Towards the quantification of the chemical mechanism of light-driven water splitting on GaN photoelectrodes.

We present results from a study addressing the unbiased water-splitting process and its side reactions on GaN-based photoelectrodes decorated with NiOx, FeOx, and CoOx nanoparticles. Observations involving physicochemical analyses of liquid and vapour phases after the experiments were performed in 1 M NaOH under ambient conditions. A water-splitting process with GaN-based photoelectrodes results in the generation of hydrogen gas and hydrogen peroxide. Quantification of the water-splitting chemical mechanism gave numerical values indicating an increase in the device performance and restriction of the GaN electrocorrosion with surface modifications of GaN structures. The hydrogen generation efficiencies are ηH2(bare GaN) = 1.23%, ηH2(NiOx/GaN) = 4.31%, ηH2(FeOx/GaN) = 2.69%, and ηH2(CoOx/GaN) = 2.31%. The photoelectrode etching reaction moieties Qetch/Q are 11.5%. 0.21%, 0.26% and 0.20% for bare GaN, NiOx/GaN, FeOx/GaN, and CoOx/GaN, respectively.

Analysis of the n-GaN electrochemical etching process and its mechanism in oxalic acid.

We studied the wet electrochemical etching of n-GaN films in oxalic acid. The electrooxidation processes occur in a potentiostatic mode in the voltage range of 5 to 20 V. We described the formation of the porous n-GaN layer structures in several ways. Firstly, we observed the microphotographs of the cross section to characterize the nanostructure. Secondly, we examined the reaction products in a liquid phase using ICP-OES and TOC-TN methods, while vapor-phase products were examined by gas chromatography. Finally, according to the product data analysis, we demonstrate a mechanism for the electrochemical oxidation of n-GaN in oxalic acid, which involves 6 electrons.