Band Alignment-Driven Space Charge Remodeling in NiFe LDH@CoOx-CNF Heterojunction for Efficient Alkaline Oxygen Evolution

Abstract

While heterojunction engineering holds promise for enhancing NiFe-based oxygen evolution reaction (OER) catalysts, poorly matched interfacial Fermi levels often hinders the formation of high-valent Ni2+δ species critical for OER activity, creating a trade-off between charge-transfer efficiency and active-phase evolution. Herein, a band alignment strategy is proposed to resolve this conflict by controlled integration of Co nanodots (20 wt%) into electrospun carbon nanofibers (CoOx-CNF), followed by robust coupling NiFe LDH nanosheets. The presence of Co nanodots enhances CNF graphitization and tailors the interfacial Fermi level offset to 1.30 eV, thereby establishing directional electron transfer channels from NiFe LDH to CoOx-CNF. The resulting space charge remodeling induces selective electron depletion at Ni sites, which synergistically promotes the formation of catalytically active Ni2+δ species while accelerating charge transfer. Therefore, such an elaborately designed NiFe LDH@CoOx-CNF catalyst achieves an ultralow overpotential of 225 mV at 10 mA cm⁻² and exceptional stability for 100 h at 100 mA cm⁻². Operando electrochemical impedance spectroscopy directly tracks microscopic interfacial reactions and charge-transfer mechanisms, while DFT calculations reveal that the band alignment-mediated space charge effect improves the electronic structure and strengthens Ni 3d-O 2p hybridization, thus lowering the Gibbs free energy barrier of the rate-determining step (*O→*OOH). This work establishes a “band alignment→space charge remodeling→kinetic enhancement” paradigm for phase-selective electrocatalyst design.