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Metal-based chalcogenides exhibit great promise for overall water splitting, yet their intrinsic catalytic reaction mechanisms remain to be fully understood. In this work, we employed operando X-ray absorption (XAS) and in situ Raman spectroscopy to elucidate the structure-activity relationships of low-crystalline cobalt sulfide (L-CoS) catalysts toward overall water splitting. The operando results for L-CoS catalyzing the alkaline hydrogen evolution reaction (HER) demonstrate that the cobalt centers in the bulk are predominantly coordinated by sulfur atoms, which undergo a kinetic structural rearrangement to generate metallic cobalt in S-Co-Co-S moieties as the true catalytically active species. In comparison, during the acidic HER, L-CoS undergoes local structural optimization of Co centers, and H 2 production proceeds with adsorption/desorption of key intermediates atop the Co-S-Co configurations. Further operando characterizations highlight the crucial formation of high-valent Co 4+ species in L-CoS for the alkaline oxygen evolution reaction (OER), and the formation of such active species was found to be far more facile than in crystalline Co 3 O 4 and Co-LDH references. These insights offer a clear picture of the complexity of active species and site formation in different media, and demonstrate how their restructuring influences the catalytic activity., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Ternary Pd-In 2 O 3 /ZrO 2 catalysts exhibit technological potential for CO 2 -based methanol synthesis, but developing scalable systems and comprehending complex dynamic behaviors of the active phase, promoter, and carrier are key for achieving high productivity. Here, we show that the structure of Pd-In 2 O 3 /ZrO 2 systems prepared by wet impregnation evolves under CO 2 hydrogenation conditions into a selective and stable architecture, independent of the order of addition of Pd and In phases on the zirconia carrier. Detailed operando characterization and simulations reveal a rapid restructuring driven by the metal-metal oxide interaction energetics. The proximity of InPd x alloy particles decorated by InO x layers in the resulting architecture prevents performance losses associated with Pd sintering. The findings highlight the crucial role of reaction-induced restructuring in complex CO 2 hydrogenation catalysts and offer insights into the optimal integration of acid-base and redox functions for practical implementation., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Nearly half of the elements in the periodic table are extracted, refined, or plated using electrodeposition in high-temperature melts. However, operando observations and tuning of the electrodeposition process during realistic electrolysis operations are extremely difficult due to severe reaction conditions and complicated electrolytic cell, which makes the improvement of the process very blind and inefficient. Here, we developed a multipurpose operando high-temperature electrochemical instrument that combines operando Raman microspectroscopy analysis, optical microscopy imaging, and a tunable magnetic field. Subsequently, the electrodeposition of Ti-which is a typical polyvalent metal and generally shows a very complex electrode process-was used to verify the stability of the instrument. The complex multistep cathodic process of Ti in the molten salt at 823 K was systematically analyzed by a multidimensional operando analysis strategy involving multiple experimental studies, theoretical calculations, etc. The regulatory effect and its corresponding scale-span mechanism of the magnetic field on the electrodeposition process of Ti were also elucidated, which would be inaccessible with existing experimental techniques and is significant for the real-time and rational optimization of the process. Overall, this work established a powerful and universal methodology for in-depth analysis of high-temperature electrochemistry.

The reported study was devoted to the investigation of viscoelastic behavior for solid and porous ultra-high molecular weight polyethylene (UHMWPE) under compression. The obtained experimental stress curves were interpreted using a two-term Prony series to represent the superposition of two coexisting activation processes corresponding to long molecular (~160 s) and short structural (~20 s) time scales, respectively, leading to good statistical correlation with the observations. In the case of porous polymer, the internal strain redistribution during relaxation was quantified using digital image correlation (DIC) analysis. The strongly inhomogeneous deformation of the porous polymer was found not to affect the relaxation times. To illustrate the possibility of generalizing the results to three dimensions, X-ray tomography was used to examine the porous structure relaxation at the macro- and micro-scale levels. DIC analysis revealed positive correlation between the applied force and relative density. The apparent stiffness variation for UHMWPE foams with mixed open and closed cells was described using a newly proposed three-term expression. Furthermore, in situ tensile loading and X-ray scattering study was applied for isotropic solid UHMWPE specimens to investigate the evolution of internal structure and orientation during drawing and stress relaxation in another loading mode.

The copper-zinc-alumina (CZA) catalyst is one of the most important catalysts. Nevertheless, understanding of the complex CZA structure is still limited and hampers further optimization. Critical to the production of a highly active and stable catalyst are optimal start-up procedures in hydrogen. Here, by employing operando X-ray absorption spectroscopy and X-ray diffraction, we follow how the industrial CZA precursor evolves into the working catalyst. Two major events in the activation drastically alter the copper- and zinc-containing components in the CZA catalyst and define the final working catalyst structure: the reduction of the starting copper(II) oxide, and the ripening and re-oxidation of zinc oxide upon the switch to catalytic conditions. These drastic events are also accompanied by other gradual, structural changes. Understanding what happens during these events is key to develop tailored start-up protocols that are aimed at maximal longevity and activity of the catalysts., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The lithiation of crystalline silicon was studied over several cycles using operando neutron reflectometry over six cycles. A thin layer of aluminum oxide was employed as an artificial coating on the silicon to suppress the solid electrolyte interphase (SEI) layer-related aging effects. Initially, the artificial SEI prevented side effects but led to increased lithium trapping. This layer degraded after two cycles, followed by side reactions, which decrease the coulombic efficiency. No hint for electrode fracturization was found even though the lithiation depth exceeded 1 μm. Two distinct zones with high and low lithium concentrations were found, initially separated by a sharp interface, which broadens with cycling. The correlation of the reflectometry results with the electrochemical current showed the lithium fraction that is lithiated in the silicon and the lithium consumed in side reactions. Also, neutron reflectometry was used to quantify the amount of lithium that remained inside of the silicon. Additional electrochemical impedance spectroscopy was used to gain insights into the electrical properties of the sample via fitting to an equivalent circuit.

This work enables highly "uniform" and "reversible" deposition of Li metal in carbonate electrolytes through a one-time rapid oxidation and reduction (ROAR) treatment. Over the years, Li metal has been plagued with irreversible dendritic growths that create isolated and unusable structures called "dead Li". Accumulation of dead Li negatively impacts the ion transport, performance, and safety of Li metal batteries. To address this long-standing problem, we have developed an in situ process to uniformly create reversible Li deposits. Our results demonstrate that a combination of high-voltage pulses, which rapidly oxidize and reduce Li in both directions (ROAR treatment), leads to strikingly more homogeneous morphology and eliminates reaction pathway transitions. We validate that ROAR treatments eliminate traditional "mossy dendrites" under extended cycling (<250 cycles) in standard carbonate-based electrolytes. Moreover, ROAR treatments create a 500% reduction in overpotential for electrodissolution/deposition and eliminate "peaking" voltage behavior.

Structural dynamics of a Mn-Na 2 WO 4 /SiO 2 catalyst were detected directly under reaction conditions during the oxidative coupling of methane via in situ XRD and operando Raman spectroscopy. A new concept of fluctuating storage and release of an active phase in heterogeneous catalysis is proposed that involves the transient generation of active sodium oxide species via a reversible reaction of Na 2 WO 4 with Mn 7 SiO 12 . The process is enabled by phase transitions and melting at the high reaction temperatures that are typically applied., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Operando analyses have provided several breakthroughs in the construction of high-performance materials and devices, including energy storage systems. However, despite the advances in electrode engineering, the formidable issues of lithium intercalation and deintercalation kinetics cannot be investigated by using planar observations. This study concerns side-view operando observation by optical microscopy of a graphite anode based on its color changes during electrochemical lithiation. Since the graphite color varies according to the optical energy gap during lithiation and delithiation, this technique can be used to study the corresponding charge-discharge kinetics. In addition, the cell configuration uses liquid electrolytes similar to commercial cells, allowing practical application. Furthermore, this side-view observation has shown that microscale spatial variations in rate and composition control the insertion and deinsertion, revealing the kinetics throughout the whole electrode. The results of this study could enhance the fundamental understanding of the kinetics of battery materials., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

It is generally believed that CO 2 electroreduction to multi-carbon products such as ethanol or ethylene may be catalyzed with significant yield only on metallic copper surfaces, implying large ensembles of copper atoms. Here, we report on an inexpensive Cu-N-C material prepared via a simple pyrolytic route that exclusively feature single copper atoms with a CuN 4 coordination environment, atomically dispersed in a nitrogen-doped conductive carbon matrix. This material achieves aqueous CO 2 electroreduction to ethanol at a Faradaic yield of 55 % under optimized conditions (electrolyte: 0.1 m CsHCO 3 , potential: -1.2 V vs. RHE and gas-phase recycling set up), as well as CO electroreduction to C 2 -products (ethanol and ethylene) with a Faradaic yield of 80 %. During electrolysis the isolated sites transiently convert into metallic copper nanoparticles, as shown by operando XAS analysis, which are likely to be the catalytically active species. Remarkably, this process is reversible and the initial material is recovered intact after electrolysis., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This study reports the use of operando small-angle neutron scattering to investigate processes in an operating Li/S battery. The combination with impedance spectroscopy yields valuable insights into the precipitation and dissolution of lithium sulfide during 10 cycles of galvanostatic cycling. The use of a deuterated electrolyte increases strongly the sensitivity to detect the sulfur and Li 2 S precipitates at the carbon host electrode and allows us to observe the time-dependent initial wetting of the system. No correlation of the scattering signal of the micropores with either lithium sulfide or sulfur is observable during the whole course of the experiment. Hence both reaction products do not precipitate inside the microporous structure but on the outer surface of the micrometer-sized carbon fibers used in this study. The excellent scattering contrast allows a detailed analysis of the formation and dissolution process of nanoscopic Li 2 S structures. While lithium sulfide particles grow homogeneously during the precipitation period, smaller Li 2 S particles dissolve first followed by a sudden dissolution of the larger Li 2 S particles.

Three-dimensional imaging using X-ray as a probe is state-of-the-art for the characterization of heterogeneous materials. In addition to simple imaging of sample morphology, imaging of elemental distribution and chemical states provides advanced maps of key structural parameters of functional materials. The combination of X-ray absorption fine structure (XAFS) spectroscopy and three-dimensional imaging such as computed tomography (CT) can visualize the three-dimensional distribution of target elements, their valence states, and local structures in a non-destructive manner. In this personal account, our recent results on the three-dimensional XAFS imaging for Pt cathode catalysts in the membrane electrode assembly (MEA) of polymer electrolyte fuel cell (PEFC) are introduced. The distribution and chemical states of Pt cathode catalysts in MEAs remarkably change under PEFC operating conditions, and the 3D XAFS imaging revealed essential events in PEFC MEAs., (© 2019 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)