High proton conductivity in a nickel(ii) complex and its hybrid membrane

Abstract

A novel nickel(II) complex, [Ni(2,2′-bpy)₃](H₂SBTC)(H₂O)₅ (1) (2,2′-bpy = 2,2′-bipyridyl), was synthesized based on [Ni(2,2′-bpy)₃]²⁺ discrete units and a partially deprotonated sulfonate–carboxylate ligand of H₄SBTC (5-sulfonyl-1,2,4-benzentricarboxylic acid). The adjacent [Ni(2,2′-bpy)₃]²⁺ cationic units were connected to H₂SBTC²⁻ anions by hydrogen bonds to form a one-dimensional (1-D) chain. The 1-D chains were further linked using hydrogen bonds from free water molecules and H₂SBTC²⁻ anions to generate a two-dimensional (2-D) plane structure. The proton conductivity of 1 reaches 1.3 × 10⁻⁴ S cm⁻¹ at 318 K, 98% RH. Furthermore, hybrid membranes composed of polyvinyl alcohol (PVA) and 1 as fillers were prepared with different mass percentages. The proton conductivity of 1@PVA-5 was found to be 1.6 × 10⁻³ S cm⁻¹ at 313 K and 98% RH. The large number of alcoholic hydroxyl groups in PVA promote the resulting conductivity.