Short-Lived Interfaces in Energy Materials

The kinetics of most chemical energy storage/conversion systems depend on the mass transport through matter, which is rate-limited by various kinetic barriers. The distinction of the barriers by static and dynamic interfaces helps in reducing their impact and therefore enhancing the overall kinetics. The concept is introduced along examples of static and dynamic interfaces in hydrogen storage, thermal energy storage in absorptive media, and electrochemical water splitting and CO2 reduction. In addition to the description of analysis methods to probe static and dynamic interfaces, the general strategy as well as concrete examples to overcome them are discussed.

Minimal synthetic enhancers reveal control of the probability of transcriptional engagement and its timing by a morphogen gradient

How enhancers interpret morphogen gradients to generate spatial patterns of gene expression is a central question in developmental biology. Although recent studies have begun to elucidate that enhancers can dictate whether, when, and at what rate a promoter will engage in transcription, the complexity of endogenous enhancers calls for theoretical models with too many free parameters to quantitatively dissect these regulatory strategies. To overcome this limitation, we established a minimal synthetic enhancer system in embryos of the fruit fly Drosophila melanogaster. Here, a gradient of the Dorsal activator is read by a single Dorsal binding site. By quantifying transcriptional activity using live imaging, our experiments revealed that this single Dorsal binding site is capable of regulating whether promoters engage in transcription in a Dorsal concentration-specific manner. By modulating binding-site affinity, we determined that a gene's decision to engage in transcription and its transcriptional onset time can be explained by a simple theoretical model where the promoter has to traverse multiple kinetic barriers before transcription can ensue. The experimental platform developed here pushes the boundaries of live-imaging in studying gene regulation in the early embryo by enabling the quantification of the transcriptional activity driven by a single transcription factor binding site, and making it possible to build more complex enhancers from the ground up in the context of a dialogue between theory and experiment.

Spin pinning effect to reconstructed oxyhydroxide layer on ferromagnetic oxides for enhanced water oxidation

Producing hydrogen by water electrolysis suffers from the kinetic barriers in the oxygen evolution reaction (OER) that limits the overall efficiency. With spin-dependent kinetics in OER, to manipulate the spin ordering of ferromagnetic OER catalysts (e.g., by magnetization) can reduce the kinetic barrier. However, most active OER catalysts are not ferromagnetic, which makes the spin manipulation challenging. In this work, we report a strategy with spin pinning effect to make the spins in paramagnetic oxyhydroxides more aligned for higher intrinsic OER activity. The spin pinning effect is established in oxideFM/oxyhydroxide interface which is realized by a controlled surface reconstruction of ferromagnetic oxides. Under spin pinning, simple magnetization further increases the spin alignment and thus the OER activity, which validates the spin effect in rate-limiting OER step. The spin polarization in OER highly relies on oxyl radicals (O∙) created by 1st dehydrogenation to reduce the barrier for subsequent O-O coupling.

Controlled Surface Reconstruction on Ferromagnetic Oxides: Spin Pinning Effect to the Oxyhydroxide Layer and Its Enhanced Oxygen Evolution Activity

The production of hydrogen by water electrolysis suffers from the kinetic barriers in the oxygen evolution reaction (OER) that limits the overall efficiency. As spin-dependent kinetics exist in OER, the spin alignment in active OER catalysts is critical for reducing the kinetic barriers in OER. It is effective to facilitate the spin polarization in ferromagnetic catalysts by applying external magnetic field, which increases the OER efficiency. However, more active OER catalysts tend to have dynamic open-shell orbital configurations with disordered magnetic moments, without showing an apparent long-range interatomic ferromagnetism; thus controlling the spin alignment of these active catalysts is challenging. In this work, we report a strategy with spin pinning effect to make the spins in active oxyhydroxides more aligned for higher intrinsic OER activity. Such strategy bases on a controllable reconstruction: ferromagnetic oxides with controlled sulfurization can evolve into stable oxide_FM/oxyhydroxide configurations with a thin oxyhydroxide layer under operando condition. The spin pinning effect is found at the interface of oxide_FM/oxyhydroxide. The spin pinning effect can promote spin selective electron transfer on OER intermediates to generate oxygens with parallel spin alignment, which facilitates the production of triplet oxygen and increases the intrinsic activity of oxyhydroxide by ~ 1 order of magnitude. Under spin pinning, the spins in oxyhydroxide can become more aligned after magnetization as long-range ferromagnetic ordering is established on the magnetic domains in oxide_FM. The OER kinetics are facilitated accordingly after magnetization, implying that the spin pinning effect is involved in the rate-determining step and this step is spin dependent. The spin polarization process in OER under spin pinning is also believed to be sensitive to the existence of active oxygen ligand (O(-)) in oxyhydroxide. When the O(-) is created in 1^st deprotonation step under high pH, the spin polarization of ligand oxygens will be facilitated, which reduces the barrier for subsequent O-O coupling and promotes the O₂ turnover.

Controlled Surface Reconstruction on Ferromagnetic Oxides: Spin Pinning Effect to the Oxyhydroxide Layer and Its Enhanced Oxygen Evolution Activity

The production of hydrogen by water electrolysis suffers from the kinetic barriers in the oxygen evolution reaction (OER) that limits the overall efficiency. As spin-dependent kinetics exist in OER, the spin alignment in active OER catalysts is critical for reducing the kinetic barriers in OER. It is effective to facilitate the spin polarization in ferromagnetic catalysts by applying external magnetic field, which increases the OER efficiency. However, more active OER catalysts tend to have dynamic open-shell orbital configurations with disordered magnetic moments, without showing an apparent long-range interatomic ferromagnetism; thus controlling the spin alignment of these active catalysts is challenging. In this work, we report a strategy with spin pinning effect to make the spins in active oxyhydroxides more aligned for higher intrinsic OER activity. Such strategy bases on a controllable reconstruction: ferromagnetic oxides with controlled sulfurization can evolve into stable oxide_FM/oxyhydroxide configurations with a thin oxyhydroxide layer under operando condition. The spin pinning effect is found at the interface of oxide_FM/oxyhydroxide. The spin pinning effect can promote spin selective electron transfer on OER intermediates to generate oxygens with parallel spin alignment, which facilitates the production of triplet oxygen and increases the intrinsic activity of oxyhydroxide by ~ 1 order of magnitude. Under spin pinning, the spins in oxyhydroxide can become more aligned after magnetization as long-range ferromagnetic ordering is established on the magnetic domains in oxide_FM. The OER kinetics are facilitated accordingly after magnetization, implying that the spin pinning effect is involved in the rate-determining step and this step is spin dependent. The spin polarization process in OER under spin pinning is also believed to be sensitive to the existence of active oxygen ligand (O(-)) in oxyhydroxide. When the O(-) is created in 1^st deprotonation step under high pH, the spin polarization of ligand oxygens will be facilitated, which reduces the barrier for subsequent O-O coupling and promotes the O₂ turnover.

Bifurcation of excited state trajectories toward energy transfer or electron transfer directed by wave function symmetry

This work explores the concept that differential wave function overlap between excited states can be engineered within a molecular chromophore. The aim is to control excited state wave function symmetries, so that symmetry matches or mismatches result in differential orbital overlap and define low-energy trajectories or kinetic barriers within the excited state surface, that drive excited state population toward different reaction pathways. Two donor–acceptor assemblies were explored, where visible light absorption prepares excited states of different wave function symmetry. These states could be resolved using transient absorption spectroscopy, thanks to wave function symmetry-specific photoinduced optical transitions. One of these excited states undergoes energy transfer to the acceptor, while another undertakes a back-electron transfer to restate the ground state. This differential behavior is possible thanks to the presence of kinetic barriers that prevent excited state equilibration. This strategy can be exploited to avoid energy dissipation in energy conversion or photoredox catalytic schemes.

Knocking down the kinetic barriers towards fast-charging and low-temperature sodium metal batteries

Current knowledge on Na metal anode has been limited on its room-temperature or high-temperature (molten Na-S system) performances. However, the properties regarding to its low-temperature and fast-charging performances are rarely...

Ternary Ruthenium Complex Hydrides for Ammonia Synthesis

Ammonia is the feedstock for nitrogen fertilizers and a potential carbon-free energy carrier, but the current production emits more CO₂ than any other chemical producing reaction in the world. The demand for decarbonizing the ammonia industry by using renewable energy has renewed research interests into catalyst development for effective N₂ reduction under mild conditions, a grand scientific challenge. Conventional heterogeneous catalysts based on metallic Fe or Ru mediate dinitrogen dissociation and hydrogenation through a relatively energy-costing pathway. The ternary ruthenium complex hydrides Li₄RuH₆ and Ba₂RuH₆ reported in this work, on the other hand, represent an entirely new class of compound catalysts, which are composed of the electron- and H-rich [RuH₆] anionic centers for non-dissociative dinitrogen reduction, where hydridic H transports electron and proton between the centers, and the Li(Ba) cations for stabilizing N_xH_y (x: 0 to 2, y: 0 to 3) intermediates. The dynamic and synergistic involvement of all the components of the ternary complex hydrides facilitates a novel reaction mechanism with a narrow energy span and perfectly balanced kinetic barriers for the multi-step process, leading to ammonia production from N₂+H₂ with superior kinetics under mild conditions.