Performance and stability of LaTiO₂N based photoanodes at varying electrolyte temperatures and irradiances

Operating conditions greatly affect the performance and lifetime of photoelectrochemical systems. Understanding these influences is required for the development of photoelectrochemical water splitting towards a practical and scalable solution for solar hydrogen generation. This study investigates the influence of two important operating parameters (i.e. irradiance and electrolyte temperature) on the efficiency and stability of LaTiO₂N-based photoanodes with NiO _x and CoO _x cocatalysts as representative examples for oxynitride electrodes. Chronoamperometry measurements at 1.23 V vs. RHE are performed exploring a wide range of irradiances (1000-119 000 W m^-2) and electrolyte temperatures (17-50 °C). An increase in the electrolyte temperature leads to a decrease in the photoanode efficiency by 52% and in the stability by 8% respectively, while higher irradiances improve initial efficiencies up to 77% but decrease the stability of the photoanodes by 38%. The most suitable operating point is obtained at a 1000 W m^-2 irradiance and an electrolyte temperature of 17 °C. Further analysis using XRD, SEM, STEM-EXD/EELS, HREM, and ICP-MS revealed that degradation is mostly driven by a cocatalyst dissolution/redeposition mechanism, which is accelerated by increased electrolyte temperatures and especially irradiances, while bulk LaTiO₂N remained stable apart from surface oxidation.