Cu2O/CuO heterojunction catalysts through atmospheric pressure plasma induced defect passivation

Epitaxial growth of CuO nanostructures on Cu2O films using atmospheric pressure plasma jet is demonstrated, that can operate without the need of transparent current collector. [Display omitted] •Fast and environment friendly route for CuO/Cu2O heterojunction synthesis.•Epitaxial growth using atmospheric pressure plasma jet.•The heterojunction electrodes can operate without transparent current collector.•High currents and stability towards electrocatalysis and photocatalysis. A novel route to fabricate Cu2O/CuO heterojunction electrodes using an atmospheric pressure plasma jet (APPJ) is demonstrated. This process promotes favourable band alignment and produces nanoscale CuO surface features from Cu2O with low density of interfacial defects. This electrode can operate without any transparent current collector, showing remarkable currents and stability towards oxygen evolution reaction (OER) (6 mA cm−2 for 2 h at pH14) as well as photocatalytic hydrogen evolution reaction (HER) activity (−1.9 mA cm−2 for 800 s at pH7). When the electrocatalytic oxygen evolution (OER) activity was measured for Cu2O/CuO electrode deposited on FTO substrate the currents increased to ~40 mA cm−2 at 0.8 V vs SCE in 1 M KOH without compensating for the electrode electrolyte surface resistance (iR correction). The composite films also exhibited a high rate towards photo degradation of Methylene Blue (MB) and phenol in the visible spectra, indicating efficient charge separation. We modelled the electronic structure of this epitaxially grown Cu2O/CuO heterojunction using density functional theory. The calculations revealed the distinctive shifts towards Fermi level of the p-band centre of O atom in Cu2O and d-band centre of Cu atom in CuO at the interface contribute towards the increased catalytic activity of the heterostructure. Another factor influencing the activity stems from the high density of excited species in the plasma introducing polar radicals at the electrode surface increasing the electrolyte coverage. This work presents the potential of APPJ functionalization to tune the surface electronic properties of copper oxide based catalysts for enhanced efficiency in OER and HER water splitting.