Electron Conduction Pathways Research Articles

Multiphase Porous Electrode Theory for the Next Generation of SOFC/SOEC Electrodes

The mixed-ionic electronic conduction (MIEC) of gadolinium doped ceria (CGO) under reduced oxygen conditions makes it an excellent fuel electrode material for SOFC/SOEC applications. As part of a composite electrode (Ni/CGO), the nickel phase offers a fast electronic conduction pathway to the current collector and may act as an electrocatalyst at the three-phase boundary. Although the Ni/CGO cermet provides superior electrochemical performance compared with older technologies such as Ni/YSZ, the models used to study MIEC materials do not capture the unique transport and kinetic physics which makes them an excellent choice for the next generation of fuel electrodes. Within the framework of multiphase porous electrode theory, this work provides a novel set of differential-algebraic equations which captures the effects of the activation overpotential on electronic defect concentration, electrostatic surface potential and ionic transport to accurately predict the current-voltage behaviour of the Ni/CGO electrode. Moreover, through concerted electron and proton tunnelling events, we unify the theory of the electrostatic surface potential with proton-coupled electron transfer kinetics.

Effects of dry powder mixing on electrochemical performance of lithium-ion battery electrode using solvent-free dry forming process

This research examines how the morphology of the electrode powder mixture affects the structure and battery performance of lithium-ion battery electrodes fabricated using a dry electrode forming process. We demonstrate that the distribution of conductive and binding additives (CBA) on the active materials (AMs) can be controlled by adjusting the rotation speed of a dry mixer. Furthermore, we show that controlling the distribution of CBA can improve the rate performance of the batteries. The tortuosity of the CBA domain in the electrodes is analyzed from SEM images of electrode cross-sections as electronic and ionic conductive pathways. Low rotation speed dry mixing results in poor dispersion of CBA, leading to the formation of long-range conductive pathways with low tortuosity. Consequently, the capacity at high rates decreases due to fewer short-range conductive pathways between the AM particles. In contrast, high rotation speed dry mixing leads to excessive dispersion of CBA, resulting in high tortuosity in both long-range and short-range conductive pathways. As a result, the capacity decreases due to fewer efficient conductive pathways throughout the electrode. We demonstrate that medium rotation speed dry mixing achieves a favorable balance between short-range and long-range conductive pathways, providing high capacity at high rates.

Enhanced electrical conductivity and lithium ion diffusion rate of LiFePO4 by Fe site and P site doping

Lithium iron phosphate (LiFePO4) with an olivine-type structure has garnered great interest due to its electrochemical activity. It is considered one of the most promising cathode materials for lithium-ion batteries because of its high discharge platform, large theoretical capacity, and excellent cycling performance and stability. However, the typical crystal structure of LiFePO4 restricts the formation of efficient electron conduction pathways and hampers the embedding and removal motion of lithium ions, resulting in low electron conductivity and a low ion diffusion rate. The experimental results show that element doping can reduce the activation energy of diffusion, increase the diffusion rate of lithium ions, improve the rate capability of lithium-ion batteries, and contribute to the improvement of its conductivity. In this work, the electronic structure and diffusion mechanism of a S/Co/Mn co-doped LiFePO4 system are systematically studied. The introduction of S, Co, and Mn atoms leads to the formation of impurity bands, resulting in a significant reduction in the bandgap from 3.593 eV to 0.190 eV, which is beneficial for improving the conductivity of LiFePO4. Moreover, the diffusion activation energy of lithium ions decreases from 0.73 eV to 0.34 eV, and the diffusion rate of lithium ions increases from 2.7 × 109 cm/s to 1.0 × 1016 cm/s. These results demonstrate that co-doping of S, Co, and Mn can effectively enhance the conductivity and diffusion rate of lithium ions in LiFePO4, providing a reliable reference for improving the electrochemical performance of lithium iron phosphate.

Graphene-Enhanced Ion Transport in Dual-Conducting Composite Films of Polyacetylene and an Imidazolium Iodide Ionic Liquid

Dual-conducting polymer films were synthesized by dispersing graphene in an aqueous solution of poly(vinyl alcohol) and 1-propyl-3-methylimidazolium iodide ([C3mim]I) ionic liquid and thermally converting the poly(vinyl alcohol) to polyene in the presence of hydroiodic acid catalyst. The electrical and mechanical properties of the resulting free-standing films of the nanocomposite, containing different concentrations of graphene, were analyzed using electrochemical impedance spectroscopy (EIS) and dynamic mechanical analysis (DMA), respectively. Nyquist plots (imaginary vs real components of the frequency-dependent impedance) showed two characteristic arcs representing the composite's electronic and ionic conduction pathways. The conductivity values corresponding to both charge transport mechanisms increased with temperature and the graphene concentration. The enhancement in electronic conductivity is expected because of graphene's high electron mobility. Interestingly, ionic conductivity also showed a significant increase with graphene concentration, approximately triple the extent of the rise in the electronic conductivity, even though the loss and storage moduli of the films increased. (Generally, a higher modulus results in lower ionic conductivities in ionic gels.) Molecular dynamics simulations of the three-component system provided some insights into this unusual behavior. Mean square displacement data showed that the diffusion of the iodide anions was relatively isotropic. The iodide diffusion coefficient was higher in a blend with 5 vol % graphene than in blends with 3 vol % graphene or no graphene. The improvement is attributed to the interfacial effects of the graphene on the free volume of the blend. Furthermore, an exclusion of the iodide ions from the vicinity of graphene was observed in the radial distribution function analysis. The increase in the effective concentration of iodide due to this exclusion and the increase in its diffusion coefficient because of the excess free volume are the primary reasons for the observed enhancement in ionic conductivity by adding graphene.

Silicon nanoparticles encapsulated in Si3N4/carbon sheaths as an anode material for lithium-ion batteries

Novel composite materials comprising of silicon nanoparticles (SiNPs) encapsulated with thin layers of silicon nitride and reduced graphene oxide shells (Si@Si3N4@rGO) are prepared using a simple and scalable method. The composite exhibits significantly improved cycling stability and rate capability compared to bare SiNPs. The presence of inactive α and β phases of Si3N4 increases the mechanical endurance of SiNPs. Amorphous SiN x , which is possibly present with Si3N4, also contributes to high capacity and Li-ion migration. The rGO sheath enhances the electronic conduction and improves the rate capability. 15-Si@Si3N4@rGO, which is prepared by sintering SiNPs for 15 min at 1300 °C, spontaneous-coating GO on Si@Si3N4, and reducing GO to rGO, delivers the highest specific capacity of 1396 mAh g−1 after 100 cycles at a current density of 0.5 A g−1. The improved electrochemical performance of 15-Si@Si3N4@rGO is attributed to the unique combination of positive effects by Si3N4 and rGO shells, in which Si3N4 mitigates the issue of large volume changes of Si during charge/discharge, and rGO provides efficient electron conduction pathways. Si@Si3N4@rGO composites are likely to have great potential for a high-performance anode in lithium-ion batteries.

Fabrication of High-Performance Visible-Blind Ultraviolet Photodetectors Using Electro-ionic Conducting Supramolecular Nanofibers.

The detection of ultraviolet (UV) light is vital for various applications, such as chemical-biological analysis, communications, astronomical studies, and also for its adverse effects on human health. Organic UV photodetectors are gaining much attention in this scenario because they possess properties such as high spectral selectivity and mechanical flexibility. However, the achieved performance parameters are much more inferior than the inorganic counterparts because of the lower mobility of charge carriers in organic systems. Here, we report the fabrication of a high-performance visible-blind UV photodetector, using 1D supramolecular nanofibers. The nanofibers are visibly inactive and exhibit highly responsive behavior mainly for UV wavelengths (275-375 nm), the highest response being at ∼275 nm. The fabricated photodetectors demonstrate desired features, such as high responsivity and detectivity, high selectivity, low power consumption, and good mechanical flexibility, because of their unique electro-ionic behavior and 1D structure. The device performance is shown to be improved by several orders through the tweaking of both electronic and ionic conduction pathways while optimizing the electrode material, external humidity, applied voltage bias, and by introducing additional ions. We have achieved optimum responsivity and detectivity values of around 6265 A W-1 and 1.54 × 1014 Jones, respectively, which stand out compared with the previous organic UV photodetector reports. The present nanofiber system has great potential for integration in future generations of electronic gadgets.

A Highly Sensitive Non-Enzymatic Sensor for the Determination of Glucose Based on Aniline-2-sulfonic acid-Modified Cu Electrode

Herein, the copper-based electrodes were successfully synthesized with galvanostatic electrodeposition method. The effect of materials obtained at different concentrations of ASA and anodization times on glucose sensing ability was investigated. During the anodization of copper foil in the presence of ASA molecules, it formed a tree branch-like structure connected to each other while decorating the electrode surface. The Cu(30)/ASA(0.02) electrode exhibited a relatively wide linear range (0.2 – 10.0 mM) and a low detection limit (0.826 µM). These excellent activities were mainly attributed to the surface morphology, which functions as highly active sites and enhanced electronic conductive pathways with the addition of ASA. In addition, the stability obtained together with the excellent sensing ability in beverages makes the electrodes useful for practical applications.

A Comparative Study of Polycrystal/Single‐Crystal LiNi0.8Co0.1Mn0.1O2 in All‐Solid‐State Li‐Ion Batteries with Halide‐Based Electrolyte under Low Stacking Pressure

Composite cathodes consisting of a LiNi0.8Co0.1Mn0.1O2 (NCM) cathode and brittle Li3InCl6 (LIC) solid‐state electrolyte (SSE) are assessed for all‐solid‐state Li‐ion battery (ASSLIB) applications under a low stacking pressure (coin‐cell configuration: ≈2.0 MPa). Herein, an investigation is conducted to understand how the internal particle morphologies of the polycrystal (PC‐)/single‐crystal (SC‐) NCM cathode materials affect the internal cracking within the composite electrodes and thereby electrode performance. Extensive debonding between NCM and LIC takes place even at a very low current density (0.03C) with high voltage (4.4 V), but substantially narrower/shorter debonding gaps are observed for SC‐NCM as compared with PC‐NCM (wider/lengthier) due to their different particle sizes. High current rates (e.g., 0.1C) bring about greater strain rates in PC‐NCM particles, resulting in widespread microcracking along the grain boundaries between primary particles and consequently creating “dead zones” that are isolated from the ionic and electronic conduction pathways. Although SC‐NCM shows microcracking within the agglomerates, individual NCM crystals remain in close contact with the SSEs because of noticeably fewer grains in the agglomerations than in the PC‐NCM secondary particles. A low‐pressure SC‐NCM ASSLIB is demonstrated with good cycle stability comparable with that of a liquid‐electrolyte cell even under stressful currents.

Cutting-Edge Green Polymer/Nanocarbon Nanocomposite for Supercapacitor—State-of-the-Art

Supercapacitors have attained a special stance among energy storage devices such as capacitors, batteries, fuel cell, and so forth. In this state-of-the-art overview on green synthesis approaches and green materials for supercapacitors, the cutting-edge green polymer/nanocarbon nanocomposite systems were explored by focusing on the design and related essential features. In this regard, various polymers were reconnoitered including conjugated polymers, thermosetting matrices, and green-cellulose-based matrices. Nanocarbon nanomaterials have also expanded research thoughtfulness for green-technology-based energy storage devices. Consequently, green polymer/nanocarbon nanocomposites have publicized fine electron conduction pathways to promote the charge storage, specific capacitance, energy density, and other essential features of supercapacitors. Future research directions must focus on the design of novel high performance green nanocomposites for energy storage applications.

Understanding the Role of Carbon Mixtures on the Polarization of Sulfur Electrodes in Lithium-Sulfur Batteries

The performance of the sulfur-carbon composite cathode in a lithium-sulfur battery is chiefly determined by the nature of the carbon materials, the total sulfur content, and the distribution of sulfur within the composite electrode. Despite years of research, the role of these major factors in achieving optimal cathode performance is not well-understood. The present study uncovers the factors arising from formulation and processing that contribute to the internal resistance and rate capability of Ketjenblack-carbon based sulfur cathodes. Despite its enormous surface area, Ketjenblack-carbon-based sulfur electrodes exhibit surprisingly poor discharge rate capability and a high polarization resistance, providing no more than 180 mAh g−1 at the C/20 rate and delivering a high specific capacity of 1200 mAh g−1 only at a very low discharge rate of C/50. Our studies uncovered that a large contribution to the polarization resistance that arises from inter-particulate contacts and charge-transfer processes occurred close to 30% depth of discharge whereupon sulfur formed thick insulating sheets on the Ketjenblack particles, requiring an additional electron-percolation pathway for reducing the polarization. By the addition of a low-surface area carbon, Super-P®, such an electron conduction pathway could be achieved; the internal resistance of the Ketjenblack cathode decreased by four times and the electrode delivered an impressive capacity of 950 mAh g−1 at C/5 rate. We anticipate that the detailed analysis of impedance and the new learnings from this study will provide the insight needed for improving the formulation and design of the sulfur cathode.

Effects of Partially Narrowed Flow Channel on Performance of Polymer Electrolyte Fuel Cell

Introduction The performance of polymer electrolyte fuel cell (PEFC) has a great dependency on the flow field pattern, which remarkably affects the distribution of reactant concentration, pressure drop, local current density, etc., and is supposed to be a solution of the PEFCs’ grand-scale commercialization. The gas diffusion layer (GDL) is utilized in a cell to provide a uniform in-plane reactant concentration distribution and electron conduction pathway. On the other hand, the local oxygen concentration under the rib tends to be relatively low, which negatively affects the cell performance. To promote the gas transfer in both of in-plane and through-plane directions, the flow field with narrowed structure was considered, as employed in Toyota 2nd-generation MIRAI, which slightly increases the pressure drop across the whole flow filed but force a portion of the reactant gas to transport through the GDL to the catalytic layer under the gas channels and ribs. However, a brief and clear understanding of the effect of the gas transfer promoted by the narrowed structure is still lack of report. In this study, the effects of flow fields with different geometrical shapes of the narrowed structure on the cell performance were directly measured by experiments and analyzed by theoretical model. The results are potentially helpful for cell design. Experimental The membrane electrode assembly (MEA) with 10 mm thick catalytic layer and Nafion® ionomer and membrane (DuPont NR-212) was set up in a JARI-type cell. The polarization curves were measured with 4 kinds of gas channels: parallel (PN0), parallel with staggered 1-mm-long narrowed structures (PSN1), parallel with neat-arranged 1-mm-long and 3-mm-long narrowed structures (PNN1, PNN3), whose geometries are shown in Fig. 1. The manifolds of gas channels have wider size than the separated channels in order to ensure an equal flow rate in each separated channel. 200 sccm H2 and 100 sccm O2 + 400 sccm N2 (20 °C, 1 atm) were supplied to anode and cathode respectively. The dew points of the humidifiers were 65 °C. The cell was operated at 80 °C and 1 atm. Results and Discussion The simulation was proceeded in isothermal conditions, and the anisotropies of gas permeability and diffusivity in GDL were considered. The reaction kinetics was obtained by experiments. The experimental polarization curves exhibit a good agreement with the simulation results, as shown in Fig. 2. The cell performance of PSN1=PNN1>PNN3>PN0. The gas channels with narrowed structures show better performance since a part of reactant gas flows into the GDL so that the mass transfer is enhanced. Fig. 3 shows the current density distribution of each gas channels obtained by calculation. Comparing to the PN0, higher current density generates where the narrowed structures are placed, and the average oxygen partial pressure on the whole catalytic surface increased 17.5%, 17.3% and 10.8% in case of PSN1, PNN1 and PNN3, as shown in Fig. 4.The narrowed structure increases the gas convection in through-plane and in-plane directions. In case of the PSN1, the staggered narrowed structures cause the pressure gradient between gas channels, so that 5.4 % of gas in the odd-numbered gas channels flows to the even-numbered gas channels, shown as Fig. 5. However, in case of the PNN1, although nearly no pressure gradient exists between the gas channels, the performance is similar to the PSN1, which indicates the enhancement of gas transfer in the in-plane direction is unobvious.On the other hand, the effective field, where the narrowed structures enhance the gas transfer, is wider than the geometries of narrowed structures itself. The distances of higher current density in the gas flow directions comparing to the PN0 are longer than the length of narrowed structures, shown as Fig. 6. It indicates that the PNN3 has narrower effective gas transfer enhanced field than the PNN1, so that the PNN3 has lower cell performance than the PNN1. Conclusions The narrowed structures in the parallel channel heighten the gas transfer to the catalytic layer surface, so that the cell performance is improved. This effect mainly exists in the through-plane direction, in case of the presented experimental conditions. The width of the narrowed structure should not be too large which may cause the waste of the effective gas transfer enhanced field. In addition, the non-linear relationship between cell performance improvement and pressure drop is going to be further discussed. Acknowledgment This work was supported by the FC Platform Program: Development of design-for-purpose numerical simulators for attaining long life and high performance project (FY 2020–FY 2024) conducted by the New Energy and Industrial Technology Development Organization (NEDO), Japan. Figure 1

Wood-Based Cathodes for High-Performance Lithium-Sulfur Batteries

Lithium-ion batteries (LIBs) are dominant electrochemical energy storage systems in rapidly growing electronic markets. However, the conventional anode and cathode materials have limited specific capacity and quickly approach their theoretical limit. Hence, alternate battery chemistry beyond LIBs is required. Lithium-sulfur (Li-S) batteries are noteworthy energy storage systems due to their high theoretical capacity (1672 mAh/g), high theoretical energy density (2600 Wh/kg), and low cost of raw materials. Unfortunately, commercialization of Li-S batteries is hindered by the low electronic conductivity of sulfur and intermediate polysulfides, polysulfide dissolution and shuttle effect, volume expansion of elemental sulfur during the charge/discharge process, and lithium dendrite growth at the anode side. To address these challenges, various strategies such as modification of sulfur hosts, electrolyte optimization, and separator modifications have been employed. Initially, researchers encapsulated sulfur in various carbonaceous materials to mitigate the polysulfide shuttle. Later, a new active material, called sulfurized polyacrylonitrile (SPAN), was developed to mitigate the polysulfide shuttle and extend the life cycle of Li-S batteries. The main advantage of the SPAN over elemental sulfur is that it is more effective in mitigating polysulfide dissolution and shuttling due to the presence of the C−S bonds, consequently preventing the loss of active material. On the other hand, due to the limited number of binding sites in the SPAN structure, the sulfur content of SPAN materials is limited to 40 – 44 wt.%. To compete with the state-of-the-art LIBs, the Li-S batteries should provide an areal capacity of >5 mAh/cm2, corresponding to a sulfur loading of >5 mg/cm2. Realizing such a high S loading using 2D planar current collectors (e.g., aluminum foil) without compromising specific capacity and cycling stability is practically unrealistic. Using synthetic materials (e.g., graphene foam, graphene aerogel, metal-organic framework), three-dimensional (3D) electrode architectures with high SPAN loading and efficient electron and ion conductive pathways have been constructed. However, preparing these 3D electrodes mainly involves synthetic raw materials, harsh chemicals, and costly fabrication processes. Porous carbon frameworks derived from biomass, which are plant-based materials derived from nature, are alternative candidates. Biomass structures with interconnected channels over multiple length scales can provide a natural 3D template for electrochemical energy storage systems.In this study, we took advantage of the inherent porous structure of natural wood and engineered 3D frameworks using a delignification/low-temperature pyrolysis approach. A block of Balsa wood was sliced into thin sheets parallel to the tree growth direction. To facilitate the permeation of active material into the cellular structure, we first subjected the wood to a facile chemical treatment to remove lignin and hemicellulose. The delignified wood (DW) was then converted to an ultra-lightweight carbonized DW (CDW) scaffold using a low-temperature pyrolysis approach. To prepare CDW scaffolds, the DW sheets were pyrolyzed at 500, 600, 700, and 1000 °C. Continuous electron transport through the CDW conductive network and ion transport along the highly porous cellular body makes intrinsic and effective charge transfer through the CDW scaffold. SPAN active material was synthesized by pyrolyzing a mixture of elemental S and polyacrylonitrile under nitrogen flow and then using it to prepare an aqueous slurry of SPAN, CMC, and carbon black with a mass ratio of 70:15:15. To prepare the cathodes, CDWs were cut into squares with an area of 1.00 ± 0.05 cm2, dipped into a beaker of SPAN slurry, and kept under a vacuum. SPAN-impregnated free-standing electrodes (SPAN@CDW) were dried and utilized for electrochemical studies. The unique design of the SPAN@CDW electrode, wherein the interconnected pathways run in three-dimension, ensured effective electron and ion transport within the cathode. Thus, SPAN@CDW cathodes exhibited an excellent rate capability, with discharge capacities >1000 mAh/gs at 1C (1672 mA/g). The electrode with CDW pyrolyzed at 600 °C, and S loading of ~2 mg/cm2 exhibited a high specific capacity of ~1350 mAh/gs after 500 cycles at 0.1C, indicating good cycling stability. We also demonstrated the fabrication of SPAN@CDW electrodes with a high S loading of ~12.3 mg/cm2, which could deliver a high areal capacity of ~15.1 mAh/cm2 at 0.1C.

(Invited) Effects of the Alloy Composition on Cycling Performance of Cu-Ni Alloy Cathodes in All-Solid-State-Fluoride-Shuttle Batteries

Metal fluorides generally have low electric conductivities. Hence, if a single metal (e.g. Cu) is used as the cathode active material for a fluoride-shuttle battery (FSB), the electric resistance in the cathode increases after the fluoridation reaction (charging).1,2 Hence, repeating charging and discharging leads to significant drop in capacity. If an alloy consisting of two metal elements with different fluorination/defluorination potentials is used as the cathode active material, one metal element behaves as a conductive metal even when the other metal element is fluorinated, and the increase in electric resistance can be suppressed. So, we evaluated Cu-Ni binary alloys as cathode active materials for FSB in this study.The standard redox potentials (25 °C) of NiF2/Ni and CuF2/Cu are +0.11 V and +0.72 V (vs. PbF2/Pb), respectively. 3 Although NiF2 is an insulating compound, Cu behaves as a metal, providing electron conduction pathways. Additionally, the crystal structures of Cu and Ni are commonly fcc structures, with lattice constants of 3.597 Å and 3.499 Å, respectively, so that Cu-Ni alloys exhibit solid solutions in the full composition range above 380 °C in the phase diagram. Hence, the Cu-Ni alloy is considered to be an ideal alloy system that hardly separates different phases and can provide highly-dense-interconnecting-electron-conduction pathways within the whole cathode like veins.Cu x Ni1−x (x = 0, 0.3, 0.5, 0.7, 1.0) films with thicknesses of approximately 3 nm were sputter-deposited onto 0.5-mm-thick LaF3 solid electrolytes to form all-solid-state PbF2/LaF3/Cu x Ni1−x cells. Charging/discharging curves and Nyquist plots of the cells were measured under high vacuum (< 10−3 Pa) at 140 °C. Acknowledgment This paper is based on the results obtained from projects, JPNP16001 and JPNP21006, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References Okazaki et al., ACS Energy Lett., 2, 1460 (2017).Yamamoto et al., ACS Appl. Energy Mater. , 2, 6153 (2019).Gschwind et al., J. Fluor. Chem., 182, 76 (2016).

Preparation of Nanocrystalline Nb-Doped SnO2 on Mesoporous Carbon for PEFC Electrocatalysts

Platinum-based nanoparticles decorated on carbon supports (Pt/C) are widely used as electrocatalysts in polymer electrolyte fuel cells (PEFCs). Meanwhile, SnO2 is more stable than carbon at high potentials in cathodic environments. Highly durable Pt/SnO2/C electrocatalysts have therefore previously been developed using carbon nanomaterials as an electron-conducting backbone and SnO2 as a stable support layer for highly dispersed platinum nanoparticles. Here, we report on the development of Pt/SnO2/C electrocatalysts based on mesoporous carbon (MC) scaffolds. The electron conduction pathway through SnO2 was minimized by reducing the SnO2 loading. The use of Pt/SnO2/MC electrocatalysts resulted in high activity towards the oxygen reduction reaction (ORR) as well as excellent start-stop voltage cycling durability in half-cell conditions.

Porous, columnar shaped iron rich oxide synthesis for lithium-ion batteries from metallurgical grade, domestic, high carbon ferro-chromium alloys

With this article, first time in the open literature, the synthesis, and the characterization of an anode material from a domestic, intermediate product (i.e. ferrochromium alloy) have been carried out. The presented approach sets an example for many researchers in the future, as it allows the fabrication of low carbon footprint electrodes cost-effectively without using materials that can cause serious harm to the environment during their production processes. The research consists of two steps. First, a dihydrate iron-rich oxalate in the columnar structure is attained by selectively precipitating manganese, nickel, and cobalt together with iron, from the leachate of the domestic ferrochromium alloy with sulphuric acid. Then, once the powder is calcinated in a vacuum at 180˚C for 3 h, the anhydrous iron-rich oxalate (S1) powder is obtained and tested as an anode material. Moreover, the dihydrate iron-rich oxalate powder is calcinated in an argon atmosphere at 550˚C for 2 h to successfully fabricate porous, columnar-shaped iron-rich oxide (S2) powder. Galvanostatic tests demonstrate that the calcination affects both the structure and the morphology, hence the electrochemical performance: After 250 cycles, S2 delivers 1034.75 mAh g-1, whilst S1 performs 725.39 mAh g-1. The characterizations reveal that the presence of Mn, Ni, Co, along with Fe, increases the cycleability by creating additional electron conductive pathways in the powder. Moreover, owing to the porosity formed as a result of the calcination in the argon atmosphere, both the mechanical tolerance of the anode against the volumetric expansion that occurs during the reaction with lithium and the electrolyte/electrode contact are improved which lead to a better cycle performance even at higher current loads.

(Invited) Electrodeposition of Dense Lithium and Sodium Battery Cathodes for Solid-State Batteries

Conventional Li-ion batteries are formed using slurry-cast electrodes whose random nature and porosity limits both energy density and rate performance. Slurry-cast electrodes also are generally incompatible with solid-state batteries unless the slurry contains solid electrolyte particles in addition to active material. While such composite electrodes, consisting of a mixture of active material, solid electrolyte, and potentially conductive additives are under active investigation, such designs exhibit power and energy limitations due to the tortuosity of the ion and electron conduction pathways. I will present our work on the molten salt electrodeposition of thick and nearly dense Na and Li-based cathodes on metallic current collectors, including cathodes based on LiCoO2, NaCoO2, LiMn2O4, and Al-doped LiCoO2 which overcomes some of these challenges. The capacities are near-theoretical, and the crystallinities and electrochemical performance are comparable, or in some cases, even better than powders synthesized at much higher temperatures. A very attractive element of the electrodeposition process is control of the crystallographic orientation of the deposited film. For example, the crystallography can be oriented such that the fast electron and ion conduction directions are perpendicular to the substrate. Finally, I will discuss solid-state batteries built these electrodes and how the crystallography of the electrode | solid-electrolyte interface impacts interfacial reactions, rate performance, and cycle life.

Water cluster encapsulated polyoxometalate-based hydrogen-bonded supramolecular frameworks (PHSFs) as a new family of high-capacity electrode materials

Water cluster encapsulated polyoxometalate (POM)-based hydrogen-bonded supramolecular frameworks (PHSFs) are novel advanced high-capacity electrode materials for supercapacitors thanks to synergistic effects from internal components as well as the existence of numerous electronic transports and proton conductive pathways formed by hydrogen bond interactions. In this work, three new water cluster encapsulated PHSFs: [Cu2(H2O)4H2(imbta)4](PMo12O40)2·6H2O (1), [Cu (H2O)2H4(pybta)4](PMo12O40)2·2H2O (2) and [Ag2H7(pybta)6(PMo12O40)3]·12H2O (3) as well as one new PHSF: [AgH2(imbta)2](PMo12O40) (4) were hydrothermally synthesized, where the imbta and pybta are 1-imidazol-1-ylmethyl-1H-benzotriazole and 1-pyridin-3-ylmethyl-1H-benzotriazole, respectively. The electrochemical properties of the four compound-based electrodes were estimated by cyclic voltammetry, galvanostatic charge-discharge, electrochemically active surface area, and electrochemical impedance spectroscopy. In particular, due to the unique water-cluster-encapsulated PHSF structure with a large number of O–H⋯O interactions, the 1-based electrode has the highest specific capacitance of 710 F·g−1 at 1 A·g−1 among all the four electrodes, which is superior to that of most POM-based electrodes to date. Furthermore, the 1-based electrode exhibits an excellent capacitance retention about 91.2 % after 1000 cycles at a high charge/discharge current density of 10 A·g−1. The results of this study provide inspiration and guidance for the construction of PHSF-based electrode materials, which have broad application potential in a new-generation of high-performance energy storage devices.

Crinkly Polypyrrole-Modified reduced graphene oxide loaded Pd nanoparticles as Highly efficient electrocatalyst for ethylene glycol oxidation

Exploration of suitable support materials for noble metal nanocatalysts to reduce the mass loading and optimize the electrocatalytic performance for ethylene glycol oxidation reaction (EGOR) remains a key challenge. Herein the crinkly polypyrrole (PPy)-modified reduced graphene oxide (rGO) was prepared through a facile and efficient in-situ polymerization approach and utilized as the support for Pd nanoparticles. PPy as “spacers” coating on the surface of rGO nanosheets, inhibiting the aggregation and restacking, which greatly increased the available surface area of rGO. Furthermore, this interface-rich structure can offer an efficient pathway for electron conduction, which helps to improve the electrochemical properties of the catalyst. More impressively, the optimized Pd-PPy-rGO1 nanocomposite outperforms the Pd-PPy and commercial Pd-C with the higher mass activity/specific activity (5550.2 mA mgPd-1/30.0 mA cm−2), the improved intrinsic activity (TOF value of 6.5 s−1) and the enhanced stability toward electrocatalytic EGOR. The superior electrocatalytic performance benefits from the increased specific surface area of the crinkly and interface-rich PPy-rGO and the high utilization efficiency of Pd active sites during the EGOR. This work is expected to give a rational avenue to design interface-rich conducting polymer-rGO nanocomposite support for fuel cells anode catalysts.

Exploring leakage in dielectric films via automated experiments in scanning probe microscopy

Electronic conduction pathways in dielectric thin films are explored using automated experiments in scanning probe microscopy (SPM). Here, we use large field of view scanning to identify the position of localized conductive spots and develop an SPM workflow to probe their dynamic behavior at higher spatial resolution as a function of time, voltage, and scanning process in an automated fashion. Using this approach, we observe the variable behaviors of the conductive spots in a 20-nm-thick ferroelectric Hf0.54Zr0.48O2 film, where conductive spots disappear and reappear during continuous scanning. There are also fresh conductive spots that develop during scanning. The automated workflow is universal and can be integrated into a wide range of microscopy techniques, including SPM, electron microscopy, optical microscopy, and chemical imaging.

Light alters microbiota and electron transport: Evidence for enhanced mesophilic digestion of municipal sludge

Light as an environmental factor can affect the process of anaerobic digestion, but there is no systematic study in municipal wastewater sludge mesophilic digestion. In this study, the effects of light on the performance of the anaerobic digestion system and photo-anaerobic microbiota (PAM) were evaluated in lighted anaerobic batch digesters (LABRs). The methane yield from the reactor under the dark condition (LABR0) was 179.2 mL CH4/g COD, which was lower than 305.4 mL CH4/g COD and 223.0 mL CH4/g COD (n = 3, p < 0.05) from reactors under the light intensity of 3600 lm (LABR1) and 7200 lm (LABR2), respectively. The dominant genera in the bacterial and archaeal communities were Bacillus and Methanosarcina under light conditions, Enterococcus and Methanobacterium under dark conditions. And these two bacteria acted as electroactive bacterial genera, indicating that light changes the combination of direct interspecies electron transfer (DIET) microbial partners and activates the DIET pathway for methane production. The electron conduction pathways analysis further suggests that biological DIET (bDIET) between microbial biomass, rather than DIET via conductive material (cDIET) between microbes and conductive materials, is promoted and behaves as the dominant factor enhancing methane production under light conditions. The morphology of microorganisms and the amount and properties of EPS corroborate these views. Our findings are guided to anaerobic digester constructions under the outdoor environment with light exposure.