Sequence control of metals in MOF by coordination number precoding for electrocatalytic oxygen evolution

Abstract

Inorganic porous materials are prevailing in energy storage, environment remediation, and catalysis; however, it is attractive to control the spatial arrangement of heterometals in these materials with atomic accuracy. Here, we report the precise positioning of metals with identical valence, coordination number, and similar size, such as Zn (II) and Co (II), to generate an alternating sequence in a multivariate (MTV) metal-organic framework (MOF), ZnCo-MTV-MOF-699, with a rare sheet secondary building unit. This is achieved by precoding their coordination number in a parent MOF, ZnCo-MOF-69C, followed by single-crystal-to-single-crystal transformation, where the entire process is monitored in situ by time-resolved small-angle X-ray scattering. Coordination number precoding of other metal pairs, Zn-Ni and Zn-Cu, in MTV-MOFs is also obtained. The sequence-coded MTV-MOF exhibits a much lower overpotential than that of the non-coded counterpart in oxygen evolution reaction, unveiling the power of metal sequence control. • Single crystals of heterometallic MOF composed of 2D sheet SBUs have been synthesized • Heterometals with similar size and valence are arranged in an alternating sequence • In situ SAXS unveils the change of metal coordination number in crystal conversion • Sequence-coded MOF exhibits a much lower overpotential than that of the non-coded one The sequence of heterometals in multivariate (MTV) metal-organic frameworks (MOFs) is like the “gene” of these porous materials, dictating their macroscopic physical properties. Currently, there are not many effective means to control such sequences. The sequence precoding method demonstrated here allows for the precise control of the spatial arrangement of heterometals in 2D sheet secondary building units (SBUs), as confirmed by both single-crystal diffraction and in situ small-angle powder X-ray scattering. The metals are arranged in a rare alternating sequence, despite their similarity in coordination environments, valence, and ionic radius. The sequence-coded ZnCo-MTV-MOF-699 exhibits an overpotential of 231 mV versus reversible hydrogen electrode (RHE) at a standard current density of 10 mA cm −2 , better than the benchmark IrO 2 , 314 mV, and rivaling most MOF-based oxygen evolution reaction (OER) catalysts. This method stands as a new way to design multivariate functional materials for electrocatalysis. Precise positioning of metals with an alternating sequence is achieved in MTV-MOF with sheet secondary building units by coordination numbers precoding and single-crystal-to-single-crystal conversion.