An Electrode with Two‐Level Porosity for Electro‐Fenton: Carbon Nanofiber‐Functionalized Macroporous Nickel Foam

Abstract Carbon is an established electrode material in electrochemical reactors, e.g., for the generation of hydrogen peroxide (H₂O₂). Common structures are graphite felts or carbon fibers. These materials usually lack adequate electrochemical activity, hence more selectively active moieties need to be introduced. Furthermore, the commonly porous materials require immobilization concepts which normally include polymeric binders that partly block the porous surface and may entail secondary pollution. This work introduces carbon nanofibers (CNFs), synthesized on nickel foams via catalytic carbon decomposition, as a novel, binder‐free electrode with two‐level porosity. The fibers are in the range of few nanometers and comprise embedded nickel nanoparticles (30–250 nm). The CNFs are deposited as a thin layer on a nickel foam, not affecting its intrinsically open‐porous nature. The as‐synthesized CNF/Ni foams show H₂O₂ production rates as high as 1.1 mg h⁻¹ cm⁻² at pH 3 and a cathodic potential of 0.11 V versus reversible hydrogen electrode (RHE) through multiple reaction pathways catalyzed by CNF and embedded nickel nanoparticles. In an electro‐Fenton process, the removal of carbamazepine (CBZ), a frequently detected micropollutant in water bodies is assessed, demonstrating an almost complete depletion after 10 min (c_CBZ,0 = 4 mg L⁻¹). These results unveil the potential of the integrated production of CNF/Ni foam electrodes with scale‐up perspectives for oxygen reduction reactions.