H2- and NH3-treated ZnO nanorods sensitized with CdS for photoanode enhanced in photoelectrochemical performance

• Effect of solid state doping of H/N in ZnO: redshift and enhanced IR absorption.
• Optimized length/diameter of ZnO nanorod for the maximum electrode performance.
• Direct measurement of electrode performance by hydrogen gas production rate.
• Discussion of the ultimate effects of the bandgap, doping, and nanostructures.

A ZnO/CdS core-shell nanorod structure is studied for use as photoanode in photoelectrochemical cell for water splitting. The focus is to examine the effect of hydrogen and/or nitrogen doping of ZnO nanorods on its performance as photoanode. ZnO nanorods hydrothermally synthesized on ITO glass substrate are heat-treated in pure hydrogen ambient and then in atmospheric pressure of ammonia for H- and N-doping of ZnO. The H- and/or N-doped ZnO nanorod structure (N/H:ZnO) reveal an enhanced photocurrent and photo-to-current conversion efficiency in comparison to untreated ZnO nanorods by shifting the absorption edge towards visible region and increasing absorption of infrared region wavelengths. CdS sensitization of the nanorods is also studied. The morphology and properties of the samples are examined by SEM, XRD, UV–vis absorption and photoluminescence. Optimization of the ZnO nanorod growth and CdS coating processes are also undertaken. An optimized N/H:ZnO nanorods sensitized by CdS layer yields a photocurrent density of ∼12.61 mA cm−2 at 0 V (vs. SCE) and photon-to-current conversion efficiency of ∼4.5% (at −0.73 V vs. SCE) in 0.5 M Na2S solution under a simulated solar light. The H2 gas generation with the optimal structure is about 6 mL h−1 cm−2.