Partial exfoliation of carbon nanofibers to enhance Ni-N-C active sites for oxygen evolution reaction

Carbon nanofibers (CNF) are promising substrates for Ni–N–C electrocatalysts in the oxygen evolution reaction (OER) due to their high electrical conductivity and remarkable resistance to oxidative degradation under harsh anodic conditions. However, this highly graphitic character limits the incorporation of single-atom species. Here, we introduce a partial exfoliation strategy via controlled oxidation (Tour method) of CNF to engineer surface defects and enhance Ni–N incorporation. This route partially exfoliates the CNF surface, increasing defect density and surface accessibility, as confirmed by electrochemical characterization, without compromising the structural integrity of nanofilaments. The controlled modification enables up to a tenfold increase in Ni-N coordination sites, as quantified by XPS, while HAADF-STEM confirms the presence of atomically dispersed Ni sites, with an enhancement of oxygen evolution current density above six-fold relative to the unmodified substrate. A trade-off situation is required between sufficient oxidation to host active sites, and excessive exfoliation leading to partial destruction of the surface. Interestingly, the faradaic efficiency remains above 90% towards oxygen evolution, demonstrating that defect engineering through partial exfoliation effectively balances structural integrity and active site exposure. Durability experiments reveal robust performance of the most performing catalyst, with the transformation of partial content of Ni-N sites into NiOOH. This approach highlights the tunability of carbon matrices to optimize catalytic performance through controlled defect generation. • Ni-N-C catalysts on carbon nanofibers are explored for OER in AEM electrolysis • The extent of CNF oxidation is easily controllable with KMnO 4 concentration • Partial exfoliation of CNF boosts the formation of active sites and OER activity • Carbon nanofibers are proven viable substrates for Ni-N-C SACs