Franz Hennies

Breakthroughs in battery research are imperative to provide society with batteries that are safe and sustainable, have a high energy density, and have a long cycle life at low cost. Recent advances in research methodologies, the emergence of new market opportunities, and strategic funding schemes have allowed not only large, but also small companies, universities, and public research organizations to play an increasingly significant role in the advancement of battery technology. Challenges in battery technology development are multifaceted; therefore, a collaborative approach is crucial to bring together various stakeholders and ensure access to the full range of technical and scientific expertise. To grasp the core properties of electrode materials, electrolytes, and interfaces and to identify the mechanisms of battery degradation and failure, a multidisciplinary analytical approach is crucial. This strategy relies on the unique and complementary potential of advanced characterization techniques available at synchrotron and x-ray free electron laser facilities. Science-to-industry interactions are expected to increase the development of new standardized setups to approach realistic operando conditions. Therefore, rapid access to instruments, including high-throughput ex-situ, in-situ and operando capabilities, is key to accelerating the development of safe and sustainable batteries. The purpose of this paper is to discuss how the characterization needs of the battery community can be met by establishing a collaboration network based on a meta-infrastructure model, where the emphasis will be on collaboration and the sharing of experience and data. The proposed methodology considers the urgency in the battery community and the necessary technical developments to reach the scope of collaboration and focuses in particular on the needs for standardization, big data challenges, and open data approaches.

The unique opportunity to study and control electron-nuclear quantum dynamics in coupled potentials offered by the resonant inelastic X-ray scattering (RIXS) technique is utilized to unravel an anomalously strong two-electron one-photon transition from core-excited to Rydberg final states in the CO molecule. High-resolution RIXS measurements of CO in the energy region of 12–14 eV are presented and analyzed by means of quantum simulations using the wave packet propagation formalism and ab initio calculations of potential energy curves and transition dipole moments. The very good overall agreement between the experimental results and the theoretical predictions allows an in-depth interpretation of the salient spectral features in terms of Coulomb mixing of “dark” with “bright” final states leading to an effective two-electron one-photon transition. The present work illustrates that the improved spectral resolution of RIXS spectra achievable today may call for more advanced theories than what has been used in the past.

We utilized femtosecond time-resolved resonant inelastic X-ray scattering and ab initio theory to study the transient electronic structure and the photoinduced molecular dynamics of a model metal carbonyl photocatalyst Fe(CO)₅ in ethanol solution. We propose mechanistic explanation for the parallel ultrafast intra-molecular spin crossover and ligation of the Fe(CO)₄ which are observed following a charge transfer photoexcitation of Fe(CO)₅ as reported in our previous study [Wernet et al., Nature 520, 78 (2015)]. We find that branching of the reaction pathway likely happens in the ¹A₁ state of Fe(CO)₄. A sub-picosecond time constant of the spin crossover from ¹B₂ to ³B₂ is rationalized by the proposed ¹B₂ → ¹A₁ → ³B₂ mechanism. Ultrafast ligation of the ¹B₂ Fe(CO)₄ state is significantly faster than the spin-forbidden and diffusion limited ligation process occurring from the ³B₂ Fe(CO)₄ ground state that has been observed in the previous studies. We propose that the ultrafast ligation occurs via ¹B₂ → ¹A₁ → ¹A′ Fe(CO)₄EtOH pathway and the time scale of the ¹A₁ Fe(CO)₄ state ligation is governed by the solute-solvent collision frequency. Our study emphasizes the importance of understanding the interaction of molecular excited states with the surrounding environment to explain the relaxation pathways of photoexcited metal carbonyls in solution.

A high precision five rotation-axes polarimeter using transmission multilayers as polarizers and reflection multilayers as analyzers has been designed and manufactured. To cover the extreme ultraviolet regime, Mo/Si, Cr/C, Sc/Cr, and W/B₄C multilayers for transmission and reflection have also been designed and produced. The polarimeter mechanics is supported on a hexapod to simplify the alignment relative to photon beam. The instrument is designed so that it can be easily transferred between different beamlines.

Transition-metal complexes have long attracted interest for fundamental chemical reactivity studies and possible use in solar energy conversion^1,2. Electronic excitation, ligand loss from the metal centre, or a combination of both, creates changes in charge and spin density at the metal site^{3,4,5,6,7,8,9,10,11} that need to be controlled to optimize complexes for photocatalytic hydrogen production⁸ and selective carbon–hydrogen bond activation^9,10,11. An understanding at the molecular level of how transition-metal complexes catalyse reactions, and in particular of the role of the short-lived and reactive intermediate states involved, will be critical for such optimization. However, suitable methods for detailed characterization of electronic excited states have been lacking. Here we show, with the use of X-ray laser-based femtosecond-resolution spectroscopy and advanced quantum chemical theory to probe the reaction dynamics of the benchmark transition-metal complex Fe(CO)₅ in solution, that the photo-induced removal of CO generates the 16-electron Fe(CO)₄ species, a homogeneous catalyst^12,13 with an electron deficiency at the Fe centre^14,15, in a hitherto unreported excited singlet state that either converts to the triplet ground state or combines with a CO or solvent molecule to regenerate a penta-coordinated Fe species on a sub-picosecond timescale. This finding, which resolves the debate about the relative importance of different spin channels in the photochemistry of Fe(CO)₅ (refs 4, 16,17,18,19 and 20), was made possible by the ability of femtosecond X-ray spectroscopy to probe frontier-orbital interactions with atom specificity. We expect the method to be broadly applicable in the chemical sciences, and to complement approaches that probe structural dynamics in ultrafast processes.

Liquid water molecules interact strongly with each other, forming a fluctuating hydrogen bond network and thereby giving rise to the anomalous phase diagram of liquid water. Consequently, symmetric and asymmetric water molecules have been found in the picosecond time average with IR and optical Raman spectroscopy. With subnatural linewidth resonant inelastic x-ray scattering (RIXS) at vibrational resolution, we take sub-femtosecond snapshots of the electronic and structural properties of water molecules in the hydrogen bond network. We derive a strong dominance of nonsymmetric molecules in liquid water in contrast to the gas phase on the sub-femtosecond timescale of RIXS and determine the fraction of highly asymmetrically distorted molecules.