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[Display omitted] • Anionic, cationic, and multi-ion vacancies in transition-metal-based electrocatalysts. • The chemical and physical methods in regard to the generation of atomic vacancies. • The advanced techniques to probe the structures and properties of atomic vacancies. • Key factors/parameters for mechanistic investigation on atomic vacancies. • Instructive perspectives of atomic vacancy engineering for boosted water splitting. Green hydrogen production from electrocatalytic water splitting is drawing growing interests to meet the needs of sustainable development. The efficiency of water splitting is governed by the electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Atomic vacancies have demonstrated significant advancements to modulate the electrocatalytic performance. Herein, the latest progresses of atomic vacancy engineering are systematically summarized, including the representative methods for generating different vacancies, the advanced microscopic and spectroscopic techniques for identifying vacancies, and the electrochemical and theoretical approaches for understanding the effect of vacancies and exploiting new atomic vacancies. The internal relations between specific vacancy regulation route and enhanced catalytic performance are discussed in terms of the improved electronic structure, the lowered energy barrier, and the optimized adsorption/desorption behavior of intermediate species. Beyond that, the synergistic effects between atomic vacancy and dopant/ single-atom/ nanocluster/ heterojunction are elucidated. At the end, instructive outlooks are proposed for in-depth understanding on atomic vacancies and scaling-up water splitting for the industrial application. [ABSTRACT FROM AUTHOR]

Formaldehyde (HCHO) is the main source of indoor air pollutant. HCHO sensors are therefore of paramount importance for timely detection in daily life. However, existing sensors do not meet the stringent performance targets, while deactivation due to sensing detection at room temperature, for example, at extremely low concentration of formaldehyde (especially lower than 0.08 ppm), is a widely unsolved problem. Herein, we present the Ag nanoparticles (Ag NPs) sensitized dispersed In2O3 nanograin via a low-fabrication-cost hydrothermal strategy, where the Ag NPs reduces the apparent activation energy for HCHO transporting into and out of the In2O3 nanoparticles, while low concentrations detection at low working temperature is realized. The pristine In2O3 exhibits a sluggish response (Ra/Rg = 4.14 to 10 ppm) with incomplete recovery to HCHO gas. After Ag functionalization, the 5%Ag-In2O3 sensor shows a dramatically enhanced response (135) with a short response time (102 s) and recovery time (157 s) to 1 ppm HCHO gas at 30 °C, which benefits from the Ag NPs that electronically and chemically sensitize the crystal In2O3 nanograin, greatly enhancing the selectivity and sensitivity. [ABSTRACT FROM AUTHOR]