Caozheng Diao

Oxygen-redox pathways offer a potential route beyond the thermodynamic scaling limitations of conventional metal-redox mechanisms, providing an opportunity to develop oxygen evolution catalysts for efficient and durable anion exchange membrane water electrolysis. However, direct O–O coupling through oxygen-redox chemistry remains difficult because the formation of triplet O₂ requires spin-compatible oxygen intermediates, whereas spin-mismatched coupling is energetically unfavorable. Here we show that electrochemical reconstruction of V-doped CoS₂ produces a cobalt oxyhydroxide catalyst with abundant coordinatively unsaturated Co–O units. These local structures strengthen Co–O electronic interactions, generate oxygen-hole states and activate Co-centered unpaired spins, thereby enabling spin-conserved radical oxygen coupling. The resulting catalyst couples low-overpotential OER activity (185 mV at 10 mA cm⁻²) with efficient anion exchange membrane water electrolysis performance, delivering 6.35 A cm⁻² at 2.0 V and sustained operation at 1 A cm⁻² for 2000 h. This work establishes spin control in metal oxyhydroxides as a design principle for efficient and durable anion exchange membrane water electrolysis.

The surfaces of strongly correlated materials can exhibit exotic properties that differ substantially from the bulk. Investigation of these surface effects requires both high quality surfaces, and an experimental technique capable of disentangling surface and underneath layers or bulk. Herein, we overcome these two challenges, using newly developed grazing-incident-angle resonant soft x-ray and magnetic scattering techniques to study ultrathin films of Spin(S) = 1/2 La₂CuO₄, the parent compound of high-critical-temperature (high-T_c) superconductor. We observe emergent surface magnetic ordering and surface-like electronic dipole layers at room temperature. As a function of temperature, intrinsic holes from Cu²⁺ and O^2- ions are mitigated from the surface into subsurface layers and back into the surface. The intrinsic hole and oxygen ion mitigation have different rates, yielding strong temperature hysteresis. Supported with theoretical calculations, these surface orderings consist of a mixture of Cu²⁺ 3d⁹ (S = 1/2) and Cu¹⁺ 3d¹⁰-like (S = 0) with strong magneto-electronic coupling through the many-body upper Hubbard band. Our results highlight intrinsic holes and oxygen ion mitigations, yielding surface-like electronic dipole and magnetic orderings and the potential of grazing-incident-angle resonant soft X-ray and magnetic scattering to elucidate, layer-by-layer, magnetic and electronic structures."

Interactions among various electronic states, such as charge density waves (CDWs), magnetism, and superconductivity, are pivotal in strongly correlated systems. While the relationship between CDWs and superconductivity has been extensively studied, the interplay between CDWs and magnetic order remains largely elusive. Kagome lattices, with their intrinsic nontrivial topology, charge order, and magnetism, provide a compelling framework for investigating these interactions. In this work, we unravel the orbital origins of magnetic moment modulation induced by CDW in the kagome magnet FeGe, a system exhibiting a unique coupling between CDW and magnetism. The combination of x-ray absorption spectroscopic experiments and first-principles calculations shed light on the temperature-dependent behavior of Fe3d–Ge4p orbital hybridization and corroborate its significant impact on the magnetic properties of FeGe. These findings introduce an orbital dimension to the correlation between charge and magnetic degrees of freedom, advancing our understanding of the intriguing quantum phases resulting from this interplay.

Ferromagnetic insulators and plasmons have attracted a lot of interest due to their rich fundamental science and applications. Recent research efforts have been made to find dopant-free ferromagnetic insulators and unconventional plasmons independently both in strongly correlated electron systems. However, our understanding of them is still lacking. Existing dopant-free ferromagnetic insulator materials are mostly limited to complex d- or f-systems with extremely low Curie temperature, low-symmetry structure, and strict growth conditions on specific substrates, limiting their compatibility with industrial applications. Unconventional plasmon is, on the other hand, a quasiparticle that originates from the collective excitation of correlated-charges, yet they are rarely explored, particularly in ferromagnetic insulator materials. Herewith, we present a novel, room temperature dopant-free ferromagnetic Mott-like insulator with a high-symmetry structure in unconventional strongly correlated s band of low-dimensional highly oriented single-crystal gold quantum dots (HOSG-QDs) on MgO(001). Interestingly, HOSG-QDs show new high-energy correlated-plasmons with low-plasmonics-loss. With a series of state-of-the-art experimental techniques, we find that the Mott-insulating state is tunable with surprisingly strong spin-splitting and spin polarization accompanied by strong s–s transitions, disappearance of Drude response, and generating new Mott-like gap. Supported with a series of theoretical calculations, the interplay of quantum confinement, many-body electronic correlations, and hybridizations tunes electron–electron correlations in s band and determines the ferromagnetism, Mott-like insulator, and high-energy correlated-plasmons. Our result shows a new class of room temperature dopant-free ferromagnetic Mott-like insulator and high-energy correlated-plasmons with low-loss in strongly correlated s band and opens unexplored applications of low-dimensional gold in spin field-effect transistors and plasmonics.

The interplay of electron-electron and electron-lattice interactions plays an important role in determining exotic properties in strongly correlated electron systems. Of particular interest is quasi-one-dimensional SrNbO _x metals, which are perovskite-related layered Carpy-Galy phases. Quasi-one-dimensional metals often exhibit a charge density wave (CDW) accompanied by lattice distortion; however, to date, the presence of a CDW in a quasi-one-dimensional metallic Carpy-Galy phase has not been detected. Here, we report the discovery of two distinct and simultaneous commensurate CDWs in Sr_0.95NbO_3.37 using resonant soft X-ray scattering (RSXS), namely, an electronic-(001) superlattice below ~ 200 K and an electronic-(002) Bragg peak. We also observe a non-electronic-(002) Bragg peak showing lattice distortion below ~ 150 K. Through the temperature dependence and resonance profile of these CDWs and the lattice distortion, as well as the relationship between the wavelength and charge density, these CDWs are determined to be Wigner crystals and Peierls-like instabilities, respectively. The electron‒electron interaction is strong and dominant even up to 350 K, and upon cooling, it drives the electron–lattice interaction. The correlation length of the electronic-(001) superlattice is surprisingly larger than that of the electronic-(002) Bragg peak, and the superlattice is highly anisotropic. Supported by theoretical calculations, the CDWs are determined by the charge anisotropy and redistribution between the O-2p and Nb-4d orbitals, and the strength of the electronic-(001) superlattice is within the strong coupling limit.

Photocatalytic overall water splitting into hydrogen and oxygen is desirable for long-term renewable, sustainable and clean fuel production on earth. Metal sulfides are considered as ideal hydrogen-evolved photocatalysts, but their component homogeneity and typical sulfur instability cause an inert oxygen production, which remains a huge obstacle to overall water-splitting. Here, a distortion-evoked cation-site oxygen doping of ZnIn₂S₄ (D-O-ZIS) creates significant electronegativity differences between adjacent atomic sites, with S₁ sites being electron-rich and S₂ sites being electron-deficient in the local structure of S₁–S₂–O sites. The strong charge redistribution character activates stable oxygen reactions at S₂ sites and avoids the common issue of sulfur instability in metal sulfide photocatalysis, while S₁ sites favor the adsorption/desorption of hydrogen. Consequently, an overall water-splitting reaction has been realized in D-O-ZIS with a remarkable solar-to-hydrogen conversion efficiency of 0.57%, accompanying a ~ 91% retention rate after 120 h photocatalytic test. In this work, we inspire an universal design from electronegativity differences perspective to activate and stabilize metal sulfide photocatalysts for efficient overall water-splitting.