Modulating conductivity type of cuprous oxide (Cu2O) films on copper foil in aqueous solution by comproportionation

Cuprous oxide (Cu2O) is an attractive material for photoelectrochemical (PEC) hydrogen production or photovoltaic application, because of its appropriate band gap, low material cost and non-toxic. In this paper, Cu2O films were obtained by comproportionation in acid cupric sulfate solutions with varying concentrations of potassium nitrate. Photoelectrochemical and electrochemical experiments, such as zero-bias photocurrent responses, voltammograms, and Mott-Schottky measurements, show that the Cu2O films grown in low (<= 0.75 mol dm(-3)) and high (>= 1.00 mol dm(-3)) nitrate ion concentrations presented n-type and p-type conductivity, respectively. Open circuit potential and polarization behavior were monitored to investigate the mechanism of modulating conductivity type. Nitrate ions consume protons in the plating solution during comproportionation with different concentrations of nitrate ions creating different pH at the Cu2O/solution interface. This gradient leads to the transformation of Cu2O films conductivity changing from n-type to p-type with increasing the concentration of nitrate ions in the plating solution. This method could be used to fabricate homojunction electrode on metal substrate for PEC hydrogen production or photoelectric application. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.