Brønsted Acid-Functionalized Ionic Co(II) Framework: A Tailored Vessel for Electrocatalytic Oxygen Evolution and Size-Exclusive Optical Speciation of Biothiols
Ranadip Goswami, Kannimuthu Karthick, Sandeep Das, Sonal Rajput, Nilanjan Seal, Biswarup Pathak, Subrata Kundu, Subhadip Neogi
Abstract
Metal–organic frameworks (MOFs) not only combine globally demanded renewable energy generation and environmental remediation onto a single platform but also rationalize structure–performance synergies to devise smarter materials with remarkable performance. The robust and non-interpenetrated cationic MOF exemplifies a unique bifunctional scaffold for the efficient electrochemical oxygen evolution reaction (OER) and ultrasensitive monitoring of biohazards. The microporous framework containing Brønsted acid-functionalized [Co2(μ2-OH)(CO2)2] secondary building units (SBUs) exhibits remarkable OER performance in 1 M KOH, requiring 410 mV overpotential to obtain 10 mA cm–2 anodic current density, and a low Tafel slope of 55 mV/dec with 93.1% Faradaic efficiency. Apart from the high turnover frequency and electrochemically assessable surface area, steady OER performance over 500 cycles under potentiodynamic and potentiostatic conditions result in long-term catalyst durability. The highly emissive attribute from nitrogen-rich fluorescent struts benefits the MOF in recyclable and selective fluoro-detection of three biothiols (l-cysteine, homocysteine, and glutathione) in water with a fast response time. In addition to colorimetric monitoring in the solid and solution phases, control experiments validate size-exclusive biothiol speciation through molecular-dimension-mediated pore diffusion. The role of SBUs in the OER mechanism is detailed from density functional theory-derived free energy analysis, which also validates the importance of accessible N-sites in sensing via portraying framework–analyte supramolecular interactions.