As the world focuses on sustainable energy, green hydrogen has garnered attention for its clean power potential. A research team led by Professor Hyungyu Jin and Professor Jeong Woo Han has made significant progress in green hydrogen production. Their development of an iron-based catalyst, Fe-poor NiFe2O4 (NFO), has revolutionized thermochemical water splitting efficiency. Unlike traditional oxides, NFO's phase transformation mechanism allows for increased oxygen capacity at lower temperatures, achieving a remarkable 0.528% water-to-hydrogen conversion efficiency. The study not only boosts efficiency but also delves into the atomic-level active sites within iron oxide materials that are crucial for hydrogen production. By combining experimental techniques and computational simulations, the team identified the structural active sites responsible for driving hydrogen production, offering a pathway for designing more effective catalysts. With a focus on sustainability, the research proposes a cost-effective hydrogen production method utilizing abundant iron oxides and potentially harnessing solar or industrial waste heat for energy. This work exemplifies the synergy between experimental and computational sciences in unveiling fundamental principles for cleaner energy production.