Robust Th-MOF-Supported Semirigid Single-Metal-Site Catalyst for an Efficient Acidic Oxygen Evolution Reaction

Constructing metal–organic framework (MOF) electrocatalysts toward an acidic oxygen evolution reaction (OER) remains a huge challenge owing to the generally poor stability of MOFs during the acidic OER process. Herein, Th-MOF-supported semirigid single-metal-site catalysts of MCl2@Th-BPYDC (M = Cu, Co, Ni) were prepared by postmetalation of a bipyridyl Th-MOF (Th-BPYDC) crystal toward an acidic OER. Impressively, the structure of the anchoring single-metal site can be well resolved by single-crystal X-ray diffraction, giving a near-square-planar MN2Cl2 coordination geometry, indicative of its potential as a double-accessible open-metal site and an unusual semirigid character because of two rotatable charge-balance Cl– anions. The optimal CoCl2@Th-BPYDC not only discloses an outstanding acidic OER activity comparable to commercial IrO2 but also exhibits a high electrocatalytic stability, which is attributed to the combination of the robust rigid Th-BPYDC framework, the strong chelating coordination between single-metal-site with bipyridine N in BPYDC ligand, and an accessible open single-metal site. More importantly, as unveiled by theoretical calculations and kinetic analysis, the single-metal-site catalysts show an unusual semirigid character during the OER process, totally different from the well-known MN4 rigid single-site catalysts since Cl atoms are found to rotate freely to provide suitable geometric space when attaching and activating reaction intermediates, thus largely reducing the reaction energy barrier.