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Modulating the microenvironment of single‐atom catalysts (SACs) is critical to optimizing catalytic activity. Herein, we innovatively propose a strategy to improve the local reaction environment of Ru single atoms by precisely switching the crystallinity of the support from high crystalline and low crystalline, which significantly improves the hydrogen evolution reaction (HER) activity. The Ru single‐atom catalyst anchored on low‐crystalline nickel hydroxide (Ru−LC−Ni(OH)2) reconstructs the distribution balance of the interfacial ions due to the activation effect of metal dangling bonds on the support. Single‐site Ru with a low oxidation state induces the aggregation of hydronium ions (H3O+), leading to the formation of a local acidic microenvironment in alkaline media, breaking the pH‐dependent HER activity. As a comparison, the Ru single‐atom catalyst anchored on high‐crystalline nickel hydroxide (Ru−HC−Ni(OH)2) exhibits a sluggish Volmer step and a conventional local reaction environment. As expected, Ru−LC−Ni(OH)2 requires low overpotentials of 9 and 136 mV at 10 and 1000 mA cm−2 in alkaline conditions and operates stably at 500 mA cm−2 for 500 h in an alkaline seawater anion exchange membrane (AEM) electrolyzer. This study provides a new perspective for constructing highly active single‐atom electrocatalysts. [ABSTRACT FROM AUTHOR]

Monodisperse pancake-like/flower-like/leaf-like GdBO 3 samples have been successfully synthesized via a designed hydrothermal conversion method using H 3 BO 3 , Na 2 B 4 O 7 ·10H 2 O, or NaBO 2 ·4H 2 O as boron sources, respectively. It was found that different boron sources have crucial influences on the formation and morphology of the products. The Gd(OH) 3 nanorods precursors were prepared through a simple hydrothermal process, which then served as sacrificial templates for the fabrication of GdBO 3 micropancakes/microflowers/microleaves via a hydrothermal conversion process. FT-IR spectra confirm that vaterite-type GdBO 3 can be synthesized by this method. The possible formation mechanisms for different microstructures were put forward on the basis of a series of time-dependent control experiments. The products have similar stacked arrangements driven by the minimization of the interfacial and surface energy of the hydrothermal system. An investigation on the photoluminescence (PL) properties of GdBO 3 :Eu 3+ samples with different morphologies indicates that the PL properties of as-obtained GdBO 3 :Eu 3+ phosphors are strongly dependent on their morphology and crystallinity. The flower-like structure exhibits the strongest red emission. [ABSTRACT FROM AUTHOR]