The optimization of surface morphology of Au nanoparticles on WO₃ nanoflakes for plasmonic photoanode

Among many candidates for photoanode materials of photoelectrochemical (PEC) cell, nanostructured tungsten trioxide (WO₃) 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. WO₃ nanoflakes (WO₃ NFs), which have merits on its high surface area and crystallinity, have been actively studied for this manner but solar-to-hydrogen efficiency of WO₃ 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 WO₃. However, it still needs optimization on its amount, shape, coverage, and etc. Here, we synthesized WO₃ 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/WO₃ nanocomposite structure with various size, interparticle distance, and coverage of AuNPs were fabricated. These AuNPs/WO₃ NFs type photoanode achieve high light absorption both in UV and visible range and consequently higher photocurrent density. The optimized AuNPs/WO₃ nanocomposite photoanode exhibits 1.01 mA cm^-2 of photocurrent density, which is increased to 19.8% compared with bare WO₃ 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.