Applications In Electrochemical Devices Research Articles

A Convergent Understanding of Charged Defects

ConspectusHistorically, defects in semiconductors and ionic conductors have been studied using very different approaches. In the solid-state ionics community, nonstoichiometry and defect thermochemistry are often probed directly through experiments. The dependency of defect concentrations on chemical conditions (typically oxygen pressure) are modeled using a physical chemistry framework and compactly represented by the well-known Brouwer diagrams. In contrast, defects in electronic materials are now studied primarily with computational approaches─often density functional theory (DFT)─based on semiconductor physics in which the energy of defect formation also has an explicit dependence on the Fermi level, making the defect energy diagram multidimensional. As charged defects begin to attract the attention of experts from both schools of thought for applications in thermoelectrics, solar cells, batteries, fuel cells, and other electrochemical devices, a consistent understanding of charged defects addressing the apparent gaps in the two approaches is necessary.This Account reviews both methods using a common notation and thermodynamics to clarify misunderstandings between the fields. We demonstrate the equivalence between the Brouwer diagrams obtained from DFT calculated defect energy diagrams and those constructed using the simple analytical theory described in physical chemistry textbooks. We show how the explicit Fermi level dependence of defect energy in semiconductor physics appears as an electron concentration in the mass action law using a constant defect energy defined in a standard state, ΔGd⊖. ΔGd⊖ can also be visualized on a defect energy diagram. Furthermore, we develop the utility of a Brouwer band diagram to compactly map defect and charge concentration as well as important electronic dopability information in compound semiconductors over a multidimensional chemical potential space into a single 2-dimensional plot.Semiconductors and ion conductors often have distinct mechanisms to compensate for the additional charge introduced by extrinsic (or impurity) doping with aliovalent species. Whereas such extrinsic doping in ionic conductors (e.g., Gd doped CeO2–x) results in the formation of intrinsic ionic defects (e.g., VO), in the case of traditional semiconductors (e.g., P doped Si) free electronic charge carriers are formed. Using the example of thermoelectric Mg3Sb2, which can exhibit both these mechanisms depending on chemical conditions, we explain charge compenstaion of extrinsic dopants (e.g., doping efficiency) using the simple mass action laws for intrinsic defect reactions.

Magnesium ion conducting free-standing biopolymer blend electrolyte films for electrochemical device application

Solid polymer blend electrolyte films composed of 70 wt.% of chitosan (CS) and 30 wt.% of methylcellulose (MC) were prepared with different weight percentages of MgCl2 by solution casting method. FTIR analysis demonstrated the interactions between blend and MgCl2, XRD study revealed the amorphous nature of the films. Thermogravimetric analysis (TGA) was carried out to study the thermal stability. Electrical impedance spectroscopy (EIS) study showed that the bulk resistance decreased with increasing salt concentration and is due to the influence of carrier concentration. From EIS measurement, the highest value of DC conductivity at ambient temperature (30 °C) was found to be 2.75 × 10−3 Scm−1 for the sample containing 30 wt.% of MgCl2. The voltage stability window of the highest conducting film was found to be 3.86 V. The total ionic transference number was found to be 0.98. Finally, the highest conducting polymer electrolyte was employed to construct a primary magnesium ion battery.

Entropy stabilization of two-dimensional transition metal dichalcogenide alloys: A density functional theory study

As high-entropy alloying provides an increasingly important avenue for widening the set of functional materials for a variety of applications, it is useful to uncover synthesis routes that do not rely on large temperatures for achieving entropic stabilization. Focusing on transition-metal dichalcogenides, we present direct computational evidence from density functional theory calculations that high-entropy disulfide (HES) alloys with five cations from groups 4–6 are thermodynamically stable at temperatures routinely achievable in conventional deposition systems. While all 126 sulfide combinations with five group 4–6 transition metals are thermodynamically favorable at low (<800 K) or medium (<1200 K) temperatures, we show that electronegativities, valence electron concentrations, and atomic radii of cations can help predict whether an HES alloy is stable in the 1-H or the 1-T structure. Furthermore, replacing one of the five cations with another, from outside groups 4–6, can still yield HES alloys with nearly planar layer morphologies and stabilization temperatures below 1200 K, albeit with some localized defects. These results demonstrate that a wide range of stable HES alloys can be synthesized experimentally as 2D layers, thereby providing facile ways for expanding the materials’ space with potential applications in electrochemical devices, catalysis, energy storage, or sensing.

Synaptic Current Response of a Liquid Ga Electrode via a Surface Electrochemical Redox Reaction in a NaOH Solution.

An ionic device using a liquid Ga electrode in a 1 M NaOH solution is proposed to generate artificial neural spike signals. The oxidation and reduction at the liquid Ga surface were investigated for different bias voltages at 50 °C. When the positive sweep voltage from the starting voltage (VS) of 1 V was applied to the Ga electrode, the oxidation current flowed immediately and decreased exponentially with time. The spike and decay current behavior resembled the polarization and depolarization at the influx and extrusion of Ca2+ in biological synapses. Different average decay times of ∼81 and ∼310 ms were implemented for VS of −2 and −5 V, respectively, to mimic the synaptic responses to short- and long-term plasticity; these decay states can be exploited for application in binary electrochemical memory devices. The oxidation mechanism of liquid Ga was studied. The differences in Ga ion concentration due to VS led to differences in oxidation behavior. Our device is beneficial for the organ cell–machine interface system because liquid Ga is biocompatible and flexible; thus, it can be applied in biocompatible and flexible neuromorphic device development for neuroprosthetics, human cell–machine interface formation, and personal health care monitoring.

Proton and Oxygen-Ion Conductivities of Hexagonal Perovskite Ba5In2Al2ZrO13.

The hexagonal perovskite Ba5In2Al2ZrO13 and In3+-doped phase Ba5In2.1Al2Zr0.9O12.95 were prepared by the solid-state synthesis method. The introduction of indium in the Zr-sublattice was accompanied by an increase in the unit cell parameters: a = 5.967 Å, c = 24.006 Å vs. a = 5.970 Å, c = 24.011 Å for doped phase (space group of P63/mmc). Both phases were capable of incorporating water from the gas phase. The ability of water incorporation was due to the presence of oxygen deficient blocks in the structure, and due to the introduction of oxygen vacancies during doping. According to thermogravimetric (TG) measurements the compositions of the hydrated samples corresponded to Ba5In2Al2ZrO12.7(OH)0.6 and Ba5In2.1Al2Zr0.9O12.54(OH)0.82. The presence of different types of OH−-groups in the structure, which participate in different hydrogen bonds, was confirmed by infrared (IR) investigations. The measurements of bulk conductivity by the impedance spectroscopy method showed that In3+-doping led to an increase in conductivity by 0.5 order of magnitude in wet air (pH2O = 1.92·10−2 atm); in this case, the activation energies decreased from 0.27 to 0.19 eV. The conductivity−pO2 measurements showed that both the phases were dominant proton conductors at T < 500 °C in wet conditions. The composition Ba5In2.1Al2Zr0.9O12.95 exhibited a proton conductivity ~10−4 S·cm−1 at 500 °C. The analysis of partial (O2−, H+, h•) conductivities of the investigated phases has been carried out. Both phases in dry air (pH2O = 3.5·10−5 atm) showed a mixed (oxygen-ion and hole) type of conductivity. The obtained results indicated that the investigated phases of Ba5In2Al2ZrO13 and Ba5In2.1Al2Zr0.9O12.95 might be promising proton-conducting oxides in the future applications in electrochemical devices, such as solid oxide fuel cells. Further modification of the composition and search for the optimal dopant concentrations can improve the H+-conductivity.

Electrical Characteristics of Metal Contacts to Carbon Nanowalls

The electrical characteristics of metal contacts to vertically-aligned nanographite structures, the so-called carbon nanowalls (CNWs), are examined using nickel as the electrode material. The total resistance between a pair of electrodes on CNWs is regarded as the sum of the serial resistance of CNWs and two metal-CNWs contacts to measure the contact resistance and specific contact resistivity by the transmission line method and transfer line method, respectively. The contact resistance and resistivity are around 2.8 Ω and 0.1 Ω cm2, respectively, at room temperature and decrease gently to 2.4 Ω and 0.06 Ω cm2, respectively, when the temperature is increased up to 300 °C. The apparent activation energy corresponding to the conduction barrier at the contact is in the range of 10−3 eV to 10−2 eV, which is comparable with that for the sheet resistance of CNWs. The contact resistance occupies a large portion of the total resistance between a pair of electrodes even at high temperatures, thus affecting electrical signal measurement in electronic and electrochemical device applications.

Isomeric effects of poly-viologens on electrochromic performance and applications in low-power electrochemical devices

Electrochromic (EC) behaviors of poly-viologens are tuned by selecting positions ( ortho ( o ) , meta ( m ), and para ( p )) of the benzene rings linked to 4,4′-bipyridine. All-in-one type EC devices (ECDs) are conveniently fabricated by adding poly-viologens to highly conductive solid-state polymeric gel electrolytes. The maximum transmittance contrast (Δ T ) of the o -poly-viologen based ECD is much lower than that of the other isomers, and its bleaching is not reversible, whereas a large Δ T and high stability are achieved with the m - and p -poly-viologens. Considering the high solubility of the m -poly-viologen in ion gels, it is anticipated to have a larger hydrodynamic size, leading to low diffusivity (∼1.1 × 10 −12 cm 2 /s for cationic and ∼2.7 × 10 −12 cm 2 /s for anionic current). As a result, the m -poly-viologen ECD shows a superior memory effect and long-lasting colored state without voltage supply. This feature allows us to demonstrate a low-power ECD based on the m -poly-viologen, which only requires ∼3.54 μW/cm 2 to maintain the transmittance below 30%. The results indicate that adjusting the isomeric molecular structure of poly-viologen EC chromophores is an effective way to control their EC performance. • Three isomeric poly-viologens are designed and synthesized for electrochromic (EC) chromophores. • Poly-viologens with a larger hydrodynamic size exhibit a lower diffusivity and a higher memory effect. • EC devices with meta -poly-viologens consume very low power of ∼3.54 μW/cm 2 to maintain colored state.

Investigation of N–S-based graphene quantum dot on sodium alginate with ammonium thiocyanate (NH4SCN) biopolymer electrolyte for the application of electrochemical devices

Investigation of N–S-based graphene quantum dot on sodium alginate with ammonium thiocyanate (NH4SCN) biopolymer electrolyte for the application of electrochemical devices

Synergistic effect of sodium content for tuning Sm2O3 as a stable electrolyte in proton ceramic fuel cells

Samarium oxide (Sm2O3), a rare earth sesquioxide, shows that a great potential in proton-conducting fuel cells. However, the stability of Sm2O3 based cell remains a challenge. Herein we reported a facile method for enhancing the stability via the incorporation of sodium content into Sm2O3. This study discloses that the existence of sodium induces phase transition of Sm2O3 from monoclinic to cubic phase beneficial for fast proton transportation. Further mechanism investigation reveals that the cubic phase structure of Sm2O3 is stabilized resulting from substitution of sodium. Compared with commercial Sm2O3 (CSM), the fuel cell employing Na–Sm2O3 (NSM) as electrolyte delivers an improved peak power density of 570 mW cm−2 and the extended stability over 100 h under 130 mWcm−2 at 520 °C. In this study, NSM is successfully developed as a stable electrolyte material for proton conduct fuel cells, expanding its application in electrochemical devices.

Studies on the ions transportation behavior of alginate doped with H+ carrier-based polymer electrolytes

In the present work, amorphous bio-based polymer electrolytes (BBPEs) using alginate polymer as a matrix host and doped with varying amounts of ammonium iodide (NH4I) have been developed via the solution casting technique. The physicochemical properties of alginate-NH4I BBPEs were evaluated by using X-Ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), electrical impedance spectroscopy (EIS), and transference number measurement (TNM). The BBPEs film containing 25 wt % of NH4I possessed the highest ionic conductivity of 1.29 × 10−4 S cm−1, the highest amorphous phase, and good thermal stability of up to 234 °C. Based on the Nyquist fitting approaches, the ionic conductivity of the BBPEs was primarily influenced by the ion transportation, which was due to the interplay of segmental motion between the alginate and NH4I, and also the H+ hopping mechanism, as shown by FTIR. The proton transference number (tH+ = 0.41) suggests that alginate BBPEs are promising materials in electrochemical device applications.

Experimental and Theoretical Advances on Single Atom and Atomic Cluster‐Decorated Low‐Dimensional Platforms towards Superior Electrocatalysts

AbstractThe fundamental relationship between structure and properties, which is called “structure‐property”, plays a vital role in the rational designing of high‐performance catalysts for diverse electrocatalytic applications. Low‐dimensional (LD) nanomaterials, including 0D, 1D, 2D materials, combined with low‐nuclearity metal atoms, ranging from single atoms to subnanometer clusters, are currently emerging as rising star nanoarchitectures for heterogeneous catalysis due to their well‐defined active sites and unbeatable metal utilization efficiencies. In this work, a comprehensive experimental and theoretical review is provided on the recent development of single atom and atomic cluster‐decorated LD platforms towards some typical clean energy reactions, such as water‐splitting, nitrogen fixation, and carbon dioxide reduction reactions. The upmost attractive structural properties, advanced characterization techniques, and theoretical principles of these low‐nuclearity electrocatalysts as well as their applications in key electrochemical energy devices are also elegantly discussed.

Synthesis of CoFe2O4/MWCNTs Nanohybrid and its Effect on the Optical, Thermal, and Conductivity of PVA/CMC Composite as an Application in Electrochemical Devices

Synthesis of CoFe2O4/MWCNTs Nanohybrid and its Effect on the Optical, Thermal, and Conductivity of PVA/CMC Composite as an Application in Electrochemical Devices

Inorganic‐Organic Hybrid Anion Conducting Membranes Based on Ammonium‐Functionalized Polyethylene Pyrrole‐Polyethylene Ketone Copolymer

Back Cover: In article number 2100409 by Voto Di Novo and co-workers, the incorporation of tantalum oxide into trimethylammonium-functionalized polyethylene pyrrole-co-polyethylene ketone is carried out for the preparation of inorganic–organic hybrid anion exchange membranes, which are promising candidates for application in electrochemical energy conversion devices.

Effect of graphene quantum dot on sodium alginate with ammonium formate (NH4HCO2) biopolymer electrolytes for the application of electrochemical devices

Effect of graphene quantum dot on sodium alginate with ammonium formate (NH4HCO2) biopolymer electrolytes for the application of electrochemical devices

Ultrathin microporous carbon/few-layer graphene heterostructure for supercapacitor application

The heterostructure consisting of ultrathin microporous carbon and graphene can exhibit many interesting properties benefiting from their unique physicochemical structure, and thus possess a great potential application in electrochemical energy storage devices. Herein, we report a novel catalysis strategy to construct nanometer-thick microporous carbon/few-layer graphene (FLG) heterostructure in the tens-of-nanometer-thick shells of hollow carbon spheres (HCSs). The thickness of microporous carbon in heterostructure can be reduced by intercalating more FLG sheets. Nano-sized thickness increases exposure ratio of micropores and shortens ion transport distance besides good conductivity of FLG sheets. The meso- and macropores in heterostructure further improves ion adsorption of high-density open micropores. The obtained ultrathin microporous carbon/FLG heterostructure shows high special capacitance (Cs) of 187 F·g−1 at 5.0 mV·s−1 and excellent rate capability. Furthermore, the loading of heterostructure electrode increases by 15 times, the Cs is up to 192 F·g−1 at 5.0 mV·s−1 with more excellent rate performance and robust long-term charge-discharge recyclability. After the loading mass increased by 29 times (2.85 mg·cm−2), the electrochemical performance still remains stable, indicating a great potential for supercapacitor application. The mechanism behind these phenomena was studied.

Silver Nanoparticle Decorated on Reduced Graphene Oxide-Wrapped Manganese Oxide Nanorods as Electrode Materials for High-Performance Electrochemical Devices

In this work, silver nanoparticles decorated on reduced graphene oxide (rGO) wrapped manganese oxide nanorods (Ag-rGO@MnO2) were synthesized for an active electrode material. MnO2 nanorods were synthesized via a hydrothermal route, and their coating with GO and subsequent reduction at a higher temperature resulted in rGO@MnO2. A further addition of Ag on rGO@MnO2 was performed by dispersing rGO@MnO2 in AgNO3 solution and its subsequent reduction by NaBH4. X-ray diffraction (XRD) analysis showed peaks corresponding to MnO2 and Ag, and the absence of a peak at 2θ = 26° confirmed a few layered coatings of rGO and the absence of any graphitic impurities. Morphological analysis showed Ag nanoparticles anchored on rGO coated MnO2 nanorods. Apart from this, all other characterization techniques also confirmed the successful fabrication of Ag-rGO@MnO2. The electrochemical performance examined by cyclic voltammetry and the galvanic charge–discharge technique showed that Ag-rGO@MnO2 has a superior capacitive value (675 Fg−1) as compared to the specific capacitance value of rGO@MnO2 (306.25 Fg−1) and MnO2 (293.75 Fg−1). Furthermore, the electrode based on Ag-rGO@MnO2 nanocomposite showed an excellent capacity retention of 95% after 3000 cycles. The above results showed that Ag-rGO@MnO2 nanocomposites can be considered an active electrode material for future applications in electrochemical devices.

Delafossite CuCrO2 nanoparticles as possible electrode material for electrochemical supercapacitor

Delafossites are popularly known materials for thermoelectric and electrochemical device applications due to their layered structural features. In this paper, delafossite CuCrO2 nanoparticles (NPs) have been synthesized using a simple chemical procedure and are investigated as a supercapacitor material. To determine the phases of delafossite CuCrO2 NPs, the morphological and phase formation experiments were conducted using diffraction patterns and microscopic analysis. The cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) studies were performed to evaluate the supercapacitative behavior of delafossite CuCrO2 NPs. As prepared delafossite CuCrO2 NPs based electrode showed an outstanding electrochemical property as compared to annealed delafossite CuCrO2 NPs at 300–500 °C. A good specific capacitance of ∼464.7 Fg-1 at 0.01 Vs-1 was found for the fabricated supercapacitor using non-annealed delafossite CuCrO2 NPs based electrode, which was further validated by GCD results. The electrochemical supercapacitor fabricated with both non-annealed and annealed delafossite CuCrO2 NPs displayed considerably the outstanding cycling stability by maintaining up to ∼88% after 5000 cycles. This work sets the pace for a new and efficient method of preparing delafossite CuCrO2 for high-performance electrochemical supercapacitors.

Studies on the effect of H+ carrier toward ionic conduction properties in alginate-ammonium sulfate complexes–based polymer electrolytes system

The present work highlights the contribution of ammonium sulfate (NH4)2SO4 as H+ carriers in alginate-based solid polymer electrolytes (SPEs) that were successfully prepared via a solution casting technique. The Fourier transform infrared analysis revealed that molecular interactions between the host polymer and the ionic dopant complexes occurred at the wavenumbers 3700–2500 cm−1, 1800–1500 cm−1, and 1200–900 cm−1. These regions corresponded to the O-H stretching, COO− and C-O-C, moieties of alginate, respectively, which coordinated with the H+ carrier from (NH4)2SO4. At ambient temperature, the optimum ionic conductivity was obtained at 3.01 × 10−5 S cm−1 for the sample containing 10 wt.% of (NH4)2SO4. The IR-deconvolution approach shows that the ionic conduction enhancement is governed by the ionic mobility and the diffusion coefficient of H+ carriers, and the findings show that the present biopolymer, which is an alginate-based SPEs system, has an excellent possibility to be used as electrolytes for application in electrochemical devices.

Design of Ordered Mesoporous CeO2-YSZ Nanocomposite Thin Films with Mixed Ionic/Electronic Conductivity via Surface Engineering.

Mixed ionic and electronic conductors represent a technologically relevant materials system for electrochemical device applications in the field of energy storage and conversion. Here, we report about the design of mixed-conducting nanocomposites by facile surface modification using atomic layer deposition (ALD). ALD is the method of choice, as it allows coating of even complex surfaces. Thermally stable mesoporous thin films of 8 mol-% yttria-stabilized zirconia (YSZ) with different pore sizes of 17, 24, and 40 nm were prepared through an evaporation-induced self-assembly process. The free surface of the YSZ films was uniformly coated via ALD with a ceria layer of either 3 or 7 nm thickness. Electrochemical impedance spectroscopy was utilized to probe the influence of the coating on the charge-transport properties. Interestingly, the porosity is found to have no effect at all. In contrast, the thickness of the ceria surface layer plays an important role. While the nanocomposites with a 7 nm coating only show ionic conductivity, those with a 3 nm coating exhibit mixed conductivity. The results highlight the possibility of tailoring the electrical transport properties by varying the coating thickness, thereby providing innovative design principles for the next-generation electrochemical devices.

Rational design of porous Ru‐doped CuO nanoarray on carbon cloth: Toward reversible catalyst layer for efficient Li‐O 2 batteries

Until now, in case of Li-O2 batteries, catalyst materials are applied by simple mixing with carbon black, which causes large overpotential due to limited active surface of the catalyst, leading to low energy efficiency and short cycle life. Accordingly, in previous studies, significant advances have been witnessed in the synthesis of various electrode materials with three-dimensional (3-D) structures for application in electrochemical energy storage devices. Herein, the 1-D@3-D catalyst layer design and efficient active site formation strategy help to enable an efficient Li-O2 battery. In particular, it should be noted that the 1-D@3-D catalyst layer has great potential for maximizing the active contact area between the electrolyte and the catalyst materials and promoting the rapid diffusion of products and reactants through their stereoscopic structure. The 1-D Ru-doped CuO nanorod array on 3-D carbon cloth (Ru-CuO/RuO2@CC) is demonstrated via 7,7,8,8-Tetracyanoquinodimethane-solution deposition, and thermal oxidation process. A comprehensive kinetic study using linear sweep voltammetry reveals that the Ru-CuO/RuO2@CC has superior ORR/OER performance compared to a CuO nanorods-loaded carbon cloth and a CuO/RuO2 nanoparticles-loaded carbon cloth. The Ru-CuO/RuO2@CC as a catalyst layer combined cell is achieved 1.0 mA h cm−2 (=3075 mA h gc−1) during 30 cycles with a low overpotential decay rate of 0.88% per cycle.