Granular Boron-doped Diamond with Controlled Doping for Coupled Anodic Peroxydisulfate Formation and Cathodic Activation in a Three-Dimensional Electrochemical System

Conventional particle electrodes often exhibit limited catalytic activity, poor corrosion resistance and inadequate long-term stability. In addition, in sulfate-containing electrolytes, anodic formation of peroxydisulfate (PDS) is unavoidable. The restricted accumulation and low effective utilization of PDS, caused by decomposition and low current efficiency, ultimately limit pollutant removal performance. In this work, granular boron-doped diamond (G-BDD) electrodes were constructed by depositing BDD films onto spherical SiC substrates through hot filament chemical vapor deposition (HFCVD). Controlled incorporation of boron significantly enhanced electrical conductivity and interfacial electron-transfer kinetics. When integrated into a three-dimensional (3D) electrochemical system, the optimized G-BDD-0.9% electrode markedly improved PDS electrogeneration, reaching 9.12 mM within 30 min, far exceeding that of a conventional two-dimensional (2D) system. Crucially, the PDS generated in the anode chamber of the 3D system is transported to the cathode via a circulation strategy, where electrochemical activation yields SO 4 · - , ·OH, and 1 O 2 . This coupled PDS generation and activation pathway significantly accelerated tetracycline (TC) degradation. The 3D-circulation system achieved 87% TC removal efficiency, with a reaction rate constant 2.71 times higher than the 2D system and reduced the energy consumption to 4.02 kWh m -3 order -1 . Mechanistic investigations confirmed that PDS originates from both direct sulfate oxidation and radical-mediated reactions at the anode, while cathodic activation synergistically enhances oxidative capacity. Overall, the G-BDD electrodes, combined with the integrated strategy of anodic PDS formation and cathodic electroactivation, demonstrate strong potential for advancing electrochemical oxidation technologies and enabling more efficient degradation of persistent organic pollutants in future applications.