Highly durable, coking and sulfur tolerant, fuel-flexible protonic ceramic fuel cells.

Protonic ceramic fuel cells, like their higher-temperature solid-oxide fuel cell counterparts, can directly use both hydrogen and hydrocarbon fuels to produce electricity at potentially more than 50 per cent efficiency1,2. Most previous direct-hydrocarbon fuel cell research has focused on solid-oxide fuel cells based on oxygen-ion-conducting electrolytes, but carbon deposition (coking) and sulfur poisoning typically occur when such fuel cells are directly operated on hydrocarbon- and/or sulfur-containing fuels, resulting in severe performance degradation over time3-6. Despite studies suggesting good performance and anti-coking resistance in hydrocarbon-fuelled protonic ceramic fuel cells2,7,8, there have been no systematic studies of long-term durability. Here we present results from long-term testing of protonic ceramic fuel cells using a total of 11 different fuels (hydrogen, methane, domestic natural gas (with and without hydrogen sulfide), propane, n-butane, i-butane, iso-octane, methanol, ethanol and ammonia) at temperatures between 500 and 600 degrees Celsius. Several cells have been tested for over 6,000 hours, and we demonstrate excellent performance and exceptional durability (less than 1.5 per cent degradation per 1,000 hours in most cases) across all fuels without any modifications in the cell composition or architecture. Large fluctuations in temperature are tolerated, and coking is not observed even after thousands of hours of continuous operation. Finally, sulfur, a notorious poison for both low-temperature and high-temperature fuel cells, does not seem to affect the performance of protonic ceramic fuel cells when supplied at levels consistent with commercial fuels. The fuel flexibility and long-term durability demonstrated by the protonic ceramic fuel cell devices highlight the promise of this technology and its potential for commercial application.

Predictive Modeling of COVID-19 Intensive Care Unit Patient Flows and Nursing Complexity: A Monte Carlo Simulation Study.

This study aimed to develop a Monte Carlo simulation model to forecast the number of ICU beds needed for COVID-19 patients and the subsequent nursing complexity in a French teaching hospital during the first and second pandemic outbreaks. The model used patient data from March 2020 to September 2021, including age, sex, ICU length of stay, and number of patients on mechanical ventilation or extracorporeal membrane oxygenation. Nursing complexity was assessed using a simple scale with three levels based on patient status. The simulation was performed 1000 times to generate a scenario, and the mean outcome was compared with the observed outcome. The model also allowed for a 7-day forecast of ICU occupancy. The simulation output had a good fit with the actual data, with an R2 of 0.998 and a root mean square error of 0.22. The study demonstrated the usefulness of the Monte Carlo simulation model for predicting the demand for ICU beds and could help optimize resource allocation during a pandemic. The model's extrinsic validity was confirmed using open data from the French Public Health Authority. This study provides a valuable tool for healthcare systems to anticipate and manage surges in ICU demand during pandemics.

The effect of grain size on the hydration of BaZr0.9Y0.1O3-δ proton conductor studied by ambient pressure X-ray photoelectron spectroscopy.

Three BaZr0.9Y0.1O3-δ (BZY10) pellets were prepared using different sintering processes, resulting in samples with different grain sizes, from 0.3 to 5 microns. Ambient pressure X-ray photoelectron spectra were recorded in argon, steam and oxygen atmospheres (100 mTorr) in the 300-500 °C temperature range. Deconvolution of O 1s peaks reveals 4 distinct contributions: sub-surface lattice oxide, termination layer oxides, OH- and gas-phase steam in wet environments. The OH- contribution of the O 1s peak includes sub-surface incorporation of protonic defects in the lattice related to hydration as well as surface hydroxylation and molecular water adsorption. The OH- concentration increases with grain size and with decreasing the analysis depth. These results suggest that grain boundaries associated with the larger grains adsorbed water more effectively. Thus, larger grains, which increase proton conductivity in BZY10, may also enhance catalytic activity for carbonaceous fuel oxidation by facilitating increased hydration and surface carbon removal.

Location of deuterium sites at operating temperature from neutron diffraction of BaIn0.6Ti0.2Yb0.2O2.6-n(OH)2n, an electrolyte for proton-solid oxide fuel cells.

A fundamental understanding of the doping effect on the hydration mechanism and related proton diffusion pathways are keys to the progress of Proton-Solid Oxide Fuel Cell (H(+)-SOFC) technologies. Here, we elucidate the possible interplay between the crystal structure upon hydration and the conductivity properties in a promising perovskite type H(+)-SOFC electrolyte, BaIn0.6Yb0.2Ti0.2O2.6-n(OH)2n. Thermal X-ray and neutron diffractions, neutron time-of-flight scattering along with thermal gravimetric analysis reveal the structural features of BaIn0.6Ti0.2Yb0.2O2.6-n(OH)2n at fuel cell operating temperatures. Between 400-600 °C, BaIn0.6Yb0.2Ti0.2O2.6-n(OD)2n (n < 0.042) remains in a disordered perovskite structure with high anisotropies in the form of oblate spheroids for oxygen. At 400 °C, the presence of oxygen and proton static disorder is clearly established. Yet, the insertion of mobile protons in 24k sites does not induce long-range structural distortion while facilitating both inter- and intra-octahedral proton transfers via quasi-linear O-DO bonds, strong hydrogen bonding, and octahedral tilting. This experimental evidence reveals that the co-doping approach on Ba2In2O5 enhances greatly protonic conductivity levels by enabling a continuous proton diffusion pathway through BaIn0.6Yb0.2Ti0.2O2.6-n(OH)2n. These new insights into the doping effect on the proton-transfer mechanism offer new perspectives for the development of H(+)-SOFC electrolyte materials.

The formation mechanism of fluorescent metal complexes at the Li(x)Ni(0.5)Mn(1.5)O(4-δ)/carbonate ester electrolyte interface.

Electrochemical oxidation of carbonate esters at the Li(x)Ni(0.5)Mn(1.5)O(4-δ)/electrolyte interface results in Ni/Mn dissolution and surface film formation, which negatively affect the electrochemical performance of Li-ion batteries. Ex situ X-ray absorption (XRF/XANES), Raman, and fluorescence spectroscopy, along with imaging of Li(x)Ni(0.5)Mn(1.5)O(4-δ) positive and graphite negative electrodes from tested Li-ion batteries, reveal the formation of a variety of Mn(II/III) and Ni(II) complexes with ß-diketonate ligands. These metal complexes, which are generated upon anodic oxidation of ethyl and diethyl carbonates at Li(x)Ni(0.5)Mn(1.5)O(4-δ), form a surface film that partially dissolves in the electrolyte. The dissolved Mn(III) complexes are reduced to their Mn(II) analogues, which are incorporated into the solid electrolyte interphase surface layer at the graphite negative electrode. This work elucidates possible reaction pathways and evaluates their implications for Li(+) transport kinetics in Li-ion batteries.

Nanoscale Li, Na, and K ion-conducting polyphosphazenes by atomic layer deposition.

A key trailblazer in the development of thin-film solid-state electrolytes has been lithium phosphorous oxynitride (LiPON), the success of which has led to recent progress in thin-film ion conductors. Here we compare the structural, electrochemical, and processing parameters between previously published LiPON and NaPON ALD processes with a novel ALD process for the K analogue potassium phosphorous oxynitride (KPON). In each ALD process, alkali tert-butoxides and diethylphosphoramidate are used as precursors. To understand the ALD surface reactions, this work proposes a reaction mechanism determined by in-operando mass spectrometry for the LiPON process as key to understanding the characteristics of the APON (A = Li, Na, K) family. As expected, NaPON and LiPON share similar reaction mechanisms as their structures are strikingly similar. KPON, however, exhibits similar ALD process parameters but the resulting film composition is quite different, showing little nitrogen incorporation and more closely resembling a phosphate glass. Due to the profound difference in structure, KPON likely undergoes an entirely different reaction mechanism. This paper presents a comprehensive summary of ALD ion conducting APON films as well as a perspective that highlights the versatility of ALD chemistries as a tool for the development of novel thin film ion-conductors.

Atomic Layer Deposition of Sodium Phosphorus Oxynitride: A Conformal Solid-State Sodium-Ion Conductor.

The development of novel materials that are compatible with nanostructured architectures is required to meet the demands of next-generation energy-storage technologies. Atomic layer deposition (ALD) allows for the precise synthesis of new materials that can conformally coat complex 3D structures. In this work, we demonstrate a thermal ALD process for sodium phosphorus oxynitride (NaPON), a thin-film solid-state electrolyte (SSE), for sodium-ion batteries (SIBs). NaPON is analogous to the commonly used lithium phosphorus oxynitride SSE in lithium-ion batteries. The ALD process produces a conformal film with a stoichiometry of Na4PO3N, corresponding to a sodium polyphosphazene structure. The electrochemical properties of NaPON are characterized to evaluate its potential in SIBs. The NaPON film exhibited a high ionic conductivity of 1.0 × 10-7 S/cm at 25 °C and up to 2.5 × 10-6 S/cm at 80 °C, with an activation energy of 0.53 eV. In addition, the ionic conductivity is comparable and even higher than the ionic conductivities of ALD-fabricated Li+ conductors. This promising result makes NaPON a viable SSE or passivation layer in solid-state SIBs.

Assessing Substitution Effects on Surface Chemistry by in Situ Ambient Pressure X-ray Photoelectron Spectroscopy on Perovskite Thin Films, BaCe xZr0.9- xY0.1O2.95 ( x = 0; 0.2; 0.9).

Performance of proton-solid oxide fuel cells (H+-SOFC) is governed by ion transport through solid/gas interfaces. Major breakthroughs are then intrinsically linked to a detailed understanding of how parameters tailoring bulk proton conductivity affect surface chemistry in situ, at an early stage. In this work, we studied proton and oxygen transport at the interface between H+-SOFC electrolyte BaCe xZr0.9- xY0.1O2.95 ( x = 0; 0.2; 0.9) thin films and the gas (100 mTorr of H2O and O2) by using synchrotron-based ambient pressure X-ray photoelectron spectroscopy at operating temperature (>400 °C). We developed highly textured BaCe xZr0.9- xY0.1O2.95 epitaxial thin films, which exhibit high level of in-plane proton conductivity, that is, up to 0.08 S cm-1 at 500 °C for x = 0.9. Upon applying 100 mTorr water partial pressure above 300 °C, major changes are observed only in the O 1s and Y 3d core level spectra, with a clear Zr/Ce ratio dependency. OH- formation is favored by Ce content while initiated near Y. Hydration is also associated with surface secondary phase growth comprising oxygen-under-coordinated yttrium and/or yttrium hydroxide. With BaCe0.2Zr0.7Y0.1O2.95, high levels of ionic conductivities and chemical stability are obtained as a result of the optimized surface reaction kinetics, with low activation energy barrier for proton transport while restraining formation of OH-/SO42- adsorb species.

A study of room-temperature LixMn1.5Ni0.5O4 solid solutions.

Understanding the kinetic implication of solid-solution vs. biphasic reaction pathways is critical for the development of advanced intercalation electrode materials. Yet this has been a long-standing challenge in materials science due to the elusive metastable nature of solid solution phases. The present study reports the synthesis, isolation, and characterization of room-temperature LixMn1.5Ni0.5O4 solid solutions. In situ XRD studies performed on pristine and chemically-delithiated, micron-sized single crystals reveal the thermal behavior of LixMn1.5Ni0.5O4 (0 ≤ x ≤ 1) cathode material consisting of three cubic phases: LiMn1.5Ni0.5O4 (Phase I), Li0.5Mn1.5Ni0.5O4 (Phase II) and Mn1.5Ni0.5O4 (Phase III). A phase diagram capturing the structural changes as functions of both temperature and Li content was established. The work not only demonstrates the possibility of synthesizing alternative electrode materials that are metastable in nature, but also enables in-depth evaluation on the physical, electrochemical and kinetic properties of transient intermediate phases and their role in battery electrode performance.

Interrelationships among Grain Size, Surface Composition, Air Stability, and Interfacial Resistance of Al-Substituted Li7La3Zr2O12 Solid Electrolytes.

The interfacial resistances of symmetrical lithium cells containing Al-substituted Li7La3Zr2O12 (LLZO) solid electrolytes are sensitive to their microstructures and histories of exposure to air. Air exposure of LLZO samples with large grain sizes (∼150 µm) results in dramatically increased interfacial impedances in cells containing them, compared to those with pristine large-grained samples. In contrast, a much smaller difference is seen between cells with small-grained (∼20 µm) pristine and air-exposed LLZO samples. A combination of soft X-ray absorption (sXAS) and Raman spectroscopy, with probing depths ranging from nanometer to micrometer scales, revealed that the small-grained LLZO pellets are more air-stable than large-grained ones, forming far less surface Li2CO3 under both short- and long-term exposure conditions. Surface sensitive X-ray photoelectron spectroscopy (XPS) indicates that the better chemical stability of the small-grained LLZO is related to differences in the distribution of Al and Li at sample surfaces. Density functional theory calculations show that LLZO can react via two different pathways to form Li2CO3. The first, more rapid, pathway involves a reaction with moisture in air to form LiOH, which subsequently absorbs CO2 to form Li2CO3. The second, slower, pathway involves direct reaction with CO2 and is favored when surface lithium contents are lower, as with the small-grained samples. These observations have important implications for the operation of solid-state lithium batteries containing LLZO because the results suggest that the interfacial impedances of these devices is critically dependent upon specific characteristics of the solid electrolyte and how it is prepared.