Abstract
Significant progress is currently being made in understanding the behavior of copper oxide (CuO) at positive potentials, approximately 1.7 V, under electrochemical conditions. While it is assumed to be hydrated Cu2O3 at this potential with ∆G = 208.5 kJ/mol, this hypothesis awaits validation. However, our calculations show that bulk CuOOH has ∆G ~209.5 kJ/mol, indicating Cu+3 possibly in the form of bulk CuOOH. To verify this, we employ a combination of density functional theory (DFT) electronic structure calculations and simulated Raman spectra. This approach allows us to examine the electrocatalytic activity of CuOOH polymorphs, including Cmc21 (β-CuOOH), Pmn21 (γ-CuOOH), and C2/m (δ-CuOOH), for the OER at this potential. Our calculations indicate a presence of stable square planar, non-magnetic γ/δ-CuOOH phase, and the calculated volume Pourbaix diagram highlights γ/δ-CuOOH as the newly discovered active phase governing the OER in alkaline media. This finding is further supported by simulated Raman spectroscopy, revealing distinct features corresponding to Cu3+ species at 552 and 573 cm-1, closely matching experimental data peak at 587 cm-1 only present under highly oxidizing conditions. Next, we compare the theoretical overpotentials of all CuOOH surfaces with O and OH-vacancy at the bridge site as the active site, and the surface-adsorbed OH* on a CuO surface. We find that the (021) surface of CuOOH and the (002) surface of CuOOH are the most active, characterized by an overpotential ranging from 0.36V to 0.50 V. Lastly, we demonstrate that the overpotential of the CuOOH (021) surface can be improved further by surface substitution of Cu by Fe. This finding could explain the experimentally observed enhancement in the OER activity of FeyCu1−yOOH thin films with increasing Fe content. This work expands our knowledge in understanding the active phases governing OER in alkaline media but also paves the way for the development of more efficient electrocatalysts for renewable energy applications. Figure 1
Published Version
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