Bimetal-Organic Frameworks from in Situ-Activated NiFe Foam for Highly Efficient Water Splitting

Nickel-iron foam (NFF) has high air permeability and a high specific surface area because of its connected pore structure and high porosity, making it an ideal catalyst support material. However, it is challenging to effectively utilize metal ions in the NFF to prepare new advanced electrocatalysts without introduction of metal species. Here, we demonstrate that activated metal ions in NiFe foam serve as the support and metal sources for in situ synthesis of NiFe bimetal-organic frameworks (NFF-MOF). Specifically, by further acidification to activate NiFe metal ions on the NFF backbone, and then to generate active NFF-MOF species through the participation of the organic ligand, the resulting NFF-MOF material exhibits significantly improved electrocatalytic performance toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with ultralow overpotentials of 81 and 250 mV at a current density of 10 mA cm-2, respectively. Density functional theory calculations and experimental results suggest that the NFF-MOF from the in situ-activated NiFe foam promotes transport and separation of charge because of highly uniform dispersed metal sites, high porosity, and an ordered 3D skeleton structure, thus accelerating the electrochemical HER and OER. This work brings new insights for the development of next-generation high-efficiency electrocatalysts.