also significantly enhance anionic redox in the bulk, thus realizing extraordinary capacity.

Efficient Synthesis of Flower-Ball Structured CuFeS2 as Advanced Anode Material for Lithium-Ion Batteries Across Wide Temperature Ranges.

Transition metal sulfides stand as potential anode candidates for lithium-ion batteries offering high capacity, redox reversibility, and safety. However, cycling-induced volume variations and slow kinetics hinder their application. Here, CuFeS2 with a flower-ball nanosheet structure is synthesized via a hydrothermal method, enhancing electrolyte infiltration, Li+ transport, and cycle life. CuFeS2 exhibits a large initial discharge specific capacity of 532.4 mAh g-1 at 500 mA g-1 with 95.7% initial Coulombic efficiency, retaining an impressive 90.5% (481.6 mAh g-1) of its initial capacity after 300 cycles. Remarkably, at 2000 mA g-1 for 700 cycles, it maintains a high specific capacity of 487.1 mAh g-1 with an 89.4% capacity retention rate. Moreover, it maintains excellent reversibility at both high temperature (60 °C) and low temperature (-25 °C) and demonstrates excellent electrochemical performance even under high loading conditions. Consequently, CuFeS2 holds immense promise as a lithium-ion battery anode material, offering fast charging, safety, high capacity, and long life.