Improved capacitive performances and electrocatalytic reduction activity by regulating the bonding interaction...

Electrochemical performances can be effectively improved by introducing metal-organic units (MOUs) into polyoxometalates (POMs). However, regulating the bonding strength between POMs and MOUs at the molecular level to improve the electrochemical performance is a challenging task. Three new POM-based metal-organic complexes (MOCs), namely H{Zn₂(Hpytty)₂(H₂O)₈[CrMo₆(OH)₆O₁₈]}·2H₂O (1), H{Zn₂(Hpyttz)₂(H₂O)₆[CrMo₆(OH)₆O₁₈]}·8H₂O (2), and {(μ₂-OH)₂Zn₆(pyttz)₂(H₂O)₁₀[TeMo₆O₂₄]}·2H₂O (3) (H₂pytty = 3-(pyrazin-2-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, H₂pyttz = 3-(pyrid-2-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), were obtained. Single-crystal X-ray diffraction shows that the bonding strength (from the hydrogen bond to the coordination bond) between Zn-bistriazole-pyrazine/pyridine units and diverse Anderson-type POMs gradually increases from complexes 1 to 3. Glassy carbon electrodes modified with complex 3 (3-GCE) has the highest specific capacitance, which is 930 F g^-1 at 1 A g^-1. Moreover, carbon paste electrodes (1-3-CPEs) modified with complexes 1-3 are used as electrochemical sensors for detecting Cr(VI) ions, with limits of detection well below the World Health Organization (WHO) maximum level in drinking water.