Accelerating Oxygen Evolution with a Low Symmetry Complex Ion of Tricyanidoferrate as a Catalytic Precursor

The sluggish kinetics of anode oxygen evolution is a key factor limiting the water-splitting hydrogen production efficiency. Unlike conventional optimization approaches, this study investigates low-symmetry complex ions [Fe(qcq)(CN)₃]^- (Hqcq = 8-(2-quinolin-2-ylcarboxamido)quinoline) as catalytic precursors for the reaction. This complex ion is utilized for its unique coordination configuration, expected to enhance the metal sites' intrinsic catalytic activity. The results show that when the MOF-like (metal organic frameworks) material constructed by [Fe(qcq)(CN)₃]^- and nickel salt is loaded on multiwalled carbon nanotubes, it exhibits remarkable enhanced oxygen evolution catalytic performance. By adjusting the loading amount on CNTs, the optimal catalytic performance in 1 M KOH was attained when the mass fraction of CNTs was set at 60%. The overpotential at a current density of 10 mA is only 215 mV, and the Tafel slope is as low as 53.92 mV dec^-1. Further research reveals an extraordinary catalytic mechanism: the qcq ligand on the iron site leaches and then recoordinates with nickel. Density functional theory calculations demonstrate that ligand participation induces coordination configuration optimization of Ni²⁺ active sites, resulting in enhanced oxygen evolution reaction performance. This work provides insights into special coordination effects in nonprecious metal-based oxygen evolution catalysts and strategies for their optimization.