A team of scientists in Japan has made significant strides in green hydrogen production by developing new materials and methods to enhance efficiency and safety. The researchers successfully operated a 100m2 green hydrogen reactor outdoors for three years, marking a notable achievement. Green hydrogen, which integrates renewable energy sources like wind and solar, offers a sustainable alternative to fossil fuel-based hydrogen. The team, led by Takashi Hisatomi of Shinshu University, utilized photocatalysts to convert sunlight and water into green hydrogen, emphasizing the potential for energy storage and usage irrespective of time or weather conditions. To improve efficiency, the scientists adopted a two-step water-splitting system and devised a screen-printing technique to create scalable photocatalyst sheets. These sheets, connecting two-step photocatalysts through a conductive layer, demonstrated enhanced performance and ease of maintenance compared to previous liquid slurry designs. The team's innovation showcased a 1.5 times increase in solar energy conversion efficiency under natural sunlight, indicating promising advancements in green hydrogen technology. However, challenges persist in scaling up the conversion rate, with the current 1% needing to reach 5% for economic viability and competitiveness with natural gas-derived hydrogen. Kazunari Domen, the senior author, emphasized the necessity of enhancing solar-to-chemical energy conversion efficiency for mass production and large-scale plant construction. The researchers also stressed the role of governments in establishing safety and environmental standards to support the evolving green hydrogen sector, fostering infrastructure development and regulatory frameworks. The research, featured in the journal Frontiers in Science, underscores the transformative potential of green hydrogen and the ongoing efforts to address key technological and efficiency challenges for a sustainable energy future.