Cobalt(ii)-bridged triphenylamine and terpyridine-based donor–acceptor coordination polymer as an efficient trifunctional electrocatalyst

Abstract

We present a novel redox-active hybrid coordination polymer TPA-tpd-Co donor–acceptor pair, synthesized via Schiff-base condensation and self-assembly, where Co(II) is stabilized by triphenylamine and terpyridine ligand. The polymer exhibits a charge-separated state and semiconducting behavior at room temperature with an optical bandgap of 2.0 eV, indicating facile charge transfer. The microscopic images reveal irregular spherical morphology, and multi-point BET analysis showed substantial permanent porosity and surface area of 84.6 m² g⁻¹ (d = 3.1 nm), indispensable for channeled charge transfer during electrocatalysis. The powder XRD and HR-TEM unveil the presence of low-angle crystallinity in the polymer. With a low amount of cobalt (2.6 wt%) the polymer exhibits trifunctionality at a low onset potential of 0.80 V vs. RHE for the ORR, and overpotentials of 440 and 428 mV at 10 mA cm⁻² for the OER (alkaline media), and HER (acidic media) with substantial stability for 12 hours in any pH environment. Our DFT computational studies gave the free energy for a plausible reaction mechanism and descriptors in conjunction with confirming that TPA-tpd-Co is an exquisite donor–acceptor pair with HOMO–LUMO positionings and a gap of 1.63 eV. The aqueous Zn–air battery also shows appreciable stability for 21 hours with a low voltage window of 1 V and an adequate specific capacity of 529 mA h g⁻¹_Zn. The observations inspire and suggest that TPA-based π-conjugated metal–organic coordination polymers pave the way for the development of a new and efficient tri-functional electrocatalyst.