Mixed-Ligand-Architected 2D <b>Co(II)-MOF</b> Expressing a Novel Topology for an Efficient Photoanode for Water Oxidation Using Visible Light

Abstract

The structural diversity of Co(II) metal centers is known to influence their physicochemical properties. A novel two-dimensional (2D) Co(II)-MOF {[Co₅(HL)₄(dpp)₂(H₂O)₂(μ-OH)₂]·21H₂O} n has been designed and synthesized by adopting a mixed-ligand strategy, using 1,3-di(4-pyridyl)propane (dpp) colinker with a flexible spacer H₃L (H₃L: 5-(2 carboxybenzyloxy)isophthalic acid). Co(II)-MOF features a 2D network, which is further interpenetrated among the equivalent sets and therefore results in a 3D supramolecular network. Topologically, the entire network can be viewed as a (3,4,8)-connected three-nodal net with the extended point symbol of {4.5.7}4{4¹².5².7¹⁰.9⁴}{5².8.9².10}2, duly assigned to the novel topological type smm2. The functional utility of Co(II)-MOF is demonstrated by employing it toward oxygen evolution reaction (OER) in a photoelectrochemical cell, exhibiting appreciable photocurrents of up to 5.89 mA/cm² when used as an anode in a photoelectrochemical cell, while also displaying encouraging electrocatalytic currents of 9.32 mA/cm² (at 2.01 V vs RHE) for the OER. Moreover, detailed electrochemical impedance spectroscopy studies confirm enhanced charge-transfer kinetics and improved conductivity under illumination with minimal effect of interfacial phenomena. This work provides a reference for the expanding field of research into applications of MOF materials and establishes MOF materials as favorable candidates for sustainable and efficient design of electrodes for water splitting.