Coordination tuning of Ni/Fe complex-based electrocatalysts for enhanced oxygen evolution†

Abstract

Non-noble oxygen evolution reaction (OER) catalysts have garnered considerable attention in recent years. Alkaline OER catalysts based on coordination complexes exhibit high performance but often undergo irreversible ligand dissociation, resulting in less active solid-state oxides/hydroxides. Here, the robust coordination between 2,2′-bpy and Ni/Fe metal centers was utilized in the simple synthesis of NiFe(2,2′-bpy)_n@CNT (2,2′-bpy = 2,2′-bipyridyl, CNT = carbon nanotube), which showed highly efficient alkaline OER performance. The Ni/Fe to 2,2′-bpy ratio was determined to be n = 2 for the highest activity, exhibiting enhanced performance with an overpotential of 240 mV in 1 M KOH and a high turnover frequency (TOF) value of 1.86 s⁻¹, outperforming ligand-free Ni/Fe oxides/hydroxides. DFT simulations suggest that the activity enhancement is due to the optimized electronic density around the metal sites arising from strong 2,2′-bpy coordination to the Ni/Fe centers, highlighting the potential for improving non-noble OER catalysts through fine coordination tuning.