Hierarchical Carbon‐Based Electrocatalyst with Functional Separation Properties for Efficient pH Universal Nitrate Reduction

The electrocatalytic reduction of nitrate (eNO₃ ^-RR) to ammonia (NH₃) across varying pH is of great significance for the treatment of practical wastewater containing nitrate. However, developing highly active and stable catalysts that function effectively in a wide pH range remains a formidable challenge. Herein, a hierarchical carbon-based metal-free electrocatalyst (C-MFEC) of winged carbon coaxial nanocables (W-CCNs, in situ generated graphene nanosheets and outside carbon layer with abundant topological defects from pristine carbon nanotubes, CNTs), is prepared through moderate oxidation of CNTs and the subsequent introduction of topological defects. The W-CCNs feature functional separation properties, with an inner core of pristine CNTs that facilitates efficient charge transfer, while the outer shell is composed of in situ generated graphene nanosheets and carbon layers enriched with topological defects characterized by distinct carbon atom configurations, which play a crucial role in promoting the adsorption of NO₃ ^-, the dissociation of water, and the N─H bond formation. This innovative design enables the C-MFEC to exhibit outstanding performance for eNO₃ ^-RR, operating efficiently with the NH₃ yield rates of 49.5, 75.3, and 88.1 g h^-1 g_cat. ^-1 in acidic, neutral, and alkaline media, respectively. Such performance metrics not only outshine C-MFECs but also rival or surpass those of certain metal-based catalysts.