Mixed-​ligand-devised anionic MOF with divergent open Co(II)-nodes as chemo-resistant, bi-functional material for electrochemical water oxidation and mild-condition tandem CO2 fixation

Abstract

Metal-organic frameworks (MOFs) combine unique merits of heterogeneous and molecular catalysts, where purposeful implantation of task-specific functionalities along the pore structure can promise electrocatalytic oxygen evolution reaction (OER) and cascade chemical valorization of CO2. Although, both these attributes are crucial for renewable energy and environmental remediation, their effective amalgamation over a single platform is hitherto unexplored, yet extremely demanding. The chemically robust, and non-penetrated charged framework CSMCRI-10 (CSMCRI = Central Salt & Marine Chemicals Research Institute) exemplifies activation induced generation of high density Co(II) nodes with diverse open coordination positions along the unidirectional porous channels, and act as unique bi-functional material. Building on the presence of redox-active [Co2(µ2-OH)(COO)4] secondary building units, the activated framework (10a) demonstrates efficient water oxidation in alkaline medium (1 M KOH). The MOF requires only 396 mV overpotential to reach 10 mA/cm2 anodic current density, and possesses a Tafel slope of 102 mV/decade with admirable 95.1% Faradaic efficiency, signifying high rate of oxygen evolution reaction. The OER turn-over frequency is found to be within the range of best reported values (0.03s−1), and the framework stability is preserved in both potentiodynamic and potentiostatic conditions over 500 consecutive cycles. Further, the Lewis acid functionalized 10a benefits solvent-free CO2 conversion to cyclic carbonate in highly synergistic manner with adequate reusability and broad substrate scope. To the best of tandem catalysis, rarest oxidative carboxylation of CO2 and styrene is realized via single-step styrene carbonate synthesis with exceptional conversion under relatively mild reaction condition.