In this study we control the surface structure of Cu thin-film catalysts to probe the relationship between active sites and catalytic activity for the electroreduction of CO 2 to fuels and chemicals. Here, we report physical vapor deposition of Cu thin films on large-format (∼6 cm 2 ) single-crystal substrates, and confirm epitaxial growth in the <100>, <111>, and <751> orientations using X-ray pole figures. To understand the relationship between the bulk and surface structures, in situ electrochemical scanning tunneling microscopy was conducted on Cu(100), (111), and (751) thin films. The studies revealed that Cu(100) and (111) have surface adlattices that are identical to the bulk structure, and that Cu(751) has a heterogeneous kinked surface with (110) terraces that is closely related to the bulk structure. Electrochemical CO 2 reduction testing showed that whereas both Cu(100) and (751) thin films are more active and selective for C-C coupling than Cu(111), Cu(751) is the most selective for >2e− oxygenate formation at low overpotentials. Our results demonstrate that epitaxy can be used to grow singlecrystal analogous materials as large-format electrodes that provide insights on controlling electrocatalytic activity and selectivity for this reaction.carbon dioxide reduction | epitaxy | electrocatalysis | copper T he electrochemical reduction of CO 2 (CO 2 R) is a process that could couple to renewable energy from wind and solar to directly produce fuels and chemicals in a sustainable manner. However, developing catalysts is a major challenge for this reaction, and significant advances are needed to overcome the issues of poor energy efficiency and product selectivity. One reason for these issues is that there are a limited number of catalysts that can effectively convert CO 2 to products that require more than two electrons (>2e − products), e.g., methane, methanol, ethylene, etc. (1, 2). Therefore, developing catalysts that are effective for CO 2 R to >2e − products would greatly improve prospects for utilization, and such an endeavor requires a deeper understanding of the relevant surface chemistry.Out of the polycrystalline metals, Cu is the only one that has shown a propensity for CO 2 R to >2e − products at considerable rates and selectivity (2, 3). To date, its uniqueness is reflected by how nearly all work on catalysts with improved activity and selectivity for >2e − products is based on Cu (4-6). However, polycrystalline Cu is not particularly selective toward any one >2e − reduction product (7). Thus, it is critical to understand what active site motifs lead to this unique selectivity for further reduced products and to apply this knowledge to develop new materials with this electrocatalytic behavior.Single-crystal studies on Cu have shown that CO 2 R activity and selectivity are extremely sensitive to surface structure. In particular, facet sensitivities for C-C coupling are the most widely studied, with experimental reports concluding that Cu(100) terraces and any orientation of step sites are more...

We present a study of the lattice response to the compressive and tensile biaxial stress in

Lithium, with its high theoretical specific capacity and lowest electrochemical potential, has been recognized as the ultimate negative electrode material for next-generation lithium-based high-energy-density batteries. However, a key challenge that has yet to be overcome is the inferior reversibility of Li plating and stripping, typically thought to be related to the uncontrollable morphology evolution of the Li anode during cycling. Here we show that Li-metal texturing (preferential crystallographic orientation) occurs during electrochemical deposition, which governs the morphological change of the Li anode. X-ray diffraction pole-figure analysis demonstrates that the texture of Li deposits is primarily dependent on the type of additive or cross-over molecule from the cathode side. With adsorbed additives, like LiNO and polysulfide, the lithium deposits are strongly textured, with Li (110) planes parallel to the substrate, and thus exhibit uniform, rounded morphology. A growth diagram of lithium deposits is given to connect various texture and morphology scenarios for different battery electrolytes. This understanding of lithium electrocrystallization from the crystallographic point of view provides significant insight for future lithium anode materials design in high-energy-density batteries.

Oxide heterostructures often exhibit unusual physical properties that are absent in the constituent bulk materials. Here, we report an atomically sharp transition to a ferromagnetic phase when polar antiferromagnetic LaMnO3 (001) films are grown on SrTiO3 substrates. For a thickness of six unit cells or more, the LaMnO3 film abruptly becomes ferromagnetic over its entire area, which is visualized by scanning superconducting quantum interference device microscopy. The transition is explained in terms of electronic reconstruction originating from the polar nature of the LaMnO3 (001) films. Our results demonstrate that functionalities can be engineered in oxide films that are only a few atomic layers thick.

At extreme pressures and temperatures, such as those inside planets and stars, common materials form new dense phases with compacted atomic arrangements and unusual physical properties. The synthesis and study of new phases of matter at pressures above 100 GPa and temperatures above 104 K—warm dense matter—may reveal the functional details of planet and star interiors, and may lead to materials with extraordinary properties. Many phases have been predicted theoretically that may be realized once appropriate formation conditions are found. Here we report the synthesis of a superdense stable phase of body-centred-cubic aluminium, predicted by first-principles theories to exist at pressures above 380 GPa. The superdense Al phase was synthesized in the non-equilibrium conditions of an ultrafast laser-induced microexplosion confined inside sapphire (α-Al2O3). Confined microexplosions offer a strategy to create and recover high-density polymorphs, and a simple method for tabletop study of warm dense matter.

Lithium metal is the ultimate anode choice for high energy density rechargeable lithium batteries. However, it suffers from inferior electrochemical performance and safety issues due to its high reactivity and the growth of lithium dendrites. It has long been desired to develop a materials coating on Li metal, which is pinhole-free, mechanically robust without fracture during Li metal deposition and stripping, and chemically stable against Li metal and liquid electrolytes, all while maintaining adequate ionic conductivity. However, such an ideal material coating has yet to be found. Here we report a novel synthesis method by reacting clean molten lithium foil directly with pure nitrogen gas to generate instantaneously a pinhole-free and ionically conductive α-Li3N film directly bonded onto Li metal foil. The film consists of highly textured large Li3N grains (tens of μm) with (001) crystalline planes parallel to the Li metal surface. The bonding between textured grains is strong, resulting in a mechanically robust film which does not crack even when bent to a 0.8 cm curvature radius and is found to maintain pinhole-free coverage during Li metal deposition and stripping. The measured ionic conductivity is up to 5.2 × 10–4 S cm–1, sufficient for maintaining regular current densities for controllable film thicknesses ranging from 2 to 30 μm. This Li3N coating is chemically stable, isolating the reactive metallic lithium from liquid electrolyte, prevents continuous electrolyte consumption during battery cycling, and promotes dendrite-free uniform lithium plating/stripping underneath. We demonstrated Li|Li4Ti5O12 cells with stable and flat potential profiles for 500 cycles without capacity decay or an increase in potential hysteresis.

A defining feature of emergent phenomena in complex oxides is the competition and cooperation between ground states. In manganites, the balance between metallic and insulating phases can be tuned by the lattice; extending the range of lattice control would enhance the ability to access other phases. We stabilized uniform extreme tensile strain in nanoscale La0.7Ca0.3MnO3 membranes, exceeding 8% uniaxially and 5% biaxially. Uniaxial and biaxial strain suppresses the ferromagnetic metal at distinctly different strain values, inducing an insulator that can be extinguished by a magnetic field. Electronic structure calculations indicate that the insulator consists of charge-ordered Mn4+ and Mn3+ with staggered strain-enhanced Jahn-Teller distortions within the plane. This highly tunable strained membrane approach provides a broad opportunity to design and manipulate correlated electron states.

The two-dimensional (2D) to three-dimensional (3D) morphological transition in strained Ge layers grown on Si(001) is investigated using scanning tunneling microscopy. The initial step takes place via the formation of 2D islands which evolve into small ( approximately 180 A) 3D islands with a height to base diameter ratio of approximately 0.04, much smaller than the 0.1 aspect ratio of 105-faceted pyramids which had previously been assumed to be the initial 3D islands. The "prepyramid" Ge islands have rounded bases with steps oriented along <110> and exist only over a narrow range of Ge coverages, 3.5-3.9 monolayers.