Highly tuneable proton-conducting coordination polymers derived from a sulfonate-based ligand

Abstract

Developing a new type of high-performing proton-conducting electrolyte associated with proton exchange membrane fuel cells (PEMFCs) is one of the attractive and challenging topics in the modern energy field. Here, three coordination compounds have been synthesized via the HCl steaming-assisted conversion approach by using multiple functional groups including the sulfonate group and the Cl⁻ or HPO₄²⁻ group, namely, Cu₂H₂(Hspip)₂Cl₄·H₂O (1), Cu(H₂spip)Cl₂·H₂O (2) and CuH(Hspip)(HPO₄)·H₂O (3) (where H₂spip is 2-sulfophenylimidazo(4,5-f)(1,10)-phenanthroline). We disclose the relationship between the structure characteristics and the nature of proton conductivity. The protonated sulfonate group together with the halide Cl⁻ group plays a positive role in increasing proton conductivity; meanwhile, the packing mode of the structure is also an important factor influencing proton conduction. The compounds exhibit high proton conductivity values in the range of 10⁻⁴–10⁻² S cm⁻¹ at 95 °C and 97% relative humidity (RH), in which compound 2 exhibited the highest value of 1.09 × 10⁻² S cm⁻¹ at 97% RH and 368 K.