Highly active copper‐based electrocatalyst for water oxidation at neutral pH

The sluggish kinetics of the oxygen evolution reaction at the anode severely limits the hydrogen production at the cathode in water spitting systems. While electrocatalytic systems based on cheap and earth-abundant metal copper catalysts have been promising for water oxidation under basic conditions, only very few examples with high overpotential can be operated under acidic or neutral conditions, even though hydrogen evolution in the latter case is much easier. This work presents an efficient and robust Cu-based molecular catalyst, which self-assembles as a periodic film from its precursors under aqueous conditions on the surface of glassy carbon electrodes (GCE). This film catalyzes the oxygen evolution reaction (OER) under neutral conditions with impressively low overpotential. In controlled potential electrolysis, a stable catalytic current of 1.0 mA/cm2 can be achieved at only 2.0 V (vs. RHE) and no remarkable decrease in the catalytic current is observed even after prolonged bulk electrolysis. The catalyst displays first-order kinetics and a single site mechanism for water oxidation with a TOF (kcat) of 0.6 s-1. DFT calculations are performed to study the OER behavior of the periodic Cu(TCA)2 (HTCA = 1-mesityl-1H-1,2,3-triazole-4 carboxylic acid) film and reveal that TCA defects within the film create Cu(I) active sites which can provide a low overpotential route for OER. This route involves Cu(I), Cu(II)-OH, Cu(III)=O and Cu(II)-OOH intermediates and is enabled at a potential of 1.54 V (vs. RHE), requiring an overpotential of 0.31 V. This corresponds well with an overpotential of ~ 0.29 V obtained experimentally for the grown catalytic film after 100 CV cycles at pH=6. However, to reach a higher current density of 1 mA cm−2, an overpotential of 0.72 V is required.