Proton-conducting Electrolyte Research Articles

Proton conductivity and mobility in Sr-doped LaScO3 perovskites

In this work, we set out to investigate the electrical conductivity of single-phase and high-density La1-xSrxScO3-δ (x = 0.05; 0.1) ceramics depending on temperature and рО2 and рН2О. The crystal structure of materials was characterized by XRD method. The samples show the structure of an orthorhombic perovskite with a Pnma space group. The unit cell volume increases along with the Sr concentration. The microstructure features of samples were investigated by SEM analysis. The transference numbers of protons and oxygen-ions were determined by the EMF (electromotive force) measurements in a gas concentration cell. In addition, the proton, oxygen-ion and hole conductivities were evaluated from the рО2-dependencies of electrical conductivity at different humidity. The results obtained using both methods showed a good level of agreement. It is found that the partial conductivity of each charge carrier in La1-xSrxScO3-δ increases along with an increase in the concentration of the Sr dopant from x = 0.05 to x = 0.1. The highest proton conductivity about 3 × 10−2 S cm−1 is achieved for La0·9Sr0.1ScO3-δ at 800 °C. The mobility of proton defects increases with Sr concentration and reaches 2.5 × 10−4 cm2 V−1 s−1 at 800 °C for La0·9Sr0.1ScO3-δ. Thus, La0·9Sr0.1ScO3-δ should be considered as a promising proton-conducting electrolyte for various electrochemical devices, such as protonic ceramic fuel cells.

Effect of High Ammonium Salt Concentration and Temperature on the Structure, Morphology, and Ionic Conductivity of Proton-Conductor Solid Polymer Electrolytes Based PVA.

Polyvinyl alcohol (PVA) based proton-conducting solid polymer electrolyte was prepared with a high salt concentration of ammonium nitrate (NH4NO3) by the technique of solvent casting. From the X-ray diffraction studies, the semicrystalline nature of PVA with the inclusion of NH4NO3 was studied. XRD analysis indicates that the highest ion conductive sample exhibits the minimum crystalline nature. The decreasing trend of Jonscher-exponent with temperature rise reveals that the present system is insured by the correlated barrier hopping (CBH) model. The maximum room temperature conductivity was found to be 5.17 × 10−5 S/cm for PVA loaded 30 wt.% of NH4NO3. The ionic transport of the proton-conducting solid polymer electrolyte was studied at the temperature range of 303–353 K. The conductivity-temperature relationship of the systems was analyzed using both the Arrhenius and Vogel–Tammann–Fulcher (VTF) models to explain the ionic hopping mechanism for the system.

Constructing p-sulfonatothiacalix[4]arene-based coordination squares as new type of efficient proton-conducting solid electrolytes

To develop high-conductivity solid-state proton-conducting materials is a hot topic in the fuel-cell technology. Herein, p-sulfonatothiacalix[4]arene was chosen as the terminal ligand to construct porous coordination compounds, {[Co4Cl(H2TC4AS)]4(BDC)8}12- (CIAC-240) and {[Co4Cl(H4TC4AS)]4(SIP)8}12- (CIAC-241) (Na4H4TC4AS = tetrasodium p-sulfonatothiacalix[4]arene; H2BDC = isophthalic acid; NaH2SIP = 5-sulfoisophthalic acid sodium salt). Both structures are featured with some window frame-like squares which are constructed by bridging the shuttlecock-like Co4-TC4AS secondary building units (SBUs) with the BDC/SIP ligands and further stacked into the supramolecular extended structures. The proton conduction and vapor adsorption of the compounds were discussed and compared. The experimental results gave the maximum values of 3.22 mS cm−1 and 11.6 mS cm−1 for the proton conductivity of CIAC-240 and CIAC-241, respectively.

Features of Electrophoretic Deposition of a Ba-Containing Thin-Film Proton-Conducting Electrolyte on a Porous Cathode Substrate

This paper presents the study of electrophoretic deposition (EPD) of a proton-conducting electrolyte of BaCe0.89Gd0.1Cu0.01O3-δ (BCGCuO) on porous cathode substrates of LaNi0.6Fe0.4O3−δ (LNFO) and La1.7Ba0.3NiO4+δ (LBNO). EPD kinetics was studied in the process of deposition of both a LBNO sublayer on the porous LNFO substrate and a BCGCuO electrolyte layer. Addition of iodine was shown to significantly increase the deposited film weight and decrease the number of EPD cycles. During the deposition on the LNFO cathode, Ba preservation in the electrolyte layer after sintering at 1450 °C was achieved only with a film thickness greater than 20 μm. The presence of a thin LBNO sublayer (10 μm) did not have a pronounced effect on the preservation of Ba in the electrolyte layer. When using the bulk LBNO cathode substrate as a Ba source, Ba was retained in a nominal amount in the BCGCuO film with a thickness of 10 μm. The film obtained on the bulk LBNO substrate, being in composition close to the nominal composition of the BCGCuO electrolyte, possessed the highest electrical conductivity among the films deposited on the various cathode substrates. The technology developed is a base step in the adaptation of the EPD method for fabrication of cathode-supported Solid Oxide Fuel Cells (SOFCs) with dense barium-containing electrolyte films while maintaining their nominal composition and functional characteristics.

Plasticized H+ ion-conducting PVA:CS-based polymer blend electrolytes for energy storage EDLC application

In this work, plasticized proton-conducting polymer blend electrolytes based on poly (vinyl alcohol): chitosan were synthesized, characterized, and utilized in an electric double-layer capacitor (EDLC). A structural study was performed using X-ray diffraction. The scarification and decrease of intensity of the crystalline peak were detected upon the addition of glycerol plasticizer (GP). The morphological appearance of the plasticized blend electrolyte films was examined through scanning electron microscopy, in which the role of GP on ion dissociation was indicated to be important. Electrochemical impedance spectroscopy was performed to estimate the conductivity of the films. Before the EDLC application, other electrochemical techniques, such as transference number measurement (TNM), linear sweep voltammetry (LSV), and cyclic voltammetry (CV), were carried out. To evaluate the performance of the EDLC, the charge–discharge profile was then examined. The EDLC has been cycled 250 times at a current density of 0.75 mA cm−2. The specific capacitance (Cspe) of the EDLC, which is known as an essential parameter, was found to be constant after the first cycle. The reduction in Cspe value was correlated with the increase of equivalent series resistance. Finally, the manners of energy (E) and power (P) densities as a function of the number of cycles were studied.

Recent advances and perspectives of fluorite and perovskite-based dual-ion conducting solid oxide fuel cells

High-temperature solid-state electrolyte is a key component of several important electrochemical devices, such as oxygen sensors for automobile exhaust control, solid oxide fuel cells (SOFCs) for power generation, and solid oxide electrolysis cells for H2 production from water electrolysis or CO2 electrochemical reduction to value-added chemicals. In particular, internal diffusion of protons or oxygen ions is a fundamental and crucial issue in the research of SOFCs, hypothetically based on either oxygen-ion-conducting electrolytes or proton-conducting electrolytes. Up to now, some electrolyte materials based on fluorite or perovskite structure were found to show certain degree of dual-ion transportation capability, while in available electrolyte database, particularly in the field of SOFCs, such dual-ion conductivity was seriously overlooked. Actually, few concerns arising to the simultaneous proton and oxygen-ion conductivities in electrolyte of SOFCs inevitably induce various inadequate and confusing results in literature. Understanding dual-ion transportation behavior in electrolyte is indisputably of great importance to explain some unusual fuel cell performance as reported in literature and enrich the knowledge of solid state ionics. On the other hand, exploration of novel dual-ion conducting electrolytes will benefit the development of SOFCs. In this review, we provide a comprehensive summary of the understanding of dual-ion transportation in solid electrolyte and recent advances of dual-ion conducting SOFCs. The oxygen ion and proton conduction mechanisms at elevated temperature inside oxide-based electrolyte materials are first introduced, and then (mixed) oxygen ion and proton conduction behaviors of fluorite and perovskite-type oxides are discussed. Following on, recent advances in the development of dual-ion conducting SOFCs based on fluorite and perovskite-type single-phase or composite electrolytes, are reviewed. Finally, the challenges in the development of dual-ion conducting SOFCs are discussed and future prospects are proposed.

Structural and electrical properties of novel phosphate based composite electrolyte for low-temperature fuel cells

Lowering the operating temperature of solid-electrolyte based fuel cells is an attractive approach to achieve highly efficient energy conversion devices for the next-generation demands. The present work aims to develop proton-conducting electrolyte materials for low-temperature fuel cells. In this regard, a host matrix of gadolinium-doped cerium pyrophosphate (CGP) has been reinforced by cesium pentahydrogen diphosphate (CPP) to deliver dense electrolyte material. The composite electrolyte materials were formulated with different compositions and examined for the phase purity, sinterability, functional group, and electrical conductivities. It was found that the reinforcement by CPP assisted formation of a core-shell structure, which accelerated the proton migration by the acidic dissolution of proton into the shell. This acidic dissolution fastens the kinetics of hydrolysis of the electrolyte resulting in a maximum ionic conductivity of about 9 mS cm−1 at 110 °C under humidified air (pH2O = 0.12 atm) atmosphere. Besides, a maximum ionic conductivity of 0.8 mS cm−1 was also achieved at 230 °C under dry air atmosphere. Moreover, the entire composite electrolytes realized a remarkable densification (>95%) which substantiate the practical suitability of the presented materials to be used for the low-temperature fuel cells.

Electrochemical sensors based on proton-conducting electrolytes for determination of concentration and diffusion coefficient of CO2 in inert gases

The monitoring of CO2 levels in gases has important environmental, technological and energy applications. In the present work, results of the fabrication and testing of an amperometric-type sensor based on a proton-conducting material for analysing the concentration of carbon dioxide (CO2) in inert gases at elevated temperatures are presented. The analysis consists in reading the limiting current values determined during preliminary tests, obtaining the calibration dependence on variation of CO2 concentration and further using it for the investigation of gas mixtures. Experimental results show that the sensor is able to precisely detect CO2 concentration ranging between ~2 and 14 vol% in a wet N2 atmosphere at an intermediate-temperature range (500–600 °C) with a response time of ~30 min. Moreover, the possibility of estimating diffusion coefficients for CO2–N2 mixtures is also demonstrated. These results open a new window for high-temperature electrochemical analysis of gas mixtures, when solid-state gas sensors and proton-conducting electrolyte membranes are jointly utilised.

Enhancing the flash-sinterability of BaZr0.1Ce0.7Y0.2O3-δ proton-conducting electrolyte by nickel oxide doping for possible application in SOFCs

In the present work, effects of nickel oxide doping on flash-sinterability of BaZr0.1Ce0.7Y0.2O3-δ compound were investigated. A single-phase BZCY7 powder was synthesized by the solid-state reaction route. The effects of using 0.5, 1, 1.5, and 2 wt% of NiO additive on flash sintering of BZCY7 samples were examined. It was revealed that using 0.5 wt% of NiO additive can reduce the onset temperature of flash sintering in all the applied electric fields in the range of 100–500 V/cm and significantly enhances the sinterability of the BZCY7 compound. Microstructural investigations, using field emission scanning electron microscopy and energy-dispersive X-ray mapping, showed that NiO doping can lead to larger grain sizes, while no detectable segregation or second phase was observed. Utilizing electrochemical impedance spectroscopy, the total conductivity of samples at 600 and 700 °C was measured as 4.4 × 10−3 and 7.0 × 10−3 S/cm for the undoped BZCY7, and 8.6 × 10−3 and 1.4 × 10−2 S/cm for the 0.5 wt% NiO doped BZCY7 sample, respectively. The activation energies of conduction were determined as 0.37 and 0.41 eV for the doped and undoped samples, which represent the presence of predominant and facile protonic conduction.

Grain boundary space charge modulation in BaZr0.8Y0.2-xMxO3−δ with transition metal (M= Ni, Co, Fe, and Zn) co-doping

The higher grain boundary resistance of proton-conducting ceramic electrolytes such as BaZrO3 drops the total conductivity. In the present study, BaZr0.8Y0.2-xMxO3−δ electrolyte with various transition metals (M= Ni, Co, Fe, and Zn) with molar concentrations (x = 0.01, 0.03 & 0.05) were prepared by hydrothermal assisted precipitation method. The structural analysis, such as XRD and Raman, revealed the presence of the cubic perovskite phase of barium zirconate. The existence of space charge layer was confirmed by nonlinear behaviour of the grain boundary resistance on applying DC bias. The Mott–Schottky analysis performed at 200 °C in reducing atmosphere showed a reduction in barrier potential from 0.24 to 0.13 V upon the addition of the secondary dopants. The elastic energy minimization by dopant segregation and electrostatic interaction between the charged defects and dopants suppress the space charge layer. The transition metal dopant, especially Ni and Fe, segregates along the grain boundary and acts as the counterbalance for charged defects. Besides, Fe act as perfect sintering aid which leads to higher densification (>99%) as well as higher protonic conductivity of 21.2 mScm−1 at 600 °C. These results imply that the transition metal ions as co-dopant influence the space charge effect and the density of the barium zirconate electrolyte.

Proton-Conducting Polyoxometalates as Redox Electrolytes Synergistically Boosting the Performance of Self-Healing Solid-State Supercapacitors with Polyaniline

Energy storage devices with high volumetric and gravimetric capacitance are in urgent demand due to the booming market of portable and wearable electronics. Using redox-active molecules as electrol...

High-Performance Proton-Conducting Fuel Cell with B-Site-Deficient Perovskites for All Cell Components

Proton-conducting fuel cells (PCFCs) with a perovskite-type proton-conducting electrolyte show many advantages over conventional oxygen-ion-conducting ceramic fuel cells. Both electrode catalytic a...

Electrical properties and chemical stability of Br addition in BaCe0.8Gd0.2O3-α proton-conducting electrolyte

The effects of bromine (Br) addition on electrical properties and chemical stability of Gd-doped barium cerate proton-conducting electrolyte were investigated. BaCe0.8Gd0.2O2.8±δBr0.2 (BCGBr) and BaCe0.8Gd0.2O3-α (BCG) powders with CuO as sintering aid were obtained via a solid-state reaction. The results of X-ray fluorescence (XRF) confirm that only trace amounts of Br are present in BCGBr after high temperature sintering at 1600 °C, indicating that Br addition influences stoichiometry but not directly the physicochemical properties. Nevertheless, the XRD results from the treated BCGBr and BCG electrolyte pellets show that the chemical stability of BCGBr in water and/or CO2-containing atmospheres is conspicuously improved. The conductivities of electrolyte sintered at 1600 °C for 10 h were investigated in various atmospheres by AC impedance technique. The total conductivity (σtot) of BCGBr under wet Ar is lower than that of BCG. Partial-conductivities components ((proton (σOHO·), oxygen ion (σVO··), and hole (σh·)) are presented for BCGBr according to the defect structure model. The results show that the proton conductivity of BCGBr remains nearly constant over the 550–750 °C temperature range. Although σtot of Br-synthesized sample slightly decreases, the BCGBr exhibits a high σOHO· (0.058 S cm−1 at 750 °C) under pH2O = 0.038 atm and pO2 = 1 atm. P-type and oxygen ion conduction are dominant in an oxidative atmosphere (pO2 = 1 atm) at 650 °C. Under low oxygen conditions (pO2 = 10−4 atm), BCGBr shows the behavior of mixed conduction (oxygen ions (VO··) and protons (OHO·)). Besides, the main carriers in BCGBr oxide change from OHO· to VO·· as temperature increased.

Iontronics Using V2CTx MXene-Derived Metal-Organic Framework Solid Electrolytes.

Electronic applications of porous metal–organic frameworks (MOFs) have recently emerged as an important research area. However, there is still no report on using MOF solid electrolytes in iontronics, which could take advantage of the porous feature of MOFs in the ionic transport. In this article, MXene-derived two-dimensional porphyrinic MOF (MX-MOF) films are demonstrated as an electronic-grade proton-conducting electrolyte. Meanwhile, the MX-MOF film shows high quality, chemical stability, and capability of standard device patterning processes (e.g., dry etching and optical and electron beam lithography). Using the commercialized nanofabrication processes, an electric double-layer (EDL) transistor is demonstrated using the MX-MOF film (derived from V2CTx MXene) as an ionic gate and MoS2 film as a semiconducting channel layer. The EDL transistor, operated by applying an electric field to control the interaction between ions and electrons, is the core device platform in the emerging iontronics field. Therefore, The MX-MOF, confirmed as a solid electrolyte for EDL transistor devices, could have a significant impact on iontronics research and development.

RETRACTED: Proton transport enabled by a field-induced metallic state in a semiconductor heterostructure.

Tuning a semiconductor to function as a fast proton conductor is an emerging strategy in the rapidly developing field of proton ceramic fuel cells (PCFCs). The key challenge for PCFC researchers is to formulate the proton-conducting electrolyte with conductivity above 0.1 siemens per centimeter at low temperatures (300 to 600°C). Here we present a methodology to design an enhanced proton conductor by means of a Na x CoO2/CeO2 semiconductor heterostructure, in which a field-induced metallic state at the interface accelerates proton transport. We developed a PCFC with an ionic conductivity of 0.30 siemens per centimeter and a power output of 1 watt per square centimeter at 520°C. Through our semiconductor heterostructure approach, our results provide insight into the proton transport mechanism, which may also improve ionic transport in other energy applications.

Development of high-performance sensor based on NiO/SnO2 heterostructures to study sensing properties towards various reducing gases

In this work, we report the spontaneous formation of NiO nanoparticles-decorated onto smooth SnO2 nanofibers, which is an inexpensive and scalable method for yielding a high composite surface area via a simple two-step synthesis process based on electrospinning and the hydrothermal method. A Nickel Oxide proton-conducting electrolyte is deposited homogeneously over a large surface area in a transparent solution, mixed and decorated onto Tin dioxide nanofibers, as evidenced by cross sectional imaging of the electrospun nanofibers. The composite based on nanoparticle-decorated fibers enlarges the surface area of the exposed electrolyte, which fundamentally improves the overall gas sensing performance. The crystal structure, morphology, and physio-chemical surface state of the NiO/SnO2-based specimen are comprehensively examined using XRD, SEM, TEM, HRTEM, EDX, and photoelectron (XPS) spectroscopy. The composite based on NiO/SnO2 nanoparticle-decorated fibers exhibits an optimistic mesoporous nature with a huge specific area, which is key for superior gas sensors. The result reveals that NiO/SnO2 nanoparticle-decorated fibers with an average size of 180–260 nm in diameter, where the average length of fibers was about 1.5 μm. The composite-based heterojunction of NiO/SnO2 nanoparticle-decorated fibers enhances the adsorption of oxygen molecules, which show fast response, good selectivity and quick recovery speed against ethanol gas at an optimal temperature of about 160 °C. The maximum sensitivity response of the sensor-based composite NiO/SnO2 nanoparticle-decorated fibers was 23.87 in respect of 100 ppm ethanol gas at a low temperature of 160 °C; this is approximately about 7.2 times superior to that of pure SnO2 nanofibers. The superior gas sensing capabilities of a composite based on NiO/SnO2 nanoparticle-decorated fibers may be attributable to the enhanced catalytic effect of the small sized NiO nanoparticles on smooth SnO2 nanofibers, together with the p/n heterojunction effects between NiO and SnO2 heterostructures.

SrZr0.9Y0.1O3−δ thin films by in-situ synthesis of triple alkoxide for protonic ceramic electrolyser membranes

Synthesis of the proton-conducting electrolyte SrZr0.9Y0.1O3−δ(SZY) was undertaken by the sol–gel method employing an all-alkoxide route from reaction of strontium alkoxide produced in-situ and commercial zirconium and yttrium alkoxides. The solution was homogenized by a previous ligand exchange in 2-methoxyethanol to control the polycondensation rate and achieve SZY at the low final firing temperature of 700–800 °C. SZY thin films (~270 nm) were assisted by dip-coating on different substrates and characterized by scanning and transmission electron microscopy, grazing X-ray diffraction and confocal micro-Raman spectroscopy, revealing well-crystallized SZY phase with orthorhombic symmetry (space group, Pnma). Impedance spectroscopy of a thin film deposited on a quartz substrate revealed that protons contribute to transport in wet conditions as confirmed by a lower conductivity in D2O-humidified air (1.02 eV) compared to H2O-wetted air (0.99 eV), with the difference in activation energy consistent with a conductive isotope effect.

Comprehensive models for evaluating electrolyte hole conductivity and its impacts on the protonic ceramic fuel cell

Solid oxide fuel cell with proton-conducting electrolyte is a clean and efficient device for electricity generation. This kind of electrolyte exhibits both protonic and hole conductivities at intermediate temperature. The former one is necessary, while the latter one would cause leakage current and loss of output voltage. The electrolyte hole conductivity is a major concern due to its remarkable impact on the cell capacity. Hereby, a practical model is proposed to evaluate the effective hole conductivity of the working cell. Compared with previous models, conductivity distribution in the electrolyte is fully considered, which makes this model more applicable to a variety of working conditions. Furthermore, by accounting for leakage current, conductivity distribution within the electrolyte as well as involved polarizations, a comprehensive model for predicting cell output is developed. In the aspect of experiment, cell samples with different electrolyte thicknesses are fabricated, and are served as illustrative cases to examine our model. The calculated output voltages accord with our experiments. Meanwhile, impacts of operating conditions on both electrolyte conductivities and electric energy utility are quantified by our model. Our model is helpful to the cell designer when predicting cell capacity and its proper working conditions.

CeO2 coated NaFeO2 proton-conducting electrolyte for solid oxide fuel cell

Nowadays, the low-temperature operation has become an inevitable trend for the development of SOFCs. Transition metal layered oxides are considered as promising electrolyte materials for low-temperature solid oxide fuel cells (LT-SOFCs). In this work, we report the CeO2 coated NaFeO2 as an electrolyte material for LT-SOFC. The study results revealed that the piling of CeO2 significantly influenced the open-circuit voltage (OCV) as well as the power output of the fuel cells. In comparison with pure NaFeO2, the denser structure of CeO2 coated NaFeO2 leads to higher OCV (1.06 V, 550 °C). The electrochemical impedance spectrum (EIS) fitted results showed that NaFeO2–CeO2 composites possessed higher ionic boundary conductivity. This is because that the hetero-interfaces between NaFeO2 and CeO2 provide fast ion conducting path. The high ionic conductivity of CeO2 coated NaFeO2 lead to admirable fuel cell power output of 727 mW cm−2 at 550 °C.

Red algae-derived k-carrageenan-based proton-conducting electrolytes for the wearable electrical devices

Proton-conducting non-porous nature of k-carrageenan-based flexible solid electrolytes was prepared by facile solution casting technique. Altering the composition of NH4COOH, free ion percentage (%) was improved significantly and contributed vital role on the proton conductivity to an utmost level of 8.54 × 10−4 Scm−1. Especially, increasing the composition of protonic carrier, electrochemical stability window was tuned tremendously and topmost value of 6.3 V was captured for the 0.4 (M wt%) NH4COOH added electrolyte. Also, interfacial adhesion energy of the electrolytes was enhanced to the maximum level of 96.27 Jm−2, inferred from contact angle measurements. The obtained significant electrochemical performance of k-carrageenan-based samples is an excellent substitute direction towards the cost-effective and eco-friendly wearable electrical applications.