Piotr M Kowalski

Forschungszentrum Jülich · Institute of Energy and Climate Research (IEK)

Fundamental understanding of electrochemical interfaces is a prerequisite for designing well performing and economically viable electrocatalyst materials. The rapid increase in supercomputing power accompanied by methodical improvements in atomistic simulations enables an accelerated computer-aided materials design process. Our research in this con...

Non‐volatile memristors dynamically switch between high (HRS) and low resistance states (LRS) in response to electrical stimuli, essential for electronic memories, neuromorphic computing, and artificial intelligence. High‐entropy Prussian blue analogs (HE‐PBAs) are promising insertion‐type battery materials due to their diverse composition, high st...

Protic ionic liquids (PILs) are promising candidates as electrolytes for proton exchange polymer membrane fuel cells. In order to optimize their properties, a detailed understanding of the molecular interactions within the bulk and at the electrode–electrolyte interface is needed, which can be obtained by infrared spectra. A prerequisite for extrac...

Polymer-electrolyte fuel cells operating at a temperature above 100 °C would allow for easier water management and a simplified system design. Available electrolytes such as fluoropolymers grafted with sulfonic acid...

A hydrogen‐based energy system will be the backbone of a future energy grid using renewable energies. It is widely accepted that polymer electrolyte membrane fuel cells (PEMFCs) are promising converters of chemical energy stored as hydrogen into electrical energy. An increase of the operation temperature from below 80°C to above about 160°C is cons...

Exsolution-active catalysts allow for the formation of highly active metallic nanoparticles, yet their long-term thermal stability remains a challenge. In this work, the dynamics of exsolved Ni nanoparticles are probed in situ with atomically resolved secondary electron imaging in an environmental STEM. STEM pre-characterization shows embedded NiOx...

Garnet-type solid electrolytes stand out as promising Li-ion conductors for the next-generation batteries. It has been demonstrated that the inherent properties of garnets can be tailored by introducing various dopants into their crystal structures. Recently, there has been a growing interest in the concept of high entropy stabilization for materia...

This study explores multi-component garnet-based materials as solid electrolytes for all-solid-state lithium batteries. Through a combination of computational and experimental approaches, we investigate the thermodynamic and structural properties of lithium lanthanum zirconium oxide garnets doped with various elements. Applying density functional t...

Trends of the electrocatalytic activities across transition metals are typically explained by d-band properties such as center or upper edge positions in relation to Fermi levels. Here, the universality of...

Ra,Ba)SO4 solid solutions are commonly encountered as problematic scales in subsurface energy-related applications, e.g., geothermal systems, hydraulic fracturing, conventional oil and gas, etc. Despite its relevance, its crystallization kinetics were never determined because of radium (226), high radioactivity (3.7 × 10¹⁰ Bq g⁻¹), and utilization...

Atomistic structure and stability of Li-rich high-entropy layered oxide cathode materials are studied. A significant structural change including Li/Ni interchange, TM migration, and secondary phase formation leading to capacity fading is found.

The high‐entropy approach is applied to monoclinic Prussian White (PW) Na‐ion cathodes to address the issue of unfavorable multilevel phase transitions upon electrochemical cycling, leading to poor stability and capacity decay. A series of Mn‐based samples with up to six metal species sharing the N‐coordinated positions was synthesized. The materia...

The high‐entropy approach is applied to monoclinic Prussian White (PW) Na‐ion cathodes to address the issue of unfavorable multilevel phase transitions upon electrochemical cycling, leading to poor stability and capacity decay. A series of Mn‐based samples with up to six metal species sharing the N‐coordinated positions was synthesized. The materia...

This work combines spectroscopic and photometric data of the polluted white dwarf WD 0141−675 which has a now retracted astrometric super-Jupiter candidate and investigates the most promising ways to confirm Gaia astrometric planetary candidates and obtain follow-up data. Obtaining precise radial velocity measurement for white dwarfs is challenging...

Understanding the degradation mechanisms of organic compounds in an extreme radiolysis induced environment is important for designing efficient organic extractants for the separation of radionuclides from used nuclear fuel. In this paper, we present an in-depth computational chemistry-based molecular level analysis of the radiolytic degradation of...

The availability of well performing and cost efficient energy storage devices is of utmost importance for a smooth transition to sustainable energy. Lithium-ion batteries (LIBs) have been successfully commercialized and widely used in various portable devices. Functional materials with higher voltages and greater capacity are needed to further boos...

Doping with Fe boosts the electrocatalytic performance of NiOOH for the oxygen evolution reaction (OER). To understand this effect, we have employed state-of-the-art electronic structure calculations and thermodynamic modeling. Our study reveals that at low concentrations Fe exists in a low-spin state. Only this spin state explains the large solubi...

In the last decade, the use of Machine and Deep Learning (MDL) methods in Condensed Matter physics has seen a steep increase in the number of problems tackled and methods employed. A number of distinct MDL approaches have been employed in many different topics; from prediction of materials properties to computation of Density Functional Theory pote...

Efficient electrochemical energy storage and conversion require high performance electrodes, electrolyte or catalyst materials. In this contribution we discuss the simulation-based effort made by Institute of Energy and Climate Research at Forschungszentrum Jülich (IEK-13) and partner institutions aimed at improvement of computational methodologies...

A combined experimental and theoretical investigation is presented which examines the compressibility of two SrUO4-x polymorphs, α and β, under hydrostatic conditions and explains the contrasting chemical and mechanical behaviours of these in terms of differences in oxygen defect formation chemistry. Via Rietveld refinements against in situ neutron...

A novel polymorph of ThB2O5, denoted as β-ThB2O5, was synthesised under high-temperature high-pressure (HT/HP) conditions. Via single crystal X-ray diffraction measurements, β-ThB2O5 was found to form a three-dimensional (3D) framework structure where thorium atoms are ten-fold oxygen coordinated forming tetra-capped trigonal prisms. The only other...

We performed classical molecular dynamics (CMD) simulations of water structures on Pb(100) and (111) surfaces. The main objective was to test the capability of Interface force field to reproduce water structures obtained from more computationally intensive ab initio molecular dynamics (AIMD) simulations. At the same length and time scales we found...

Using the linear response-based constrained local density approximation (cLDA) approach we systematically computed the Hubbard U parameters for series of 3d, 4d, and 5d transition metals. We compare the results with estimations by the constrained random phase approximation (cRPA) method and discuss the performance of the self-consistent density fun...

Single-phase monazite-type ceramics are considered as potential host matrices for the conditioning of separated plutonium and minor actinides. Sm-orthophosphates were synthesised and their behaviour under irradiation was investigated with respect to their long-term performance in the repository environment. Sintered SmPO4 pellets and thin lamellae...

With the recent development of high entropy materials, an alternative approach to develop advanced functional materials with distinctive properties that show improved values compared to conventional materials has been provided. The high entropy concept was later successfully transferred to metal fluorides and high entropy fluorides (HEFs) were succ...

Reprocessing of spent nuclear fuel aims at improving resource efficiency and reducing its radiotoxicity and heat production in the long term. The necessary separation of certain metal ions from the spent fuel solutions can be achieved using different solvent extraction processes. For the scenario of the EURO-GANEX process, the use of the new, modif...

Protic ionic liquids are promising electrolytes for fuel cell applications. They would allow for an increase in the operation temperatures to more than 100 °C, facilitating water and heat manage-ment and thus increasing overall efficiency. As ionic liquids consist of bulky charged molecules, the structure of the electric double layer will significa...

Pyrochlore compounds (A 2 B 2O7) have a large applicability in various branches of science and technology. These materials are considered for use as effective ionic conductors for solid state batteries or as matrices for immobilization of actinide elements, amongst many other applications. In this contribution we discuss the simulation-based effort...

Nickel-based oxides are highly active, cost effective materials for the oxygen evolution reaction in alkaline conditions. Recent experimental studies have revealed the importance of surface deprotonation and alkali metal cation adsorption on the activity of Ni oxide surfaces, in contact with aqueous alkaline electrolyte. As a first step to elucidat...

Self-consistent modeling of the interface between a solid metal electrode and a liquid electrolyte is a crucial challenge in computational electrochemistry. In this contribution, we adopt the ESM-RISM computational framework to study the charged interface between a Pt(111) surface partially covered with chemisorbed oxygen and an aqueous acidic elec...

Nickel-based oxides are highly active, cost effective materials for the oxygen evolution reaction in alkaline conditions. Recent experimental studies have revealed the importance of surface deprotonation and alkali metal cation adsorption on the activity of Ni oxide surfaces, in contact with aqueous alkaline electrolyte. As a first step to elucidat...

Nickel-based oxides are highly active, cost effective materials for the oxygen evolution reaction in alkaline conditions. Recent experimental studies have revealed the importance of surface deprotonation and alkali metal cation adsorption on the activity of Ni oxide surfaces, in contact with aqueous alkaline electrolyte. As a first step to elucidat...

Applying physical pressure in the uranyl-sulfate system has resulted in the formation of the first purely inorganic uranyl oxo-salt phase with a considerable uranyl bend: Na4[(UO2)(SO4)3]. In addition to a strong bend of the typically almost linear O═U═O, the typically equatorial plane is broken up by two out-of-plane oxygen positions. Computationa...

With a combination of atomistic modeling and experimental techniques, we have investigated the structural and elastic parameters of sodium borosilicate glasses, including irradiation‐induced changes. Both approaches show that the Young's modulus depends linearly on the density of material. The simulated glass density and boron speciation match also...

Li x FePO 4 orthophosphates and fluorite- and pyrochlore-type zirconate materials are widely considered as functional compounds in energy storage devices, either as electrode or solid state electrolyte. These ceramic materials show enhanced cation exchange and anion conductivity properties that makes them attractive for various energy applications....

A systematic investigation examining the origins of structural distortions in rutile-related ternary uranium AUO4 oxides using a combination of high-resolution structural and spectroscopic measurements supported by ab initio calculations is presented. The structures of β-CdUO4, MnUO4, CoUO4, and MgUO4 are determined at high precision by using a com...

The composition dependence of the lattice constant, a, in AxB1-xO2-0.5xV0.5x, fluorite-type solid solutions (B = Zr, A = {Nd-Yb, Y}, V = oxygen vacancy) is characterized by changes in slope at x ~ 1/3, which cannot be described by existing models. Moreover, over the range of 0.15 ≤ x ≤ 1/3 the a vs. x data on all systems can be fitted with a linear...

We performed systematic ab initio calculations of the formation enthalpies of Ln2B2O7-type (B=Ti,Sn,Hf,Zr) compounds in pyrochlore, weberite and defect fluorite structure. The comparison with the experimental data shows that except the B=Ti case, the defect fluorite phase is unstable in the entire range of considered compositions and weberite struc...

Valence band electronic structure of mixed uranium oxides (UO2, U4O9, U3O7, U3O8, UO3) has been studied by the resonant inelastic X-ray scattering (RIXS) technique at the U M5 edge and by computational methods. We show here that the RIXS technique and recorded U 5f-O 2p charge transfer excitations can be used to proof the validity of theoretical ap...

Computational modeling is an important aspect of the research on nuclear waste materials. In particular, atomistic simulations, when used complementary to experimental efforts, contribute to the scientific basis of safety case for nuclear waste repositories. Here we discuss the state-of-the-art and perspectives of atomistic modeling for nuclear was...

Doping by Cr is used to improve the performance of uranium dioxide (UO2)-based nuclear fuel. However, the mechanism of structural incorporation of Cr remains unclear. Here, in order to understand this process on the atomic scale and the redox state of Cr in UO2-based nuclear fuel, we performed intensive ab initio atomistic simulations of the Cr dop...

The safe management of high‐level nuclear wastes, including their final disposal in a deep geological repository, requires a sound scientific understanding of the processes affecting the various materials present in the multibarrier system of the disposal facility, including the radioactive waste forms. Thus materials science aspects play an import...

Computational modeling is an important aspect of the research on nuclear waste materials. In particular, atomistic simulations, when used complementary to experimental efforts, contribute to the scientific basis of safety case for nuclear waste repositories. Here we discuss the state-of-the-art and perspectives of atomistic modeling for nuclear was...

Rare earth zirconates, such as Nd2Zr2O7, crystallise with the pyrochlore structure and are a group of materials which have been suggested as potential nuclear waste forms for actinide immobilisation. In this work, a new hydroxide co-precipitation route is presented to investigate the incorporation of Pu into Nd2Zr2O7. The plutonium content was vari...

The present study investigates possible use of Layered Double Hydroxides (LDH) for Tc(VII) remediation. Mg/Al– and Mg/Fe–LDH were obtained by a hydrothermal route and thermally activated at 450 °C, which was shown to significantly improve the Tc(VII) removal efficiency. Based on XRD investigation of Tc–LDH phases, the uptake Tc(VII) from the soluti...

Studtite, [UO2(η2-O2)(H2O)2].2H2O and metastudtite [UO2(η2-O2)(H2O)2] are important phase alteration of UO2 in a spent nuclear fuel repository and has previously been shown to react with Np(V). In this work we extend the study to Am(V) on a tracer scale and show spectroscopic evidence that the Am is incorporated into the structure of studtite as Am...

A calorimetric and thermodynamic investigation of two alkali-metal uranyl tungstates, Cs4UO24WO5W2O8O2(cr) and Cs4[UO27WO53O3](cr), was undertaken. Both phases were synthesized by solid-state sintering of a mixture of cesium nitrate, tungsten (VI) oxide and gamma-uranium (VI) oxide at high temperature. The synthetic products were characterized by X...

We performed extensive and accurate atomistic simulations of elastic and heat transport properties of series of rare-earth orthophosphate ceramics LnPO4 (Ln = La, …, Lu and Y) in monazite and xenotime structures. The results show clear trends in the elastic moduli along the lanthanide-series, which complement the existing experimental data on these...

Lanthanide phosphates (LnPO4) are considered as a potential nuclear waste form for immobilization of Pu and minor actinides (Np, Am, and Cm). In that respect, in the recent years we have applied advanced atomistic simulation methods to investigate various properties of these materials on the atomic scale. In particular, we computed several structur...

When considering f elements, solvent extraction is primarily used for the removal of lanthanides from ore and their recycling, as well as for the separation of actinides from used nuclear fuel. Understanding the complexation mechanism of metal ions with organic extractants, particularly the influence of their molecular structure on complex formatio...

Valence band electronic structure of mixed uranium oxides (UO2, U4O9, U3O7, U3O8, b-UO3) has been studied by the resonant inelastic X-ray scattering (RIXS) technique at the U M5 edge and...

The uptake of 226Ra to various cement hydration phases such as calcium-silicate-hydrates (C-S-H), ettringite (AFt) and monosulfate (AFm) as well as hardened cement pastes (HCP) made from ordinary Portland cement and low pH cement, respectively, was studied in batch-type sorption experiments under anoxic conditions. Besides sorption kinetics, the ef...

This study combines spectroscopic and computational investigations to understand the incorporation of curium (Cm³⁺) in rhabdophane and monazite solid-solutions. In monazites, Cm³⁺ incorporation occurs on one specific lattice site. The local order around the dopant in these monazites is dependent on the solid-solution composition. La-rich hydrated r...

In situ synchrotron powder X-ray diffraction measurements have demonstrated that SrUO4 undergoes a reversible phase transformation under reducing conditions at high temperatures, associated with the ordering of oxygen defects resulting in a lowering of crystallographic symmetry. When substoichiometric rhombohedral α-SrUO4- x, in space group R3̅ m w...

The minerals studtite, [UO2(η2-O2)(H2O)2]·2H2O, and metastudtite, [UO2(η2-O2)(H2O)2], are uranyl peroxide minerals that are major oxidative alteration phases of UO2 under conditions of geological storage. The dehydration of studtite has been studied using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy. XPS of the U 4f regi...

A quantitative understanding of the principle factors that govern their geochemical behavior is required to employ boron and its isotopes as geochemical tracers of any vapor-, liquid- or melt-mediated process in the Earth’s interior. Feedback between experiments and computational predictions are required to gain insight into the processes driving i...