The optimization of surface morphology of Au nanoparticles on WO 3 nanoflakes for plasmonic photoanode.

Among many candidates for photoanode materials of photoelectrochemical (PEC) cell, nanostructured tungsten trioxide (WO ₃ ) is regarded as one of the most promising materials due to its superior electrical properties and adequate bandgap (∼2.8 eV) and band edge position. WO ₃ nanoflakes (WO ₃ NFs), which have merits on its high surface area and crystallinity, have been actively studied for this manner but solar-to-hydrogen efficiency of WO ₃ NFs based photoanode is still not sufficient both in light absorption and charge separation. Plasmon-induced enhancement using Au nanoparticles is excellent approach for both the efficiency of light absorption and charge separation of WO ₃ . However, it still needs optimization on its amount, shape, coverage, and etc. Here, we synthesized WO ₃ NFs by solvothermal growth and decorated gold nanoparticles on these nanoflakes by e-beam evaporation and rapid thermal annealing process in a row. By this process, a large-area AuNPs/WO ₃ nanocomposite structure with various size, interparticle distance, and coverage of AuNPs were fabricated. These AuNPs/WO ₃ NFs type photoanode achieve high light absorption both in UV and visible range and consequently higher photocurrent density. The optimized AuNPs/WO ₃ nanocomposite photoanode exhibits 1.01 mA cm ^-2 of photocurrent density, which is increased to 19.8% compared with bare WO ₃ nanoflakes. Field emission-scanning electron microscope, x-ray diffraction, UV-vis spectrometer analysis were measured to analyze the morphology and crystallinity and relationship between structure and PEC performance.