Tailoring Electronegativity of Bimetallic Ni/Fe Metal-Organic Framework Nanosheets for Electrocatalytic Water Oxidation

The performance-limiting half reaction of electrochemical water splitting is the anodic oxygen evolution reaction (OER). The increased adsorption, especially chemical adsorption capacity, of the OER intermediate *O on anode materials is one of the key factors to improve the performance of the anodic electrocatalysts. In this research, we tuned the electronegativity of anode materials to tailor their chemical adsorption capacity in OER by modulating the metal ion composition in the secondary building unit in metal-organic frameworks (MOFs). Nanosheet Fe(III)-MIL-88A has been prepared as a parent catalyst in this research due to its high charger transfer capability and stability. Ni2+ ions with lower electronegativity have been introduced to exchange Fe3+ sites in Fe(III)-MIL-88A, which would lead to decrease of the overall electronegativity of the MOF anode, accompanied by the electron density shift from Ni2+ to Fe3+ via bridge oxygen. Porous MOFs with lower overall electronegativity significantly improved their adsorption capacity for *O intermediate, thereby accelerating the OER performance during operation. Our research hints at the potential that the electronegativity of porous anodes could be fine-tuned to optimize their adsorption capability for the high-efficient hydrogen production during electrocatalytic water splitting.

Automated summary

By tuning the metal ion composition in metal-organic frameworks, the electronegativity of anode materials can be tailored to improve their chemical adsorption capacity in OER. Introducing Ni2+ ions to exchange Fe3+ sites decreases the overall electronegativity of the MOF anodes, enhancing their adsorption capacity for *O intermediate and accelerating OER performance.