Developments and applications of the OPTIMADE API for materials discovery, design, and data exchange

The Open Databases Integration for Materials Design (OPTIMADE) application programming interface (API) empowers users with holistic access to a growing federation of databases, enhancing the accessibility and discoverability of materials and chemical data. Since the first release of the OPTIMADE specification (v1.0), the API has undergone significant development, leading to the upcoming v1.2 release, and has underpinned multiple scientific studies. In this work, we highlight the latest features of the API format, accompanying software tools, and provide an update on the implementation of OPTIMADE in contributing materials databases. We end by providing several use cases that demonstrate the utility of the OPTIMADE API in materials research that continue to drive its ongoing development

Mechanical and electrochemical properties of mixed transition metal oxides in cathode materials

Ein vielversprechender Ansatz zur Verbesserung der Leistungsfähigkeit von Kathodenmaterial für Lithium-Ionen-Batterien liegt in der Metallmischung. In dieser Arbeit nutzten wir Rechnungen mit Dichtefunktionaltheorie um elektrochemische Eigenschaften von LiM${_x}$M'$_{1-x}$PO$_{4}$ (M,M'= Übergangsmetalle) Olivinphosphat und LiNi$_{x}$Mn$_{y}$Co$_{1-x-y}$O$_{2}$ Schichtoxiden zu berechnen. Die verschiedenen Fälle haben wir hinsichtlich ihrer Bildungsenergie, Volumenänderung bei Interkalation, Interkalationsspannung, thermische Stabilität und Energiedichte klassifiziert. Unsere Resultate zeigen dass partielle Substitution der Eisenlage durch LiFePO$_{4}$ mit Nickel die Energiedichte sowie die elektronische Leitfähigkeit vergrössern und gleichzeitig die Volumenänderung bei (De-)Interkalation minimieren kann. Wir konnten zeigen, dass die beste elektrochemische Performance sowie ein Minimum der Volumenvariation in Schichtoxiden für ternäre Mischungen von LiNi$_{0.33}$Mn$_{0.33}$Co$_{0.33}$O$_{2}$ zu finden ist

Sn-Doped Hematite for Photoelectrochemical Water Splitting: The Effect of Sn Concentration

Hematite-based photoanodes have been intensively studied for photoelectrochemical water oxidation. The n-type dopant Sn has been shown to benefit the activity of hematite anodes. We demonstrate in this study that Sn-doped hematite thin films grown by atomic layer deposition can achieve uniform doping across the film thickness up to at least 32 mol%, far exceeding the equilibrium solubility limit of less than 1 mol%. On the other hand, with the introduction of Sn doping, the hematite crystallite size decreases and many twin boundaries form in the film, which may contribute to the low photocurrent observed in these films. Density functional theory calculations with a Hubbard U term show that Sn doping has multiple effects on the hematite properties. With increasing Sn4+ content, the Fe2+ concentration increases, leading to a reduction of the band gap and finally to a metallic state. This goes hand in hand with an increase of the lattice constant

Why Tin-Doping Enhances the Efficiency of Hematite Photoanodes for Water Splitting-The Full Picture

The beneficial effects of Sn(IV) as a dopant in ultrathin hematite (α‐Fe2O3) photoanodes for water oxidation are examined. Different Sn concentration profiles are prepared by alternating atomic layer deposition of Fe2O3 and SnO x . Combined data from spectrophotometry and intensity‐modulated photocurrent spectroscopy yields the individual process efficiencies for light harvesting, charge separation, and charge transfer. The best performing photoanodes are Sn‐doped both on the surface and in the subsurface region and benefit from enhanced charge separation and transfer. Sn‐doping throughout the bulk of the hematite photoanode causes segregation at the grain boundaries and hence a lower overall efficiency. Fe2O3 (0001) and terminations, shown to be dominant by microstructural analysis, are investigated by density functional theory (DFT) calculations. The energetics of surface intermediates during the oxygen evolution reaction (OER) reveal that while Sn‐doping decreases the overpotential on the (0001) surface, the Fe2O3 orientation shows one of the lowest overpotentials reported for hematite so far. Electronic structure calculations demonstrate that Sn‐doping on the surface also enhances the charge transfer efficiency by elimination of surface hole trap states (passivation) and that subsurface Sn‐doping introduces a gradient of the band edges that reinforces the band bending at the semiconductor/electrolyte interface and thus boosts charge separation

How photocorrosion can trick you: a detailed study on low-bandgap Li doped CuO photocathodes for solar hydrogen production

The efficiency of photoelectrochemical tandem cells is still limited by the availability of stable low band gap electrodes. In this work, we report a photocathode based on lithium doped copper(II) oxide, a black p-type semiconductor. Density functional theory calculations with a Hubbard U term show that low concentrations of Li (Li0.03Cu0.97O) lead to an upward shift of the valence band maximum that crosses the Fermi level and results in a p-type semiconductor. Therefore, Li doping emerged as a suitable approach to manipulate the electronic structure of copper oxide based photocathodes. As this material class suffers from instability in water under operating conditions, the recorded photocurrents are repeatedly misinterpreted as hydrogen evolution evidence. We investigated the photocorrosion behavior of LixCu1−xO cathodes in detail and give the first mechanistic study of the fundamental physical process. The reduced copper oxide species were localized by electron energy loss spectroscopy mapping. Cu2O grows as distinct crystallites on the surface of LixCu1−xO instead of forming a dense layer. Additionally, there is no obvious Cu2O gradient inside the films, as Cu2O seems to form on all LixCu1−xO nanocrystals exposed to water. The application of a thin Ti0.8Nb0.2Ox coating by atomic layer deposition and the deposition of a platinum co-catalyst increased the stability of LixCu1−xO against decomposition. These devices showed a stable hydrogen evolution for 15 minutes

Brokering between tenants for an international materials acceleration platform

The future of materials science is borderless, cooperative, and distributed across the globe. This necessitates flexible, reconfigurable software defined research workflows, which we herein demonstrate by integrating multiple disciplines and modalities. Our brokering approach to research orchestration exposes entire laboratories in a cooperative multi-tenancy platform that is asynchronous, modular, and resilient. To the best of our knowledge, this constitutes the first international materials acceleration platform (MAP) which is herein demonstrated through a battery electrolyte workflow that ran in five countries over two weeks. We discuss the lessons learned from multi-tenancy and fault tolerance and chart a way to a universal battery MAP with fully ontology- based schemas and cost-aware orchestration

The Role of Composition of Uniform and Highly Dispersed Cobalt Vanadium Iron Spinel Nanocrystals for Oxygen Electrocatalysis

Cation substitution in transition-metal oxides is an important approach to improve electrocatalysts by the optimization of their composition. Herein, we report on phase-pure spinel-type CoV_2–<i>x</i>Fe_<i>x</i>O₄ nanoparticles with 0 ≤ <i>x</i> ≤ 2 as a new class of bifunctional catalysts for the oxygen evolution (OER) and oxygen reduction reactions (ORR). The mixed-metal oxide catalysts exhibit high catalytic activity for both OER and ORR that strongly depends on the V and Fe content. CoV₂O₄ is known to exhibit a high conductivity, while in CoFe₂O₄ the cobalt cation distribution is expected to change due to the inversion of the spinel structure. The optimized catalyst, CoV_1.5Fe_0.5O₄, shows an overpotential for the OER of ∼300 mV for 10 mA cm^–2 with a Tafel slope of 38 mV dec^–1 in alkaline electrolyte. DFT+<i>U</i>+SOC calculations on cation ordering confirm the tendency toward the inverse spinel structure with increasing Fe concentration in CoV_2–<i>x</i>Fe_<i>x</i>O₄ that starts to dominate already at low Fe contents. The theoretical results also show that the variations of oxidation states are related to the surface region, where the redox activity was found experimentally to be manifested in the transformation of V³⁺ → V²⁺. The high catalytic activity, facile synthesis, and low cost of the CoV_2–<i>x</i>Fe_<i>x</i>O₄ nanoparticles render them very promising for application in bifunctional electrocatalysis