Effect of Interfacial Electric Field on 2D Metal/Graphene Electrocatalysts for CO Reduction Reaction.

Understanding the influence of local electric fields on electrochemical reactions is crucial for designing highly selective electrocatalysts for CO reduction reactions (CORR). In this study, we provide a theoretical investigation of the effect of the local electric field induced by the negative-biased electrode and cations in the electrolyte on the energetics and reaction kinetics of CORR on 2D hybrid metal/graphene electrocatalysts. Our findings reveal that the electronic structures of the CO molecule undergo substantial modification, resulting in the increased adsorption energy of CO on metal/graphene structures, thus reducing the initial barrier of the CORR mechanism.

Electrocatalysts for Inorganic and Organic Waste Nitrogen Conversion.

Anthropogenic activities have disrupted the natural nitrogen cycle, increasing the level of nitrogen contaminants in water. Nitrogen contaminants are harmful to humans and the environment. This motivates research on advanced and decarbonized treatment technologies that are capable of removing or valorizing nitrogen waste found in water.

Monitoring Redox Processes in Lithium-Ion Batteries by Laboratory-Scale Operando X-ray Emission Spectroscopy.

Tracking changes in the chemical state of transition metals in alkali-ion batteries is crucial to understanding the redox chemistry during operation. X-ray absorption spectroscopy (XAS) is often used to follow the chemistry through observed changes in the chemical state and local atomic structure as a function of the state-of-charge (SoC) in batteries. In this study, we utilize an operando X-ray emission spectroscopy (XES) method to observe changes in the chemical state of active elements in batteries during operation.

2D Metal/Graphene and 2D Metal/Graphene/Metal Systems for Electrocatalytic Conversion of CO to Formic Acid.

Efficiently transforming CO into renewable energy sources is crucial for decarbonization efforts. Formic acid (HCOOH) holds great promise as a hydrogen storage compound due to its high hydrogen density, non-toxicity, and stability under ambient conditions. However, the electrochemical reduction of CO (CO RR) on conventional carbon black-supported metal catalysts faces challenges such as low stability through dissolution and agglomeration, as well as suffering from high overpotentials and the necessity to overcome the competitive hydrogen evolution reaction (HER).

Catalysis Sans Catalyst Loss: The Origins of Prolonged Stability of Graphene-Metal-Graphene Sandwich Architecture for Oxygen Reduction Reactions.

Over the past decades, the design of active catalysts has been the subject of intense research efforts. However, there has been significantly less deliberate emphasis on rationally designing a catalyst system with a prolonged stability. A major obstacle comes from the ambiguity behind how catalyst degrades.

Iron Phosphide Confined in Carbon Nanofibers as a Free-Standing Flexible Anode for High-Performance Lithium-Ion Batteries.

Iron phosphide with high specific capacity has emerged as an appealing candidate for next-generation lithium-ion battery anodes. However, iron phosphide could undergo conversion reactions and generally suffer from a rapid capacity degradation upon cycling due to its structure pulverization. Chemomechanical breakdown of iron phosphide due to its rigidity has been a challenge to fully realizing its electrochemical performance.

Atomic Structure and Dynamics of Epitaxial Platinum Bilayers on Graphene.

Platinum atomic layers grown on graphene were investigated by atomic resolution transmission electron microscopy (TEM). These TEM images reveal the epitaxial relationship between the atomically thin platinum layers and graphene, with two optimal epitaxies observed. The energetics of these epitaxies influences the grain structure of the platinum film, facilitating grain growth in-plane rotation and assimilation of neighbor grains, rather than grain coarsening from the movement of grain boundaries.

Cobalt phosphide embedded in a graphene nanosheet network as a high-performance anode for Li-ion batteries.

Cobalt phosphide (CoP) is a potential alternative to Li-ion battery (LIB) anodes due to its high specific capacity. However, there remain challenges, including low rate capability and rapid capacity degradation, because of its structural pulverization and poor electrical conductivity. Here, we demonstrate an effective strategy to enhance CoP-based anodes by developing a CoP/graphene nanocomposite.

Sandwiched Graphene Interdiffusion Barrier for Preserving Au@Pt Atomically Thin Core@Shell Structure and the Resulting Oxygen Reduction Reaction Catalytic Activity.

The concept of a core-shell metallic structures, with a few atomic layers of the "shell" metal delineated from the "core" metal with atomic sharpness opens the door to a multitude of surface-driven materials properties that can be tuned. However, in practice, such architectures are difficult to retain due to the entropic cost of a segregated near-surface architecture, and the core and surface atoms inevitably mix through interdiffusion over time. We present here a systematic study of interdiffusion in a Pt on Au core-shell architecture and the role of an interrupting single layer of graphene sandwiched between them.

Defect engineering in 1D Ti-W oxide nanotube arrays and their correlated photoelectrochemical performance.

Understanding the nature of interfacial defects of materials is a critical undertaking for the design of high-performance hybrid electrodes for photocatalysis applications. Theoretical and computational endeavors to achieve this have touched boundaries far ahead of their experimental counterparts. However, to achieve any industrial benefit out of such studies, experimental validation needs to be systematically undertaken.

Layer-by-layer evolution of structure, strain, and activity for the oxygen evolution reaction in graphene-templated Pt monolayers.

In this study, we explore the dimensional aspect of structure-driven surface properties of metal monolayers grown on a graphene/Au template. Here, surface limited redox replacement (SLRR) is used to provide precise layer-by-layer growth of Pt monolayers on graphene. We find that after a few iterations of SLRR, fully wetted 4-5 monolayer Pt films can be grown on graphene.

Operando and in situ X-ray spectroscopies of degradation in La0.6Sr0.4Co0.2Fe0.8O(3-δ) thin film cathodes in fuel cells.

Information from ex situ characterization can fall short in describing complex materials systems simultaneously exposed to multiple external stimuli. Operando X-ray absorption spectroscopy (XAS) was used to probe the local atomistic and electronic structure of specific elements in a La0.6Sr0.

Thermo-Active Behavior of Ethylene-Vinyl Acetate | Multiwall Carbon Nanotube Composites Examined by in Situ near-Edge X-ray Absorption Fine-Structure Spectroscopy.

NEXAFS spectroscopy was used to investigate the temperature dependence of thermally active ethylene-vinyl acetate | multiwall carbon nanotube (EVA|MWCNT) films. The data shows systematic variations of intensities with increasing temperature. Molecular orbital assignment of interplaying intensities identified the 1s → π* and 1s → π* transitions as the main actors during temperature variation.

Elucidating the oxide growth mechanism on platinum at the cathode in PEM fuel cells.

Simulations of platinum oxidation in literature have yet to fully replicate an experimental cyclic voltammogram. In this manuscript a mechanism for platinum oxidation is proposed based upon the results of in operando X-ray absorption spectroscopy, where it was found that PtO2 is present at longer hold times. A new method to quantify extended X-ray absorption fine structure data is presented, and the extent of oxidation is directly compared to electrochemical data.

Near-edge X-ray absorption fine structure studies of electrospun poly(dimethylsiloxane)/poly(methyl methacrylate)/multiwall carbon nanotube composites.

This work describes the near conduction band edge structure of electrospun mats of multiwalled carbon nanotube (MWCNT)-polydimethylsiloxane-poly(methyl methacrylate) by near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Effects of adding nanofillers of different sizes were addressed. Despite observed morphological variations and inhomogeneous carbon nanotube distribution, spun mats appeared homogeneous under NEXAFS analysis.

Electrical polarization of titanium surfaces for the enhancement of osteoblast differentiation.

Electrical stimulation has been used clinically to promote bone regeneration in cases of fractures with delayed union or nonunion, with several in vitro and in vivo reports suggesting its beneficial effects on bone formation. However, the use of electrical stimulation of titanium (Ti) implants to enhance osseointegration is less understood, in part because of the few in vitro models that attempt to represent the in vivo environment. In this article, the design of a new in vitro system that allows direct electrical stimulation of osteoblasts through their Ti substrates without the flow of exogenous currents through the media is presented, and the effect of applied electrical polarization on osteoblast differentiation and local factor production was evaluated.

Synthesis and growth mechanism of thin-film TiO2 nanotube arrays on focused-ion-beam micropatterned 3D isolated regions of titanium on silicon.

In this paper, the fabrication and growth mechanism of net-shaped micropatterned self-organized thin-film TiO2 nanotube (TFTN) arrays on a silicon substrate are reported. Electrochemical anodization is used to grow the nanotubes from thin-film titanium sputtered on a silicon substrate with an average diameter of ~30 nm and a length of ~1.5 μm using aqueous and organic-based types of electrolytes.

Architecture-dependent surface chemistry for Pt monolayers on carbon-supported Au.

Pt monolayers were grown by surface-limited redox replacement (SLRR) on two types of Au nanostructures. The Au nanostructures were fabricated electrochemically on carbon fiber paper (CFP) by either potentiostatic deposition (PSD) or potential square wave deposition (PSWD). The morphology of the Au/CFP heterostructures, examined using scanning electron microscopy (SEM), was found to depend on the type of Au growth method employed.

Interactions of oxygen and ethylene with submonolayer Ag films supported on Ni(111).

We investigate the oxidation of, and the reaction of ethylene with, Ni(111) with and without sub-monolayer Ag adlayers as a function of temperature. The addition of Ag to Ni(111) is shown to enhance the activity towards the ethylene epoxidation reaction, and increase the temperature at which ethylene oxide is stable on the surface. We present a systematic study of the formation of chemisorbed oxygen on the Ag-Ni(111) surfaces and correlate the presence and absence of O(1-) and O(2-) surface species with the reactivity towards ethylene.

Interface architecture determined electrocatalytic activity of Pt on vertically oriented TiO(2) nanotubes.

The surface atomic structure and chemical state of Pt is consequential in a variety of surface-intensive devices. Herein we present the direct interrelationship between the growth scheme of Pt films, the resulting atomic and electronic structure of Pt species, and the consequent activity for methanol electro-oxidation in Pt/TiO(2) nanotube hybrid electrodes. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) measurements were performed to relate the observed electrocatalytic activity to the oxidation state and the atomic structure of the deposited Pt species.

Soft X-ray characterization technique for Li batteries under operating conditions.

O K-edge and Co L-edge near-edge X-ray absorption fine structure has been used to examine the cathode of an intact solid-state lithium ion battery. The novel technique allowed for the simultaneous acquisition of partial electron yield and fluorescence yield data during the first charge cycle of a LiCoO(2)-based battery below the intercalation voltage. The chemical environments of oxygen and cobalt at the surface are shown to differ chemically from those in the bulk.

The structure of a metallic glass system using EXELFS and EXAFS as complementary probes.

The short-range atomic order around all three constituent atoms in a prototypical bulk metallic glass (BMG) system was probed in a complementary way, using extended X-ray absorption fine structure for neighborhood of the higher atomic number elements, and extended energy loss fine structure (EXELFS) for the lower atomic number ones. The Pd(x)Ni((80-x))P((20)) system is a prototype for a whole class of BMG formers which are 80% transition metal and 20% metalloid. We find that the structure of these BMGs could be explained in terms of those of glasses at the end of the BMG range, namely, Pd(60)Ni(20)P(20) and Pd(30)Ni(50)P(20).