Efficient Alkaline Water Oxidation with a Regenerable Nickel Pseudo-Complex
Peikun Zhang, Pai Wang, Wei Wang, Qianbao Wu, Mengjun Xiao, Roger Alberto, Yanning Zhang, Chunhua Cui
Abstract
Efficient and robust electrocatalysts are required for the oxygen evolution reaction (OER). Photosystem II-inspired synthetic transition metal complexes have shown promising OER activity in water-poor or mild conditions, yet challenges remain in the improvement of current density and performance stability for practical applications in alkaline electrolytes in contrast to solid-state oxide catalysts. Here, we report that a nickel pseudo-complex (bpy)zNiOxHy (bpy = 2,2′-bipyridine) catalyst, which bridges solid oxide and molecular catalysts, exhibits the highest OER activity among nickel-based catalysts with a turnover frequency of 1.1 s–1 at an overpotential of 0.30 volts, even outperforming iron-incorporated nickel (oxy)hydroxide under an identical nickel mass load. Benefiting from the strong coordination between bpy and nickel, this (bpy)zNiOxHy catalyst exhibits long-term stability in highly alkaline media at 1.0 mA cm–2 for over 200 h and at 20 mA cm–2 for over 60 h. Our findings indicate that dynamically coordinating a small amount of bpy in the catalyst layer efficiently sustains highly active nickel sites for water oxidation, demonstrating a general strategy for improving the activity of transition metal sites with active ligands beyond the incorporation of metal cations to form double-layered hydroxides.