Lattice-mismatched MOF-on-MOF nanosheets with rich oxygen vacancies show fast oxygen evolution kinetics for large-current water splitting

Constructing defective heterojunctions is crucial for enhancing the intrinsic activity of metal-organic framework (MOF)-based electrocatalysts for efficient alkaline water splitting, yet it remains a significant challenge. Here, we present a novel oxygen-vacancy-rich MOF-on-MOF heterojunction nanosheet catalyst (Ni NDC@Fe BDC/CP) fabricated on carbon fiber paper through lattice mismatch. Experimental and theoretical analyses reveal that this catalyst, with an ultra-thin nanosheet morphology (∼ 4.3 nm), abundant oxygen defects, and a tightly coupled heterojunction interface, facilitate interfacial charge transport. It optimizes the d-band center, enhances oxygen-containing intermediate adsorption, and promotes the formation of highly active Ni(Fe)OOH species, significantly boosting OER performance. In comparison to individual Ni NDC/CP and Fe BDC/CP, the obtained Ni NDC@Fe BDC/CP exhibits competitive OER performance, delivering an overpotential of 192/239 mV at a current density of 10/100 mA cm −2 and a small Tafel slope of 38.8 mV dec −1 . When coupled with Pt/C/CP in an overall water splitting device, the Ni NDC@Fe BDC/CP (+) ||Pt/C/CP (−) achieves a cell voltage as low as 1.43 and 1.54 V at 10 and 100 mA cm −2 , respectively, surpassing benchmark catalysts RuO 2 and Pt/C.