Facile synthesis of a nickel-quinizarin metal coordination compound as a binder-free electrode for efficient alkaline oxygen evolution reaction.

In this work, we present the first systematic study of a metal coordination compound (MCC) based on nickel and 1,4-dihydroxyanthraquinone (quinizarin) as an OER catalyst. The nickel-quinizarin complex referred to as NiQ was synthesized using a facile solvothermal route and a crystalline product was obtained that exhibited excellent structural integrity. Structural data of the as-prepared crystals were obtained by synchrotron microcrystal X-ray diffraction. In the solid state, the Ni(ii) metal centre existed in a distorted octahedral geometry. The complex is further stabilized in the solid state by π-π-stacking interactions between the anthraquinone rings. The redox features of the complex were analysed through cyclic voltammetry (CV), suggesting the involvement of Ni(ii) metal centres in undergoing an oxidation reaction on the application of an anodic sweep. The electrocatalytic performance of NiQ was evaluated by drop casting NiQ slurry on FTO coated glass plates (NiQ@FTO) directly without needing additional binders or conducting particles and running in 1.0 KOH using a three-electrode system. NiQ@FTO achieved an overpotential as low as 300 mV at 10 mA cm-2, surpassing those of many previously reported coordination complex-based OER catalysts. Furthermore, it demonstrated excellent stability over prolonged electrolysis with no significant degradation. The present work not only reports a new class of 1,4-dihydoxyanthraquinone based MCCs as highly active and durable OER catalysts but also offers useful insights into the structure activity relationship, which could be beneficial in future electrocatalysis.