A comprehensive new review published in ENGINEERING Energy (formerly Frontiers in Energy) outlines the future of green hydrogen production, demonstrating how sunlight can directly convert seawater vapor into hydrogen fuel through an innovative integrated system. The analysis, led by researchers from the Technology Innovation Institute in Abu Dhabi and the University of Waterloo, provides a detailed roadmap for overcoming the critical challenges that have hindered large-scale seawater hydrogen production.
As global demand for clean hydrogen accelerates, conventional approaches face fundamental obstacles. Direct seawater electrolysis suffers from chlorine evolution, catalyst corrosion, and light-blocking bubbles, while membrane-based desalination adds cost and complexity. The review identifies photothermal-photocatalytic vapor splitting as a transformative alternative that separates water purification from hydrogen generation, enabling optimized, scalable systems.
“Seawater is our most abundant water source, but its complex chemistry has been a major barrier,” explains Dr. Hongxia Li, lead author from the Technology Innovation Institute. “By first converting seawater to pure vapor using solar heat, then splitting that vapor photocatalytically, we create a two-step process that’s inherently safer and more efficient than direct seawater splitting.”
Key Innovation Pathways
The review systematically analyzes three critical design strategies:
- Precision Vapor Control: Achieving temperatures above 100°C requires active solar concentration. The team evaluated optical systems (parabolic troughs, solar towers, Fresnel lenses) that can generate steam at 128°C and 250 kPa, alongside thermal concentration approaches using porous absorbers to localize heat. While optical concentration offers higher efficiency, thermal concentration provides simpler, lower-cost solutions for distributed applications.
- Salt-Free Operation: Perhaps the most significant breakthrough involves preventing salt accumulation that plagues conventional systems. The review highlights three proven strategies: back-diffusion designs that continuously return salt to bulk water, Janus membranes with hydrophobic surfaces that block salt ions, and revolutionary contactless evaporation that physically separates the absorber from seawater. A contactless “solar umbrella” design demonstrated stable operation even with hypersaline solutions, achieving zero brine discharge.
- Advanced Photocatalysts: The analysis reveals that vapor-phase splitting overcomes key liquid-phase limitations. Without water’s UV absorption and bubble interference, catalysts achieve more efficient light harvesting. Novel materials like alkali-treated ZnFe₂O₄ nanoparticles showed 3.9× higher hydrogen yield than untreated catalysts, while MoSₓ/TiO₂ hybrids achieved rates of 11.09 mmol/(g·h). The review documents a record 9.2% solar-to-hydrogen (STH) efficiency using concentrated solar light.
Scaling from Lab to Industry
The review bridges laboratory proof-of-concepts with industrial reality. At lab scale, a floating 1 m² platform using single-atom Cu/TiO₂ produced 79.2 mL hydrogen daily under natural sunlight. A charred wood-based system achieved 248.1 μmol/(m²·h) from seawater, leveraging wood’s natural porosity for both water transport and electron transfer.
Industrial-scale implementations are emerging. A 100 m² array of panel reactors in Japan operated autonomously for months, achieving 0.76% STH efficiency—the largest photocatalytic hydrogen system reported. The NEOM “solar dome” project, covering 26,500 km², demonstrates the massive potential for integrating vapor generation with hydrogen production.
Critical Bottlenecks and Future Directions
Despite progress, the review identifies urgent challenges:
- Efficiency Gap: Most systems achieve <3% STH efficiency, far from the 10% target for commercial viability. The narrow UV response of most catalysts wastes 97% of solar spectrum energy.
- Material Durability: Long-term stability under high temperature and humidity remains unproven at scale.
- System Integration: Optimizing cooperation between photothermal and photocatalytic components requires better spectral management—using long wavelengths for heat and short wavelengths for catalysis.
Significance for Energy Transition
This comprehensive analysis provides the first systematic framework for seawater-to-hydrogen technology, guiding researchers toward high-impact innovations. By decoupling water purification from hydrogen generation, the vapor-splitting approach offers unprecedented flexibility for solar-driven fuel production in coastal regions worldwide.
“With targeted materials development and optimized system design, we believe seawater vapor splitting can become a cornerstone of the global hydrogen economy,” says Dr. Xiao-Yu Wu, corresponding author from the University of Waterloo. “This review lights the path forward.”
Publication Details
The review article, “From seawater to hydrogen via direct photocatalytic vapor splitting: A review on device design and system integration,” was published in ENGINEERING Energy (formerly Frontiers in Energy), 2024, Volume 18, Issue 3, Pages 291–307.
DOI: 10.1007/s11708-024-0917-9
Article Link: https://doi.org/10.1007/s11708-024-0917-9
This work was supported by the Canada Research Chair Tier I—Zero-Emission Vehicles and Hydrogen Energy Systems and the Natural Sciences and Engineering Research Council of Canada (NSERC).
Journal Citation:
Li, H., Ahmed, K. W., AbdelSalam, M. A., Fowler, M., & Wu, X-Y. (2024). From seawater to hydrogen via direct photocatalytic vapor splitting: A review on device design and system integration. Frontiers in Energy, 18(3), 291–307. https://doi.org/10.1007/s11708-024-0917-9
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