Toward stable photoelectrochemical water splitting using NiOOH coated hierarchical nitrogen-doped ZnO-Si nanowires photoanodes

Abstract

Photoelectrochemical (PEC) water splitting is regarded as the most promising method to generate “green hydrogen”, and zinc oxide (ZnO) has been identified as one of the promising candidates for PEC water splitting owing to its straddling band alignment with the water redox level. However, its PEC performance is limited due to its wide bandgap and anticipated by photocorrosion in an aqueous medium. In this work, we present strategic improvements in the PEC water splitting performance of ZnO nanowires (NWs) by nitrogen (N)-doping along with photostability by the core–shell deposition of a NiOOH cocatalyst. Highly crystalline hierarchical ZnO NWs were fabricated on Si NWs (ZnO-Si HNWs) using a metal organic chemical vapor deposition approach. The NWs were then N-doped by annealing in an NH3 atmosphere. The N-doped ZnO-Si HNWs (N:ZnO-Si HNWs) showed enhanced visible light absorption, and suppressed recombination of the photogenerated carriers. As compared to ZnO-Si HNWs (0.045 mA cm−2 at 1.23 V vs RHE), the N:ZnO-Si HNWs (0.34 mA cm−2 at 1.23 V vs RHE) annealed in NH3 ambient for 3 h at 600 °C showed 7.5-fold enhancement in the photocurrent density. NiOOH-deposited N:ZnO-Si HNW photoanodes with a photostability of 82.21% over 20000 s showed 10.69-fold higher photocurrent density (0.48 mA cm−2 at 1.23 V vs RHE) than ZnO-Si HNWs.