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Solid-state electrolytes overcome many challenges of present-day lithium ion batteries, such as safety hazards and dendrite formation1,2. However, detailed understanding of the involved lithium dynamics is missing due to a lack of in operando measurements with chemical and interfacial specificity. Here we investigate a prototypical solid-state electrolyte using linear and nonlinear extreme-ultraviolet spectroscopies. Leveraging the surface sensitivity of extreme-ultraviolet-second-harmonic-generation spectroscopy, we obtained a direct spectral signature of surface lithium ions, showing a distinct blueshift relative to bulk absorption spectra. First-principles simulations attributed the shift to transitions from the lithium 1 s state to hybridized Li-s/Ti-d orbitals at the surface. Our calculations further suggest a reduction in lithium interfacial mobility due to suppressed low-frequency rattling modes, which is the fundamental origin of the large interfacial resistance in this material. Our findings pave the way for new optimization strategies to develop these electrochemical devices via interfacial engineering of lithium ions.

Li7La3Zr2O12 (LLZO) garnet-based oxides are a promising class of solid electrolytes used as the separator in all-solid-state batteries (ASSBs). While LLZO is considered to have a wide electrochemic...

Poly(ethylene oxide) (PEO) was the first lithium‐ion conducting polymer developed 50 years ago and is still the most popular electrolyte matrix for solid‐state lithium metal batteries. While many studies focus on increasing PEO ionic conductivity through doping with Li salts, little work has addressed using PEO and Li directly to generate Li+‐conducting species in situ. Reaction between PEO and Li leads to ionic conductivity largely from Li+, in contrast to the case of added salts where the anion contribution dominates. Herein, electrochemical impedance spectroscopy shows the ionic conductivity of PEO thin films increases up to three orders of magnitude (from 10−7 to 10−4 S cm−1) when contacted with Li at elevated temperature. This is due to the reduction of ether bonds, which produces lithium alkoxides that are responsible for Li+ transport. Density functional theory analysis confirms this mechanism as thermodynamically favorable. X‐ray photoelectron spectroscopy also shows the presence of organolithium species and Li2O, which are responsible for propagating reactions with PEO and forming an electronically insulating layer at the PEO–Li interface that halts further reaction, respectively. The underlying mechanisms of Li–polymer electrolyte reactions is clarified and new pathways for in situ Li+ doping of polymer electrolytes is presented.

A remaining challenge for the deployment of proton-exchange membrane fuel cells is the limited durability of platinum (Pt) nanoscale materials that operate at high voltages during the cathodic oxygen reduction reaction. In this work, atomic-scale insight into well-defined single-crystalline, thin-film and nanoscale surfaces exposed Pt dissolution trends that governed the design and synthesis of durable materials. A newly defined metric, intrinsic dissolution, is essential to understanding the correlation between the measured Pt loss, surface structure, size and ratio of Pt nanoparticles in a carbon (C) support. It was found that the utilization of a gold (Au) underlayer promotes ordering of Pt surface atoms towards a (111) structure, whereas Au on the surface selectively protects low-coordinated Pt sites. This mitigation strategy was applied towards 3 nm Pt3Au/C nanoparticles and resulted in the elimination of Pt dissolution in the liquid electrolyte, which included a 30-fold durability improvement versus 3 nm Pt/C over an extended potential range up to 1.2 V. Deployment of proton-exchange membrane fuel cells is limited by the durability of Pt-nanoscale catalysts during cathodic oxygen reduction reactions. Dissolution processes on single crystalline and thin film surfaces are now correlated leading to the design of PtAu catalysts with suppressed dissolution.

The poor activity and stability of electrode materials for the oxygen evolution reaction are the main bottlenecks in the water-splitting reaction for H2 production. Here, by studying the activity–stability trends for the oxygen evolution reaction on conductive M1OxHy, Fe–M1OxHy and Fe–M1M2OxHy hydr(oxy)oxide clusters (M1 = Ni, Co, Fe; M2 = Mn, Co, Cu), we show that balancing the rates of Fe dissolution and redeposition over a MOxHy host establishes dynamically stable Fe active sites. Together with tuning the Fe content of the electrolyte, the strong interaction of Fe with the MOxHy host is the key to controlling the average number of Fe active sites present at the solid/liquid interface. We suggest that the Fe–M adsorption energy can therefore serve as a reaction descriptor that unifies oxygen evolution reaction catalysis on 3d transition-metal hydr(oxy)oxides in alkaline media. Thus, the introduction of dynamically stable active sites extends the design rules for creating active and stable interfaces. Understanding what underpins the activity and stability of oxygen evolution catalysts is an ongoing issue in the field of water splitting. Now, researchers show that balancing the rate of Fe dissolution and deposition over a metal hydr(oxy)oxide host yields dynamically stable Fe active sites, with the Fe–host interaction key to the performance.

Understanding ionic transport across interfaces between dissimilar materials and the intrinsic chemical stability of such interfaces is a fundamental challenge spanning many disciplines and is of particular importance for designing conductive and stable solid electrolytes for solid-state Li-ion batteries. In this work, we establish a surface science-based approach for assessing the intrinsic stability of oxide materials in contact with Li metal. Through a combination of experimental and computational insights, using Nb-doped SrTiO3 (Nb/STO) single crystals as a model system, we were able to understand the impact of crystallographic orientation and surface morphology on the extent of the chemical reactions that take place between surface Nb, Ti, and Sr upon reaction with Li. By expanding our approach to investigate the intrinsic stability of the technologically relevant, polycrystalline Nb-doped lithium lanthanum zirconium oxide (Li6.5La3Zr1.5Nb0.5O12) system, we found that this material reacts with Li metal through the reduction of Nb, similar to that observed for Nb/STO. These results clearly demonstrate the feasibility of our approach to assess the intrinsic (in)stability of oxide materials for solid-state batteries and point to new strategies for understanding the performance of such systems.

A facile and template-free method is reported to synthesize a new thin film structure: polyaniline (PANI) film/nanotubes (F/N) structure. The PANI F/N is a 100-nm thick PANI film embedded with PANI nanotubes. This well-controlled method requires no surfactant or organic acid as well as relatively low concentration of reagents. Synthesis condition studies reveal that aniline oligomers with certain structures are responsible for guiding the growth of the nanotubes. Electrical characterization also indicates that the PANI F/N possesses similar field-effect transistor characteristics to bare PANI film. With its 20% increased surface-area-to-volume (S/V) ratio contributed by surface embedded nanotubes and the excellent p-type semiconducting characteristic, PANI F/N shows clear superiority compared with bare PANI film. Such advantages guarantee the PANI F/N a promising future toward the development of ultra-high sensitivity and low-cost biosensors © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017

High-temperature annealing in air is used to produce SrTiO3 (111) surfaces with two types of atomically flat terraces: those that promote photoanodic reactions and those that promote photocathodic reactions. Surface potential measurements show that the photocathodic terraces have a relatively more positive surface potential than the photoanodic terraces. After depositing thin TiO2 films on the surface, from 1 to 13 nm thick, the surface of the film above the photocathodic terraces also has photocathodic properties, similar to those of the bare surface. While a more positive surface potential can be detected on the surface of the thinnest TiO2 films (1 nm thick), it is undetectable for thicker films. The persistence of the localized photocathodic properties on the film surface, even in the absence of a measurable difference in local potential, indicates that the charge associated with specific terraces on the bare SrTiO3 (111) surface remains localized at the TiO2/SrTiO3 interface and that the buried charg...

SrTiO3(110) orientated crystals have been heated to temperatures between 1000 °C and 1200 °C in air, alone or in the presence of powder reservoirs of TiO2 or Sr3Ti2O7. In these conditions, the surface is terminated by two types of atomically flat terraces. One has a relatively higher surface potential and promotes the photochemical reduction of silver (it is photocathodic) and the other has a relatively lower surface potential and promotes the photochemical oxidation of lead (it is photoanodic). Measurements of the step heights between the terraces indicate that the surfaces with different properties have different terminations. By adjusting the time and temperature of the anneal, and in some cases including reservoirs of TiO2 or Sr3Ti2O7, it is possible to change the surface area fraction from 98% photocathodic to 100% photoanodic. The surface is more photocathodic when the annealing temperature is lower, the duration shorter, and if Sr3Ti2O7 is present. The surface is more photoanodic if the temperature is higher, the annealing duration longer, and if TiO2 is present. The results make it possible to control the surface potential and the ratio of photocathodic to photoanodic area on the SrTiO3(110) surface.

The orientation dependence of the visible-light stimulated photochemical reduction of aqueous Ag+ on polycrystalline hematite Fe2O3 was determined by observing the relative amount of reduced Ag0 on crystals of known surface orientation over all possible orientations. The results show that surfaces oriented within 20° of the (11¯02) plane are the most active and surfaces close to the (0001) plane are the least active. A strong correlation is observed between the orientation-dependent activity and the orientation-dependent surface potential measured by scanning Kelvin probe force microscopy. Surfaces near the most active (11¯02) plane and the least active (0001) plane are, respectively, at the most positive and the least positive ends of the potential range among all grains. The trends in activity are concluded to arise from a combination of internal fields associated with surface charges and bulk transport effects.

The grain-by-grain orientation relationships between an Fe2O3 film, grown using pulsed laser deposition, and a polycrystalline SrTiO3 substrate were determined using electron backscatter diffraction. This high-throughput investigation, we call combinatorial substrate epitaxy, enables the characterization of film growth on all grain orientations in a single experiment, allowing the determination of the preferred epitaxial orientation (PEO) of this non-isostructural film/substrate pair. Heavily-twinned rhombohedral α-Fe2O3 (hematite) grew epitaxially over the entire orientation space of the cubic perovskite substrate. Over 500 local orientation relationships (ORs) were investigated and more than 90% of these ORs, regardless of the interface plane normal, could be described using a single epitaxial OR: 0001 10 1 ¯ 0 Fe 2 O 3 111 1 1 ¯ 0 SrTiO 3 . This OR aligns the eutactic (nearly close-packed) planes and directions between these dissimilar crystal structures. Importantly, the growth of Fe2O3 on a single crystalline (100)-SrTiO3 results in several different orientation relationships. These results suggest that growth on high Miller-index (low-symmetry) surfaces provides more general information about the PEO than growth on low Miller-index (high-symmetry) surfaces. The epitaxial film growth on high Miller-index surfaces and the overwhelming observation of the eutaxial OR support the hypothesis that a very small number of simple crystallographic descriptors guide epitaxial film growth over all of orientation space, even for non-isostructural film/substrate pairs.

Intercalated nanoparticles are used to determine the adhesion energies of 2‐D layers to different substrates such as graphene and MoS2 to Au, Pt, SiNx, and SiO2 substrates. The figure illustrates an intercalated nanoparticle between the substrate and graphene. Through this method, Au shows the strongest adhesion energy of 7687.10 and 1207.26 mJ m−2 for graphene and MoS2, respectively.

Nano-leaf bismuth vanadate (BiVO4), which acts as an active photocatalyst for O2 evolution under visible light irradiation, was synthesized by a wet chemical method. The BiVO4 photocatalyst was obtained by the reaction of Bi(NO3)3·5H2O and NH4VO3 at a low temperature (60 °C). Both the morphology and the crystal phase of the synthesized product can be tuned by changing the concentrations of the precursor. The O2 evolution activity of BiVO4 nano-leaves from photocatalytic water splitting under visible light irradiation ( λ >420 nm) is significantly higher than that of the BiVO4 sample synthesized by a traditional solid state reaction method, and the activity can be further improved by annealing the samples.