A review on solar energy-based indirect water-splitting methods for hydrogen generation

The distinguish generation methods regarding hydrogen generation using solar energy as a triggering agent are discussed in this paper, specifically indirect techniques. Two broadly classified processes are direct and indirect. The Direct processes exhibit high thermal efficiency, but their low conversion efficiency, maximum heat dissipation, and the lack of readily available heat resistive materials in abundance put the indirect processes relatively on the higher rank. The indirect methods include bio photolysis, thermochemical, photolysis, and electrolysis. There are promising features of indirect ways. Bio-photolysis provides zero pollution; the photolysis method reduces the carbon footprint in the environment; Thermochemical is meritorious in low electricity consumption due to high heat generation in the process; Electrolysis proves its worth in negligible pollution and considerable efficiency. The energy and exergy efficiency for hydrogen yielding are compared, and it is found that electrolysis has the highest energy and exergy efficiency. In terms of raw material availability, thermochemical ranks very low as compared to photolysis (abundant solar energy), bio-photolysis (a readily available bio-agent), and electrolysis (electrolytic agents to carry out the process).