The synergetic effect of graphene on Cu2O nanowire arrays as a highly efficient hydrogen evolution photocathode in water splitting

Abstract

A one dimensional (1D) Cu₂O straddled with graphene is proposed as a highly promising and stable photocathode for solar hydrogen production. The Cu₂O nanowire arrays modified with an optimized concentration of graphene provide much higher improved photocurrent density −4.8 mA cm⁻², (which is two times that of bare 1D Cu₂O, −2.3 mA cm⁻²), at 0 V vs. RHE under AM 1.5 illumination (100 mW cm⁻²) and solar conversion efficiency reaching 3.3% at an applied potential of −0.55 V vs. the Pt counter electrode. Surprisingly, 1D Cu₂O with an optimum graphene concentration exhibits an inspiring photocurrent density from 2.1 to 1.1 mA cm⁻² at a higher positive potential range of 0.2–0.4 V vs. RHE, which is 300–550% higher compared with that of bare 1D Cu₂O. This is the highest value ever reported for a Cu₂O-based photocathode at such a positive potential. After 20 minutes of standard solar irradiation, 83% of the initial photocurrent density was retained for the nanocomposite which is more than five times compared to the bare Cu₂O (14.5%). A Faradic efficiency of 74% was obtained for the evolved H₂ gas measurement. To get evidence for the photostability of the graphene modified photocathode, detailed characterization was carried out. The high PEC performance of the graphene/Cu₂O nanocomposite is attributed to the improved crystallinity and the synergetic effect of graphene in absorbing visible light, suppressing the charge recombination and photocorrosion of the photoelectrode by preventing direct contact with the electrolyte. This inexpensive photocathode prepared free of noble metals, showed enhanced high photocurrent density with good stability and is a highly promising photocathode for solar hydrogen production.