Hierarchical CuO photocathodes with cobalt doping for efficient photoelectrochemical water-splitting

Hierarchical cobalt-doped copper oxide (Co/CuO) photocathodes for photoelectrochemical water splitting (PEC-WS) are an effective and promising strategy to enhance light harvesting. Here, hierarchical Co/CuO photocathodes were deposited <i>via</i> the effective-cost SILAR technique. Crystal structural properties of Co/CuO films were examined <i>via</i> X-ray diffraction (XRD). XRD results confirmed the monoclinic structure and polycrystalline nature of Co/CuO. Field emission scanning electron microscopy images display a hierarchical "flower-like" morphology with nanoscale features resembling petals. All films exhibit a relatively uniform distribution of flower-like structures. The transmittance spectra of Co-doped and undoped CuO photoelectrodes were measured to study their optical properties. Increasing the Co contents led to an optical energy band gap increase. Additionally, the applied photon to current conversion efficiency (ABPE%) and electrochemical impedance spectroscopy (EIS) are comprehensively studied. Moreover, stability and incident photon to current conversion efficiency (IPCE%) were studied for optimum photoelectrode. The CuO sample with an optimal Co dopant of 3% exhibit a maximum photocurrent density of -1.5 mA cm^-2 at -0.4 V <i>vs.</i> RHE about triple that of pure CuO photocathode, an ABPE of 0.35% at -0.4 V <i>vs.</i> RHE, and outstanding electrochemical stability in alkaline medium.