Simulated three-dimensional boron-doped diamond anode applied to the treatment of organic-polluted wastewater with simultaneous hydrogen production

Three-dimensional (3D) electrode architectures have emerged as a promising strategy to improve the electrochemical treatment of wastewater, since they offer an increased electroactive area ( A e ) and enhanced mass transfer. However, the interplay among A e , mass transfer, and electrode potential distribution in three-dimensional electrodes remains poorly understood. This work investigated these effects using aromatic compounds, carboxylic acids, herbicides, multicomponent electrolytes, and real wastewaters, under different hydrodynamic conditions. A simulated three-dimensional boron-doped diamond (BDD) anode (3DS-BDD), assembled by stacking commercial mesh-BDD (M-BDD) electrodes, was developed to distinguish the contributions of A e and mass transfer coefficients ( k m ). Cyclic voltammetry showed that A e increased from 41.6 to 107 cm 2 , while Sherwood-Reynolds correlations revealed modified transport behavior. Although 3DS-BDD exhibited higher apparent mass transfer parameters ( k m A ), the corresponding k m values were lower than for the M-BDD electrode. Electrode potential measurements revealed a non-uniform distribution, demonstrating that the increase in k m A originated from the enlarged area, rather than intrinsic mass transfer enhancement. Electrooxidation followed pseudo-first order kinetics, while hydrogen evolution proceeded with near-unity Faradaic efficiency, irrespective of the wastewater composition. Comparable k m values for all the organic matrices indicated that mass transfer governed by reactor hydrodynamics, rather than pollutant properties. The results showed that the most efficient reactors should combine enlarged A e with higher k m . The proposed modular 3M-BDD concept addresses these requirements by preserving the favorable hydrodynamics of individual mesh electrodes, while providing a large A e , offering a promising strategy for the scale-up of electrochemical wastewater treatment integrated with low-carbon hydrogen production.