Proton-conducting Ceramic Electrolytes Research Articles

High-Temperature Mechanical–Conductive Behaviors of Proton-Conducting Ceramic Electrolytes in Solid Oxide Fuel Cells

Proton-conducting solid oxide fuel cells (P-SOFCs) are widely studied for their lower working temperatures than oxygen-ion-conducting SOFCs (O-SOFCs). Due to the elevated preparation and operation temperatures varying from 500 °C to 1500 °C, high mechanical stresses can be developed in the electrolytes of SOFCs. The stresses will in turn impact the electrical conductivities, which is often omitted in current studies. In this work, the mechanical–conductive behaviors of Y-doped BaZrO3 (BZY) electrolytes for P-SOFCs under high temperatures are studied through molecular dynamics modeling. The Young’s moduli of BZY in fully hydrated and non-hydrated states are calculated with different Y-doping concentrations and at different temperatures. It is shown that Y doping, oxygen vacancies, and protonic point defects all lead to a decrease in the Young’s moduli of BZY at 773 K. The variations in the conductivities of BZY are then investigated by calculating the diffusion rates of protons in BZY at different triaxial, biaxial, and uniaxial strains from 673 K to 873 K. In all cases, the diffusion rate present a trend of first increasing and then decreasing from compression state to tension state. The variations in elementary affecting factors of proton diffusion, including hydroxide rotation, proton transfer, proton trapping, and proton distribution, are then analyzed in detail under different strains. It is concluded that the influences of strains on these factors collectively determine the changes in proton conductivity.

Effect of NiO Addition on the Sintering and Electrochemical Properties of BaCe0.55Zr0.35Y0.1O3-δ Proton-Conducting Ceramic Electrolyte.

Proton ceramic fuel cells offer numerous advantages compared with conventional fuel cells. However, the practical implementation of these cells is hindered by the poor sintering activity of the electrolyte. Despite extensive research efforts to improve the sintering activity of BCZY, the systematic exploration of the utilization of NiO as a sintering additive remains insufficient. In this study, we developed a novel BaCe0.55Zr0.35Y0.1O3-δ (BCZY) electrolyte and systematically investigated the impact of adding different amounts of NiO on the sintering activity and electrochemical performance of BCZY. XRD results demonstrate that pure-phase BCZY can be obtained by sintering the material synthesized via solid-state reaction at 1400 °C for 10 h. SEM analysis revealed that the addition of NiO has positive effects on the densification and grain growth of BCZY, while significantly reducing the sintering temperature required for densification. Nearly fully densified BCZY ceramics can be obtained by adding 0.5 wt.% NiO and annealing at 1350 °C for 5 h. The addition of NiO exhibits positive effects on the densification and grain growth of BCZY, significantly reducing the sintering temperature required for densification. An anode-supported full cell using BCZY with 0.5 wt.% NiO as the electrolyte reveals a maximum power density of 690 mW cm-2 and an ohmic resistance of 0.189 Ω cm2 at 650 °C. Within 100 h of long-term testing, the recorded current density remained relatively stable, demonstrating excellent electrochemical performance.

(Digital Presentation) Iron-Based Electrode Structures for Ammonia Electrosynthesis Cells with Proton-Conducting Ceramic Electrolytes

Ammonia electrosynthesis is considered promising for the production of ammonia as an energy carrier, as the process could provide greater flexibility and compatibility to the fluctuations of renewable energy than the industrial Haber-Bosch process. One approach for enhancing the ammonia formation rate is the electrochemical promotion of catalysis (EPOC) [1], in which a non-faradaic acceleration of ammonia synthesis is observed; however, much of the mechanism remains unclear. Further mechanistic insight would aid in designing better electrode structures that are suited for efficient ammonia electrosynthesis. In this presentation, we explore the mechanism underlying the electrochemical promotion of ammonia synthesis, using electrochemical cells with iron-based cathodes on a proton-conducting BaCe0.9Y0.1O3 (BCY) electrolyte.Previously, our group reported that the ammonia formation rate of a cathodically polarized cell can be enhanced by adding H2 to the cathode gas feed (commonly pure N2) [2, 3]. Further kinetic and isotopic analysis using deuterium showed that the primary hydrogen source for the ammonia produced was the gaseous hydrogen feed, rather than the protons conducted via the electrolyte [4]. Cells with a porous pure Fe cathode resulted in higher ammonia formation rates than those with a porous 10 wt.% Fe-BCY cathode, suggesting that the pure Fe surfaces near the cathode-electrolyte interface, as opposed to the triple phase boundaries, are active for ammonia electrosynthesis [3]. However, the 10 wt.% Fe-BCY cathode, fabricated by the impregnation method, was thought to be limited by lack of Fe network formation needed for electron conduction.In this study, we fabricated a cermet cathode with the composition 56 wt.% Fe-BCY, aiming for Fe and BCY to form separate networks for electron and proton conduction, respectively. Electrochemical cells of the configurations Pt|BCY|Fe and Pt|BCY|Fe-BCY [Fig. 1a], with similar Fe mass (0.5 and 0.4 mg) were compared. Ammonia synthesis was conducted in a single-chamber reactor at 500-600˚C with a 50% H2/50% N2 feed. The gaseous ammonia produced was captured by bubbling into a dilute H2SO4 solution and quantified via high-performance liquid chromatography.Using the pure Fe electrode, an ammonia formation rate of 1.3 × 10-8 mol s-1 cm-2 (26 mmol gFe -1 h-1) was obtained at 600˚C and -1 V [Fig. 1b]. This corresponds to an almost 5-fold increase in ammonia formation compared to the catalytic reaction at 0 V. In contrast, a lower ammonia formation rate of 7.0 × 10-9 mol s-1 cm-2 (17 mmol gFe -1 h-1) was obtained using the Fe-BCY electrode at the same conditions. Despite the cermet electrode having a slightly higher current density, and despite the comparable iron loading on the two cells, the pure Fe cell still resulted in a faster ammonia formation rate per electrode area and per iron mass. As the cermet electrode is expected to have a significantly longer triple phase boundary length, from the comparison of these two electrochemical cells, the triple phase boundaries do not appear to be the primary active sites. We further analyze the roles of the bulk Fe surfaces and the Fe/BCY triple phase boundaries, by examining the effect of the electrode thickness and by post-experiment cross-sectional electron microscopy approaches.AcknowledgementsThis work was supported by JSPS KAKENHI Grant Number JP21H04938.

Iron-Based Electrode Structures for Ammonia Electrosynthesis Cells with Proton-Conducting Ceramic Electrolytes

Ammonia electrosynthesis was conducted using proton-conducting ceramic electrolysis cells in a single chamber supplied with mixed N2 and H2, to determine the active electrode regions for the electrochemical promotion of catalysis (EPOC). Cells with Fe-based cathodes of either a metal, cermet, or mixed ionic-electronic conductor (MIEC) structure were compared, to assess whether the triple-phase boundaries (TPBs) or the Fe catalyst surfaces are more effective for ammonia synthesis. Upon cathodic polarization at 600˚C, high ammonia formation rates on the order of 10−8 mol s−1 cm−2 were obtained with both Fe metal and Fe-BaZr0.8Y0.2O3 (Fe-BZY) cermet cathodes. Comparisons of the three electrode structures suggest that when H2 is also supplied to the cathode, ammonia formation occurring on bulk Fe surfaces leads to a greater promotional effect than that at TPBs. There also remains a possibility that the interfacial layer formed at the cathode-electrolyte interface due to cation interdiffusion aids ammonia formation.

Redox-stable composite electrodes for CH4 conversion reactors based on proton ceramic electrochemical cells

Electrochemical reactors based on proton-conducting ceramic electrolytes show a great potential in the conversion of hydrocarbons by enabling the intensification via the in-situ extraction of the H2 produced. However, non-oxidative operation conditions lead to the progressive coke formation on the catalyst and electrodes and thus, an oxidative regeneration cycle is required to restore the catalyst activity. Consequently, newly redox-stable electrodes are required to enable operation under both non-oxidative H2-extraction and coke-oxidation conditions. Here, four composite materials were investigated as redox-stable electrode backbones for their integration in proton-conducting cells, composed by the proton conductor BaCe0.2Zr0.7Y0.1O3-δ (BCZY27) and La0.85Sr0.15FeO3 (LSF8515), La0.5Sr0.5FeO3 (LSF55), La0.84Sr0.16Cr0.5Mn0.5O3 (LSCM) or La0.8Sr0.2MnO3 (LSM). Chemical compatibility with the electrolyte and electrochemical performance were characterized in the range 500–800 °C. LSCM/BCZY27 and LSM/BCZY27 showed the best performance. The electrode activity was boosted by catalytically activating with Pt and CeO2 nanoparticles while exhibiting outstanding stability upon redox cycling. LSM/BCZY27+Pt/CeO2 showed the lowest polarization resistance, i.e., achieving 0.7 Ω cm2 at 700 °C in 10% CH4 and 9% H2 and 0.14 Ω cm2 in air, revealing a high potential as redox-stable electrode for non-oxidative hydrocarbon conversion in electrochemical reactors.

Accelerated kinetics of hydrogen oxidation reaction on the Ni anode coupled with BaZr0.9Y0.1O3-δ proton-conducting ceramic electrolyte via tuning the electrolyte surface chemistry

Owing to the promise of proton mobility in solids, proton ceramic fuel cells (PCFCs) have demonstrated their great potential for operating at the low temperature range of 400-600˚C. For speeding up electrode reactions in PCFCs, the kinetics of the hydrogen oxidation reaction (HOR) on the Ni anode coupled with BaZr0.9Y0.1O3-δ (BZY10) proton-conducting ceramic electrolyte (abbreviated as Ni/BZY10) was investigated in correlation to the electrolyte surface chemistry. It was found that thermal annealing treatments are an effective approach to tune the surface chemistry of BZY10 (ABO3 perovskite structure) electrolytes, resulting in progressively Ba segregation toward the outer surface and enriched Y cations in B-site at subsurface. As the post-annealing temperature of BZY10 electrolytes increase from 600˚C to 1500˚C, the polarization resistance for the corresponding BZY10-based half cells decreases by a factor of 3 and 6 at the testing condition of open circuit potential and anodic overpotential, respectively. Considering a core-space-charge layer model at the Ni/BZY10 interface, the segregation of net charged Y cations (YZr') at the subsurface can partially counterbalance the positive electric potential induced by accumulation of protons in the outer surface, led to a reduced electrical potential and thus the accelerated HOR kinetics on the Ni/BZY10.

A comparative investigation on protonic ceramic fuel cell electrolytes BaZr0.8Y0.2O3-δ and BaZr0.1Ce0.7Y0.2O3-δ with NiO as sintering aid

Solid oxide fuel cells based on proton-conducting ceramic electrolytes, i.e., protonic ceramic fuel cells (PCFCs), are promising in operating at intermediate to low temperature. BaZr0.8Y0.2O3-δ (BZY) and BaZr0.1Ce0.7Y0.2O3-δ (BZCY) are two typical electrolyte materials for PCFCs. However, there is still a lack of basis for making a choice between the two materials. In this paper, we present a comparison investigation on practical BZY and BZCY electrolytes with NiO of 2 mol.% as sintering aid. Their crystal structure, sinterability, microstructure, and electrical conductivity in humid air and hydrogen (3% H2O) are measured and analyzed. Anode-supported PCFCs based on the two electrolyte materials are prepared and their electrochemical performances are tested and analyzed in association with an examination on their microstructure. The results show that both materials can be densified after sintered with NiO aid at 1400 °C for 6h. Ni is doped into the interstitial of BZY while it occupies the B site of perovskite lattice of BZCY. The sintered BZY has small grains and many grain boundaries while BZCY has large grains and much fewer grain boundaries, resulting in lower conductivity of BZY than that of BZCY. A PCFC with BZY electrolyte gives a peak power density of 360 mW cm−2 at 700 °C, while this value for a PCFC with BZCY is 855 mW cm−2. Although the performances of BZCY seems much better than those of BZY, a stability test in 10% CO2-containing Ar at 650 °C shows BZY is stable while BZCY reacts with CO2 to form BaCO3 and CeO2.

Accelerated Kinetics of Hydrogen Oxidation Reaction on the Ni Anode Coupled with Bazr0.9y0.1o3-Δ Proton-Conducting Ceramic Electrolyte Via Tuning the Electrolyte Surface Chemistry

Accelerated Kinetics of Hydrogen Oxidation Reaction on the Ni Anode Coupled with Bazr0.9y0.1o3-Δ Proton-Conducting Ceramic Electrolyte Via Tuning the Electrolyte Surface Chemistry

Chemically Inert Hydrocarbon-Based Slurries for Rapid Laser Sintering of Thin Proton-Conducting Ceramics

The process of rapid laser sintering of thin BaZrO3–BaCeO3-based proton-conducting electrolytes is being developed for easy fabrication of ceramic fuel cells and electrolyzers. However, cracks on the electrolytes caused by volume change due to chemical reactions between the basic ceramic constituents and the polar solvents during wet processing has been problematic. In order to address this issue, the use of chemically inert saturated-hydrocarbon-based slurries comprised of hexadecane, polybutene, and a long-chain saturated fatty acid were investigated in this work. By optimizing slurry composition and laser sintering conditions, a 20 mm long, 4 mm wide, 13.5-μm-thick and 97%-dense BaCe0.7Zr0.1Y0.07Sm0.13O3-d membrane showing proton conductivity on the order of 10−4 S•cm−1 at 600 °C was successfully prepared in just three seconds by laser sintering. The use of saturated-hydrocarbon-based slurries will facilitate wet processing and rapid laser sintering of proton-conducting ceramic electrolytes.

Techno-Economic Analysis of CO2-to-Fuel with a Proton-Conducting Ceramic Sabatier Electrolyzer

As intermittent renewable electricity generation achieves higher market penetration, the need for robust storage and dispatch capabilities become more pronounced. In this report, we present a techno-economic analysis based around a levelized cost of storage (LCOS) calculation for a Sabatier Electrolyzer to illustrate the value proposition of electrolyzer technology. The Sabatier Electrolyzer is illustrated in Figure 1A; the CO2 feed to the fuel electrode is upgraded to CH4 through heterogeneous catalysis with hydrogen. The hydrogen is produced through water electrolysis at the steam electrode. When driven by surplus electricity, the Sabatier Electrolyzer presents an energy-storage option with CO2-to-fuels.The electrolyzer features a proton-conducting ceramic electrolyte (BaCe0.4Zr0.4Y0.1Yb0.1O3-d) that has shown encouraging performance under fuel-cell and H2O-electrolysis applications. The Sabatier chemistry (CO2 + 4 H2 = CH4 + 2 H2O) occurs within the porous fuel electrode, a nickel-ceramic composite, where protons emerging from the ceramic phase react with CO2 or recombine to form H2 over the nickel phase. The exothermic Sabatier reaction can be balanced by the endothermicity of H2O electrolysis improving plant-level thermal balance and higher efficiency.This report explores the economic potential of a commercial-scale Sabatier electrolyzer plant from the perspective of levelized cost of storage (LCOS). This LCOS is based on similar analyses conducted for lithium-ion batteries, flow batteries, flywheels, and pumped-hydro facilities. The model combines plant-level round-trip efficiency (RTE), overnight capital costs, variable operations and maintenance (O&M) costs, and charging costs into a time value of money (TVM) financial model. The model is exercised to estimate the lifetime cost of energy storage for the plant.The protonic-ceramic electrolyzer presents a perhaps unusual materials set. While protonic-ceramic fuel cells have demonstrated high performance and encouraging durability at the lab scale, the materials have also shown undesirable electronic conduction that can substantially decrease electrolysis efficiency, boosting costs. The electrochemical model captures the substantial impact of protonic-ceramic electrochemical performance on LCOS, and is validated by lab-scale experimental measurements of protonic-ceramic Sabatier Electrolyzer cells. Results were scaled to yield the commercial-scale LCOS.Sensitivity analyses demonstrate the primary cost drivers behind the commercial-scale Sabatier Electrolyzer plant. Key cost drivers include Faradaic efficiency, methane yield, utility cost of electricity, and cost of sequestered CO2. Depending on operational parameters, the LCOS of the commercial-scale Sabatier Electrolyzer plant ranges from $4,319 down to $348 per MWh of storage potential. Figure 1

Numerical Simulation of OXIDE-ION Blocking Effect in Hydrogen Permeable Metal-Supported Fuel Cell

Protonic ceramic fuel cells (PCFCs) have been drawing considerable attentions because of their potential for high-power operating at intermediate temperature (IT), 400–600°C, which is a salient issue for their practical implementation. BaZr0.1Ce0.7Y0.2O3, popular proton-conducting ceramic electrolyte material, has notably high conductivity of 9 × 10−3 S cm−1 at 500°C [1], but vast majority of power outputs in current PCFC literature still lag far behind 1.0 W cm−2 at the IT regime. In general, PCFCs have structure of porous anode support composed proton-conducting ceramic electrolyte and metallic Ni. Meanwhile, a hydrogen membrane fuel cell (HMFC), which consist of a dense hydrogen-permeable metal anode and kindred electrolyte material, has achieved extraordinary performances of 1.4 W cm−2 at 600°C [2]. This is higher than any others ever reported to the best of our knowledge. However, what give rise to such high performance is obscure. Here, we simulated effect of oxide-ion blocking at anode/electrolyte on defect profile in HMFC and compared them with those of PCFCs to elucidate origins of the high performance.The one-dimensional concentration profiles of three charged defect carriers: oxygen vacancy, proton, and oxygen hole at steady state were computed based on Nernst–Planck–Poisson model with defect thermodynamics of BaZr0.8Y0.2O3 [3]. In PCFC, membrane is equilibrated with O2, H2, and H2O gases. In HMFC, however, boundary conditions at the anodic surface are unknown since the surface is sealed by dense metal anode. We made an assumption that a flux of oxygen vacancy is kept at 0 inside the electrolyte membrane of HMFC [4].Simulations confirm that oxide-ion blocking at an electrolyte/anode interface greatly modifies the defects’ distribution across the membrane. Positively charged oxygen vacancies are depressed near electrolyte/anode interface owing to the oxide-ion blocking, and thus, protonic defects are alternatively accumulated near the regions for the charge neutrality preservation, which results in the enhancement of local proton conductivity (Attached image). Accordingly, the superior performance of HMFC to PCFC is attributable the proton pumping by utilizing the oxygen chemical potentials.

Studying Proton Conducting Ceramic Electrolyte Stability with in Situ Raman Spectroscopy

Ceramic-based proton conducting fuel cells (PCFCs) are attractive devices for directly converting chemical energy to electrical energy. Like conventional solid oxide fuel cells (SOFCs), PCFCs are fuel flexible and efficient. Because PCFC electrolytes conduct protons rather than oxides, these devices can function between 400˚C and 600˚C, temperatures that are much lower than the ≥700˚C required for SOFC operation. PCFC technology remains relatively new, however, meaning that fundamental questions about electrochemical redox mechanisms, material compatibility and device resilience must be answered before PCFCs become a viable technology for commercial development.In this work, we use in situ vibrational Raman spectroscopy and ex situ XPS to examine the chemical stability of yttria-stabilized barium zirconate (BZY) and ceria doped BZY (BZCY) – both common PCFC electrolytes – as a function of temperature and chemical stress. In particular, in situ Raman data show that electrolyte surface and near surface composition is sensitive to steam in reducing environments with new features appearing in vibrational spectra. (The reducing environment consisted of 25% H2 in Ar; all humidified conditions included 3% H2O from running the incident gas(es) through a room temperature bubbler.) Spectral changes indicate that that the electrolyte structure and/or composition is changing on the electrolyte surface and in the near surface region (as defined by the penetration depth of the incident Raman excitation light). These changes are reversible and vibrational spectra return to their original appearance when steam is removed from the reducing atmosphere. Two important points to note are 1) new spectral features only appear within a limited temperature window between 300˚C and 450˚C and 2) new spectral features do not appear when the ambient atmosphere is inert (Ar), inert with steam (Ar with 3% H2O), or simply a reducing atmosphere (H2 in Ar). While spectral changes are reversible, the steam-altered electrolytes can be isolated by quickly cooling materials showing extraneous vibrational features back to room temperature under a humidified environment. This ability allows for additional ex situ analysis using conventional surface science methods. XPS data suggest that humidified H2 leads to enhanced Ba content on the electrolyte surface raising interesting questions about the role(s) played by surface segregation and secondary phase formation on the catalytic activity and charge transport properties of PCFC electrolytes.

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.

A 5 × 5 cm2 protonic ceramic fuel cell with a power density of 1.3 W cm–2 at 600 °C

In spite of various advantages of protonic ceramic fuel cells over conventional fuel cells, distinct scepticism currently remains about their applicability because of lower-than-predicted performance and difficulty with scale-up. These challenges mainly stem from the refractory nature of proton-conducting ceramic electrolytes and the low chemical stability of these materials during the sintering process. Here, we present the fabrication of a physically thin, structurally dense and chemically homogeneous electrolyte, BaCe0.55Zr0.3Y0.15O3-δ (BCZY3), through a facile anode-assisted densification of the electrolyte on a structurally and compositionally uniform anode support, which resulted in breakthroughs in performance and scalability. A BCZY3-based protonic ceramic fuel cell with a size of 5 × 5 cm2 exhibits an area-specific ohmic resistance of 0.09 Ω cm2 and delivers a power as high as 20.8 W per single cell at 600 °C. Protonic ceramic fuel cells (PCFCs) operate at lower temperatures than solid oxide fuel cells but suffer from lower performances, especially during scale-up. Here, the authors report a 25 cm2 PCFC based on a BaCe0.55Zr0.3Y0.15O3–δ electrolyte that displays a record-high power density of 20.8 W at 600 °C.

Energy efficiency of ionic transport through proton conducting ceramic electrolytes for energy conversion applications

In this study, the efficiency of ionic transport through proton-conducting ceramic electrolytes for energy conversion applications was discussed.

Electrochemical Ammonia Synthesis Via Nitrogen Reduction Under Mild Conditions

Ammonia is produced commercially via the Haber-Bosch (HB) process, which produced 144 million tonnes of ammonia 2014, approximately 88% of which is used in the fertilizer industry [1,2]. However the HB process requires very high temperatures and pressures and as a result it is only be done in large plants which consume large amounts of power and generate large quantities of CO2 from the production of the hydrogen used in the HB process[1,2]. It is estimated that the HB process accounts for nearly 1% of annual global power consumption [3]. Due to the sheer scale of the HB process, distribution from the point of production to the point of use becomes an additional carbon and energy burden. Alternative methods of manufacturing ammonia that enable small scale, distributed generation at the point of use using renewable energy and sustainable feedstocks could have a great impact on global CO2 emissions. Electrochemical synthesis of ammonia at low temperatures and pressures is one promising solution that has recently begun to gain more attention as a viable method of sustainable, on-site generation of NH3. Several electrochemical approaches to NH3 synthesis have been reported in the literature with varying success, included high temperature proton-conducting ceramic electrolytes, molten hydroxides, PEM membrane and AEM membrane systems and more [4,5,6]. Most low temperature and low pressure production rates range between 10-12 and 10-8 mol NH3 cm-2 s-1 with Faradaic efficiencies that are typically very low on the order of 5% due to the competing hydrogen evolution reaction (HER) [4,5,6]. Cathode catalysts that enable increased NH3 production rates while suppressing the HER are critical to realizing the benefits of sustainable electrochemical synthesis of ammonia. As a result catalysts that adsorb nitrogen more strongly than hydrogen must be investigated for an efficient electrochemical synthesis. By utilizing alkaline media, non-platinum group metals (PGMs) may become feasible catalysts, thus lowering costs and use of very limited global supply of PGM. The electrochemical synthesis of ammonia was run under mild temperatures and pressures in alkaline media according to the following reactions: (1) (2) where reactions (1) and (2) take place at the cathode and anode of the electrochemical cell, respectively. The overall reaction leads to the synthesis of ammonia with a theoretical cell voltage of 0.059 V, according to: (3) Humidified nitrogen is flowed over a Pt/Ir electrode where it is reduced to ammonia (Eq. 1), and hydroxide ions are transported through a gel electrolyte to the anode where they are oxidized hydrogen to produce water (Eq. 2). The major challenge associated with electrochemical production of ammonia is the competing HER which can occur at the cathode. In order to mitigate this issue we hypothesize that using a polymer based gel electrolyte to control the amount of water present in the system could allow us to limit the HER, thus increasing the efficiency of the reaction. We believe that by using this process we will be able to examine different catalysts for nitrogen reduction in order to find a catalyst where the HER is less dominant [7].

Fabrication of reducing atmosphere electrodes (fuel electrodes) by electroless plating of copper on BaZr0.9−xCexY0.1O3−δ – A proton-conducting ceramic

Copper appears to be an interesting fuel electrode material for proton-conducting ceramic electrolytes (such as BaZr0.9−xCexY0.1O3−δ) because it is stable at high temperatures in reducing and hydrocarbon-containing atmospheres. However, when deposited using organometallic Cu pastes/inks, these electrodes suffer from poor performance due to delamination issues and coating thickness (10–20 μm). Alternatively, electroless plating (ELP) is a method of depositing metal films – without utilizing electric power – that can achieve much thinner coatings than with pastes. In this work ELP of Cu was shown to be an alternative to Cu pastes for electrode fabrication on the non-electrically conductive, proton-conducting ceramic BaZr0.8Ce0.1Y0.1O3−δ. Pd, Ru, and Cu were investigated as activation catalysts, on which Cu was then plated. All three were found to produce thin electrodes (∼1 μm) with good electrode/electrolyte adhesion. Scanning electron microscopy coupled with energy dispersive x-ray spectroscopy, x-ray fluorescence and x-ray diffraction were used to characterize the Cu-based ELP electrodes. Additionally, the ELP process was shown to be transferable to tubular substrates without significant modification to the procedure.

Electrochemical moisture analysis by combining oxygen- and proton-conducting ceramic electrolytes

The fabrication and characterization of a new intermediate-temperature electrochemical cell for analyzing moisture concentrations in gas mixtures are discussed in the present investigation. The as-fabricated electrochemical cell consists of a diffusion barrier and two ceramic materials based on a yttria-stabilized zirconia (YSZ) electrolyte with unipolar oxygen ion conductivity and a Sr-doped lanthanum yttrate (La0.9Sr0.1YO3−δ, LSY) electrolyte with proton transport properties. The possibility of measuring humidity in a nitrogen atmosphere is demonstrated and the operational capability of the cell is evaluated. The original design of the proposed electrochemical cell opens new opportunities in electrochemical analysis and in the application of proton-conducting electrolytes, including the simultaneous measurement of the concentration and the mutual diffusion coefficient of water in gases.

Pulsed laser deposition of epitaxial MgO buffer layer for proton-conducting ceramic electrolytes

This work studies the deposition of epitaxial MgO thin films with thickness of 40nm deposited on bare Si (100) wafer using pulsed laser deposition (PLD), which can serve as a buffer layer for subsequent growth of textured Y-BaZrO3 with high proton-conductivity. The success of epitaxial deposition were achieved by careful preparation of Si substrate by pre-etching with HF solution, as well as by optimizing deposition parameters including oxygen partial pressure and substrate temperatures. Epitaxial (100) MgO film with cubic lattice structure and the lattice constant of 4.21Å were obtained, which showed highly lattice match with Y-BaZrO3 perovskite of 4.21Å.

Nanoporous palladium anode for direct ethanol solid oxide fuel cells with nanoscale proton-conducting ceramic electrolyte

Abstract In this work, we demonstrate the operation of micro-solid oxide fuel cells (μ-SOFCs) with nanoscale proton-conducting Y-BaZrO 3 (BZY) electrolyte to avoid the fuel crossover problem for direct ethanol fuel cells (DEFCs). The μ-SOFCs are operated with the direct utilisation of ethanol vapour as a fuel and Pd as anode at the temperature range of 300–400 °C. The nanoporous Pd anode is achieved by DC sputtering at high Ar pressure of 80 mTorr. The Pd-anode/BYZ-electrolyte/Pt-cathode cell show peak power densities of 72.4 mW/cm 2 using hydrogen and 15.3 mW/cm 2 using ethanol at 400 °C. No obvious carbon deposition is seen from XPS analysis after fuel cell test with ethanol fuel.