Zhi-Hao Wang

Controllable chemical doping is an effective strategy to tailor electronic structure and charge‐carrier dynamics in semiconductors, especially in one‐step‐excitation semiconductor photocatalysts. However, achieving a controllable dopant distribution within a single‐particle photocatalyst without compromising its well‐defined redox facets remains a significant challenge. Here, using a two‐step molten‐salt synthesis as a controlled platform, we reveal facet‐selective Al ³⁺ incorporation in SrTiO ₃ while preserving the desired cuboctahedron morphology with exposed {100}/{111} facets. Increasing the Al ³⁺ supply within this morphology‐preserving window leads to a pronounced facet‐anisotropic distribution within individual particles, with the Al content along {111} exceeding that along {100} by more than twofold from the surface toward the bulk. This facet‐anisotropic distribution enhances the inter‐facet electrostatic asymmetry associated with the intrinsic built‐in electric field. As a demonstration, 4.0 mol% Al‐doped SrTiO ₃ delivers an apparent quantum yield of 81.1% at 335 nm for overall water splitting, producing H ₂ and O ₂ in a stoichiometric 2:1 ratio with a hydrogen evolution rate of 3364.13 µmol·h ⁻¹ . This work establishes facet‐resolved dopant distribution as a spatial design parameter for efficient particulate photocatalysis.

Two-step thermochemical cycles offer a clean route for hydrogen and oxygen production but are typically limited to high temperatures exceeding 1500 °C. Lowering operating temperatures would enable the use of alternative heat sources such as industrial waste heat. Here, we report Pr₃ZrO₈ as a new enabling material for efficient intermediate-temperature redox cycling, with thermal reduction at 900 °C in argon and steam oxidation at 400 °C. Pr₃ZrO₈ adopts a face-centered cubic structure similar to CeO₂ but exhibits significantly greater oxygen deficiency, achieving average oxygen and hydrogen fluxes of 331.7 and 70.3 µmol·g^-1, respectively, over ten cycles at 20%H₂O. These values surpass those of leading CeO_2₋δ and perovskite oxides under comparable or more severe conditions. In-situ neutron and X-ray diffraction determine the phase stability boundaries of Pr₃ZrO₈, while density functional theory identifies O-H bond cleavage as the rate-limiting step. These results establish Pr₃ZrO₈ as a promising material for intermediate-temperature thermochemical oxygen and hydrogen production.

Single-crystal semiconductor-based photocatalysts exposing unique crystallographic facets show promising applications in energy and environmental technologies; however, crystal facet engineering through solid-state synthesis for photocatalytic overall water splitting is still challenging. Herein, we develop a novel crystal facet engineering strategy through solid-state recrystallization to synthesize uniform SrTiO₃ single crystals exposing tailored {111} facets. The presynthesized low-crystalline SrTiO₃ precursors enable the formation of well-defined single crystals through kinetically improved crystal structure transformation during solid-state recrystallization process. By employing subtle Al³⁺ ions as surface morphology modulators, the crystal surface orientation can be precisely tuned to a controlled percentage of {111} facets. The photocatalytic overall water splitting activity increases with the exposure percentage of {111} facets. Owing to the outstanding crystallinity and favorable anisotropic surface structure, the SrTiO₃ single crystals with 36.6% of {111} facets lead to a 3-fold enhancement of photocatalytic hydrogen evolution rates up to 1.55 mmol·h^-1 in a stoichiometric ratio of 2:1 than thermodynamically stable SrTiO₃ enclosed with isotropic {100} facets.

Cuprous halides (CuX; X = Cl, Br, or I) have been extensively investigated in the literature, but many of their fundamental properties are still not very well understood. For example, debate about their crystal stability, i.e., whether the ground-state structures of CuX are zinc-blende, still exists. By performing rigorous first-principles calculations for CuX using an accurate hybrid functional, we unambiguously demonstrate that CuX are indeed stable in the zinc-blende structure, but their accurate description requires careful treatment of the exchange interaction. Previous calculations based on local or semilocal density functionals underestimated the important contributions from exchange interactions and thus underestimated the energy separation between the unoccupied 4s and occupied 3d orbitals in Cu, resulting in an overestimation of the s-d coupling and the energy reduction of distorted CuX. Our study clarifies a long-standing and highly debated issue with regard to ground-state structures of CuX and advances the physics of phase stability and the importance of s-d coupling in semiconductors.