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Defects in the crystal structure of nanomaterials are important for their diverse applications. As, defects in 2D framework allow surface confinement effects, efficient molecular accessibility, high surface‐area to volume‐ratio and lead to higher catalytic activity, but it is challenging to expose defects of specific metal on the surface of 2D alloy and find the correlation between defective structure and electrocatalytic properties with atomic precision. Herein, the work paves the way for the controlled synthesis of ultrathin porous Ir–Cu nanosheets (NSs) with selectively iridium (Ir) rich defects to boost their performance for acidic oxygen evolution reaction (OER). X‐ray absorption spectroscopy reveals that the oxidized states of Ir in defects of porous NSs significantly impact the electronic structure and decline the energy barrier. As a result, porous Ir–Cu/C NSs deliver improved OER activity with an overpotential of 237 mV for reaching 10 mA cm−2 and exhibit significantly higher mass activity than benchmark Ir/C under acidic conditions. Therefore, the present work highlights the concept of constructing a selective noble metal defect‐rich open structure for catalytic applications. [ABSTRACT FROM AUTHOR]

• Surface ion isolated platinum-thiocyanate catalyst enables efficient electrosynthesis of H 2 O 2. • The PtSCN 4 /C exhibits high mass activity and ultra-long stability in acidic media. • A weakened absorption of *OOH on the ion isolated Pt surface is the origin of 2e– ORR pathway. • Fast degradation of organic pollution was achieved by the on-site H 2 O 2 generation system. Electrosynthesis of hydrogen peroxide (H 2 O 2) through oxygen reduction reaction (ORR) is an attractive alternative to the traditional anthraquinone process. It offers decentralized and on-site generation of H 2 O 2 with a cost-effective system. Noble metals electrocatalysts through alloying or in a single-atomic structure and a few non-precious metals have been demonstrated with high selectivity but the stability remains challenging. Here, we propose a surface ion isolated platinum-thiocyanate (PtSCN x) catalyst as a promising electrocatalyst for the H 2 O 2 electrosynthesis in acidic media. The SCN– binding remarkably weakens the absorption of crucial *OOH intermediate on the Pt surface, leading to the change of ORR electron transfer pathway. The carbon supported PtSCN x exhibits an onset potential of 0.68 V (versus RHE) and ∼ 90% selectivity. Significantly, the PtSCN x /C shows a continual and stable electrolysis over 130 h, which outperforms the state-of-the-art 2e– ORR catalysts. Moreover, an on-site electrochemical rapid removal of organic pollutant is achieved through an electro-Fenton process. [ABSTRACT FROM AUTHOR]

• A concept of isolating active sites by ion poisoning for the electrosynthesis of H 2 O 2. • SCN− was screened as the most efficiently poisoned Pt/C catalysts for two-electron ORR. • The catalysts exhibited high activity and selectivity towards H 2 O 2 production in acidic media. Precious metal-based catalysts have been explored intensively for the electrocatalysis of oxygen reduction reaction (ORR). Alloying with heteroatoms, for instance, Hg to isolate precious metal sites are reported to convert the ORR from four-electron (4e−) to two-electron (2e−) pathway. The 2e− ORR could be used for the electrochemical production of hydrogen peroxide (H 2 O 2) as a sustainable route instead of industrial anthraquinone-mediated catalysis. Isolating active sites provides a breakthrough strategy to regulate electron transfer pathway of ORR. However, the highly toxic mercury limits the practical use. Herein we employ a simple ion poisoning strategy, by virtue of the strong ion coordination effects to regulate the classic Pt/C catalyst for the electrochemical H 2 O 2 production through ORR in acid media. The representative SCN− poisoned Pt/C catalyst displayed high activity and selectivity of over 90% at a wide range of potentials. The stability tests showed negligible performance lost after 30 hours. The present work offers a promising poisoning strategy to regulate precious catalysts for selectively electrochemical production of H 2 O 2. Image, graphical abstract [ABSTRACT FROM AUTHOR]