Oxygen vacancies (OVs) play a crucial role in the catalytic activity of metal-based catalysts; however, their activation mechanism toward peroxydisulfate (PDS) still lacks reasonable explanation. In this study, by taking bismuth bromide (BiOBr) as an example, we report an OV-mediated PDS activation process for degradation of bisphenol A (BPA) employing singlet oxygen (1O2) as the main reactive species under alkaline conditions. The experimental results show that the removal efficiency of BPA is proportional to the number of OVs and is highly related to the dosage of PDS and the catalyst. The surface OVs of BiOBr provide ideal sites for the inclusion of hydroxyl ions (HO–) to form BiIII–OH species, which are regarded as the major active sites for the adsorption and activation of PDS. Unexpectedly, the activation of PDS occurs through a nonradical mechanism mediated by 1O2, which is generated via multistep reactions, involving the formation of an intermediate superoxide radical (O2 •–) and the redox cycle of Bi­(III)/Bi­(IV). This work is dedicated to the in-depth mechanism study into PDS activation over OV-rich BiOBr samples and provides a novel perspective for the activation of peroxides by defective materials in the absence of additional energy supply or aqueous transition metal ions.

Electrocatalytic nitrate reduction sustainably produces ammonia and alleviates water pollution, yet is still challenging due to the kinetic mismatch and hydrogen evolution competition. Cu/Cu 2 O heterojunction is proven effective to break the rate-determining NO 3 À -to-NO 2 À step for efficient NH 3 conversion, while it is unstable due to electrochemical reconstruction. Here we report a programmable pulsed electrolysis strategy to achieve reliable Cu/Cu 2 O structure, where Cu is oxidized to CuO during oxidation pulse, then regenerating Cu/Cu 2 O upon reduction. Alloying with Ni further modulates hydrogen adsorption, which transfers from Ni/Ni(OH) 2 to N-containing intermediates on Cu/Cu 2 O, promoting NH 3 formation with a high NO 3 À -to-NH 3 Faraday efficiency (88.0 � 1.6 %, pH 12) and NH 3 yield rate (583.6 � 2.4 μmol cm À 2 h À 1 ) under optimal pulsed conditions. This work provides new insights to in situ electrochemically regulate catalysts for NO 3 À -to-NH 3 conversion.

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