Thiacalixarene-based {Co/Fe}₁₆ coordination clusters: bimetallic synergistic effect for an enhanced oxygen evolution reaction

The integration of heterometallic units into coordination clusters used for the oxygen evolution reaction (OER) can enhance their electrocatalytic performance. Herein, we report the syntheses of a series of coordination clusters, namely Co₁₆, {CoFe}₁₆-a, {CoFe}₁₆-b, {CoFe}₁₆-c and Fe₁₆, assembled from different metal precursors (CoCl₂·6H₂O and/or FeCl₃·6H₂O), p-tert-butylsulfonylcalix[4]arene (H₄TC4A-SO₂), and 1,3-bis(2H-tetrazol-5-yl)benzene (BTTAB). These clusters feature box-like entities in which four M₄-(TC4A-SO₂) polynuclear secondary building units (PSBUs) in a square arrangement are bridged by eight BTTAB ligands. Among these PSBU-based coordination clusters, {CoFe}₁₆-b exhibits a better OER activity with an overpotential of 285.3 mV at a current density of 10 mA cm⁻² and a Tafel slope of 72.8 mV dec⁻¹ due to the synergistic effect between Co and Fe with an optimized molar ratio.