Multi-electron Reactions Research Articles

Boosting Multielectron Reaction Stability of Sodium Vanadium Phosphate by High-Entropy Substitution.

Na3V2(PO4)3 (NVP) based on the multielectron reactions between V2+ and V5+ has been considered a promising cathode for sodium-ion batteries (SIBs). However, it still suffers from unsatisfactory stability, caused by the poor reversibility of the V5+/V4+ redox couple and structure evolution. Herein, we propos a strategy that combines high-entropy substitution and electrolyte optimization to boost the reversible multielectron reactions of NVP. The high reversibility of the V5+/V4+ redox couple and crystalline structure evolution are disclosed by in situ X-ray absorption near-edge structure spectra and in situ X-ray diffraction. Meanwhile, the electrochemical reaction kinetics of high-entropy substitution NVP (HE-NVP) can be further improved in the diglyme-based electrolyte. These enable HE-NVP to deliver a superior electrochemical performance (capacity retention of 93.1% after 2000 cycles; a large reversible capacity of 120 mAh g-1 even at 5.0 A g-1). Besides, the long cycle life and high power density of the HE-NVP∥natural graphite full-cell configuration demonstrated the superiority of HE-NVP cathode in SIBs. This work highlights that the synergism of high-entropy substitution and electrolyte optimization is a powerful strategy to enhance the sodium-storage performance of polyanionic cathodes for SIBs.

Carbon-based synergistic catalysis with transition metal dichalcogenides for electrocatalytic oxygen evolution/reduction

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are considered as two of the most critical processes in various renewable energy systems, including multi-electron transfer reactions. However, the kinetics of ORR/OER are usually sluggish, significantly impeding their related applications. This review article summarizes the research advancements in electrocatalytic ORR/OER achieved using traditional noble metals, transition metal dichalcogenides (TMDCs), and carbon-based materials. Exploring diverse engineering strategies, such as defect engineering, strain engineering, and alloying, takes full advantage of the inherent energy band tunability of TMDCs and the advantages of carbon materials, including tunable specific surface area, high conductivity, and good stability. These strategies aim to regulate the intrinsic activity of materials and boost the apparent activity of the electrocatalytic ORR/OER. Finally, the challenges and prospects along this research line are proposed.

A Novel NASICON-Type Na3.5MnCr0.5Ti0.5(PO4)3 Nanofiber with Multi-electron Reaction for High-Performance Sodium-Ion Batteries

A Novel NASICON-Type Na3.5MnCr0.5Ti0.5(PO4)3 Nanofiber with Multi-electron Reaction for High-Performance Sodium-Ion Batteries

Fluoride Doping Na3Al2/3V4/3(PO4)3 Microspheres As Cathode Materials for Sodium-Ion Batteries with Multielectron Redox.

Sodium-ion batteries (SIBs) are potential candidates for large energy storage usage because of the natural abundance and cheap sodium. Nevertheless, improving the energy density and cycling steadiness of SIB cathodes remains a challenge. In this work, F-doping Na3Al2/3V4/3(PO4)3(NAVP) microspheres (Na3Al2/3V4/3(PO4)2.9F0.3(NAVPF)) are synthesized via spray drying and investigated as SIB cathodes. XRD and Rietveld refinement reveal expanded lattice parameters for NAVPF compared to the undoped sample, and the successful cation doping into the Na superionic conductor (NASICON) framework improves Na+ diffusion channels. The NAVPF delivers an ultrahigh capacity of 148 mAh g-1 at 100mA g-1 with 90.8% retention after 200 cycles, enabled by the activation of V2+/V5+ multielectron reaction. Notably, NAVPF delivers an ultrahigh rate performance, with a discharge capacity of 83.6 mAh g-1 at 5000mA g-1. In situ XRD demonstrates solid-solution reactions occurred during charge-discharge of NAVPF without two-phase reactions, indicating enhanced structural stability after F-doped. The full cell with NAVPF cathode and Na+ preintercalated hard carbon anode shows a large discharge capacity of 100 mAh g-1 at 100mA g-1 with 80.2% retention after 100 cycles. This anion doping strategy creates a promising SIB cathode candidate for future high-energy-density energy storage applications.

Solar driven ammonia synthesis with Co-TiOx and Ag nanowires enhanced Cu2ZnSnS4 photocathodes

Restoring ammonia from waste nitrate stands as a promising strategy for reducing reliance on the energy-intensive Haber-Bosch process and tackling environmental pollutants. Advancing the catalytic aspects of photoelectrochemical (PEC) ammonia synthesis via waste nitrate reduction is of great importance to enhance its viability for sustainable chemical production. However, this process still suffers from low ammonia faradaic efficiency (FE) with high operational potential due to its involvement in multi-electron reactions. Herein, we integrated a cobalt-doped TiOx (Co-TiOx) cocatalyst and Ag nanowires (NWs) electron extraction layer onto TiOx/CdS/Cu2ZnSnS4 (CZTS) photocathode, achieving nearly 100 % ammonia FE and an onset potential of ∼0.49 V vs. RHE. Evidenced by the in-situ synchrotron-radiated FTIR (SR-FTIR) and theoretical calculations, the increased ratio of surface oxygen vacancy sites (Vo) induced by Co-TiOx is crucial for the key reaction intermediates adsorption (i.e. *NO3 and *NO2) for subsequent ammonia production. Moreover, the transparent Ag NWs facilitates the electron extraction from TiOx/CdS/CZTS to the surface catalytic sites. Powered by CZTS solar cells, a standalone solar-to-ammonia system has been demonstrated with outstanding activity and catalytic performance.

N-Containing Na2VTi(PO4)3/C for Aqueous Sodium-Ion Batteries.

Phosphates featuring a 3D framework offer a promising alternative to aqueous sodium-ion batteries, known for their safety, cost-effectiveness, scalability, high power density, and tolerance to mishandling. Nevertheless, they often suffer from poor reversible capacity stemming from limited redox couples. Herein, N-containing Na2VTi(PO4)3 is synthesized for aqueous sodium-ion storage through multi-electron redox reactions. It demonstrates a capacity of 155.2mAhg-1 at 1Ag-1 (≈ 5.3C) and delivers an ultrahigh specific energy of 55.9Whkg-1 in a symmetric aqueous sodium-ion battery. The results from insitu X-ray diffraction analysis, ex situ X-ray photoelectron spectroscopy analysis, and first-principle calculations provide insights into the local chemical environment of sodium ions, the mechanisms underlying capacity decay during cycling, and the dynamics of ion and electron transfer at various states of charge. This understanding will contribute to the advancement of electrode materials for aqueous sodium-ion batteries.

Three-Coordinate Nickel and Metal-Metal Interactions in a Heterometallic Iron-Sulfur Cluster.

Biological multielectron reactions often are performed by metalloenzymes with heterometallic sites, such as anaerobic carbon monoxide dehydrogenase (CODH), which has a nickel-iron-sulfide cubane with a possible three-coordinate nickel site. Here, we isolate the first synthetic iron-sulfur clusters having a nickel atom with only three donors, showing that this structural feature is feasible. These have a core with two tetrahedral irons, one octahedral tungsten, and a three-coordinate nickel connected by sulfide and thiolate bridges. Electron paramagnetic resonance (EPR), Mössbauer, and superconducting quantum interference device (SQUID) data are combined with density functional theory (DFT) computations to show how the electronic structure of the cluster arises from strong magnetic coupling between the Ni, Fe, and W sites. X-ray absorption spectroscopy, together with spectroscopically validated DFT analysis, suggests that the electronic structure can be described with a formal Ni1+ atom participating in a nonpolar Ni-W σ-bond. This metal-metal bond, which minimizes spin density at Ni1+, is conserved in two cluster oxidation states. Fe-W bonding is found in all clusters, in one case stabilizing a local non-Hund state at tungsten. Based on these results, we compare different M-M interactions and speculate that other heterometallic clusters, including metalloenzyme active sites, could likewise store redox equivalents and stabilize low-valent metal centers through metal-metal bonding.

Charged Microdroplets as Microelectrochemical Cells for CO2 Reduction and C-C Coupling.

Charged microdroplets offer novel electrochemical environments, distinct from traditional solid-liquid or solid-liquid-gas interfaces, due to the intense electric fields at liquid-gas interfaces. In this study, we propose that charged microdroplets serve as microelectrochemical cells (MECs), enabling unique electrochemical reactions at the gas-liquid interface. Using electrospray-generated microdroplets, we achieved multielectron CO2 reduction and C-C coupling to synthesize ethanol using molecular catalysts. These catalysts effectively harness and relay electrons, enhancing the longevity of solvated electrons and enabling multielectron reactions. Importantly, we revealed the intrinsic relationship between the size and charge density of a MEC and its reaction selectivity. Employing in situ mass spectrometry, we identified reaction intermediates (molecular catalyst adducts with HCOO) and oxidation products, elucidating the CO2 reduction mechanism and the comprehensive reaction procedure. Our research underscores the promising role of charged microdroplets in pioneering new electrochemical systems.

A NASICON-type Na3.67Cu0.17Fe0.5V1.33(PO4)3 cathode with multi-electron reaction for high-energy sodium-ion battery

A NASICON structured Na3.67Cu0.17Fe0.5V1.33(PO4)3 (NCFVP) sodium-ion battery cathode material with multi-electron redox reaction has been designed. The obtained NCFVP demonstrates a high capacity, high energy density, and ideal cyclability.

Redox Couple Modulation in NASICON Phosphates toward High-Performance Cathodes for Na-Ion Batteries

Natrium superionic conductor (NASICON)-type phosphates have aroused a great interest as cathode materials for sodium-ion batteries (SIBs) by virtue of their stable 3-dimensional frameworks, flexible molecular formula tunability, and superior ionic conductivity. Nevertheless, the intrinsic low electronic conductivity and relatively low theoretical specific capacity place obstacles in their way toward achieving higher electrochemical performance. In addition, only 2-electron reactions in most NASICON cathodes and poor reversibility of high-voltage redox couples severely limit their energy density. To address the above tough issues, an in-depth understanding of transition metal selection, elements ratio optimization, and Na-storage mechanism is of paramount importance. Here, this mini review summarizes the latest progresses on the NASICON-type phosphate cathodes for SIBs from the perspective of redox couple modulation. NASICON cathodes featuring high operating voltage and multielectron reactions are discussed in detail. Finally, the remaining challenges and personal outlooks based on redox couple regulation are put forward, shedding light on the designing rules for high-energy and long-durability NASICON-type phosphate cathodes for SIBs in the future.

Multi-electron redox reactions with iron and vanadium ions at a mixed phosphate–sulfate electrode during sodium intercalation

By combining the structural robustness of a mixed phosphate–sulfate matrix with multiple redox couples of Fe and V and capacitive behaviour of rGO, a novel sodium-related electrode material operating well at elevated temperatures is proposed.

An Energy-Efficient Tellurium Electrode Enabled by Cs2TeI6 Perovskite Structure for Durable Aqueous Zn-Te Batteries

Tellurium (Te) is a promising high-capacity electrode material for aqueous zinc-ion batteries, capable of multi-electron redox reactions. However, the inherent hydrolysis of oxidized Te4+ exhibits significant polarization during redox, rendering...

Strategies to alleviate distortive phase transformations in Li-ion intercalation reactions: an example with vanadium pentoxide.

Chemical and electrochemical Li-ion insertion in transition metal oxides, either via a phase transformation reaction (ions insert into specific crystallographic sites of the host lattice) or a solid solution insertion (ions distribute uniformly throughout the host lattice), enables high energy density electrochemical energy storage. Many phase transformation cathode materials, that undergo two-phase reactions, exhibit high theoretical capacities arising from multi-electron redox reactions. However, challenges in distortive phase transformations and uncontrolled phase nucleation, propagation, segregation, and co-existence continue to limit the energy density, (dis)charging rate performances, and cycling stability of available phase transformation cathode materials. Vanadium pentoxide (V2O5), a classical layered intercalation host material with high theoretical capacity, undergoes irreversible structural changes and capacity fading when intercalating more than one lithium ion per V2O5 unit in its thermodynamically stable phase. Here, we review recent synthetic strategies to alter the V-O connectivity, thereby alleviating distortive phase transformations and promoting solid solution-based Li-ion insertion in V2O5. We also summarize several widely accessible and classical molecular-based analytical tools that can provide local structural dynamics and phase transformation mechanism information on the lithiation of V2O5, including single-crystal X-ray diffraction, infrared and Raman spectroscopy, electron paramagnetic resonance, and nuclear magnetic resonance spectroscopy.

Influence of Mo/V coupled multi-electron reactions and the crystalline phase transition of VO2 on high specific capacity of lithium-ion batteries

To further improve the specific capacity and stability of amorphous vanadium-based lithium-ion battery cathode materials, MoS2 was introduced for the first time into the 70V2O5–30Li3PO4 (VP) glass cathode system. Both Mo and S participated in the redox reaction, achieving for the first time an increase in the V4+ content from 21.8% to 50.4%. This improved the electrical conductivity. Moreover, the realization of a Mo/V multi-electron coupling reaction promoted the capacity. The precipitation of LiV2O5 and MoP2O8 nanocrystals during electrocycling enhanced the cycling stability and reaction kinetics. Compared to VP, the capacity of 67V2O5–30Li3PO4–3MoS2 (VPMo3) was enhanced by more than 50% at a current density of 100 mA g-1, and the capacity retention after 50 cycles was improved by about 20%. Notably, the VO2 nanocrystals precipitated during the melt preparation underwent a metal-insulator phase transition (MIT), and their structural transformation affected conductivity.

Processing mechanism synergizing surface and intercalation pseudocapacitance engineering fast-charging Li-based anode materials

Pseudocapacitive material can achieve rapid charge and discharge response. In this study, a vanadium-based conductive network hydrate (Na0.13Mg0.02)V2O5·0.98H2O (NMVO) was designed. The Na+ and Mg2+ in NMVO are sandwiched between two layers of vacancy-ordered prisms and monoclinic nanonetwork V3O7 (VO2:V2O5 = 1:1) to form a conductive network with a layer spacing of up to 11.67 Å, this structure facilitates rapid interlayer diffusion of cations and enhanced conductivity. Reduction-NMVO (r-NMVO) with hierarchical heterostructures was prepared via an in-situ electrochemical process to generate interlayer vanadium-based active sites (LiV3O8, LiV2O5, Na3V3O8, MgVO3) with multi-electron reaction, which enhanced the generation of surface redox pseudocapacitance. The interlayer heterostructure is integrated with the core of the precursor V3O7 to form an active site-rich conductive network with strong pulse impact resistance, which promotes the generation of intercalated pseudocapacitance and increases the cycle stability of the electrode. This intercalation-surface redox pseudocapacitive mechanism was confirmed by first-principles, in-situ, and ex-situ characterization analysis. The r-NMVO|Li battery still maintains a capacity of 95.5 % after 65,500 cycles at a current density of 50 A g−1. These results contribute directly to the realization of stable, fast charge and discharge material design.

Measurements of Dioxygen Formation in Catalytic Electrochemical Water Splitting

Water oxidation is a multielectron complex reaction that produces molecular oxygen as the final product. The article addresses the lack of confirmation of oxygen product formation in electrochemical oxygen evolution reaction (OER) studies, despite the extensive research conducted on catalysts for water splitting. It critically evaluates the trend observed in many studies that solely rely on electrochemical methods for OER quantification without confirming the oxygen product via complementary analytical techniques. The omission of measuring evolved oxygen gas leaves a crucial gap in the quantification of the OER process and raises concerns about the validity and accuracy of reported results. Analytical techniques, such as gas chromatography, Rotating Ring-Disk Electrode (RRDE), fluorescence oxygen probes, Clark electrode, and volumetry are critically analyzed and described to ensure the reliability and credibility of voltammetry and bulk electrolysis to provide a more accurate assessment of the OER process.

(Invited) Nanostructured Metal Fluorides as Earth-Abundant High-Capacity Cathodes

Current battery technologies use intercalation chemistries that rely on nickel-manganese-cobalt (NMC) oxide cathodes and graphite (Gr) anodes. These materials can store and release lithium reversibly, but they have limited interstitial sites to hold Li. In contrast, conversion-type materials, which typically use less expensive and earth-abundant elements such as Fe, Cu, O, and S, enable extremely high capacity by reacting directly with the host material to form completely different structures. Among various conversion compounds, FeF2, CuF2, and the solid-solution Cu1-xFexF2 are some of the few capable of multi-electron redox reactions, offering high specific capacity and energy density and relatively high voltages [1-4]. These earth-abundant, high-capacity cathode materials have the potential to double or triple the energy density of current intercalation-based cathodes at less than ½ the cost. However, there are some fundamental challenges that have hindered practical applications of Cu/Fe-based fluorides, including i) Cu/Fe dissolution during charging leading to irreversible capacity loss [5, 6], ii) the highly ionic nature of the Cu(Fe)-F bond that induces poor electronic conductivity, hampering reaction kinetics and reversibility [1], and iii) the high mobility of Cu/Fe ions that can cause aggregation and continuous coarsening of nanoparticles, leading to segregation from other components and ultimately disrupting the conductive network [7].In this presentation, we will provide an overview of recent progress in addressing some of the challenges associated with Cu/Fe-based fluoride cathodes through synthesis/processing and interfacial engineering [3, 8-10]. With specific examples, we will explain how nano-structuring is essential to conversion redox and maintaining local electronic and ionic transport over cycling [2, 4, 7, 11]. Furthermore, we will discuss the fundamental principles and requirements for designing electrodes and electrolytes that maximize energy density, rate, and cycling stability of Cu/Fe-based fluoride cathodes, providing our perspectives on the pathways of implementing these cathodes into full cells for large-scale applications.

Multi-electron collaborative photo-Fenton-like system for indoor air purification: A case study of Cu(II) grafted BaTiO3 with oxygen vacancies

Indoor air purification belongs to one of the most important and traditional applications of photocatalysis, which brings forward an impending need for more efficient photocatalytic systems. Herein, we initiated a multi-electron collaborative photo Fenton-like system for mineralization of indoor volatile organic compounds by jointly modified with oxygen vacancies and Cu(II) clusters on barium titanate. Oxygen vacancies effectively increase the visible light absorption and photoinduced charge separation efficiency. Benefiting from the energy level match with oxygen vacancies and Cu(II) species, the trapped electrons in the oxygen vacancies can effectively migrate towards Cu(II) clusters. More importantly, the Cu species that have received electrons can trigger the multi-electron reduction of oxygen to in-situ form H2O2 through the redox of Cu(II)/Cu(I). In parallel, the reactive •OH radicals can be effectively produced by the photo-like Fenton reaction. Thus, the newly developed barium titanate based photocatalysts exhibit over 38-fold improvement in the removal efficiency of volatile organic compounds (in terms of CO2 evolution rate) by virtue of the strong oxidizing power of holes in the valance band and multi-electron photoFenton-like reaction to generate •OH radicals. Notably, the absorbed H2O molecules play an indispensable role in the formation process of in-situ H2O2. Thus, even under high-humidity condition, our photocatalysts present stable and high photocatalytic activity, which provides great potential for practical applications in indoor air purification.

Realizing high-performance glucose sensing in sweat: Synergistic use of nickel oxide nanosheets as photoelectrodes and the masking effect of Mo-POM for photoelectrochemical detection

The detection of blood glucose plays a crucial role in clinical practice, and the innovative use of sweat as a substitute for blood has brought significant practical value in the detection of blood glucose. However, lactic acid (LA) has been found to be the main interfering substance on the detection of glucose in sweat. In this study, a photoelectrochemical sensing system was constructed by using NiO nanosheets as photosensitive materials and molybdenum-based polyoxometalate clusters (Mo-POM) as masking agents. Mo-POM, an ideal electron-capturing agent, effectively promoted the spatial separation of photo-generated charge carriers in NiO nanosheets, thereby enhancing the oxidation rate of glucose on the valence band of NiO and significantly improving the detection sensitivity. Mo-POM also exhibited the characteristics of an electron sponge, facilitating fast and reversible multi-electron transfer reactions and effectively masking certain redox substances, especially lactic acid, thus greatly enhancing the selectivity of the glucose sensor. The photoelectrochemical (PEC) sensor constructed using Mo-POM has excellent sensing capability with high sensitivity to detect glucose at a minimum concentration of 1 nM. The detection limit of the sensor is 0.33 nM (S/N = 3). This sensor can be reliably applied to the detection of glucose in sweat and the accuracy of the results was verified by gas chromatography-mass spectrometry.

Synergetic impact of oxygen and vanadium defects endows NH4V4O10 cathode with superior performances for aqueous zinc-ion battery

Owing to multi-electron redox reactions and versatile cation storage capabilities, laminated structured metallic vanadate of NH4V4O10 (NHVO) has been regarded as a kind of promising cathode materials for aqueous Zn-ion batteries with satisfactory electrochemical performance. Nevertheless, the NHVO cathode is still limited by the sluggish electrochemical kinetics and structural instability. Here, defect engineering was conducted to introduce the vanadium (V) and oxygen (O) dual defects into NHVO cathode for improving electrochemical performance. As revealed experimentally and theoretically, the migration of Zn-ion inside V/O-defected NHVO cathode can be effectively fostered by increasing active sites, lowering the migration barrier and reducing Gibbs free energy, which are rooted in the synergy impact of the presence of O defect and V defect. As the consequence, the outstanding electrochemical performance has been achieved, which delivers higher capacity of 489 mAh g−1 at 0.5 A g−1 with the capacity retention of 98 % after 100 cycles and exhibits singular cyclic stability at 15 A g−1, maintaining reversible capacity of 198 mAh g−1 after 8000 cycles. This synergistic strategy paves an avenue for accelerating the application of HNVO-based cathode for aqueous Zn-ion battery with satisfactory electrochemical performance and lifespan, advancing the approach of “carbon neutrality” society.