Publikationen

Artificial leaves could be the breakthrough technology to overcome the limitations of storage and mobility through the synthesis of chemical fuels from sunlight, which will be an essential component of a sustainable future energy system. However, the realization of efficient solar-driven artificial leaf structures requires integrated specialized materials such as semiconductor absorbers, catalysts, interfacial passivation, and contact layers. To date, no competitive system has emerged due to a lack of scientific understanding, knowledge-based design rules, and scalable engineering strategies. Here, we will discuss competitive artificial leaf devices for water splitting, focusing on multi-absorber structures to achieve solar-to-hydrogen conversion efficiencies exceeding 15%. A key challenge is integrating photovoltaic and electrochemical functionalities in a single device. Additionally, optimal electrocatalysts for intermittent operation at photocurrent densities of 10-20 mA cm^-2 must be immobilized on the absorbers with specifically designed interfacial passivation and contact layers, so-called buried junctions. This minimizes voltage and current losses and prevents corrosive side reactions. Key challenges include understanding elementary steps, identifying suitable materials, and developing synthesis and processing techniques for all integrated components. This is crucial for efficient, robust, and scalable devices. Here, we discuss and report on corresponding research efforts to produce green hydrogen with unassisted solar-driven (photo-)electrochemical devices. This article is protected by copyright. All rights reserved.

Phosphoric acid is commonly known either as a neutral molecule or as an anion (phosphate). We theoretically confirm by ab initio molecular dynamics simulations (AIMD) that a cationic form H4PO4+ coexists with the anionic form H2PO4- in the same salt. This paradoxical situation is achieved by partial substitution of Cs+ by H4PO4+ in CsH2PO4. Thus, HnPO4 acts simultaneously as both the positive and the negative ion of the salt. We analyze the dynamical protonation pattern within the unusual hydrogen bond network that is established between the ions. Our AIMD simulations show that a conventional assignment of protonation states of the phosphate groups is not meaningful. Instead, a better description of the protonation situation is achieved by an efficiently fractional assignment of the strongly hydrogen-bonded protons to both its nearest and next-nearest oxygen neighbors.

Proteins and peptides exhibit an immense variety of structures, which are generally classified according to simple structural motifs (mainly α helices and β sheets). Considerable efforts have been invested in understanding the relationship between chemical structure (primary structure) of peptides and their spatial motifs (secondary structure). However, little is known about the possibility to interfere intentionally in these structural driving forces, for example, by inserting (short) artificial polymer chains in the peptide backbone. Structure formation on such hybrid synthetic/biochemical polymers is still an emerging field of research. Here, molecular dynamics simulations are used to illustrate the influence of inserted polyethylene segments on the secondary structure of several peptide homopolymers. A loss of structure of ≈50% when the peptide chain length drops to ten amino acids and a practically complete absence for even shorter peptide segments.

The authors present a proof-of-concept study for the calculation of atomic forces on a solvated molecule by means of the linear density-density response function in its moment expanded representation. The density-density response function represents an efficient way to compute molecular forces for arbitrary external potentials via an ab initio scheme, without the need to perform an explicit self-consistent quantum chemical calculation for each configuration of the chemical environment. Here, the authors show that it is indeed possible to determine the atomic forces of interacting bulk-like molecular complexes due to polarization effects of the surrounding molecules with good accuracy. This study represents a significant step the practical applicability of the approach, which is still in a development phase. The potential application of the computational scheme in terms of molecular dynamics simulations is illustrated by considering a variety of cluster conformations, as they would be found within a molecular dynamics trajectory.

We explicitly compute the non-equilibrium molecular dynamics of protons in the solid acid CsH2PO4 on the micrometer length scale via a multiscale Markov model: The molecular dynamics/matrix propagation (MDM) method. Within the MDM approach, the proton dynamics information of an entire molecular dynamics simulation can be condensed into a single M × M matrix (M is the number of oxygen atoms in the simulated system). Due to this drastic reduction in the complexity, we demonstrate how to increase the length and time scales in order to enable the simulation of inhomogeneities of CsH2PO4 systems at the nanometer scale. We incorporate explicit correlation of protonation dynamics with the protonation state of the neighboring proton sites and illustrate that this modification conserves the Markov character of the MDM method. We show that atomistic features such as the mean square displacement and the diffusion coefficient of the protons can be computed quantitatively from the matrix representation. Furthermore, we demonstrate the application potential of the scheme by computing the explicit dynamics of a non-equilibrium process in an 8 μm CsH2PO4 system during 5 ms.