Ultrathin 2D–2D NiFe LDH/MOF heterojunction nanosheets: an efficient oxygen evolution reaction catalyst for water oxidation

Abstract

Designing ultrathin MOF-based heterostructural nanosheets with high conductivity and rich active sites and studying their dynamic structural evolution during the OER remain an ideal but challenging task. Here, the hierarchical NiFe LDH/MOF structure constructed using an in situ self-dissociation–assembly strategy exhibits a typical sheet-on-sheet hierarchical morphology with a thickness of approximately 1.5–4 nm. Electrochemical tests indicate that the NiFe LDH/MOF catalyst reveals an impressively low overpotential of 196 mV at 10 mA cm⁻² with a Tafel slope of 32.5 mV dec⁻¹ in the OER process, surpassing most recently reported catalysts. The overall water splitting device, incorporating the NiFe LDH/MOF, achieves competitive current densities at low cell voltages and exceptional stability, emphasizing its potential as a promising catalyst for efficient and durable water oxidation in sustainable energy conversion. Studies reveal that the unique 2D ultra-thin self-supporting array structure provides abundant active sites and high conductivity, as well as strong electronic interactions between different components and heterogeneous interfaces that jointly optimize the activation energy of active sites and oxygen-containing intermediates, thereby improving OER performance. This study also provides insights into the dynamic active sites, revealing Ni(Fe)OOH as the true active species during the OER process, thereby contributing to the rational design of heterogeneous catalysts.