In situ synthesis of reactive oxygen species (ROS) on demand via oxygen activation (OA) is significant in biological, chemical, and environmental fields. Thus, the design of OA catalysts with adequate reactivity, durability, and selectivity is critical but challenging. Here, we report a Cu x O@C core@shell photoelectrode prepared by encapsulating Cu/Cu 2 O/CuO into a carbon layer through anodic electropolymerization (electrophoresis-coupled self-assembly of carbon quantum dots). Theoretical prediction and experiments indicate that the carbon layer can effectively facilitate optical trapping and charge transfer, thus promoting photoelectric conversion and anti-photocorrosion performance of Cu x O@ C. The inner Cu x O core acts as an electron reservoir and continuously injects electrons into the outer carbon layer shell, and the carbon atoms adjacent to oxygen-enriched functional groups (C−O−C and −COOH) in the electron-rich carbon layer work as the reactive sites to adsorb O 2 and donate electrons to the antibonding orbital [lowest unoccupied molecular orbital (π*)] of dioxygen. Optimized adsorption and hydrogenation of the critical intermediates (*O 2 , *OOH, and *H 2 O 2 ) and thermodynamically tunable O−O bond cleavage enable O 2 being selectively reduced to the superoxide anion and hydroxyl radical via the mixed multielectron processes consisting of one-and three-electron pathways. Sulfamethoxazole, an emerging refractory organic contaminant widely present in the environment, can be effectively degraded (∼100% removal) in such an electrochemical platform, benefiting from the abundant ROS generated in situ. Our findings demonstrate an innovative strategy to develop highly efficient and selective OA catalysts for practical water purification.

Active chlorine species-mediated electrocatalytic oxidation is a promising strategy for ammonia removal in decentralized wastewater treatment. Flow-through electrodes (FTEs) provide an ideal platform for this strategy because of enhanced mass transport and sufficient electrochemically accessible sites. However, limited insight into spatial distribution of electrochemically accessible sites within FTEs inhibits the improvement of reactor efficiency and the reduction of FTE costs. Herein, a microfluidic-based electrochemical system is developed for the operando observation of microspatial reactions within pore channels, which reveals that reactions occur only in the surface layer of the electrode thickness. To further quantify the spatial distribution, finite element simulations demonstrate that over 75.0% of the current is accumulated in the 20.0% thickness of the electrode surface. Based on these findings, a gradient-coated method for the active layer was proposed and applied to a Ti/RuO2 porous electrode with an optimized pore diameter of ∼25 μm, whose electrochemically accessible surface area was 381.7 times that of the planar electrode while alleviating bubble entrapment. The optimized reactor enables complete ammonia removal with an energy consumption of 60.4 kWh kg–1 N, which was 24.2% and 39.9% less than those with pore diameters of ∼3 μm and ∼90 μm, respectively.

Electrocatalysis applied in energy conversions has recently been associated with nanotips that catalyze extensive fuelforming or value-adding reactions. However, the enhanced catalytic behavior governed by tip-intensified microenvironment reconstruction is particularly elusive and is yet to be understood. Here, we demonstrated a homemade visualization platform to collect information from the local microenvironment of a solution near an electrode (LMSE) with high temporal−spatial resolution, thereby figuring out the sharp-tip enhancement effect for the chlorine evolution reaction (CER). Through visualization using sensitive Cl − and pH sensors, we confirmed that periodic nanoneedles were beneficial for field-induced anion concentration, giving priority to water dissociation and synchronously creating optimal pH conditions for triggering the CER, whereby the Cl − consumption rate within the LMSE was 1.3 times higher than that of the slab counterpart. Tip-enhanced effects meanwhile endowed the local microenvironment with intensified concentration and temperature gradients for continuous transport of Cl − substrates and effective diffusion of HClO products, whereby the oxygen evolution reaction for persistent CER activities was restrained. Our study provides definitive evidence that the optimal microenvironment functionalized with tip-intensified ion concentration from the electrolyte and water dissociation at tip sites are key to stabilize the crucial reaction intermediate for superior electrocatalytic performance.