Electrochemical Redox Research Articles

Tailoring a High Loading Atomic Zinc with Weak Binding to Sodium Toward High-Energy Sodium Metal Batteries.

Single-atom materials provide a platform to precisely regulate the electrochemical redox behavior of electrode materials with atomic level. Here, a multifield-regulated sintering route is reported to rapidly prepare single-atom zinc with a very high loading mass of 24.7 wt.% by significantly improved diffusion kinetics and stronger charge transfer between zinc and nitrogen atoms. X-ray absorption near edge structure (XANES) spectra for Zn K-edges during the charge and discharge process verify the stable single-atom zinc structure and the reversible slight reduction and oxidation of Zn sites, which is much different from the previous report of the alloying reaction process. This result suggests atomic Zn acts as an active sites through weak binding with sodium to regulate the Na ion fluxes. Finally, Cu foil coated with a ≈2µm layer of such material exhibits a high Coulombic efficiency of ≈99.99% up to 1700 cycles at 1mAhcm-2. An ultra-low overpotential of 3mV and an unprecedented life span of over 3200h in a symmetrical cell is achieved. Due to the very thin coating layer, anode-free sodium battery fabricated by Na3V2(PO4)3 cathode displays a prominent energy density of 320WhKg-1, demonstrating strong potential in practical application.

Electrochemical Biosensors and Their Applications in Detection of Infectious Disease

The emergence of the new viruses, bacteria and parasites leads to the widespread infection of the disease. This requires an efficient testing instrument with high sensitivity, high selectivity and rapid speed of detection. The electrochemical method is introduced to the clinical test of a wide range of disease nowadays. Compared with the traditional method of disease detection, the electrochemical biosensor has a relatively better performance in diagnosing disease. Therefore, this work focuses on the application of electrochemical biosensors in disease diagnosis. The basic structure and the mechanism of the electrochemical biosensor is similar to the primary battery. The current can be circulated through a series of electrochemical redox reactions, and it can be generated mainly in three ways in enzymatic electrochemical biosensor. The electrode materials are mainly made by inert metals and carbon-based material. When using electrochemical biosensor to detect various infectious disease, different bioreceptors are needed to be used. They are mainly antibodies and nucleic acid probes. The nucleic acid probes can be used in all virus-caused, bacteria-caused and parasites caused disease, while the antibodies can only be used in viral disease detection. The disease-detecting electrochemical biosensor has a good prospect in the future.

Probing Photo-Assisted Charge Storage Mechanism Using Bi-Fe Perovskite Oxide Electrode for Solar Supercapacitor.

In this study, the rhombohedral crystalline pure phase BiFeO3 (BFO) of irregularly shaped spherical particles of ≈100 nm and energy bandgap of ≈2.31 eV are synthesized by sol-gel auto-combustion method and explored as electrode material for photo-assisted supercapacitor. The electronic structure studies revealed that the coexistence of heterovalent Bi and Fe elements accelerated the electrochemical redox kinetics and photo-assisted charge storage properties. The resonant photoemission studies confirmed that near the Fermi level, the valence band spectra comprised the Fe3d and O2p hybridized states. The Fe-O hybridized state felicitates the charge transfer transitions (O2p (h+) + hυ ↔ Fe3+ + e- ↔ Fe2+), which assists the intercalation/de-intercalation process of OH- anions. Therefore, BFO has delivered 26.77% photo efficiency and the enhanced specific capacity of 21 Cg-1 at 2 Ag-1 in aq. 3m KOH under illumination, which is attributed to the accelerated photo-generated charge carrier separation and storage with surface polarization effect. BFO also delivered capacitance retention of 77.5% even after 1000 continuous GCD cycles under visible light irradiation.

Surficial Engineering of Cathodic Protection Strategy via P‐Doped NiCuV Monolithic Electrode for Enhanced Hydrogen Evolution Reaction in Alkaline Media

AbstractThe concentrated alkaline passivates the monolithic electrode for electrochemical hydrogen evolution reaction (HER) in the alkaline water electrolysis (AWE) industry. Herein, a surface engineering of cathodic protection via one‐step co‐electrodeposition of P into NiCuV is presented and the achieved monolithic electrode exhibits an enhanced electrochemical catalytic behavior and constant durability with a feedback potential of −0.75 V versus the reversible hydrogen electrode (RHE) under an extremely high current density of 1A cm−2 for more than 270 h in alkaline media. The strategy of cathodic protection optimises the charge density redistribution by forming a phosphate surface layer. This preserves the particular metal (alloy) phase from oxidation while also modulating the heterarchical porous structure through P incorporation. Furthermore, an anion‐exchange membrane water electrolysis (AEMWE) with the NiCuVP serving as the HER catalyst and the NiFeCr LDH as the OER catalyst is constructed, which exhibits a current density of 912 mA cm−2 at 2 V at 80 °C with 30 wt.% KOH electrolytes. The resultant factors for activity and durability such as the electrochemical specific area, redox behaviors and surface hydrophilicity are also systematically discussed. This research presents a practical protocol for the anticorrosion and active enhancement of AWE and AEMWE cathodes.

Enhancing the Electrochemical Energy Storage of Metal-Organic Frameworks: Linker Engineering and Size Optimization.

The electric conductivity and charge transport efficiency of metal-organic frameworks (MOFs) dictate the effective utilization of built-in redox centers and electrochemical redox kinetics and therefore electrochemical performance. Reticular chemistry and the tunable microcosmic shape of MOFs allow for improving their electric conductivity and charge transfer efficiency. Herein, we synthesized two Ni-MOFs (Ni-tdc-bpy and Ni-tdc-bpe) by the solvothermal reaction of Ni2+ ions with 2,5-thiophenedicarboxylic acid (H2tdc) in the presence of conjugated 4,4'-bipyridyl (bpy) and 1,2-di(4-pyridyl)ethylene (bpe) coligands, respectively. We also synthesized two thinning Ni-MOFs (Ni-tdc-bpy(0.5) and Ni-tdc-bpe(0.5)) by adjusting the amounts of bpy and bpe, respectively. Experimental investigations revealed that linker engineering by tuning the delocalization of the N-donor dipyridyl coligands and size optimization by controlling the amount of the coligand rendered the Ni-MOF with significantly improved electrical conductivity and charge transport efficiency. Among them, Ni-tdc-bpe(0.5) possessing the bpe coligand with more strong delocalization and an optimized size exhibited an enhanced specific capacitance of 650 F g-1 at 0.5 A g-1. Moreover, the hybrid supercapacitor constructed from Ni-tdc-bpe(0.5) and activated carbon delivered an excellent energy density of 33.6 Wh kg-1 at a power density of 232.6 W kg-1.

Improving Nitric Oxide Reduction Reaction Activity of TMN4-C Model Catalysts by Axial Atom Coordination.

In comparison with the conventional four-nitrogen coordinated transition metal (TMN4), we clarify that the electrochemical nitric oxide reduction reaction (NORR) activity can be significantly improved by axially coordinating nonmetal atoms (O, F, Cl) over the metal sites. In light of an electron-withdrawing effect, the axial fifth ligand disrupts the electron distribution symmetry and regulates the local electronic structure of the metal active center. It subsequently moderates the TM-NO interaction and thus enhances the activity. In particular, MnN4O-C, FeN4O-C, CoN4O-C, and CoN4F-C are identified as promising NORR catalysts with ultralow limiting potential (UL) of -0.07, -0.07, -0.07, and -0.05 V, respectively. In addition, the axial atom can also passivate the competing hydrogen evolution reaction (HER), increasing the selectivity toward NH3 formation. It therefore can be concluded that the present work affirms a novel strategy for the rational design of advanced electrocatalysts, highlighting the significance of optimal metal-ligand match and the coordination microenvironment tuning of the active centers.

Electrochemical Oxidative Hydroxychalcogenation of Olefins with Disulfides/Thiols/Diselenides and H2O as Nucleophilic Oxygen Sources

A direct electrochemical redox reaction of olefins and disulfides/thiols/diselenides without external oxidants has been developed, which includes the hydroxychalcogenation of olefins. This procedure exhibited good functional group tolerance, and a series of β‐hydroxysulfide/β‐hydroxyselenide derivatives were obtained in moderate to good yields. Mechanistic studies and cyclic voltammetry were also conducted to elucidate the reaction process.

Electro-Fenton purification of floodwater with a poly(vinyl alcohol)-treated FeNi3@laser-induced 3D-graphene composite anode from Kraft paper

Electro-Fenton process has been recognized in recent decade as a useful method for removing water contaminants via electrochemical redox reactions at large scale. Laser-induced graphene (LIG) with 3D porous structure is an electrically conductive carbon material, which can be used as a promising electrode for electro-Fenton water purification. This work presented a straightforward synthesis of LIG electrode by direct CO2 laser scribing on the lignocellulose-based Kraft paper. The magnetic FeNi3 nanoparticles were sandwiched by two LIGs as a Fenton catalyst, which were then coated with poly(vinyl alcohol) (PVA) in cross-linking solution. The resulting PVA-treated FeNi3@LIG electrode exhibited outstanding electrochemical stability, low resistance (29 Ω/Sq), high conductivity (1,013 S/m), and fast electrochemical reaction kinetic (80 mV/dec) suitable for electro-Fenton water purification. Compared to PVA-treated LIG electrode, PVA-treated FeNi3@LIG did effectively remove contaminants in floodwater that sampled from flood-ravaged He’nan Province, China. Notably for degrading organic pollutants, the removal efficiencies of chemical oxygen demand, total nitrogen, ammonia nitrogen, total phosphorous were approximately 86 %, 70 %, 77 % and 96 %, respectively. Meanwhile, the heavy metal ions were adsorbed to cathode and reduced into metal form. The metallic selenium and arsenic ions were also removed via adsorption and precipitation. The concentration of sulfate and nitrate in floodwater decreased rapidly from 76 and 9 mg/L to 54 and 0.5 mg/L, respectively. Due to the oxidation stress and cell death during electro-Fenton process, the number of total bacteria was removed by ∼ 73 %, in particular, the fecal coliform was removed completely. The demonstrated lignocellulose LIG electrode is eco-friendly, facile and cheap (∼ 25 USD/m2), which can be made scalable using existing roll-to-roll papermaking line. This work provided new and efficient technology for floodwater treatment.

Achieving Excess Hydrogen Output via Concurrent Electrochemical and Chemical Redox Reactions on P-Doped Co-Based Catalysts with Electron Manipulation and Kinetic Regulation.

Electrolytic hydrogen production is of great significance in energy conversion and sustainable development. Traditional electrolytic water splitting confronts high anode voltage with oxygen generation and the amount of hydrogen produced at cathode depends entirely on the quantity of electric charge input. Herein, excess hydrogen output can be achieved by constructing a spontaneous hydrazine oxidation reaction (HzOR) coupled hydrogen evolution reaction (HER) system. For the hydrazine oxidation-assisted electrolyzer in this work, both the external input electrons and the electrons produced by spontaneous chemical redox reaction can reduce water, producing more hydrogen than traditional electrolytic water splitting system. The ultrafast kinetics of bifunctional P-doped Co-based catalysts plays a key role in the spontaneous feature of HzOR/HER redox reaction and low working voltage of hydrazine oxidation-assisted electrolyzer (12 mV@100mA cm-2). Theoretical calculation results and ex situ/in situ spectra demonstrate that doped P could optimize electronic structure, regulate adsorption energy of intermediates, and thus endows catalysts with ultrafast kinetics. This work provides a new pathway for the development of spontaneous oxidation-assisted hydrogen production, to achieve excess hydrogen output via concurrent electrochemical and chemical redox reactions.

Stepwise Two Electron-Transfer Processes of Naphthalene Diimide As the Soluble Negolyte and Solid Storage in Redox Target Flow Batteries

Organic redox flow batteries (RFBs) have emerged as promising energy storage systems linked to intermittent renewable energy sources. The organic redox-active molecules serve as the negolyte and posolyte (active negative and positive active electrolyte, respectively) and have developed to tune redox potential, capacity, and stability. This RFB offers potentially lower costs than vanadium RFBs due to the rising vanadium expense. Nonetheless, the capacity of organic RFBs has been limited by 0.5~2 M due to the limited solubility of organic molecules and increased viscosity, resulting in restricted energy density.To mitigate this challenge, the idea of loading solid-state charge storage into the electrolyte reservoir of RFBs has been suggested. This concept establishing redox targeting flow battery (RTFB) is, therefore, composed of soluble active molecules and storage, indicated as redox mediator (RM) and solid-state redox target (RT), respectively. The RM is responsible for the electrochemical redox event at the electrode and flows to the reservoir, where spontaneous electron transfers occur from RM to RT. Subsequently, the RM is recovered to the original state and undergoes the electrochemical redox process again at the electrode. Ideally, the capacity of RTFB relies on the electron storage ability of RT rather than the solubility of RM. Several previous reports have used polymeric materials or LiFePO4 as the insoluble RTs. They focused on the one electron-transfer process and an accessible alignment of energy levels and electron-transfer kinetics between RT and RM for reversible reactions. However, two electron-transfer processes have not yet been studied, although these systems enhance the energy density further in RTFBs.Here, we present two electron-transfer processes using naphthalene diimide (NDI) utilized as both RM and RT. We previously developed stable NDI derivatives as the negolyte in RFBs thanks to their extended-conjugation structure. In the RTFB system, we utilized these soluble NDI as the mobile RM and loaded a covalent organic framework (COF) involving NDI as the insoluble storage. Well-defined nanoporous channels with in crystalline COF provide the flow route of the soluble RM of NDI so that, ideally, all NDI included in COF (NDI-COF) can be involved in the electron-transfer process from the RM. Cyclic voltammetry of NDI-COF exhibited two cathodic peaks at –0.48 V and –0.68 V vs. NHE. Accordingly, we prepared a couple of NDI designs as the RM with different bulkiness and potential gaps from NDI-COF by introducing electron-donating and -withdrawing groups. The state of charge (SoC) of RT was inferred from the reduced state of RM in this solution, which was analyzed using open circuit potential and UV-visible spectroscopy. As a result, we observed that the NDI RM's long alkyl chain and slightly positive cathodic potential led to slow electron transfer to RM through the first cathodic reaction. Further, the second cathodic event was far slower, seemingly holding the SoC at 50% (i.e., terminating only for the first cathodic process) despite the complete two cathodic processes of RMs during the galvanostatic performance. To mitigate this challenge, we introduced RMs with more negative cathodic potential and developed RTs deposited on entangled carbon nanotubes to ensure the space, allowing the approach of RMs to the NDI in COFs, and increasing the electron-transfer efficiency. In this presentation, I will discuss details of the effectiveness of two-step electron-transfer processes using NDI materials and the related capacity enhancement. Figure 1

PtPdSn Electrocatalysts for Nitrous Oxide Reduction

Nitrous oxide (N2O) is a greenhouse gas almost 300 times more potent than CO2 and an ozone-depleting gas. N2O is increasing in the atmosphere by about one ppb per year. Electrocatalysis allows us to reduce N2O to N2 under ambient conditions at room temperature and atmospheric pressure, making electrocatalysis a promising approach for the removal of N2O. The electrochemical nitrous oxide reduction reaction (N2ORR) can be catalyzed on metals such as Pd [1,2]. Although bimetallic Au@Pd core@shell nanoparticles [3] have been reported as electrocatalysts for the N2ORR, synthetic strategies and design principles of multimetallic electrocatalysts for the N2ORR are still lacking. Herein, we report our research progress on trimetallic PtPdSn electrocatalysts for the N2ORR in acidic media, inspired by electrocatalysts for the nitrate reduction reaction (NO3RR). The electrocatalytic NO3RR to N2 proceeds via N2ORR. It has been reported that Sn/Pd-Pt(100) electrodes produce NO, N2O and N2 in the NO3RR but Sn/Pt(100) does not [4], suggesting that the Sn/Pd-Pt interface plays an important role in the electrocatalysis for the N2ORR. This study encourages us to prepare co-deposited Pt and Pd nanoparticles on fluorine-doped tin oxide using the arc plasma deposition method [5]. Pt and Pd nanoparticles deposited on fluorine-doped tin oxide show higher electrocatalytic activity for both NO3RR and N2ORR than those deposited on glassy carbon [5]. This result also supports that the Sn/Pd-Pt interface is crucial for the efficient catalysis of the N2ORR. We are now working on PtPdSn nanoparticles supported on carbon black (PtPdSn/C) for the N2ORR in acidic media [6]. PtPdSn/C shows higher N2ORR activity than bimetallic PtPd/C or PtSn/C and exhibits almost 100% Faradaic efficiency for the the N2ORR to N2 at ≥ +0.06 V vs. RHE with no competition with the hydrogen evolution reaction. The trimetallic PtPdSn electrocatalysts will be a promising candidate for the efficient removal of N2O towards a sustainable society.References.[1] A. Kudo, A. Mine, J. Electroanal. Chem., 408, 267–269 (1996).[2] B.H. Ko, B. Hasa, H. Shin, Y. Zhao, F. Jiao, J. Am. Chem. Soc., 144, 1258–1266 (2022).[3] K. Kim, J. Byun, H. Kim, K.S. Lee, H. S. Lee, J. Kim, T. Hyeon, J.J. Kim, J.W. Han, ACS Catal., 11, 15089–15097 (2021).[4] M. Kato, Y. Unuma, M. Okui, Y. Qu, J. Zheng, S. Taguchi, F. Kiguchi, M. Torihata, Y. Gao, N. Hoshi, I. Yagi, Electrochim. Acta, 398, 139281 (2021).[5] A.C. Sarker, M. Kato, I. Yagi, Electrochim. Acta, 425, 140628 (2022).[6] A.C. Sarker, M. Kato, M. Kawamura, T. Watanabe, I. Yagi, submitted.

Effects of Electrolyte Composition on the Electrochemistry of Organic Mixed Conducting Polymer Electrodes

Organic mixed ionic-electronic conductors (OMIECs) are semiconducting conjugated polymers that can transport both electrons and ions throughout their bulk. This property is enabled by electrochemical ion-insertion redox reactions that co-dope the polymer with mobile ions and electrons (or holes). These redox and mixed conduction capabilities provide functionality for applications including organic batteries, actuators, and organic electrochemical transistors. These various applications are enabled by a few fundamental OMIEC redox processes that involve polymer-electrolyte and polymer-electrode interfaces as well as mobile ions and significant amounts of incorporated solvent. Understanding the role of electrolyte in changing these redox processes can enable improved performance across a variety of devices.This work sets out to identify the role of electrolyte composition in changing the electrochemistry of a conjugated ladder polymer through a multi-faceted experimental and theoretical approach. We primarily focus our efforts on BBL, more formally called poly(benzimidazobenzophenanthroline). Using rotating disk electrochemistry, we find that electrolyte can cause a significant change in the voltage windows in which BBL is redox-active. Using operando UV-Vis and Raman spectroscopy measurements, we identify changes in BBL electrochemistry when operated in different electrolytes. To gain further insights about the redox mechanisms for this polymer, we use DFT to model our operando Raman data and principal component analysis to propose a charging mechanism that accounts for this electrolyte-dependent performance. Our results suggest that the accessible redox states of this polymer can dramatically change based on a modification of its local environment.

(Invited) How to Make and Manipulate Carbonaceous Materials Using Liquid Metals

Liquid metal-based processes offer significant possibilities in the realm of carbon-based materials. Liquid metals are highly electrically conductive, making them suitable for electrochemical redox processes. They serve as atomically smooth templating substrates for creating planar structures. The absence of interfacial forces, owing to the non-polar nature of liquid metals, facilitates self-exfoliation of the synthesized two-dimensional (2D) layers from the surface of liquid metals. In addition, liquid metals can act as natural catalysts for promoting the formation of C-C bonds and are immiscible with non-metallic systems, including electrolytes, making them compatible with various electrochemical systems. Liquid metals can also engineer carbonaceous materials in contact with their interface. These properties facilitate the construction of carbonaceous materials from various organic precursors to CO2 and also tailoring of carbon based materials using liquid metals.Room temperature synthesis and engineering of 2D graphitic materials (2D-GMs) remains an elusive goal, especially through electrochemical means. Here, it is demonstrated that liquid metals make this achievable by providing catalytic activity and an ultra-smooth templating interface conducive to Frank–van der Merwe regime growth. Moreover, they enable facile exfoliation due to the absence of interfacial forces as a non-polar liquid. The 2D-GMs is shown to be formed at a low onset potential and can be in situ doped based on the choice of organic precursors and the electrochemical setup. The synthesized materials can be tuned to exhibit porous or pinhole-free morphologies and engineered for their degree of oxidation and number of layers.In another part of the talk, the interfacial interaction between eutectic gallium–indium (EGaIn) liquid metal and graphene oxide (GO) for reducing both substrate-based and free-standing GO will be discussed. NanoIR surface mapping confirms the successful removal of carbonyl groups. Building upon this knowledge, a composite comprising assembled reduced GO sheets on LM microdroplets (LM–rGO) is presented. The LM reinforces Ga3+ coordination within the rGO assembly, thereby modifying the electrochemical interface for selective dopamine sensing by separating the peaks of interfering biologicals. Subsequently, paper-based electrodes modified with LM–rGO is shown, demonstrating the compatibility of the assembly with low-cost commercial technologies.

Synergetic Effect of LiNO3 and Fluorine-Containing Additives on Stabilizing Electrode-Electrolyte Interfaces in Lithium Metal Batteries

Lithium metal batteries (LMBs) are regarded as an ideal candidate for next-generation batteries to meet the increasing demand for high energy density batteries. Due to the high theoretical capacity (3860 mAh g-1) and the low electrochemical redox potential (- 3.04 V vs Standard Hydrogen Electrode (SHE)) of lithium metal anodes, lithium metal batteries can achieve a high energy density. However, the poor compatibility of conventional carbonate electrolytes with lithium metal anodes has limited the commercialization of LMBs. The unstable solid-electrolyte interphase (SEI) generated from the charging and discharging process leads to the dendritic growth of lithium and the continuous depletion of the electrolyte, limiting the cycle life of LMBs. Furthermore, the unstable cathode-electrolyte interphase (CEI) limits the charge transfer kinetics of Li+ and decomposes at high voltage operation of LMBs. Therefore, the formation of stable electrode-electrolyte interfaces is crucial for the adoption of LMBs. Numerous studies have been attempted to regulate the electrode-electrolyte interfaces by introducing additives to the electrolyte. Lithium nitrate (LiNO3) is an effective additive for regulating the SEI layers through the formation of a highly lithium ion-conductive SEI components derived from the reduction of NO3 - ions such as Li3N (2~4 x 10-4 S cm-1). However, it is vulnerable to volume expansion, leading to continuous consumption of the additive itself. Fluorine-containing additives such as fluoroethylene carbonate (FEC) and lithium difluoro(oxalate)borate (LiDFOB) can promote the formation of a robust, high mechanical strength (64.7 GPa) LiF-rich SEI layer to enhance the mechanical strength of the SEI layer to mitigate the lithium dendrite growth. Nevertheless, LiF can hinder the lithium ion transport, due to its low ionic conductivity (10-9 ~ 10-14 cm-2). The synergetic effect of LiF and Li3N as SEI components may be able to enable highly reversible LMBs. In addition, the LiDFOB additive have been reported to form a thin and stable CEI via B-O bonds with anchoring transition metal ions in the cathode, preventing the degradation of the cathode. The electrolyte system with FEC and LiDFOB is able to increase the cycle life of LMBs by the formation of robust SEI and CEI layer. Herein, the synergetic effects of LiNO3, FEC, and LiDFOB additive is discussed to further enhance the stability of the electrode-electrolyte interfaces for high energy density LMBs. The LiNO3 additive is sustainably released through the use of a porous film which consists of LiNO3 embedded polyacrylonitrile (PAN) nanofibers (LiNO3/PAN) to overcome the low solubility of LiNO3 in the carbonate electrolyte. Moreover, fluorine containing additives, LiDFOB and FEC are introduced with LiNO3 in order to form a LiF/Li3N-rich SEI to lengthen the life cycle of LMBs. LiDFOB-derived CEI also contributed to the enhanced stability of the cathode. Consequently, through the synergetic effects of LiNO3 and fluorine-containing additives, the capacity retention of ultra-thin Li (20 μm)||nickel-rich NCM811 cells is improved.

Improved Functionality of Ultrafast Responsive Electrochemiluminescent Device with DNA/Ru(bpy)3 2+ Hybrid Film and Various Electrolyte Compositions

Electrochemiluminescence (ECL), a light-emitting phenomenon induced by electrochemical redox reactions, has potential applications in lightweight and flexible light-emitting devices. Previously, an ultrafast ECL response of <100 μs was successfully achieved under application of alternating current voltage by using a DNA-modified electrode including Ru(bpy)3 2+, an orange ECL material. In this study, we investigated effect of electrolyte composition on the fast responsive ECL in the DNA/Ru(bpy)3 2+ hybrid film-based ECL device. As a result, the ECL intensity and lifetime of ECL were improved by introducing additional Ru(bpy)3 2+ into the electrolyte solution. The increase concentration of Ru(bpy)3 2+ inhibited dissolution of aggregated part formed on DNA/Ru(bpy)3 2+ hybrid film and increase in the amount of reactive charge in the aggregated part. Furthermore, we introduced blue-luminescent 9,10-diphenylanthracene (DPA) into the electrolyte solution of the ECL device consisting of DNA/Ru(bpy)3 2+ hybrid film. Consequently, blue ECL from DPA was obtained from the DNA/Ru(bpy)3 2+ hybrid electrode at lower applied voltage than that required to induce the redox reactions of DPA itself. This lower-voltage-drivable blue ECL was attributed to triplet–triplet energy transfer from Ru(bpy)3 2+ in the DNA/Ru(bpy)3 2+ hybrid electrode followed by a triplet–triplet annihilation upconversion reaction of DPA in the electrolyte solution. Moreover, ultrafast-response, electrochemically triggered blue luminescence from DPA was successfully observed.

Charge-Discharge Behavior of Electrochemically Prepared NaFePO4 Electrodes in Aqueous Sodium Ion Batteries

Introduction Although lithium-ion batteries, which are currently the most widely used batteries, have various advantages such as long life and high energy density, there are safety issues due to the uneven distribution of regions where lithium can be mined and the risk of ignition from organic solvents. Therefore, research and development of aqueous sodium-ion batteries, which have abundant resources and high safety, is underway. However, aqueous batteries have a low energy density, and the working potentials of the positive and negative electrodes must be within the potential window of water. Therefore, NaFePO4, which operates within about −0.6 − 0.6 V (vs. SHE) and has a high theoretical capacity of 154 mAh g−1, is promising. In a previous study, electrochemical properties were evaluated using NaFePO4 obtained by oxidizing LiFePO4 with NO2BF4 and reducing it with NaI, but its charge-discharge capacity was about 50% of the theoretical capacity, which remains challenges [1]. In this study, we prepared ion exchanged NaFePO4 (NFP) by electrochemical redox of LiFePO4 (LFP) and investigated its electrochemical properties to find an appropriate ion exchange method to achieve higher capacity. Experiments A mixture of LiFePO4 (LFP) powder as active material, a mixture of equal mass ratios of vapor grown carbon fiber (VGCF) and acetylene black (AB) as conductive additive, and polyvinylidene fluoride (PVDF) as binder with a weight ratio of 7:2:1 was coated on a Ti foil and dried overnight. A beaker cell was assembled with a Pt electrode as the counter electrode and an Ag/AgCl electrode as reference electrode.Hereafter, the potential is noted with reference to the Ag/AgCl electrode. Since the oxidation of LFP to FePO4 (FP) is known to occur at about 0.3 − 0.4 V and the reduction of FP to NFP at −0.3 − −0.4 V. [2] The LFP electrode was kept at 0.4 V for 6 hours after linear sweep voltammetry (LSV) to produce an oxidized FP electrode. The NFP electrode was then produced by reduction at −0.4 V for the same time. Charge-discharge measurements and X-ray diffraction (XRD) measurements were performed on the FP and NFP electrodes. For the charge-discharge measurements, the electrolyte was 1.0 mol dm−3 Na2SO4 aqueous solution, the current density was 77 mA g−1, and the cutoff potential was −0.4 − 0.4 V. Results and Discussion According to the XRD measurements in Fig. 1(a) and Fig. 1(b), the peaks of the fabricated FP and NFP electrodes are generally consistent with the FP and NFP peaks expected from the ICSD database, respectively, but different from the LFP and FP peaks. Therefore, the oxidation from LFP to FP was well advanced, and the reduction of FP to NFP was also well progressive.Charge-discharge measurements showed two plateaus during the oxidation of NFP, suggesting that a two-step oxidation reaction was taking place. The obtained electrode had a reversible capacity of approximately 105 mAh g−1, which was greater than the reversible capacity of the electrode in a previous study [1]. This may be due to the ion-exchange NFP electrode having more Li+ desorption and Na+ insertion than the solid-state synthesis method. Conclusion NaFePO4 electrodes electrochemically ion-exchanged from LiFePO4 showed greater reversible capacities than electrodes prepared by conventional solid-state synthesis. The results show that the NaFePO4 synthesis method of electrochemical ion exchange is superior.

Ultra-Long and Rapid Operating Sodium Metal Batteries Enabled By Multifunctional Polarizable Interface Stabilizer

Sodium metal batteries (SMBs) have been considered as one of the most favorable and economic candidates for next generation batteries to overcome low enenrgy density limitation of sodium ion batteries (SIBs) due to high theoretical specific capacity (1166 mAh g-1), low electrochemical redox potential (-2.71 V vs. SHE). However, ‘moss-like’ dendrite growth that occurs during continuous charging and discharging processes not only threatens the safety of batteries, but also poses several problems to be solved, such as electrolyte consumption, hugh volume expansion, dead Na formation, and low coulombic efficiency. The dendrite problem in the SMBs is similr to that of lithium-metal batteries (LMBs), yet the degree of the issue is further severe than LMBs. Surface stabilization of sodium metal anode should be achieved to realize SMB technologies.The introduction of functional electrolyte additives is an effective and economical way to overcome these problems and improve the cyclability of SMBs. Based on the similarity between electroplating and sodium deposition reaction, utilization of surface leveler additive in the electrolyte could allow a substantial impact to stabilize sodium metal surface during repeated deposition and stripping process.In this presentation, we confirmed the surface flattening effect of molecular dipole electrolyte additives at the anode through the Na-Na symmetric cell test. Sodium metal deposition and stripping behavior has been successfully controlled by introducing surface leveler additives for realization of SMBs. Even under rapid charging and discharging situations, additive containing Na-Na symmetric cells showed stable performance for over 2000 hours, which is 5 times longer than the pristine cell without the additive. We confirmed that controlling intrinsic properties of surface leveler additive can effectively further improve cycle performance of SMBs.[1] S.-Y. Jun, K. Shin, C. Y. Son, J. Park, H.-S. Kim, J.-Y. Hwang, W.-H. Ryu, Advanced Energy Materials, 2024, 2304504[2] S.-Y. Jun, K. Shin, Y. Lim, S. Kim, H. Kim, C. Y. Son, W.-H. Ryu, Small Structures, 2024, 5, 2300578[3] S.-Y. Jun, K. Shin, J.-S. Lee, S. Kim, J. Chun, W.-H. Ryu, Advanced Science, 2023, 10, 2301426[4] J.-S. Lee, K. Shin, S.-Y. Jun, S. Kim, W.-H. Ryu, Chemical Engineering Journal, 2023, 458, 141383 Figure 1

Fabrication and Characterization of Electrochromic Devices Utilizing CVD Graphene

Electrochromism is a function whereby the optical properties of materials change reversibly and persistently through electrochemical redox reactions driven by small electrical energy. Electrochromic devices are used in a wide range of applications including smart windows for buildings and aircraft, displays, electronic paper, and so on. The advantages of electrochromic devices include the ability to be manufactured at low cost and compatibility with non-planar and flexible surfaces. Electrochromic devices typically have a multilayer structure comprising transparent conductive electrodes, electrochromic film, ion-conducting layer, and ion-storage film. Since electrochromic devices in their uncolored state need to be transparent, the fabrication of flexible electrochromic devices requires flexible transparent conductive films as well as flexible and transparent ion-conducting layers.In this study, we aim to fabricate flexible film-type electrochromic devices using graphene films as transparent conductive electrodes. Fig. 1 illustrates the schematic images of the fabricated electrochromic devices. The electrochromic devices consist of two graphene films grown using chemical vapor deposition. Prussian blue (PB), the electrochromic material, and silver nanoparticles, which act as the ion-storage material, were electrodeposited onto each graphene film, respectively. A PVDF (polyvinylidene fluoride) porous membrane, soaked in a KCl solution as an electrolyte, was sandwiched between the two graphene electrodes to serve as a separator and ion-conducting layer. The PVDF membrane exhibits a white color due to its porous structure. Therefore, by adjusting the refractive index of the KCl solution to match that of PVDF, a transparent and flexible ion-conducting layer was formed.The graphene films were grown on copper foils by the CVD method and were then transferred onto a PET substrate using thermal press bonding with PMMA (polymethyl methacrylate) as the adhesive layer. Subsequently, copper was etched using an ammonium persulfate aqueous solution. A gold contact electrode was formed on the edge of the graphene surface by vacuum evaporation. PB was electrodeposited on one of the graphene electrode surfaces by applying a constant current of −20 μA/cm2 for 5 min in an electrolyte solution containing K3[Fe(CN)6] (5 mM), FeCl3 (5 mM), KCl (0.1 M), and HCl (0.1 M). Silver was electrodeposited on other graphene electrode surfaces by applying a constant current of −100 μA/cm2 for 5 min in an electrolyte solution containing NaNO3 (0.1 M) and AgNO3 (1 mM). The mixture of water (nd=1.333) and glycerol (nd=1.473) solution containing 0.1 M KCl was utilized to make PVDF films transparent by matching the refractive index of the electrolyte solution with that of the PVDF. By preparing the electrolyte with a water-to-glycerol ratio of 4:6, resulting in a refractive index of 1.42 for PVDF, the transmittance of PVDF immersed in this electrolyte reached almost 100%. Using this electrolyte, the EC characteristics of the film-type EC device were evaluated by Cyclic voltammetry (CV). CV curves obtained using PB/graphene as a working electrode vs Ag/graphene as a counter electrode are presented in Fig. 2, showing oxidation peaks at 0.5 V and reduction peaks at −0.2 V. It was confirmed that Prussian blue undergoes decolorization during reduction and coloration during oxidation, enabling reversible color changes between blue and transparent. Therefore, this demonstrates that the transparent and flexible PVDF layer functions as the ion-conductive layer even in the presence of 60% glycerol in the electrolyte and that the conductivity of graphene films is maintained even with a stacking structure, indicating their potential as flexible light-dimming devices.These results reveal that it was possible to fabricate flexible electrochromic devices using graphene. We believe that this work will promote further efforts to develop new multifunctional electrochromic devices that can be attached to existing glass materials such as window glass and eyeglasses to add a dimming function afterward. Figure 1

Modifying Intermolecular Interactions of Single-Ion Conducting Polymer Electrolytes through Salt Additives for Stable and High Performance Lithium Metal Batteries

Lithium metal batteries (LMBs) are emerging as a crucial breakthrough in energy storage systems due to their lowest electrochemical redox potential at -3.04V (vs. the standard hydrogen electrode) and highest theoretical capacity of 3860 mAh g-1. However, the irregular deposition on the lithium metal anode during the cycles may lead to the formation of lithium dendrites, adversely affecting the safety and performance of LMBs. Furthermore, concentration polarization can cause lithium depletion at the electrode-electrolyte interface, increasing overpotential and thereby accelerating dendrite growth. Single-ion conducting polymer electrolytes (SIPEs), in which the anion is immobilized, possess the ability to mitigate concentration polarization. Herein, we prepared a salt-in-SIPE (SiSIPE) by incorporating a salt additive (LiTFSI) into SIPEs. Spectroscopy analysis (FT-IR and Raman) and density functional theory (DFT) calculations indicated that NMA, a plasticizer that has crystallinity at 25 ℃, can form a solvation structure with LiTFSI. The intermolecular interactions inhibit the SiSIPE from crystallizing even at -80 ℃, ensure high ionic conductivity (7.0×10-4 S cm-1) at 25 ℃, and lead to a high tLi + (0.67) comparable to that of the SIPE (0.71, 2.2×10-4 S cm-1 at 25℃). Additionally, while NMA is easily decomposed above 4.0 V, the interactions ensure that the SiSIPE possesses a wide electrochemical stability window up to 4.4 V. To suppress the decomposition of the electrolyte and achieve stable cycle performance at high voltage, the electrolyte's HOMO level should be lower than that of the cathode. The DFT calculation results showed that the HOMO level of the solvation structure was found to be lower than when NMA forms hydrogen bonds with each other, which implies that it can suppress the decomposition of NMA at high voltages. Additionally, since the solvation structure has a lower LUMO level than NMA, it is preferentially used for forming the solid electrolyte interphase (SEI) layer. As a result, as shown in the X-ray photoelectron spectroscopy results, due to the salt additive, the SiSIPE forms a more stable SEI layer compared to the SIPE. This leads to improved cycle stability in both Li symmetric cell (0.1 mAh cm-2, 700 hours) and LiFePO4 full cell tests (1 C-rate, 400 cycles, 80% retention). The intermolecular design through the salt additive can not only effectively suppress lithium dendrites but also enhance stability at high voltages and improve the cycle performance of LMBs. These strategies could significantly provide a new perspective in achieving high stability and high-performance LMBs. Figure 1

Linking the Electrochemical Characteristics of Cr2O3-Ga2O3 on Glassy Carbon with the Electrocatalytic Reduction of CO2 to C2+ Products

For years copper-based electrodes were believed to be the only ones capable of reducing CO2 (CO2RR) into C2+ products1. Recently however, Cu-free electrodes have proved their ability to carry out C-C coupling, in some cases out performing copper electrodes 2–4. We, in the Bocarsly Lab, developed a Ni-enhanced Cr2O3-Ga2O3 on glassy carbon electrocatalyst able to reduce CO2 to 1-butanol with a faradaic efficiency of 42% 5, more than 10 times larger than what has previously been reported 6. Our system operates with a 900 mV overpotential in a CO2-saturated 0.1 M KCl acidic solution (pH 4.10), a difference among most systems since acidic media favors hydrogen evolution 7. Mechanistic investigations, indicate that formate is a key building block instead of CO. This is a non-common route for multi-carbon product formation in CO2RR 6,8.These results raise important questions about the characteristics of the electrocatalysts that promote both carbon-carbon bond formation and multi-electron/proton charge transfer.The Ni-enhanced Cr2O3-Ga2O3 system is particularly intriguing because it is based on an oxide mixture which is non-conducting, although it is the major constituent of the electrode interface. Electron microscopy shows that the interfacial oxide layer forms in a series of islands, in what has been described as a ‘dry riverbed’. At the nanostructure, the oxide islands contain pores of around 5-200 nm and dendrites. We have hypothesized that the role of the oxide coating resides in the alteration of the electrical double layer of the electrode rather than the transport of the electrons. This would result in the modification of the local environment that could enhance the electrocatalysis9.To investigate this hypothesis, we have employed a series of electrochemical techniques, including cyclic voltammetry, chronocoulometry, rotating disc electrode and electrochemical impedance spectroscopy; in combination with ex-situ and operando spectroscopical techniques. From the electrochemical behavior of the oxide coated glassy carbon electrode, we look to establish the relationship between its electrochemical characteristics, the electrical double layer and its role in CO2RR. Results have shown a modulation in the electrochemical response of the coated surface according to the nature of electrochemical redox probes.