Shize Yang

The mechanism behind superconductivity suppression induced by Pr substitutions in YBa ₂ Cu ₃ O _{7− δ} (YBCO) has been a mystery since its discovery: in spite of being isovalent to Y ³⁺ with a small magnetic moment, it is the only rare-earth element that has a dramatic impact on YBCO’s superconducting properties. Using angle-resolved photoemission spectroscopy (ARPES) and DFT+ U calculations, we uncover how Pr substitution modifies the low-energy electronic structure of YBCO. Contrary to the prevailing Fehrenbacher–Rice (FR) and Liechtenstein–Mazin (LM) models, the low-energy electronic structure contains no signature of any f -electron hybridization or additional f -state Fermi surface sheets. Yet, strong electron doping is observed primarily on the antibonding Fermi surface. Meanwhile, we reveal major electronic structure modifications to Cu-derived states with increasing Pr substitution: a pronounced CuO ₂ bilayer decoupling and enhanced hopping along the CuO chain, implying indirect electron-release pathways beyond simple 4 f state ionization. Our results challenge the long-standing FR/LM mechanism, and establish Pr substituted YBCO as a potential platform for exploring correlation-driven phenomena in coupled 1D–2D systems.

Efficient removal of trace acetylene from ethylene streams is essential for producing polymer-grade ethylene, yet achieving highly selective semihydrogenation without over-hydrogenation remains a long-standing challenge. A key barrier is the lack of a simple, low-cost catalyst that can activate hydrogen effectively while preventing ethylene from reacting further. Here we show that defect-rich boron nitride, prepared through a straightforward flux reconstruction method, serves as a highly selective and metal-free catalyst for acetylene semihydrogenation. The catalyst contains abundant open boron and nitrogen sites that enable efficient hydrogen activation and rapid release of ethylene, thereby avoiding over-hydrogenation. Experiments combined with isotope labeling and theoretical analysis reveal that these defects lower the energy barrier for hydrogen activation while accelerating product desorption. Our findings demonstrate a scalable strategy for defect engineering in boron nitride and highlight its potential as a robust, sustainable alternative to metal-based catalysts in industrial ethylene purification.

Current catalysts face challenges with low formate selectivity at high current densities during the CO₂ electroreduction. Here, we showcase a versatile strategy to enhance the formate production on p-block metal-based catalysts by incorporating noble metal atoms on their surface, refining oxygen affinity, and tuning adsorption of the critical oxygen-bound *OCHO intermediate. The formate yield is observed to afford a volcano-like dependence on the *OCHO binding strength across a series of modified catalysts. The rhodium-dispersed indium oxide (Rh/In₂O₃) catalyst exhibits impressive performances, achieving Faradaic efficiencies (FEs) of formate exceeding 90% across a broad current density range of 0.20 to 1.21 A cm⁻². In situ Raman spectroscopy and theoretical calculations reveal that the oxophilic Rh site facilitates *OCHO formation by optimizing its adsorption energy, placing Rh/In₂O₃ near the volcano-shaped apex. A bipolar electrosynthesis system, coupling the CO₂ reduction at the cathode with the formaldehyde oxidative dehydrogenation at the anode, further boosts the FE of formate to nearly 190% with pure hydrogen generation under an ampere-level current density and a low cell voltage of 2.5 V in a membrane electrode assembly cell.

Cobalt phthalocyanine (CoPc) is recognized for catalysing electrochemical CO₂ reduction into methanol at high Faradaic efficiency but is subject to deactivation. Cobalt tetraaminophthalocyanine (CoPc-NH₂) shows improved stability, but its methanol Faradaic efficiency is below 30%. This study addresses these limitations in selectivity, reactivity and stability by rationally designing a dual-site cascade catalyst. Here we quantify the local concentration of CO, a key intermediate of the reaction, near a working CoPc-NH₂ catalyst and show that co-loading nickel tetramethoxyphthalocyanine (NiPc-OCH₃) with CoPc-NH₂ on multiwalled carbon nanotubes increases the generation and local concentration of CO. This dual-site cascade catalyst exhibits substantially higher performance than the original single-site CoPc-NH₂/carbon nanotube catalyst, reaching a partial current density of 150 mA cm⁻² and a Faradaic efficiency of 50% for methanol production. Kinetic analysis and in situ sum-frequency generation vibrational spectroscopy attribute this notable performance improvement to molecular-scale CO spillover from NiPc-OCH₃ sites to methanol-active CoPc-NH₂ sites.

Many sub-Neptune exoplanets have been believed to be composed of a thick hydrogen-dominated atmosphere and a high-temperature heavier-element-dominant core. From an assumption that there is no chemical reaction between hydrogen and silicates/metals at the atmosphere–interior boundary, the cores of sub-Neptunes have been modeled with molten silicates and metals (magma) in previous studies. In large sub-Neptunes, pressure at the atmosphere–magma boundary can reach tens of gigapascals where hydrogen is a dense liquid. A recent experiment showed that hydrogen can induce the reduction of Fe 2 + in (Mg,Fe)O to Fe 0 metal at the pressure–temperature conditions relevant to the atmosphere–interior boundary. However, it is unclear whether Mg, one of the abundant heavy elements in the planetary interiors, remains oxidized or can be reduced by H. Our experiments in the laser-heated diamond-anvil cell found that heating of MgO + Fe to 3,500 to 4,900 K (close to or above their melting temperatures) in an H medium leads to the formation of Mg 2 FeH 6 and H 2 O at 8 to 13 GPa. At 26 to 29 GPa, the behavior of the system changes, and Mg–H in an H fluid and H 2 O were detected with separate FeH x . The observations indicate the dissociation of the Mg–O bond by H and subsequent production of hydride and water. Therefore, the atmosphere–magma interaction can lead to a fundamentally different mineralogy for sub-Neptune exoplanets compared with rocky planets. The change in the chemical reaction at the higher pressures can also affect the size demographics (i.e., “radius cliff”) and the atmosphere chemistry of sub-Neptune exoplanets.

Gd-doped ceria (GDC) is one of the most promising materials using in solid oxide fuel cell (SOFC) at median operating temperature below 700°C. It has shown high ion conductivity and stability at low/median temperatures compared with other candidate materials [ 1]. GDC is a non-stoichiometric oxide material that is known for its ability to exchange lattice oxygen with surrounding ambient environment. Adding the aliovalent dopant Gd to pure ceria enhances the oxygen exchange ability by creating more extrinsic oxygen vacancies, which results conductivity improvement [ 2]. The dopants distribution and local concentration may play an important role in oxygen exchange functionality. However, the relationship between the surface exchange rate and the atomic level defect location/distribution is not well understood. To understand a possible influence of point defect structures and location on exchange sites, it's important to develop visualization methods to locate the defects. The atomic level Gd defect concentrations can be measured using scanning transmission electron microscopy coupled with electron energy-loss spectroscopy (STEM-EELS). However, for elemental mapping, the Gd EELS signal-to-noise ratio (SNR) is low, which making it difficult to detect and quantify. To address this weakness, we present a hybrid method involving EELS and high angle-annular dark-field imaging (HAADF).

Photonic modes in dielectric nanostructures, e.g., wide gap semiconductor like CeO₂ (ceria), have the potential for various applications such as information transmission and sensing technology. To fully understand the properties of such phenomenon at the nanoscale, electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope was employed to detect and explore photonic modes in well-defined ceria nanocubes. To facilitate the interpretation of the observations, EELS simulations were performed with finite-element methods. The simulations allow the electric and magnetic field distributions associated with different modes to be determined. A simple analytical eigenfunction model was also used to estimate the energy of the photonic modes. In addition, by comparing various spectra taken at different location relative to the cube, the effect of the surrounding environment on the modes could be sensed. This work gives a high-resolution description of the photonic modes' properties in nanostructures, while demonstrating the advantage of EELS in characterizing optical phenomena locally.