Solid-state Electrochemical Devices Research Articles

Customized electrospun multilayer composite polymer electrolytes: PEO-PAN-NbO2 nanofiber membrane for enhancing the performance of lithium-ion batteries

Ground-breaking research into the development of a multilayer composite polymer electrolyte aims to enhance the safety associated with liquid electrolytes utilized in lithium batteries. The electrolyte consists of two outer layers made of electrospun poly(vinylidene fluoride) (PVDF) and a middle layer comprised of a fibrous membrane containing PEO, PAN-PEO, PEO-NbO2, and PAN-PEO-NbO2. The investigated PEO-PAN-NbO2 system demonstrates a higher room temperature ionic conductivity of 2.451 × 10−1 mS cm−1 than that of single-phase electrolyte systems. Incorporating inorganic fillers such as NbO2 into PEO polymer electrolytes, in conjunction with PAN copolymerization, significantly enhances ionic conductivity and amplifies surface area. Consequently, the utilization of these techniques that demonstrate increased polymer membranes leads to improved efficiency and security of solid-state electrochemical devices. The multilayer composite polymer electrolyte is created by continuous electrospinning, which allows for precise control and improves safety features.

Superprotonic Conductivity in a Metalloporphyrin-Based SMOF (Supramolecular Metal-Organic Framework).

Metal-organic frameworks and supramolecular metal-organic frameworks (SMOFs) exhibit great potential for a broad range of applications taking advantage of the high surface area and pore sizes and tunable chemistry. In particular, metalloporphyrin-based MOFs and SMOFs are becoming of great importance in many fields due to the bioessential functions of these macrocycles that are being mimicked. On the other hand, during the last years, proton-conducting materials have aroused much interest, and those presenting high conductivity values are potential candidates to play a key role in some solid-state electrochemical devices such as batteries and fuel cells. In this way, using metalloporphyrins as building units we have obtained a new crystalline material with formula [H(bipy)]2[(MnTPPS)(H2O)2]·2bipy·14H2O, where bipy is 4,4'-bipyidine and TPPS4- is the meso-tetra(4-sulfonatephenyl) porphyrin. The crystal structure shows a zig-zag water chain along the [100] direction located between the sulfonate groups of the porphyrin. Taking into account those structural features, the compound was tested for proton conduction by complex electrochemical impedance spectroscopy (EIS). The as-obtained conductivity is 1 × 10-2 S·cm-1 at 40 °C and 98% relative humidity, which is a remarkably high value.

Exsoluble Ni–Co alloy nanoparticles anchored on a layered perovskite for direct CO2 electrolysis

It has never been more important to develop new technologies that can reduce CO2 emissions or convert them into useful chemical products. As solid-state electrochemical devices, solid oxide electrolysis cell (SOEC) is capable of converting CO2 efficiently and selectively into CO or, when combined with water electrolysis, producing syngas (CO and H2). Herein, we demonstrate a novel layered perovskite oxide, reduced (La4Sr4)0.9Ti7.2Ni0.4Co0.4O26 (LSTNC-r), decorated by exsolved Ni-Co alloy nanoparticles for high-efficiency CO2 electrolysis. The cell renders a higher activity for electrolysis of CO2 with a current density of 1.53 A cm−2 @2.0 V and 850 °C. Faradic efficiency measurement and stability test suggest that LSTNC-r are promising fuel electrodes for high-efficient CO2 electrolysis.

Transport properties of the Ba(Zr,Ce,Y,Yb)O3−δ proton conductor: the real role of co-substitution of Y and Yb

The ionic transport number decreases with increasing Yb content in Ba(Zr,Ce,Y,Yb)O3−δ proton conducting electrolyte. High performance of the electrolyte is not due to improved electrical properties by co-substitution of Y and Yb.

A Study on Electrochemical Properties of Fuel-Electrode-Supported Reversible Solid Oxide Cells

Introduction Reversible solid oxide cells (r-SOCs) enable both power generation and steam electrolysis, and have attracted attention as a solid state electrochemical energy device for a decarbonized society (1). R-SOCs have the advantage of high efficiency due to high temperature operation, but there exist various technical issues remained in materials selection, start-up and shutdown, and long-term durability. Therefore, reducing operating temperature is desirable for practical applications (2,3). Electrode-supported cells, in which the electrode acts as a structural support, enable lower temperature operation by reducing the thickness of the electrolyte, which has certain electrical resistivity. Here in this study, the current-voltage characteristics and reversible cycle durability under r-SOC operating conditions are evaluated using fuel-electrode-supported cells, with the aim of developing r-SOCs capable of highly efficient fuel cell power generation and steam electrolysis. Experimental For the experiments, fuel-electrode-supported cells were fabricated using fuel electrode-supported half-cells (Japan Fine Ceramics, Japan), schematically shown in Fig. 1. The half-cell consists of scandia-stabilized zirconia (ScSZ: 10 mol%Sc2O3-1mol%CeO2-89 mol%ZrO2) or yttria-stabilized zirconia (YSZ: 8 mol%Y2O3-92 mol%ZrO2) electrolyte and a Ni-cermet fuel electrode, such as Ni-ScSZ or Ni-YSZ. (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) was applied for the air electrode, and Gd0.1Ce0.9O2 (GDC) was inserted between the electrolyte and the air electrode to suppress interdiffusion and chemical reactions. Four types of cells were used with different combinations of the electrolyte component (YSZ or ScSZ) in the electrolyte layer or the supporting fuel electrode.In electrochemical tests, 50%-humidified hydrogen (100 ml min-1) was supplied to the fuel electrode, and air (150 ml min-1) was supplied to the air electrode. R-SOC initial performance tests were conducted using an electrochemical analyzer (1255B, Solartron). Cell voltage and impedance were measured at 700-800°C at current densities ranging from -0.5 A cm-2 to +0.5 A cm-2. Positive current density means the value in SOFC mode, while negative current density means the value in SOEC mode. In r-SOC 1,000 cycle durability tests, cycles of switching between SOFC and SOEC operation were repeated 1,000 times by varying current density. The range of current density in the cycle tests was between -0.2 A cm-2 and +0.2 A cm-2. The cell impedance was measured before the cycling test and every 100 cycles. After each test, the cells were analyzed by using a focused-ion beam scanning electron microscopy (FIB-SEM) to observe and evaluate the electrode microstructure. Results and discussion Figure 2 (a) shows the r-SOC initial performance of each fuel-electrode-supported cell. The cell with the Ni-YSZ fuel electrode and the YSZ electrolyte showed better current voltage characteristics than other cells. Figure 2 (b) shows the r-SOC 1000-cycle durability of the cell with the Ni-YSZ fuel electrode and the YSZ electrolyte. The results showed a decrease in power generation and electrolysis performance with increasing the number of cycles in both SOFC and SOEC modes. Possible degradation mechanisms will be discussed. Acknowledgments This paper is based on results obtained from a project (Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration), JPNP20005, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Collaborative support by Prof. H. L. Tuller and Prof. B. Yildiz at Massachusetts Institute of Technology (MIT) is gratefully acknowledged. References (1) Venkataraman, M. Pérez-Fortes, L. Wang, Y. S. Hajimolana, C. Boigues-Muñoz, A. Agostini, S. J. Mcphail, F. Mar échal, J. V. Herle, and P. V. Aravind, J. Energy Storage, 24, 100782 (2019).(2) Subotić, S. Pofahl, V. Lawlor, N. H. Menzler, T. Thaller, and C. Hochenauer, Energy Proc., 158, 2329 (2019).(3) B. Mogensen, Current Opinion Electrochem., 21, 265 (2020). Figure 1

A solid-state electrochemical device for studying thermodynamic properties of non-stoichiometric oxides: Application to UO2+x

We report attempts at determining the evolution of the oxygen activity in hyper-stoichiometric uranium dioxide for very low values of deviation from stoichiometry, using a solid-state electrochemical device. To this end, solid-state oxidation cycles coupled with oxygen activity measurements are carried out on a dense polycrystalline uranium oxide sample. We thus follow the evolution of the oxygen activity in the material as it oxidises or reduces, for temperatures ranging from 1093 to 1273 K. The data are subsequently analysed using an oxygen point defect model and equilibrium constants, corresponding to the various supposed point defect equilibria, are determined. We show that the model faithfully reproduces the trends observed in the experimental data. A more detailed analysis of the equilibrium constants obtained enables us to identify more precisely the limitations of the experimental method. In particular, we highlight the fact that the presence of residual oxygen in the device prevents us from determining the desired physical quantities for stoichiometry deviations less than 10−3. Ways of circumventing these difficulties which would further allow us to determine point defect diffusion coefficients are outlined.

Studies on a novel microporous electrospun poly(vinyl alcohol)‐based polymer electrolyte membranes for high‐performance battery applications

AbstractINTRODUCTIONSolid polymer blend electrolytes are scientifically interesting promising materials as electrolytes in advanced solid state electrochemical devices applications such as batteries, electrochemical display devices, smart windows, etc. The solid polymer blend electrolyte has several advantages including high energy density, a solvent free condition, structural stability, light weight, leak proof, good electrode electrolyte contact, ease of fabrication, easy processability and good mechanical properties.OBJECTIVESThe present research work deals with the study of composition and conductivity behavior of polymer blend electrolyte complex membranes based on PVA and PVP complexed with different weight percent KClO4 salt, prepared by electrospinning technique. The resultant polymer blend electrolytes have been characterized by XRD, FTIR and AC conductivity studies.METHODSPorous PVA based nanofiber membranes were prepared using a typical electrospinning technique with a horizontal arrangement. A stainless steel needle (24 G, outer diameter: 0.50 mm, inner diameter: 0.35 mm) was connected to an electrode of a high voltage power supply (Spellman, model CZE1000R) which could generate positive DC voltages up to 30 kV and a grounded stainless steel plate was placed at 10 cm distance from the needle tip to collect the nanofiber membranes.RESULTS AND DISCUSSIONA novel electrospun polymer electrolyte membranes comprising a blend of poly (vinyl alcohol) (PVA) and poly (vinyl pyrrolidone) (PVP) containing various concentrations of potassium perchlorate KClO4 salt are prepared using electrospinning technique. The structure and complexation of the polymer electrolyte membranes have been confirmed from X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) spectral studies. The ac conductivity studies are performed to measure the ionic conductivity of the polymer electrolyte complex systems in the temperature range 298‐353 K and it is also found that the temperature dependence ionic conductivity data seems to follows the Arrhenius relation. The influence of complex membranes composition on the ionic conductivity has been discussed. The maximum ionic conductivity value is obtained to be 9.1×10−4 S cm−1 at 298 K for PVA‐PVP‐KClO4 (50‐35‐15) polymer system with 15 wt.% KClO4 salt. Scanning electron microscopy studies have been performed and reported.CONCLUSIONSFree standing, flexible complex polymer electrolyte membranes based on various compositions of PVA‐PVP‐KClO4 have been prepared. The presence of amorphous regions due to complexation of polymer salt matrices has been confirmed from XRD and FTIR analysis. The maximum value of ionic conductivity has been obtained to be 9.1 × 10−4 S cm−1 at 298 K for PVA‐PVP‐KClO4 (50‐35‐15) complex polymer electrolyte system with 15 wt.% KClO4. The excellent performance, such as high values of ionic conductivity, of polymer blend electrolyte membranes suggest that the membranes can be used as the best candidate for high performance solid state batteries.

Improve the Electrochemical Performance and Long-Term Durability of Protonic Ceramic Electrochemical Cells

Energy and environmental issues have attracted much attention in recent decades. To secure a green and sustainable energy future, we need to redesign current energy systems to move from conventional fossil fuels to renewable energy sources. The potential renewable energy from wind and solar exceeds global energy consumption; however, it is not flexible due to the intermittent nature of sunlight and wind. Thus, a robust, cost-effective, and secure technology is required to efficiently store this renewable energy. Protonic ceramic electrochemical cells (PCECs) are solid-state electrochemical devices that can directly convert between electrical energy and chemical energy (hydrogen and hydrocarbons) by operating in both electrolysis and fuel cell modes. Due to their relatively high operating temperature (~500 °C), PCECs are more favorable in terms of both thermodynamics and kinetics when compared with other similar energy-conversion technologies that are operated at a lower temperature (such as proton-exchange membrane cells). To be commercially competitive, however, several critical challenges related to performance, durability, and the Faradaic Efficiency need to be solved. In this talk, we will present our recent achievements on materials and cell design to solve these challenges. By optimizing the air electrode composition and microstructure, a dramatically enhanced electrochemical performance was achieved on both the fuel cell and the electrolysis cell. The long-term durability was improved via constructing a robust interface between the electrode and the electrolyte. We will also introduce a reliable method to measure the Faradaic Efficiency during the cell operation to the community.

Gel Polymer Electrolytes: Advancing Solid-State Batteries for High-Performance Applications.

Gel polymer electrolytes (GPEs) hold tremendous potential for advancing high-energy-density and safe rechargeable solid-state batteries, making them a transformative technology for advancing electric vehicles. GPEs offer high ionic conductivity and mechanical stability, enabling their use in quasi-solid-state batteries that combine solid-state interfaces with liquid-like behavior. Various GPEs based on different materials, including flame-retardant GPEs, dendrite-free polymer gel electrolytes, hybrid solid-state batteries, and 3D printable GPEs, have been developed. Significant efforts have also been directed toward improving the interface between GPEs and electrodes. The integration of gel-based electrolytes into solid-state electrochemical devices has the potential to revolutionize energy storage solutions by offering improved efficiency and reliability. These advancements find applications across diverse industries, particularly in electric vehicles and renewable energy. This review comprehensively discusses the potential of GPEs as solid-state electrolytes for diverse battery systems, such as lithium-ion batteries (LiBs), lithium metal batteries (LMBs), lithium-oxygen batteries, lithium-sulfur batteries, zinc-based batteries, sodium-ion batteries, and dual-ion batteries. This review highlights the materials being explored for GPE development, including polymers, inorganic compounds, and ionic liquids. Furthermore, it underscores the transformative impact of GPEs on solid-state batteries and their role in enhancing the performance and safety of energy storage devices.

A Sustainable Gel Polymer Electrolyte for Solid-State Electrochemical Devices.

Nowadays, solid polymer electrolytes have attracted increasing attention for their wide electrochemical stability window, low cost, excellent processability, flexibility and low interfacial impedance. Specifically, gel polymer electrolytes (GPEs) are attractive substitutes for liquid ones due to their high ionic conductivity (10-3-10-2 S cm-1) at room temperature and solid-like dimensional stability with excellent flexibility. These characteristics make GPEs promising materials for electrochemical device applications, i.e., high-energy-density rechargeable batteries, supercapacitors, electrochromic displays, sensors, and actuators. The aim of this study is to demonstrate the viability of a sustainable GPE, prepared without using organic solvents or ionic liquids and with a simplified preparation route, that can substitute aqueous electrolytes in electrochemical devices operating at low voltages (up to 2 V). A polyvinyl alcohol (PVA)-based GPE has been cast from an aqueous solution and characterized with physicochemical and electrochemical methods. Its electrochemical stability has been assessed with capacitive electrodes in a supercapacitor configuration, and its good ionic conductivity and stability in the atmosphere in terms of water loss have been demonstrated. The feasibility of GPE in an electrochemical sensor configuration with a mediator embedded in an insulating polymer matrix (ferrocene/polyvinylidene difluoride system) has also been reported.

Isotope Exchange Raman Spectroscopy (IERS): A Novel Technique to Probe Physicochemical Processes in situ.

Wehave developed a novel in situ methodology for the direct study of mass transport properties in oxides with spatial and unprecedented time resolution, based on Raman spectroscopy coupled to isothermal isotope exchanges. Changes in the isotope concentration, resulting in a Raman frequency shift, can be followed in real time, not accessible by conventional methods, enabling complementary insights for the study of ion transport properties of electrode and electrolyte materials for advanced solid-state electrochemical devices. The proof of concept and strengths of isotope exchange Raman spectroscopy (IERS) are demonstrated by studying the oxygen isotope back-exchange in gadolinium-doped ceria (CGO) thin films. Resulting oxygen self-diffusion and surface exchange coefficients are compared to conventional time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterisation and literature values, showing good agreement, while at the same time providing additional insight, challenging established assumptions. IERS captivates through its rapidity, simple setup, non-destructive nature, cost effectiveness and versatile fields of application and thus can readily be integrated as new standard tool for in situ and operando characterization in many laboratories worldwide. The applicability of this method is expected to consolidate ourunderstanding of elementary physicochemical processes and impact various emerging fields including solid oxide cells, battery research andbeyond. This article is protected by copyright. All rights reserved.

Sintering Aid Strategy for Promoting Oxygen Reduction Reaction on High-Performance Double-Layer LaNi0.6Fe0.4O3-δ Composite Electrode for Devices Based on Solid-State Membranes.

Strontium and cobalt-free LaNi0.6Fe0.4O3-δ is considered one of the most promising electrodes for solid-state electrochemical devices. LaNi0.6Fe0.4O3-δ has high electrical conductivity, a suitable thermal expansion coefficient, satisfactory tolerance to chromium poisoning, and chemical compatibility with zirconia-based electrolytes. The disadvantage of LaNi0.6Fe0.4O3-δ is its low oxygen-ion conductivity. In order to increase the oxygen-ion conductivity, a complex oxide based on a doped ceria is added to the LaNi0.6Fe0.4O3-δ. However, this leads to a decrease in the conductivity of the electrode. In this case, a two-layer electrode with a functional composite layer and a collector layer with the addition of sintering additives should be used. In this study, the effect of sintering additives (Bi0.75Y0.25O2-δ and CuO) in the collector layer on the performance of LaNi0.6Fe0.4O3-δ-based highly active electrodes in contact with the most common solid-state membranes (Zr0.84Sc0.16O2-δ, Ce0.8Sm0.2O2-δ, La0.85Sr0.15Ga0.85Mg0.15O3-δ, La10(SiO4)6O3-δ, and BaCe0.89Gd0.1Cu0.01O3-δ) was investigated. It was shown that LaNi0.6Fe0.4O3-δ has good chemical compatibility with the abovementioned membranes. The best electrochemical activity (polarization resistance about 0.02 Ohm cm2 at 800 °C) was obtained for the electrode with 5 wt.% Bi0.75Y0.25O1.5 and 2 wt.% CuO in the collector layer.

Construction of indigenous tin incorporated nickel dichalcogenide nanosheets for high energy all solid-state hybrid supercapacitor

Despite solid-state energy storage devices are one of the potential candidates for modern electronics, it usually suffers from poor compatibility with gel electrolyte acquiring insufficient energy density. Continuous efforts have been devoted to overcome the energy density paucity. Here, we highlight the strategy to augment the energy density of solid-state electrochemical energy storage device by constructing indigenous Sn doped nickel dichalcogenides nanosheets along with tunable composition. Micrometre size, flat nanosheets offer high compatibility to the gel electrolyte and their porous structure grant multi directional active site access. Modified electronic structure upon cation/anion substitution gain enhanced charge transfer and increased numbers of active sites. Cooperative features of nanostructures and controlled doping, boosted the specific capacity of samples from 134 to 437 mAh/g with remarkable rate retention of 42–81%. Prepared range of anion/cation/cation & anion doped nickel dichalcogenides, i.e., NiSSe, Ni0.66Sn0.33S2 and Ni0.66Sn0.33SSe further gain benefit upon coupling with freshly prepared N, S doped bio-derived carbon (OP-850). Resultant, all solid-state energy storage devices delivered 54, 78 and 127 mAh/g cell capacity at 3 A/g with outstanding energy density of 54, 78 and 102 Wh/kg, respectively. These comparative interpretations confer, Ni0.66 Sn0.33SSe//N, S doped OP-850 must be the promising all solid-state energy storage device with exceptional energy density outcome. Excellent cycle stability and LED pattern illumination demonstrate the feasibility of the device. Furthermore, such simple scalable synthesis approach could also extend to prepare other doped metal chalcogenides nanosheets, likely achieve breakthroughs in various applications.

Back Cover: Multilayered Ceramic Membrane with Ion Conducting Thin Layer Induced by Interface Reaction for Stable Hydrogen Production (Angew. Chem. Int. Ed. 6/2023)

Multilayered ceramic membranes with ion-conducting dense thin layers are essential platforms for solid-state electrochemical devices, gas separation membranes, and sensors. In their Research Article (e202210485), Heqing Jiang et al. develop a new interface-reaction-induced reassembly approach for the direct fabrication of zirconia- or ceria-based dense thin layers rooted in multilayered ceramic membranes that show robust and practical performance for upgrading fossil-fuel-derived hydrogen.

Rücktitelbild: Multilayered Ceramic Membrane with Ion Conducting Thin Layer Induced by Interface Reaction for Stable Hydrogen Production (Angew. Chem. 6/2023)

Multilayered ceramic membranes with ion-conducting dense thin layers are essential platforms for solid-state electrochemical devices, gas separation membranes, and sensors. In their Research Article (e202210485), Heqing Jiang et al. develop a new interface-reaction-induced reassembly approach for the direct fabrication of zirconia- or ceria-based dense thin layers rooted in multilayered ceramic membranes that show robust and practical performance for upgrading fossil-fuel-derived hydrogen.

Solid state electrochemical devices for hydrogen energy

The idea of nuclear-hydrogen energy draws growing interest of power engineering specialists. One of the ways to implement such a direction of development is integration of nuclear power station and high temperature electrochemical devices, namely solid oxide electrolyzers (SOE) and fuel cells (SOFC). This paper reviews the principal features of the devices and their high efficiency of energy transformation. The electrical efficiency of the SOEs can exceed 100 % at the expense of high-grade potential heat energy consumed by the electrolyzer. The efficiency of the SOFCs amounts to 70 %. The state of the art of long-term tests of single cells of SOEs and SOFC stacks are presented.

The void formation behaviors in working solid-state Li metal batteries.

The fundamental understanding of the elusive evolution behavior of the buried solid-solid interfaces is the major barrier to exploring solid-state electrochemical devices. Here, we uncover the interfacial void evolution principles in solid-state batteries, build a solid-state void nucleation and growth model, and make an analogy with the bubble formation in liquid phases. In solid-state lithium metal batteries, the lithium stripping-induced interfacial void formation determines the morphological instabilities that result in battery failure. The void-induced contact loss processes are quantified in a phase diagram under wide current densities ranging from 1.0 to 10.0 milliamperes per square centimeter by rational electrochemistry calculations. The in situ-visualized morphological evolutions reveal the microscopic features of void defects under different stripping circumstances. The electrochemical-morphological relationship helps to elucidate the current density- and areal capacity-dependent void nucleation and growth mechanisms, which affords fresh insights on understanding and designing solid-solid interfaces for advanced solid-state batteries.

(Invited) Selective CO2 Conversion in Protonic Ceramic Electrochemical Cells

Protonic ceramic electrochemical cells (PCECs) are solid-state electrochemical devices that employ proton-conducting oxides as electrolytes, which offer a promising approach for electrification of chemical manufacturing, including CO2 reduction to produce value-added chemicals. The primary advantage of PCECs is their intermediate operating temperatures (300-600 °C), which thermodynamically and kinetically favor the CO2 reduction chemistry at the negative electrode. Unfortunately, the conventional negative electrode of PCECs, such as BaZr0.8-xCexY0.2O3- \U0001d6ff-Ni or BaZr0.8-xCexY0.1Yb0.1O3- \U0001d6ff-Ni, cannot reduce CO2 to either CH4 or CO with a selectivity of >99%, leading to the production of a mixture of CO and CH4. In this talk, we will present the rationally designed negative electrodes for CO2 conversion PCECs. The PCECs equipped with the new negative electrodes selectively favor the CO2-to-CO conversion. A selectivity of ~100% toward CO has been demonstrated over a wide range of operating temperatures (400-600 °C) and applied potential/current density. The negative electrode demonstrated in this work fully suppresses the CH4 production. In situ diffuse reflectance infrared spectroscopy (DRIFTS) was performed to probe the CO2 reduction mechanisms over the negative electrodes. This work validates that PCECs equipped with the rationally designed negative electrode can selectively manufacture chemicals.

Localized Surface Oxygen Ion Transport in Sto and YSZ Observed Via Quasi in Situ Scanning Probe Microscopy

Ionic transport in solid oxides lays the fundamentals of solid-state electrochemical energy and sensor devices. While ionic transport in polycrystalline oxides has been studied for decades, most studies are reliant upon macro-scale observations where direct revelation of localized transport behavior is not feasible. In this presentation, we report a direct quasi in situ observation of oxygen ion transport in SrTiO3 (STO) and Y2O3-stabilized ZrO2 (YSZ) by leveraging scanning probe microscopy variants.First, a cluster of oxygen vacancies formed by an electrical bias at a tip-sample contact. Then, we exposed the sample to an elevated temperature to allow a facilitated ionic diffusion. The resultant lateral distribution of oxygen vacancies was obtained by Kelvin probe force microscopy (KPFM). Depth-wise distribution of oxygen vacancies were acquired by a combination of in situ etching with a diamond-coated probe and KPFM scans, which enabled an observation of ionic charge transport in a highly localized fashion in both lateral and depth-wise directions.From 3D spatial charge imaging, the activation energies of surface ionic diffusion in the lateral direction (Esurf) and those of bulk diffusion in the depth-wise direction (Ebulk) were quantified; for YSZ, Esurf = 0.34 eV and Ebulk = 1.13 eV, and for STO, Esurf = 0.50 eV and Ebulk = 1.30 eV. It was also found that the surface ion diffusivity of YSZ (1.68 × 10-8 cm2/s) is more than 3 orders of magnitude higher than that of STO (4.86 × 10-12 cm2/s), and that bulk diffusivity of YSZ (1.70 × 10-11 cm2/s) is more than 7 orders of magnitude higher than that of STO (7.61 × 10-19 cm2/s). To the best of our knowledge, this is the first study where the ionic diffusivities along the surface and into the bulk are separately quantified by direct localized observations of 3D distribution of ionic species, as opposed to a bulk measurement from which diffusivities were indirectly deduced.The authors acknowledge the support by National Science Foundation (DMR 1753383).

Rationally designed negative electrode for selective CO2-to-CO conversion in protonic ceramic electrochemical cells

Protonic ceramic electrochemical cells (PCECs) are solid-state electrochemical devices that employ proton-conducting oxides as electrolytes, which offer a promising approach for electrification of chemical manufacturing, including CO2 reduction to produce value-added chemicals (e.g., CO). The primary advantage of PCECs is their intermediate operating temperatures (300–600 °C), which thermodynamically and kinetically favor the CO2 reduction chemistry at the negative electrode. However, the conventional negative electrodes of PCECs, such as BaZr0.8−xCexY0.2O3-δ-Ni or BaZr0.8−xCexY0.1Yb0.1O3-δ-Ni, cannot reduce CO2 to either CH4 or CO with a selectivity of >99 %, leading to the production of a CO and CH4 mixture. Herein, an oxide-supported in-situ exsolved Ni-Fe alloyed nanoparticle electrocatalyst, Sr2Fe1.4Mo0.5O6-δ-Ni0.175 (SFM-Ni0.175), is first employed as the negative electrode of PCECs. The PCECs equipped with this new negative electrode selectively favor the CO2-to-CO conversion. A selectivity of ~100 % toward CO has been demonstrated over a wide range of operating temperatures (400–600 °C) and applied potentials/current densities. The negative electrode demonstrated in this work fully suppresses the CH4 production. In situ diffuse reflectance infrared spectroscopy (DRIFTS) was performed to probe the CO2 reduction mechanisms over both SFM-Ni0.175 and the traditional negative electrode (BCZYYb7111 +Ni), which indicates SFM-Ni0.175 inhibits the formation of formate species, leading to selective production of CO. This work validates that PCECs equipped with the rationally designed negative electrode can selectively manufacture chemicals.