III-nitride materials gained significant interest for their potential application in durable solid-state lighting and 'artificial photosynthesis' devices. Despite their promising properties, III-nitride systems are susceptible to electrochemical decomposition when exposed to electrolytes, leading to potential corrosion and irreversible damage to the device's active layer.

To address these challenges, researchers have explored the use of metal and metal oxide nanoparticles to enhance the lifetime and efficiency of 'artificial photosynthesis' devices; however, the III-nitride materials still face electrooxidation after prolonged exposure. Moreover, the hydrogen and oxygen generation ratios during light-driven water splitting processes on III-nitrides often remain unclear or deviate significantly from the expected 2:1 ratio if the experiment extends beyond 2 hours. To overcome these issues, understanding the chemical mechanism of the anodic oxidation of GaN is crucial for designing effective protection strategies for III-nitride-based 'artificial photosynthesis' devices.

In this dissertation, we investigate the electrochemical behavior of III-nitrides by studying the anodic oxidation reaction of n-GaN in various electrolytes. The pH value of the reaction media is varied from 0 to 13 to understand its impact on the formation of porous n-GaN nanostructures. Moreover, the study examines the water-splitting process on GaN-based photoelectrodes decorated with NiOx, FeOx, and CoOx nanoparticles. The physicochemical analyses of the liquid and vapor phases are performed to quantify both the anodic oxidation of GaN and the water-splitting chemical mechanisms.