2, IFSC, USP, São Carlos, SP, Brazil
Despite the hematite fulfills most of the requirements as photoanode in a photoelectrochemical cell, some limitations still prevent its commercial application. The poor electron-hole separation is the major issue in hematite being responsible for the low photoelectrochemical performance. In fact, the extensive charge recombination in hematite mainly occurs at the interfaces such as substrate-hematite layer and hematite-hematite grains. This work describes the impact of the substrate-hematite interface in the overall photoelectrochemical performance. The thermal treatment has an important role not only to provide the phase transformation from precursor oxy-hydroxide phase but also on surface activation for the chemical reaction. The study was conducted firstly evaluating the influence of the temperature of thermal treatment in the fluorine-doped tin oxide (FTO) substrate and then, at the FTO-hematite interface. Considering all the techniques and data analysis, it was found that the fast annealing at 750°C for 30 minutes has achieved a synergy among to the resistance to charge transport, the optimal amount of Sn-diffused (a ratio Sn:Fe of 0.17) from the substrate that leads to a suitable reduction in the recombination rate at FTO-hematite interface. The observed photoelectrochemical performance for 750-fast annealing showed an improvement of photocurrent response achieving 0.54 mA cm-2 at 1.23 VRHE and shiffiting onset potential around 200 mV. It is worth mentioning that the overall improvement of the hematite electrode observed after the annealing process was attributed to a more efficient charge separation that does not compromise the properties of the FTO substrate (surface roughness and electronic conductivity). Therefore, more investigation is underway in the laboratory to increase even more the FTO-hematite interface since the optimized annealing process was found.