A bimetallic Co4Mo8 cluster built from Mo8 oxothiomolybdate capped by a Co4-thiacalix[4]arene unit: the observation of the Co–Mo synergistic effect for binder-free electrocatalysts

Abstract

A new calixarene-supported bimetallic coordination cluster (NH₄){Co₄^II(TC4A)Cl[(Mo^VO₂)₂S(CH₃O)]₄} (+solvent) (abbr. Co₄Mo₈, H₄TC4A = p-tert-butylthiacalix[4]arene) was obtained by a solvothermal reaction. Co₄Mo₈ features a sulfur modified polyoxometalate Mo₈ cluster capped by a Co₄-TC4A unit. Co₄Mo₈ clusters directly fabricated on nickel foam (NF) were used as working electrodes, giving drastically improved electrocatalytic activities for the oxygen evolution reaction (OER) with an overpotential of 302.8 mV at 10.0 mA cm⁻² in basic media. Upon replacing Co in Co₄Mo₈ clusters with Ni or Zn, component controlled investigations indicated that the extraordinary OER performance originated from the Co–Mo synergistic effect. Furthermore, the deliberately incorporated sulfur atoms at the lower rim of Co₄Mo₈ clusters facilitated the adherence between the clusters and NF, resulting in a binder-free electrocatalyst with efficient and ultra-stable OER performance (366.8 mV at 40.0 mA cm⁻² for more than 150 hours).