A robust and efficient non-precious metal catalyst for hydrogen evolution reaction is one of the key components for carbon dioxide-free hydrogen production. Here we report that a hierarchical nanoporous copper-titanium bimetallic electrocatalyst is able to produce hydrogen from water under a mild overpotential at more than twice the rate of state-of-the-art carbon-supported platinum catalyst. Although both copper and titanium are known to be poor hydrogen evolution catalysts, the combination of these two elements creates unique copper-copper-titanium hollow sites, which have a hydrogen-binding energy very similar to that of platinum, resulting in an exceptional hydrogen evolution activity. In addition, the hierarchical porosity of the nanoporous copper-titanium catalyst also contributes to its high hydrogen evolution activity, because it provides a large-surface area for electrocatalytic hydrogen evolution, and improves the mass transport properties. Moreover, the catalyst is self-supported, eliminating the overpotential associated with the catalyst/support interface.

We studied Pt-Co bimetallic nanoparticles during oxidation in O2 and reduction in H2 atmospheres using an aberration corrected environmental transmission electron microscope. During oxidation Co migrates to the nanoparticle surface forming a strained epitaxial CoO film. It subsequently forms islands via strain relaxation. The atomic restructuring is captured as a function of time. During reduction cobalt migrates back to the bulk, leaving a monolayer of platinum on the surface.

In the present work, taking advantage of aberration-corrected scanning transmission electron microscopy, we show that the dynamic lithiation process of anode materials can be revealed in an unprecedented resolution. Atomically resolved imaging of the lithiation process in SnO2 nanowires illustrated that the movement, reaction, and generation of b = [1[overline]1[overline]1] mixed dislocations leading the lithiated stripes effectively facilitated lithium-ion insertion into the crystalline interior. The geometric phase analysis and density functional theory simulations indicated that lithium ions initial preference to diffuse along the [001] direction in the {200} planes of SnO2 nanowires introduced the lattice expansion and such dislocation behaviors. At the later stages of lithiation, the Li-induced amorphization of rutile SnO2 and the formation of crystalline Sn and LixSn particles in the Li2O matrix were observed.

Imaging the three-dimensional atomic-scale structure of complex interfaces has been the goal of many recent studies, due to its importance to technologically relevant areas. Combining atom-probe tomography and aberration-corrected scanning transmission electron microscopy (STEM), we present an atomic-scale study of ultrathin (~5 nm) native oxide layers on niobium (Nb) and the formation of ordered niobium hydride phases near the oxide/Nb interface. Nb, an elemental type-II superconductor with the highest critical temperature (T(c) = 9.2 K), is the preferred material for superconducting radio frequency (SRF) cavities in next-generation particle accelerators. Nb exhibits high solubilities for oxygen and hydrogen, especially within the RF-field penetration depth, which is believed to result in SRF quality factor losses. STEM imaging and electron energy-loss spectroscopy followed by ultraviolet laser-assisted local-electrode atom-probe tomography on the same needle-like sample reveals the NbO(2), Nb(2)O(5), NbO, Nb stacking sequence; annular bright-field imaging is used to visualize directly hydrogen atoms in bulk β-NbH.

The authors would like to correct a mistake made in the calculation of the TOF numbers presented in Table 2. The corrected values provided here include a correction to the original calculation in Table 2 regarding the gas flow rate (resulting in a substantial change in the calculated TOF) and an additional correction based on CO chemi-sorption experiments (as opposed to using a hemispherical model for the surface area based on the TEM measurements). The results of the chemisorption experiments are reported in Table S1 based on a 1:1 CO/Rh stoichiometry and indicate that the dispersions of the three catalyst samples are quite similar. CO chemisorption measurements were performed at the CleanCat Core facility at Northwestern University by using an Altamira Instruments BenchCAT 1000HP. Catalysts (0.2-0.3 g) were loaded into a U-shaped quartz reactor tube, which was weighed before and after sample addition to ensure an accurate weight measurement. This tube was then loaded into the furnace. Each catalyst was reduced at 300 8C for 2 h (10 8C min À1 ramp rate), then flushed for 30 min in He. 5%CO/He was then pulsed (595 mL loop volume) into the system 15-20 times at 30 8C to ensure the surface was saturated. Each spectrum was integrated to find the volume of CO remaining following adsorption. Surface saturation was typically reached within 10 pulses. The authors would like to thank Neil Schweitzer of the Center for Catalysis and Surface Science, Northwestern University, Illinois and David Childers of the University of Illinois at Chicago for their help with the chemisorption measurements. Although the chemisorption measurements indicate a lower dispersion for the incipient wetness impregnation (IWI)-prepared sample than may be supposed based on particle size, the Mn promoter likely blocks some sites for CO adsorption if IWI is the technique used for promotion addition. The corrected result does indicate that the samples synthesized by IWI have slightly higher TOFs than those synthesized by using strong electrostatic adsorption (SEA). However, the original paper focuses on the differences in selectivity, therefore, the correction does not influence the conclusions of the original paper. In addition, the authors wish to correct an error in Figure 7. The edge position of the Rh 2 O 3 standard was misaligned and has been fixed, in agreement with existing literature. [1] A new version of Figure 7 is provided below. The correction does not change the assignment of the state of Rh in the Mn-promoted Rh/SiO 2 catalysts. We wish to thank the anonymous reviewer (of a more recent paper on RhMn/C

We present a series of electron energy-loss spectroscopy (EELS) studies on niobium (Nb) and its oxides (NbO, NbO2, and Nb2O5) to develop a reliable method for quantifying the oxidation state in mixed niobium oxide thin films. Our approach utilizes a combination of transmission electron microscopy and EELS experiments with density functional theory calculations to distinguish between metallic niobium and the different niobium oxides. More specifically, the differences in the near-edge fine-structure of the Nb M-edge and O K-edge provide sufficient information to determine the valence state of niobium. Based on these observed changes in the core-loss edges, we propose a linear relationship that correlates the peak positions in the Nb M- and O K-edges with the Nb valence state. The methods developed in this paper are also applied to ultrathin niobium oxide films to examine the effects of low-temperature baking on the films’ oxidation states.

To control the process of cation exchange (CE) in multi-elemental system, a detailed understanding of structural changes at microscopic level is imperative. However, the synthesis of multielemental system has so far relied on the CE phenomenon of binary system which does not necessarily extend to the higher order systems. Here, a direct experimental evidence supported by theoretical calculations reveal a growth model of binary Cu-S to ternary Cu-Sn-S to quaternary Cu-Zn-Sn-S which shows that cations preferentially diffuse along specific lattice plane with the preservation of sulfuric anionic framework. In addition, we also discover that unlike the commonly accepted structure (P63mc), the metastable crystal structure of Cu-Zn-Sn-S phase possesses fixed Sn occupancy sites. By revealing the preferential nature of cations diffusion and growth mechanism, our work provides insight to control the stoichiometry and phase purity of novel multi-elemental materials.

In rechargeable lithium-ion batteries, understanding the atomic-scale mechanism of Li-induced structural evolution occurring at the host electrode materials provides essential knowledge for design of new high performance electrodes. Here, we report a new crystalline-crystalline phase transition mechanism in single-crystal Zn-Sb intermetallic nanowires upon lithiation. Using in situ transmission electron microscopy, we observed that stacks of atomic planes in an intermediate hexagonal (h-)LiZnSb phase are "shuffled" to accommodate the geometrical confinement stress arising from lamellar nanodomains intercalated by lithium ions. Such atomic rearrangement arises from the anisotropic lithium diffusion and is accompanied by appearance of partial dislocations. This transient structure mediates further phase transition from h-LiZnSb to cubic (c-)Li2ZnSb, which is associated with a nearly "zero-strain" coherent interface viewed along the [001]h/[111]c directions. This study provides new mechanistic insights into complex electrochemically driven crystalline-crystalline phase transitions in lithium-ion battery electrodes and represents a noble example of atomic-level structural and interfacial rearrangements.