Search

Catalysts with isolated active sites have demonstrated preferable H2O2productivity via the 2e−oxygen reduction reaction, but their synthesis procedures are usually sophisticated, with only a few isolated sites generated. Here, we employ perovskite as a platform for facilely constructing isolated active sites with dense populations to produce H2O2. As a proof of concept, a silver niobate catalyst, where the Ag sites are isolated by the NbO6octahedra with an atomic distance (dAg–Ag) larger than 0.39 nm, is demonstrated to show outstanding H2O2productivity at both low and high currents. Combining theoretical calculations, chemical/electrochemical surface species tuning methods, and in situtransmission electron microscopy, the isolated Ag sites in AgNbO3are determined to be the active sites for the H2O2production. This study offers an initial exploration of the perovskite structure as a platform for constructing isolated active sites, paving the way for its potential application in more fields.

Unraveling the catalyst surface structure and behavior during reactions is essential for both mechanistic understanding and performance optimization. Here we report a phenomenon of facet-dependent surface restructuring intrinsic to β-Ni(OH)2catalysts during oxygen evolution reaction (OER), discovered by the correlative ex situand operandocharacterization. The ex situstudy after OER reveals β-Ni(OH)2restructuring at the edge facets to form nanoporous Ni1–xO, which is Ni deficient containing Ni3+species. Operandoliquid transmission electron microscopy (TEM) and Raman spectroscopy further identify the active role of the intermediate β-NiOOH phase in both the OER catalysis and Ni1–xO formation, pinpointing the complete surface restructuring pathway. Such surface restructuring is shown to effectively increase the exposed active sites, accelerate Ni oxidation kinetics, and optimize *OH intermediate bonding energy toward fast OER kinetics, which leads to an extraordinary activity enhancement of ∼16-fold. Facilitated by such a self-activation process, the specially prepared β-Ni(OH)2with larger edge facets exhibits a 470-fold current enhancement than that of the benchmark IrO2, demonstrating a promising way to optimize metal-(oxy)hydroxide-based catalysts.

Direct observation of oxygen evolution reaction (OER) on catalyst surface may significantly advance the mechanistic understanding of OER catalysis. Here, we report the first real-time nanoscale observation of chemical OER on Mn2O3nanocatalyst surface using an in situliquid holder in a transmission electron microscope (TEM). The oxygen evolution process can be directly visualized from the development of oxygen nanobubbles around nanocatalysts. The high spatial and temporal resolution further enables us to unravel the real-time formation of a surface layer on Mn2O3, whose thickness oscillation reflects a partially reversible surface restructuring relevant to OER catalysis. Ex situatomic-resolution TEM on the residual surface layer after OER reveals its amorphous nature with reduced Mn valence and oxygen coordination. Besides shedding light on the dynamic OER catalysis, our results also demonstrate a powerful strategy combining in situand ex situTEM for investigating various chemical reaction mechanisms in liquid.