In Situ Controllably Self-Assembled CoFe-TDPAT Metal–Organic Framework Nanosheet Arrays on Iron Foam as Highly Efficient Bifunctional Catalytic Electrodes for Overall Water Splitting at Large Current Density

For the first time, a Co and Fe bimetallic metal-organic framework (BMOF) nanosheet array (NSA) employing 5,5′,5′'-(1,3,5-triazine-2,4,6-triyl)tris(azanediyl)triisophthalic acid (H 6 TDPAT) as the organic ligand is in situ controllably self-assembled on iron foam (IF). The obtained IF@CoFe-TDPAT NSA exhibits an oxygen evolution reaction (OER) activity much superior to most reported catalysts and even Ru and Ir-based ones and hydrogen evolution reaction (HER) activity higher than most metal-organic framework (MOF)-based catalysts. The excellent bifunctional activities are ascribed to the superhydrophilic (3D) vertically aligned, interconnected NSA of CoFe-TDPAT MOF with in situ activated coordinatively unsaturated metal sites remarkably enhancing OH − and H 2 O adsorption, accelerating electron transfer and transport, and facilitating O 2 /H 2 diffusion. When adopted as a bifunctional electrode for overall water splitting, it achieves 300 mA cm −2 at 1.753 V and exhibits negligible current decay after 100 h. This performance is the highest of recently reported noble-metal-free water electrolyzers, and even much higher than those using commercial noble metal-based catalysts. This work offers an economical, facile, and controllable strategy to fabricate low-cost, highly efficient, and bifunctional BMOF nanostructured array electrodes for large-current-density water splitting, and also sheds light on the mechanisms for in situ self-assembly and outstanding OER and HER performance of 3D free-standing complex-organic-ligand-based BMOF nanoarchitectures.