Enhanced Photoelectrochemical Water Splitting by Surface Modified Electrodeposited n-Cu2O Thin Films

A surface modification technique is developed for electrodeposited n-cuprous oxide (Cu2O) thin film electrodes to enhance water splitting in a photoelectrochemical (PEC) cell. For this, Cu2O films are modified using ammonium sulfide vapor with a unique exposure condition to produce ultrathin sulfided surface layers. To ascertain the effect of surface modification, films are investigated in a PEC cell containing 0.1 msodium acetate aqueous electrolyte using current-voltage, spectral response, and capacitance-voltage measurements. It is revealed that as a result of the surface modification, high photocurrents are produced by the surface-modified electrodes. Also, it is revealed that the Fermi level pinning presents at the Cu2O/electrolyte interface can be removed and the flat band potential can be shifted negatively by the surface modification. The experimental evidences support the idea that the surface modification can change the surface states present at the n-Cu2O/electrolyte interface. The enhancement of photocurrent may be attributed to the increase in depletion layer thickness and reduction of surface recombination of photogenerated charge carriers. The surface modification technique developed in this study for n-Cu2O films enables to produce an enhanced solar-to-hydrogen conversion efficiency of 1.47% at the bias potential of 0.553 V versus reversible hydrogen electrode.