Sculpting In-plane Fractal Porous Patterns in Two-Dimensional MOF Nanocrystals for Photoelectrocatalytic CO 2 Reduction

Herein, by choosing few-nm-thin two-dimensional (2D) nanocrystals of MOF-5 containing in-planner square lattices as a modular platform, a crystal lattice-guided wet-chemical etching has been rationally accomplished. As a result, two attractive pore patterns carrying Euclidean curvatures; precisely, plus(+)-shaped and fractal-patterned pores via ⟨100⟩ and ⟨110⟩ directional etching, respectively, are regulated in contrast to habitually formed spherical-shaped random etches on MOF surface. In agreement with the theoretical calculations, a diffusion-limited etching process has been optimized to devise high-yield of size-tunable fractal-pores on the MOF surface that tenders for a compatibly high payload of catalytic Re -complexes using the existing large edge area once modified into a free amine-group-exposed inner pore surface. Finally, on benefiting from the long-range fractal opening in 2D MOF support structure, while loaded on an electrode surface, a facilitated cross-interface charge-transportation and well-exposure of immobilized Re -catalysts are anticipated, thus realizing enhanced activity and stability of the supported catalyst in photoelectrochemical CO -to-CO reduction.