A General Strategy to Synthesize Fluidic Single Atom Electrodes for Selective Reactive Oxygen Species Production

Fine-tuning the geometric and electronic structure of catalytic metal centers via N-coordination engineering offers an effective design for the electrocatalytic transformation of O₂ to singlet oxygen (¹O₂). Herein, we develop a general coordination modulation strategy to synthesize fluidic single-atom electrodes for selective electrocatalytic activation of O₂ to ¹O₂. Using a single Cr atom system as an example, >98% ¹O₂ selectivity can be achieved from electrocatalytic O₂ activation due to the subtle engineering of Cr-N₄ sites. Both theoretical simulations and experimental results determined that "end-on" adsorption of O₂ onto the Cr-N₄ sites lowers the overall activation energy barrier of O₂ and promotes the breakage of Cr-OOH bonds to form •OOH intermediates. In addition, the flow-through configuration (k = 0.097 min⁻¹) endowed convection-enhanced mass transport and improved charge transfer imparted by spatial confinement within the lamellar electrode structure compared to that of batch reactor (k = 0.019 min⁻¹). In a practical demonstration, the Cr-N₄/MXene electrocatalytic system exhibits a high selectivity toward electron-rich micropollutants (e.g., sulfamethoxazole, bisphenol A, and sulfadimidine). The flow-through design of the fluidic electrode achieves a synergy with the molecular microenvironment that enables selective electrocatalytic ¹O₂ generation, which could be used in numerous ways, including the treatment of environmental pollution.