Abstract
In this study, ZnO nanorods (NRs) were hydrothermally grown on an Au-coated glass substrate at a relatively low temperature (90 °C), followed by the deposition of Ag2CrO4 particles via a successive ionic layer adsorption and reaction (SILAR) route. The content of the Ag2CrO4 particles on ZnO NRs was controlled by changing the number of SILAR cycles. The fabricated ZnO–Ag2CrO4 heterojunction photoelectrodes were subjected to morphological, structural, compositional, and optical property analyses; their photoelectrochemical (PEC) properties were investigated under simulated solar light illumination. The photocurrent responses confirmed that the ability of the ZnO–Ag2CrO4 heterojunction photoelectrodes to separate the photo-generated electron–hole pairs is stronger than that of bare ZnO NRs. Impressively, the maximum photocurrent density of about 2.51 mA cm−2 at 1.23 V (vs. Ag/AgCl) was measured for the prepared ZnO–Ag2CrO4 photoelectrode with 8 SILAR cycles (denoted as ZnO–Ag2CrO4-8), which exhibited about 3-fold photo-enhancement in the current density as compared to bare ZnO NRs (0.87 mA cm−2) under similar conditions. The improvement in photoactivity was attributed to the ideal band gap and high absorption coefficient of the Ag2CrO4 particles, which resulted in improved solar light absorption properties. Furthermore, an appropriate annealing treatment was proven to be an efficient process to increase the crystallinity of Ag2CrO4 particles deposited on ZnO NRs, which improved the charge transport characteristics of the ZnO–Ag2CrO4-8 photoelectrode annealed at 200 °C and increased the performance of the photoelectrode. The results achieved in the present work present new insights for designing n–n heterojunction photoelectrodes for efficient and cost-effective PEC applications and solar-to-fuel energy conversions.
Highlights
The greatest challenge in the current society is the reduction in the amount of environmental pollution and the dependence on fossil fuels
The content of the Ag2CrO4 particles on ZnO NRs was controlled by changing the number of successive ionic layer adsorption and reaction (SILAR) cycles
The maximum photocurrent density of about 2.51 mA cmÀ2 at 1.23 V was measured for the prepared ZnO–Ag2CrO4 photoelectrode with 8 SILAR cycles, which exhibited about 3-fold photo-enhancement in the current density as compared to bare ZnO NRs (0.87 mA cmÀ2) under similar conditions
Summary
The greatest challenge in the current society is the reduction in the amount of environmental pollution and the dependence on fossil fuels. The rapid recombination of photoinduced eÀ/h+ pairs strongly lowers the photoconversion efficiency.[9,10] To overcome these difficulties, the constructed heterojunction between ZnO and narrow-band-gap semiconductors with appropriate energy levels can broaden the light absorption region and facilitate the separation and transfer of photocarriers.[11,12,13,14,15] In particular, nanostructure composites containing n–n heterojunctions with direct contact between two n-type semiconductors have widespread potential applications because of the formed electric eld produced at the junction, resulting in efficient charge separation, as demonstrated in InN/ZnO,[16] Fe2O3/ZnO,[17] BiVO4/P25,18 CdWO4/Bi2O2CO3 The rapid recombination of photoinduced eÀ/h+ pairs strongly lowers the photoconversion efficiency.[9,10] To overcome these difficulties, the constructed heterojunction between ZnO and narrow-band-gap semiconductors with appropriate energy levels can broaden the light absorption region and facilitate the separation and transfer of photocarriers.[11,12,13,14,15] In particular, nanostructure composites containing n–n heterojunctions with direct contact between two n-type semiconductors have widespread potential applications because of the formed electric eld produced at the junction, resulting in efficient charge separation, as demonstrated in InN/ZnO,[16] Fe2O3/ZnO,[17] BiVO4/P25,18 CdWO4/Bi2O2CO3 (ref. 19) and ZnO/ Ag3VO4.20
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