Mixed-ligand Architected 2D Co(II) MOF Expressing Novel Topology as an Efficient Photoanode for Water Oxidation Using Visible Light.

The structural diversity of Co(II) metal centers is known to influence their physico-chemical properties. A novel 2D Co(II)-MOF {[Co5 (HL)4 (dpp)2 (H2 O)2 (µ-OH)2 ]∙21H2 O}n has been designed and synthesized by adopting mixed ligand strategy, using 1,3-di(4-pyridyl)propane (dpp) co-linker with a flexible spacer H3 L (H3 L: 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 towards 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 (EIS) 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.