Impact of Iron in Three-Dimensional Co-MOF for Electrocatalytic Water Oxidation.

The integration of iron (Fe) into a cobalt metal-organic framework (Co-MOF) tunes the electronic structure of the parent MOF as well as enhances their electrocatalytic characteristics. By using pyrazine and hydrofluoric acid, we have synthesized three-dimensional Co-MOF [CoFC4H4N2(SO4)0.5], (1), and Fe-MOF [FeFC4H4N2(SO4)0.5], (2), through a single-step solvothermal method. Further, a series of bimetallic (having both Co and Fe metal centers) MOFs [Co1-xFexFC4H4N2(SO4)0.5] were synthesized with variable concentrations of Fe, and their electrocatalytic performances were analyzed. The optimized amount of Fe significantly impacted the electrocatalytic behavior of the bimetallic MOF toward water oxidation. Particularly, the Co0.75Fe0.25-MOF needs only 239 and 257 mV of overpotential to deliver 10 and 50 mA/cm2 current density, respectively, in alkaline electrolytic conditions. The Co0.75Fe0.25-MOF shows a lower Tafel slope (42 mV/dec.) among other bimetallic MOFs and even the commercial RuO2, and it has excellent durability (with ∼8 mV increases in overpotential after 18 h of electrolysis) and 97.05% Faradaic efficiency, which further evident its catalytic excellency. These findings explore the intrinsic properties of MOF-based electrocatalysts and prospect the suitability for future water electrolysis.