Abstract:
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.