High-entropy nanomaterials offer a powerful platform for tuning catalytic and electronic properties through multi-metal synergy, yet scalable routes to monodisperse, compositionally complex nanoparticles remain limited. We present a unified set of low-temperature, colloidal synthesis strategies that enable precise control over both high-entropy oxides and high-entropy sulfides, as well as their ternary and quaternary spinel analogues. For oxide systems, we leverage Lewis-acid-catalyzed esterification and the intrinsically low solubility product (Ksp) of metal oxides to achieve <4 nm, <15% dispersity high-entropy spinel and rock-salt nanoparticles, the smallest and most uniform colloidal HEOs reported, while ensuring synchronized monomer generation for multi-cation incorporation. For sulfides, we develop scalable “heat-up” and amino-acid–assisted routes to produce monodisperse Ni_xCo_3–xS₄ and multi-metal thiospinels, including five-metal high-entropy nanodiscs and star-like nanocrystals with tunable anisotropy. We further demonstrate in-situ and ex-situ formation of hybrid nanocrystal–nanosheet heterostructures that substantially enhance catalytic activity.  Across these systems, we demonstrate homogeneous incorporation of 5–10 cations, gram-scale yields, and strong alkaline OER activity, with overpotentials as low as 283 mV at 10 mA/cm² and excellent cycling stability. Together, these results establish a general and scalable colloidal framework for designing uniform, phase-pure, compositionally complex nanocrystals—advancing both the fundamental understanding and applied performance of high-entropy materials in energy-conversion technologies.

The transition to green energy is important, and an important part of this transition is fuel cells. Recently, the investigation into using formic acid as a fuel for fuel cells has been made. But a major setback for utilising formic acid as fuel is that carbon monoxide (CO) can be formed during the oxidation of formic acid as an unwanted by-product. The produced CO can poison the catalysts used for the reaction. It is therefore important to find catalysts that can be used in fuel cells that have a higher tolerance to CO.
In this research the electrodeposited AgAuCuPdPt high-entropy alloys have been investigated as such catalysts. These high-entropy alloys have previously been investigated by Salinas Quezada, Pedersen et al. 2024[1], but the authors did not electrodeposit the high-entropy alloys. To be able to have higher control of the metal composition of the high-entropy alloys, the hypothesis that they can be electrodeposited has been tested and confirmed through-out this work.
The high-entropy alloys were tested in both a CO-saturated environment and in formic acid and compared to a platinum sample. The CO-saturation of the high-entropy alloys was also compared to that of Salinas Quezada, Pedersen et al. 2024[1], and the electrodeposited high-entropy alloys were found to have a much higher activity than previously assumed.
In the CO-saturated environment, the high-entropy alloys showed a higher oxidation current than the platinum sample, and for the formic acid oxidation, the high-entropy alloys were found to be much more effective catalysts than platinum.

Improvement of the efficiency and cost-effectiveness of the oxygen evolution reaction (OER) remains a major challenge in water electrolysis due to its complex thermodynamics and sluggish four-electron kinetics, which involve generating paramagnetic O₂ from diamagnetic species (H₂O, OH^–). Recent studies have demonstrated that tuning the magnetic state of catalysts or applying external magnetic fields can significantly impact reaction pathways in spin-dependent processes. [1] In this work, we present magnetically modulated NiCo₂O₄ as an anode catalyst for magneto-electrocatalytic (MAG-EC) OER in alkaline media. By introducing strain into NiCo₂O₄ by rapid quenching in liquid nitrogen, the magnetic moment at room temperature was enhanced by ~18%. Under a low external magnetic field of 0.32 T, strained-NiCo₂O₄ exhibited a 12.6% decrease in overpotential at 10 mA∙cm^–2, compared to only a 3% reduction for pristine NiCo₂O₄ under identical conditions. Additionally, strained NiCo₂O₄ exhibited a remarkable 125.8% enhancement in current density (geometric) at 1.68 V vs. RHE under a 0.32 T magnetic field in comparison to that obtained without applying a magnetic field. These enhancements achieved by applying a magnetic field are attributed to increased spin polarization in the ferrimagnetic catalyst arising from its strengthened magnetic moment. The results highlight a conceptual advancement in magnetically controlled electrocatalysis, demonstrating how strain engineering and magnetic-state modulation can significantly boost OER activity. The insights gained from this study may guide the future design of spin-regulated catalytic materials for a broad range of energy conversion reactions.

Transition metal nitrides are promising semiconductors for solar energy conversion and optoelectronics, offering narrower bandgaps and superior carrier transport compared to oxides. However, their synthetic complexity has limited exploration and led to poorly controlled defects. In this contribution, we use reactive co-sputtering to synthesize and engineer nanometer-scale nitride thin films with precise control over composition and doping in the Ti-Ta-N,^[1] Zr-Ta-N,^[2,3] and Hf-Ta-N systems. Starting from orthorhombic Ta₃N₅, we show that substitutional Ti doping improves photoconversion efficiency by modulating defect and recombination dynamics. While high Ti doping forms a secondary TiN phase, Zr and Hf yield tunable solid solutions in the Zr-Ta-N-(O) and Hf-Ta-N-(O) systems, exhibiting bandgap modulation and large refractive indices. Notably, a new bixbyite-type ternary compound, ZrTaN₃, forms at a 1:1 Zr:Ta ratio, showing strong visible light absorption and photoanodic activity. DFT calculations reveal a tunable direct bandgap driven by cation ordering. These results underscore the potential of both established and emerging compositionally complex nitrides for solar energy and photonic applications, and highlight the importance of precise composition engineering to tune optoelectronic and charge transport characteristics.

Compositionally complex or high entropy materials (HEMs) – solid solutions of five or more elements - are an emerging material class in the development of novel electrocatalysts. These multi-metallic compounds provide exciting new possibilities for catalyst design, and theoretical analysis predicts a great potential for HEMs as electrocatalysts, due to the almost unlimited number of unique surface sites, which enable a wide distribution of adsorption energies.[1] The field of high entropy materials catalysis enables a new, statistical approach to materials design. From an experimental viewpoint, however, HEMs come with new challenges regarding their synthesis and characterization. For direct comparison between theoretically predicted properties and the performance of the prepared catalysts, single-phase HEMs are essential.[2] Synchrotron-based X-ray diffraction and spectroscopy provide insight into nanoscale structure formation, allowing us to follow the evolution of high-entropy alloy and oxide nanoparticles during synthesis and thermal treatments. [3,4] Such studies offer a mechanistic understanding of phase formation pathways, which enables the rational tuning of synthesis conditions to produce homogeneous, well-mixed solid solutions.

These well-mixed, multi-metallic materials allow us to determine not only different structure-activity properties of nanoparticle electrocatalysts but also to explore the stability of these novel materials under electrochemical reaction conditions. Studying the dissolution and degradation behavior of model HEM catalysts in an aqueous environment, the mechanisms that underlie the degradation of multi-metallic catalysts are explored. By relating structural characterization techniques with electrochemical analyses, through, e.g., operando X-ray diffraction, we can address the question of which role element mixing can play in the activation and potential stabilization of new electrocatalysts for fuel cell and electrolysis applications.[2]

Compositionally complex halide perovskites provide a lead-free platform for engineering structure–property coupling through the competition between octahedral tilting and B-site off-centering. However, their finite-temperature phase behavior is difficult to resolve with conventional first-principles approaches because it requires large supercells and long simulations to capture slow, collective distortions. Here, we develop a machine learning interatomic potential (MLIP) within the neuroevolution potential (NEP) framework [1] to model phase transitions and local symmetry breaking in mixed B-site perovskites CsGe_xSn_1–xBr₃. The MLIP is trained on density functional theory (DFT) data spanning diverse Ge/Sn chemical environments, achieving near-DFT accuracy while enabling long-time, large-scale Monte Carlo (MC) and molecular dynamics (MD) simulations.

Benchmarking the end members with MD and group-theory-based structural analysis [2] establishes distinct instability limits that define the mixed system. For CsGeBr₃, heating induces a sequence from a polar, tilted monoclinic (Cc) phase to an intermediate polar rhombohedral (R3m) phase with vanishing long-range tilts, and finally to a cubic (Pm-3m) phase [3]. In contrast, CsSnBr₃ follows a tilt-dominated pathway from orthorhombic (Pnma) to tetragonal (P4/mbm) and then to a cubic phase [4].

Extending to CsGe_xSn_1–xBr₃, combined MC/MD simulations across composition map how Ge/Sn mixing tunes the balance and coupling between off-centering and tilt networks. We present a composition–temperature phase diagram that identifies phase boundaries and crossover regimes between Ge-driven polar distortions and Sn-stabilized tilts. Overall, this work demonstrates that NEP-based MLIP enables predictive phase diagrams and engineering of local instabilities in compositionally complex, lead-free halide perovskites, with direct relevance to stabilizing targeted structural states in nanocrystal synthesis and tailoring optoelectronic functionality.

Abstract: The development of clean and renewable energy carriers, particularly green hydrogen, has become a central objective in contemporary materials research. In this work, TiO₂/ZnO nanocomposites were synthesized and evaluated as high-performance photocatalysts for hydrogen production through water splitting. The hybrid structure was designed to take advantage of the complementary optical and electronic properties of TiO₂ and ZnO, aiming to enhance light absorption, facilitate charge separation, and reduce electron– hole recombination. Nanocomposites were prepared using controlled chemical routes, and their structural, morphological, and optical characteristics were examined through XRD, SEM, TEM, and UV– Vis spectroscopy. Photocatalytic hydrogen evolution was assessed under both UV and visible-light irradiation. The,  TiO₂/ZnO nanocomposite exhibited significantly improved hydrogen production efficiency and superior long-term stability compared to pristine TiO₂. These findings demonstrate that optimizing interfacial interactions and band-alignment in metal-oxide nanocomposites provides an effective pathway for developing next-generation photocatalysts aimed at sustainable hydrogen generation.

High-entropy alloys (HEAs) have emerged as a transformative platform for electrocatalysis. Their appeal lies in the vast compositional versatility enabled by the combination of five or more elements, which generates a rich diversity of atomic configurations and surface sites ideally suited for complex multistep reactions. Recent years have witnessed explosive growth in the development of HEMs across diverse material classes and their application to a wide range of electrochemical reactions. Yet significant challenges remain to fully harness their capabilities while managing their intrinsic structural and chemical complexity. Advancing the field requires exploring compositional space, pinpointing reaction sites, and achieving atomic-level control of surface composition and organization. In this presentation, I will describe our recent advances in the colloidal synthesis of HEA nanoparticles and demonstrate the potential of these materials as oxygen catalysts at the cathode of metal–air batteries, emphasizing opportunities to boost efficiency and stability using abundant-element compositions and rational high-entropy design.

Nanoparticles of high entropy materials are intriguing catalysts since they combine high surface areas with synergistic effects that arise from the randomization of a large number of elements throughout a crystalline lattice. However, the synthesis of high-quality nanoparticles of high entropy materials can be challenging, particularly for colloidal nanoparticles made in solution. This talk will highlight our recent efforts in synthesizing several different classes of high entropy materials as colloidal nanoparticles, including alloys, intermetallics, sulfides, oxides, and oxyhalides. By studying aliquots extracted during high entropy nanoparticle synthesis, we have been able to generate snapshots of these complex nanochemical reactions. In most cases, we find that colloidal nanoparticles of high entropy materials form stepwise in solution through heterogeneous intermediates, despite generating products that have largely homogeneous co-localization of all constituent elements. This talk will also highlight some of the catalytic properties that emerge from these high entropy nanoparticles, including for hydrogenation, hydrogen evolution, and oxygen evolution.

Universal strategies have played a transformative role in organic synthesis, offering systematic and mechanistically guided approaches for constructing complex molecules.[1-3] Retrosynthetic analysis and standardized reactions, such as Suzuki coupling and Diels-Alder reactions, utilize well-established mechanisms and predictable kinetic pathways, enabling efficient and reproducible molecular synthesis.[4-6] These synthetic methods have greatly enhanced the reproducibility and scalability of synthetic processes. In this context, there is a growing demand for a universal synthetic approach for colloidal nanocrystals (NCs) to develop reproducible and scalable techniques suitable for a broad range of materials. A robust strategy of this nature would simplify the synthesis process, facilitating precise control over NCs characteristics to meet the needs of various applications. However, achieving such universality in colloidal NCs is hindered by complex reaction chemistry, nucleation kinetics, growth dynamics, and material-specific factors like temperature, solvents, and precursor selection.[8] Surface ligand interactions further complicate standardization, making material-specific generalized protocols a viable alternative.[8, 9] Recently, Cs-based alkali metal chalcogenides have gained interest as promising semiconductors for energy conversion and storage. While theoretical studies highlight their potential, limited nanoscale exploration and high-temperature synthesis constraints impede a deeper understanding of their properties and formation mechanisms.[10]

This study presents a simple and general approach for synthesising ternary Cs-based metal chalcogenides using a metal chalcogenide synthon-based strategy. This method involves the injection of Cs precursor into an in situ-formed metal chalcogenide synthons, resulting in the formation of Cs-M-Se (M = Cu, Bi, Sb, In, Ga) nanostructures with diverse morphologies and shapes. To further demonstrate the versatility of this approach, we extended its application to metal sulfides, synthesizing Cs-M-S (M = Cu, Bi, Sb, In, Ga). Remarkably, this strategy enabled the formation of alkali metal chalcogenides at the nanoscale with a variety of shapes and morphologies while also reporting novel morphologies and shapes in intermediate metal chalcogenide synthons. Furthermore, the study explored the influence of different metal chalcogenide phases on the resulting NC phases. Morever, computational analysis of this phase transition was conducted to clarify the specific phases involved in forming the final ternary product; offering valuable insight into the principles governing this synthetic methodology. In summary, this work establishes a foundation for a scalable, adaptable approach to synthesising alkali metal chalcogenides at the nanoscale.

High-entropy materials (HEMs) have emerged as a versatile platform for diverse applications, yet colloidal high-entropy chalcogenide nanocrystals (NCs) remain largely underexplored due to synthetic challenges owing to the reactivity disparities of multiple reactive species. Here, we report the first synthesis of monodisperse high-entropy Cu based chalcogenide NCs in the tetrahedrite phase, a flexible crystal structure that accommodates multiple cations with different valencies. A majority of HEMs rely on high temperature annealing to achieve a single, homogeneous phase stabilized by high configurational entropy. Employing a sequential, low-temperature cation-exchange strategy, we start with a Cu-Zn-Sb-S quaternary sulphide template and incorporate Ag⁺ and Bi³⁺ ions, preserving the crystal phase while enabling precise control over morphology. This bottom-up soft-chemistry approach circumvents the need for high-temperature enabling entropy-stabilized NCs with control over morphology. Remarkably, the synthesized NCs are fairly monodisperse, in contrast to conventional high-entropy systems that often suffer from particle aggregation and polydispersity. When evaluated as electrocatalysts, the high entropy tetrahedrite NCs demonstrate excellent hydrogen evolution reaction (HER) activity in acidic media, with low overpotentials and favorable Tafel slopes compared to their intermediate counterparts. This work introduces a new class of colloidal high-entropy chalcogenide NCs and establishes the first high-entropy tetrahedrite phase, paving the way for entropy-stabilized chalcogenide catalysts for energy conversion applications.

Hydrogen is a zero-emission energy carrier, yet its global production remains dominated by fossil fuels. With the accelerating impacts of climate change, the transition to renewable energy sources has become critical to achieving the United Nations Sustainable Development Goal 7: Affordable and Clean Energy. Semiconductor-based artificial photosynthesis, inspired by natural photosynthetic systems, represents a promising route to generate green hydrogen through solar-driven water splitting. To improve solar energy conversion efficiency, controlling crystal morphology and crystal defects, and elucidating their effect on properties are crucial. Mixed-anion compounds have emerged as promising photocatalysts [1]. Within this class of materials, BaTaO₂N stands out as a visible-light-responsive photocatalyst (~600 nm) because of its small bandgap (E_g = 1.8 eV), suitable band edge positions for visible-light-induced water splitting, chemical stability, and nontoxicity [2,3]. Conventionally synthesized via a two-step oxide precursor and high-temperature nitridation route, BaTaO₂N crystals often suffer from defect formation, which is detrimental to their photocatalytic activity. In this work, we applied an NH₃-assisted direct flux growth method to reduce defect density, tune the bandgap via cation doping, and investigate the influence of morphology, size, and porosity on photocatalytic and photoelectrochemical performance of BaTaO₂N crystals. The findings demonstrate that the BaTaO₂N crystals grown directly by NH3-assited KCL flux method have less defect density and BaTaO₂N crystals synthesized by two-step method without KCl flux exhibit higher surface areas and enhanced photocurrents due to increased active sites facilitating efficient CoO_x cocatalyst dispersion. Furthermore, we also explored the impact of crystal shape and size on the property and photocatalytic activity of β-TaON and Ta₃N₅.  

Compositionally complex energy materials display structural and electronic behavior that develops across multiple length scales. In this talk, I will show how advanced atomistic modeling, ranging from first-principles theory to machine-learned interatomic potentials, can help clarify this global and local complexity. I first discuss the global free-energy landscape of FAPbI₃, where large-scale molecular dynamics simulations with a machine-learned potential resolve a previously unknown low-temperature structure and reveal kinetically trapped formamidinium configurations [1]. Extending to mixed-cation systems, I will show how FA/MA compositional tuning creates a morphotropic phase boundary characterized by competing octahedral tilt patterns, nanoscale structural fluctuations, and enhanced electron-phonon coupling [2]. Moving from global structural effects to local electronic ones, I will discuss self-trapped excitons in BiVO₄, where hybrid density functional theory calculations identify competing localization modes that influence charge separation and transport [3]. Together, these examples illustrate how complexity arises at different levels in energy materials, and how a holistic modeling framework is needed for linking global phase behavior to local excited-state phenomena.

Photodetectors (PDs) have been receiving increasing attention in recent years because of their potential applications in video imaging, optical communication, bioinspired sensing and smart textiles. Moreover, metal halide perovskites (MHPs) with outstanding optical and electrical properties, good mechanical flexibility, low cost and low-temperature solution-processed fabrication have become promising candidates as light harvesting materials in PDs.

Herein, I will comprehensively review the developments of PDs based on MHPs reported recently by our group. Firstly, I will provide an introduction with respect to the fabrication of perovskite single crystals, device configuration and performance parameters, followed by the specific requirements of PDs including electrode material and electrode distance.[1] Next, preparation method of self-powered single crystal perovskite-based p-n junction photodiode will be presented.[2] Then, the synthesis and characterization of MHPs nanocrystals will be demonstrated, subsequently, flexible PDs and their performances will be presented.[3] In the end, conclusions and challenges will be put forward in the field of PDs based on MHPs.

Electrodeposition offers control over nanocrystal growth through modulation of the applied current or potential, which governs precursor reduction kinetics, nucleation behavior, and local ion concentrations. However, conventional direct electrodeposition onto the working electrode often produces nanocrystals with ill-defined morphologies and aggregated states. This study introduces seed-assisted electrodeposition to overcome these limitations, enabling growth of structurally complex and compositionally well-defined multimetallic nanocrystals. We identify lattice mismatch and metal-metal bond dissociation energy as key parameters dictating the growth mode: high values of either parameter promote island-like overgrowth, while low lattice mismatch favors layer-by-layer growth. Guided by these mechanistic insights, we achieve uniform metal shell deposition across a range of bimetallic systems, including those exhibiting significant interfacial strain. Furthermore, we demonstrate the formation of hollow-shell nanocrystals by dynamically modulating the redox environment during growth and show the future scope of these structures for electrochemical C-N coupling. Collectively, these findings establish design principles for the electrochemical synthesis of complex multimetallic nanomaterials with tailored architectures.