Proton Accumulation Modulated Surface Potential in Proton Conducting Ceramics Revealed by Near-Ambient Pressure X-ray Photoelectron Spectroscopy.

Proton conducting electrochemical cells (PCECs) are efficient and clean intermediate-temperature energy conversion devices. The proton concentration across the PCECs is often nonuniform, and characterizing the distribution of proton concentration can help to locate the position of rate-limiting reactions. However, the determination of the local proton concentration under operating conditions remains challenging.

Atomically synergistic Zn-Cr catalyst for iso-stoichiometric co-conversion of ethane and CO to ethylene and CO.

Developing atomically synergistic bifunctional catalysts relies on the creation of colocalized active atoms to facilitate distinct elementary steps in catalytic cycles. Herein, we show that the atomically-synergistic binuclear-site catalyst (ABC) consisting of [Formula: see text]-O-Cr on zeolite SSZ-13 displays unique catalytic properties for iso-stoichiometric co-conversion of ethane and CO. Ethylene selectivity and utilization of converted CO can reach 100 % and 99.

Stacking influence on the in-plane magnetic anisotropy in a 2D magnetic system.

The magnetization patterns on three atomic layers thick islands of Co on Ru(0001) are studied by spin-polarized low-energy electron microscopy (SPLEEM). In-plane magnetized micrometer wide triangular Co islands are grown on Ru(0001). They present two different orientations correlated with two different stacking sequences which differ only in the last layer position.

Observation of Potential-Induced Hydration on the Surface of Ceramic Proton Conductors Using Near-Ambient Pressure X-ray Photoelectron Spectroscopy.

Interactions of ceramic proton conductors with the environment under operating conditions play an essential role on material properties and device performance. It remains unclear how the chemical environment of material, as modulated by the operating condition, affects the proton conductivity. Combining near-ambient pressure X-ray photoelectron spectroscopy and impedance spectroscopy, we investigate the chemical environment changes of oxygen and the conductivity of BaZrYO under operating condition.

Defying Thermodynamics: Stabilization of Alane Within Covalent Triazine Frameworks for Reversible Hydrogen Storage.

The highly unfavorable thermodynamics of direct aluminum hydrogenation can be overcome by stabilizing alane within a nanoporous bipyridine-functionalized covalent triazine framework (AlH @CTF-bipyridine). This material and the counterpart AlH @CTF-biphenyl rapidly desorb H between 95 and 154 °C, with desorption complete at 250 °C. Sieverts measurements, Al MAS NMR and Al{ H} REDOR experiments, and computational spectroscopy reveal that AlH @CTF-bipyridine dehydrogenation is reversible at 60 °C under 700 bar hydrogen, >10 times lower pressure than that required to hydrogenate bulk aluminum.

Reversing the Irreversible: Thermodynamic Stabilization of LiAlH Nanoconfined Within a Nitrogen-Doped Carbon Host.

A general problem when designing functional nanomaterials for energy storage is the lack of control over the stability and reactivity of metastable phases. Using the high-capacity hydrogen storage candidate LiAlH as an exemplar, we demonstrate an alternative approach to the thermodynamic stabilization of metastable metal hydrides by coordination to nitrogen binding sites within the nanopores of N-doped CMK-3 carbon (NCMK-3). The resulting LiAlH@NCMK-3 material releases H at temperatures as low as 126 °C with full decomposition below 240 °C, bypassing the usual LiAlH intermediate observed in bulk.

Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH.

Solid-state metal hydrides are prime candidates to replace compressed hydrogen for fuel cell vehicles due to their high volumetric capacities. Sodium aluminum hydride has long been studied as an archetype for higher-capacity metal hydrides, with improved reversibility demonstrated through the addition of titanium catalysts; however, atomistic mechanisms for surface processes, including hydrogen desorption, are still uncertain. Here, operando and ex situ measurements from a suite of diagnostic tools probing multiple length scales are combined with ab initio simulations to provide a detailed and unbiased view of the evolution of the surface chemistry during hydrogen release.

Non-Faradaic Li Migration and Chemical Coordination across Solid-State Battery Interfaces.

Efficient and reversible charge transfer is essential to realizing high-performance solid-state batteries. Efforts to enhance charge transfer at critical electrode-electrolyte interfaces have proven successful, yet interfacial chemistry and its impact on cell function remains poorly understood. Using X-ray photoelectron spectroscopy combined with electrochemical techniques, we elucidate chemical coordination near the LiCoO-LIPON interface, providing experimental validation of space-charge separation.

Enhanced Kinetics of Electrochemical Hydrogen Uptake and Release by Palladium Powders Modified by Electrochemical Atomic Layer Deposition.

Electrochemical atomic layer deposition (E-ALD) is a method for the formation of nanofilms of materials, one atomic layer at a time. It uses the galvanic exchange of a less noble metal, deposited using underpotential deposition (UPD), to produce an atomic layer of a more noble element by reduction of its ions. This process is referred to as surface limited redox replacement and can be repeated in a cycle to grow thicker deposits.

Fabrication, Testing, and Simulation of All-Solid-State Three-Dimensional Li-Ion Batteries.

Demonstration of three-dimensional all-solid-state Li-ion batteries (3D SSLIBs) has been a long-standing goal for numerous researchers in the battery community interested in developing high power and high areal energy density storage solutions for a variety of applications. Ideally, the 3D geometry maximizes the volume of active material per unit area, while keeping its thickness small to allow for fast Li diffusion. In this paper, we describe experimental testing and simulation of 3D SSLIBs fabricated using materials and thin-film deposition methods compatible with semiconductor device processing.

Li-Ion Synaptic Transistor for Low Power Analog Computing.

Nonvolatile redox transistors (NVRTs) based upon Li-ion battery materials are demonstrated as memory elements for neuromorphic computer architectures with multi-level analog states, "write" linearity, low-voltage switching, and low power dissipation. Simulations of backpropagation using the device properties reach ideal classification accuracy. Physics-based simulations predict energy costs per "write" operation of <10 aJ when scaled to 200 nm × 200 nm.

Origin and Tunability of Unusually Large Surface Capacitance in Doped Cerium Oxide Studied by Ambient-Pressure X-Ray Photoelectron Spectroscopy.

The volumetric redox (chemical) capacitance of the surface of CeO2-δ films is quantified in situ to be 100-fold larger than the bulk values under catalytically relevant conditions. Sm addition slightly lowers the surface oxygen nonstoichiometry, but effects a 10-fold enhancement in surface chemical capacitance by mitigating defect interactions, highlighting the importance of differential nonstoichiometry for catalysis.

Current-induced transition from particle-by-particle to concurrent intercalation in phase-separating battery electrodes.

Many battery electrodes contain ensembles of nanoparticles that phase-separate on (de)intercalation. In such electrodes, the fraction of actively intercalating particles directly impacts cycle life: a vanishing population concentrates the current in a small number of particles, leading to current hotspots. Reports of the active particle population in the phase-separating electrode lithium iron phosphate (LiFePO4; LFP) vary widely, ranging from near 0% (particle-by-particle) to 100% (concurrent intercalation).

Fast vacancy-mediated oxygen ion incorporation across the ceria-gas electrochemical interface.

Electrochemical incorporation reactions are ubiquitous in energy storage and conversion devices based on mixed ionic and electronic conductors, such as lithium-ion batteries, solid-oxide fuel cells and water-splitting membranes. The two-way traffic of ions and electrons across the electrochemical interface, coupled with the bulk transport of mass and charge, has been challenging to understand. Here we report an investigation of the oxygen-ion incorporation pathway in CeO2-δ (ceria), one of the most recognized oxygen-deficient compounds, during hydrogen oxidation and water splitting.

Atomic-layer electroless deposition: a scalable approach to surface-modified metal powders.

Palladium has a number of important applications in energy and catalysis in which there is evidence that surface modification leads to enhanced properties. A strategy for preparing such materials is needed that combines the properties of (i) scalability (especially on high-surface-area substrates, e.g.

Tunable electrical conductivity in metal-organic framework thin-film devices.

We report a strategy for realizing tunable electrical conductivity in metal-organic frameworks (MOFs) in which the nanopores are infiltrated with redox-active, conjugated guest molecules. This approach is demonstrated using thin-film devices of the MOF Cu3(BTC)2 (also known as HKUST-1; BTC, benzene-1,3,5-tricarboxylic acid) infiltrated with the molecule 7,7,8,8-tetracyanoquinododimethane (TCNQ). Tunable, air-stable electrical conductivity over six orders of magnitude is achieved, with values as high as 7 siemens per meter.

Determination of the surface structure of CeO2(111) by low-energy electron diffraction.

We determine the atomic structure of the (111) surface of an epitaxial ceria film using low-energy electron diffraction (LEED). The 3-fold-symmetric LEED patterns are consistent with a bulk-like termination of the (111) surface. By comparing the experimental dependence of diffraction intensity on electron energy (LEED-I(V) data) with simulations of dynamic scattering from different surface structures, we find that the CeO2(111) surface is terminated by a plane of oxygen atoms.

Insight into magnetite's redox catalysis from observing surface morphology during oxidation.

We study how the (100) surface of magnetite undergoes oxidation by monitoring its morphology during exposure to oxygen at ~650 °C. Low-energy electron microscopy reveals that magnetite's surface steps advance continuously. This growth of Fe3O4 crystal occurs by the formation of bulk Fe vacancies.

Oxidation stages of Ni electrodes in solid oxide fuel cell environments.

Nickel is the most commonly used anode for solid-oxide fuel cells (SOFC) due to its fast kinetics and low price. A leading cause of degradation in Ni electrodes is oxidation. Here we use operando ambient-pressure X-ray photoelectron spectroscopy (XPS) to chemically characterize the Ni electrode of a fuel cell anode during oxidation in a H2/H2O atmosphere.

Intercalation pathway in many-particle LiFePO4 electrode revealed by nanoscale state-of-charge mapping.

The intercalation pathway of lithium iron phosphate (LFP) in the positive electrode of a lithium-ion battery was probed at the ∼40 nm length scale using oxidation-state-sensitive X-ray microscopy. Combined with morphological observations of the same exact locations using transmission electron microscopy, we quantified the local state-of-charge of approximately 450 individual LFP particles over nearly the entire thickness of the porous electrode. With the electrode charged to 50% state-of-charge in 0.

Electrochemical intermediate species and reaction pathway in H2 oxidation on solid electrolytes.

We use spatially resolved photoelectron spectroscopy performed in operando to identify the reaction intermediates of the hydrogen electro-oxidation reaction on yttria-stabilized zirconia (YSZ) electrolytes with Pt electrodes. We find that hydroxyl on the zirconia electrolyte is a reaction intermediate in the hydrogen oxidation reaction and that it participates in the rate-determining step. In contrast to the general wisdom, the limiting step does not involve the transfer of charge.

Measuring fundamental properties in operating solid oxide electrochemical cells by using in situ X-ray photoelectron spectroscopy.

Photoelectron spectroscopic measurements have the potential to provide detailed mechanistic insight by resolving chemical states, electrochemically active regions and local potentials or potential losses in operating solid oxide electrochemical cells (SOCs), such as fuel cells. However, high-vacuum requirements have limited X-ray photoelectron spectroscopy (XPS) analysis of electrochemical cells to ex situ investigations. Using a combination of ambient-pressure XPS and CeO(2-x)/YSZ/Pt single-chamber cells, we carry out in situ spectroscopy to probe oxidation states of all exposed surfaces in operational SOCs at 750 °C in 1 mbar reactant gases H(2) and H(2)O.

Note: Fixture for characterizing electrochemical devices in-operando in traditional vacuum systems.

We describe a fixture that allows electrochemical devices to be studied under electrical bias in the type of vacuum systems commonly used in surface science. Three spring-loaded probes provide independent contacts for device operation and the characterization in vacuum or under in situ conditions with reactive gases. We document the robustness of the electrical contacts over large temperature changes and their reliability for conventional electrochemical measurements such as impedance spectroscopy.

Measuring individual overpotentials in an operating solid-oxide electrochemical cell.

We use photo-electrons as a non-contact probe to measure local electrical potentials in a solid-oxide electrochemical cell. We characterize the cell in operando at near-ambient pressure using spatially-resolved X-ray photoemission spectroscopy. The overpotentials at the interfaces between the Ni and Pt electrodes and the yttria-stabilized zirconia (YSZ) electrolyte are directly measured.