Comparative Overview of Water Splitting and Biological Techniques of Hydrogen Production

Hydrogen is widely regarded as a cornerstone of the global transition toward low-carbon and sustainable energy systems. However, the environmental benefits of hydrogen depend strongly on the production pathway employed. This review presents a comparative analysis of water-splitting technologies and biological methods for green hydrogen production, highlighting their operating principles, efficiencies, costs, technological readiness, and prospects. Water splitting approaches include electrolytic methods alkaline water electrolysis (AWE), proton exchange membrane (PEM), anion exchange membrane (AEM), and solid oxide electrolysis (SOEC) as well as photocatalytic and photoelectrochemical (PEC) systems. Among these, AWE and PEM are technologically mature and commercially deployed, offering high hydrogen purity and system reliability, while SOEC demonstrates superior thermodynamic efficiency at elevated temperatures. Photocatalytic and PEC techniques provide direct solar-to-hydrogen conversion but remain limited by low efficiencies, charge recombination, and material instability. Biological hydrogen production routes like biophotolysis, fermentation, gasification, and pyrolysis utilize biomass and organic waste as feedstocks, supporting circular economy principles. Gasification and pyrolysis exhibit relatively high hydrogen yields and industrial potential but require high temperatures and extensive gas cleaning. In contrast, biophotolysis and fermentation operate under mild conditions and are environmentally benign but are constrained by low production rates, oxygen sensitivity, and process instability. A critical comparison indicates that electrolytic water splitting currently offers the most viable pathway for large-scale, high-purity hydrogen production when powered by renewable electricity, whereas biological methods present attractive waste-to-energy solutions with lower technological readiness in some cases. Future development should focus on reducing capital costs, replacing precious metal catalysts, improving membrane durability, enhancing photocatalyst stability, and optimizing bioreactor performance. Integrating these advances with renewable energy systems will be essential for achieving scalable, cost-effective, and truly sustainable hydrogen production.