Clean and sustainable hydrogen, derived from advanced water-splitting approaches, stands at the forefront of efforts to decarbonize key sectors such as electricity, manufacturing, and transportation. These transformative approaches offer pathways to sustainable solutions, emphasizing the critical role of clean hydrogen in achieving a low-carbon economy. Within this context, there are at least four primary technology pathways under active research for advanced water splitting: low and high-temperature electrolysis (LTE and HTE), photoelectrochemical (PEC), and solar thermochemical (STCH) methods.

Each pathway is distinct in its approach and technology. For instance, LTE encompasses proton exchange and alkaline membranes, each providing unique technological nuances. In contrast, HTE involves proton and oxygen ion conducting membranes, offering different operational characteristics. The PEC pathway is explored through panel-like photoelectrodes and particle-based photocatalyst systems, while STCH delves into redox-active metal oxide cycles and hybrid electrochemical-thermochemical cycles. Beyond these, the field is ripe with potential for additional or hybrid pathways that may further enhance clean hydrogen production efficiency.

The diversity in these pathways leads to varying degrees of technological and commercial maturity. There is a pressing need for consistent terminology and methodologies to compare and contrast these pathways. Such standardization is vital for multiple purposes, ranging from shaping policy development to guiding research agendas and corresponding investments. While there might be common standards and benchmarks for these pathways, their unique requirements and needs must be acknowledged, particularly considering their differing maturity levels and material/device considerations.

A critical challenge in advancing water splitting hydrogen research is the urgent need for consistency within and across individual technology pathways. This uniformity is essential for effectively evaluating and comparing the potential of each pathway. The current lack of consistency, agreed-upon benchmarks, protocols, standards, research priorities, or roadmaps presents significant barriers. These obstacles hinder entry into the field, complicate communication with decision-makers, and impede general outreach efforts.

To address these challenges, Volume II for this research topic follows the success of Volume I (20 articles, 64k total views, and downloads to date), and seeks scholarly contributions and perspectives that focus on advanced water splitting techniques where the primary energy source is renewable or at least carbon-free. We invite articles that offer comparisons, materials screening, characterization protocols, benchmarks, techno-economic analyses, system analyses, and research priorities or roadmaps for any and all advanced water splitting pathways.

This Research Topic is comprehensive but not limited to the following areas:

• Development of protocols, standards, or benchmarks for characterizing various aspects of hydrogen production from advanced water splitting, utilizing technologies such as photoelectro-chemistry, low-temperature electrolysis (proton or alkaline membrane), intermediate and high-temperature electrolysis (proton or oxygen ion conducting), or solar thermochemical processes.

• Techno-economic and life-cycle analyses examining the societal impacts of sustainable hydrogen production across different pathways.

• Creation of roadmaps and identifying research priorities to navigate the economic and commercial viability of these diverse pathways.

Through this collective effort, the aim is to lower barriers, disseminate best practices, and create a solid foundation in accelerated materials, device, and systems research, development, and deployment for the broader research community.

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Advanced Water Splitting Technologies Development: Best Practices and Protocols Volume II