Photocatalytic materials designed for hydrogen production from seawater represent a promising avenue for sustainable energy generation, leveraging abundant solar energy and seawater resources. However, the complex chemistry of seawater, particularly the presence of chloride ions and competing reactions, poses significant challenges. This article explores the development of corrosion-resistant photocatalytic systems, their material compositions, and their performance in real-world applications.

Seawater is an attractive feedstock for hydrogen production due to its vast availability, but its high chloride content accelerates corrosion in photocatalytic systems. Chloride ions can degrade photocatalysts by attacking active sites, reducing efficiency, and shortening material lifespans. To mitigate this, researchers have developed protective coatings such as aluminum oxide (Al2O3), which forms a barrier against chloride penetration while maintaining photocatalytic activity. Al2O3-coated electrodes have demonstrated improved durability in seawater environments, with some studies reporting stable operation for over 1,000 hours without significant performance loss.

Another critical challenge is the competition between hydrogen evolution and chloride oxidation reactions. In seawater, chloride ions can be oxidized to chlorine gas, which not only reduces hydrogen yield but also poses safety and environmental concerns. Selective catalysts that favor the hydrogen evolution reaction (HER) over chloride oxidation are essential. Molybdenum disulfide (MoS2) has emerged as an effective co-catalyst due to its high HER activity and resistance to chloride poisoning. When combined with titanium dioxide (TiO2), the resulting TiO2/MoS2 composite exhibits enhanced charge separation and reduced electron-hole recombination, leading to higher hydrogen production rates. Experimental data indicate that TiO2/MoS2 systems can achieve hydrogen evolution rates exceeding 5 mmol g⁻¹ h⁻¹ under simulated solar irradiation in seawater.

Bismuth vanadate (BiVO4) is another promising material due to its visible-light absorption and moderate bandgap. However, its susceptibility to photocorrosion in seawater limits its practical application. To address this, researchers have incorporated protective layers such as cobalt phosphate (Co-Pi) or nickel-based coatings, which act as both corrosion inhibitors and HER promoters. Modified BiVO4 systems have shown hydrogen production rates of up to 3 mmol g⁻¹ h⁻¹ while maintaining stability for several hundred hours in saline conditions.

Material stability and salt tolerance are critical for long-term performance. Recent advances in nanostructuring have enabled the design of photocatalysts with tailored surface properties that resist chloride adsorption. For example, hierarchical TiO2 structures with controlled porosity reduce chloride interaction while maximizing light absorption. Similarly, doping strategies, such as nitrogen or sulfur incorporation, enhance corrosion resistance by modifying the electronic structure of the photocatalyst. These approaches have been validated in laboratory-scale experiments, with some materials retaining over 90% of their initial activity after prolonged exposure to seawater.

Pilot-scale demonstrations have provided valuable insights into the scalability of these technologies. A notable example is a 10 m² photocatalytic reactor tested in coastal environments, which achieved a daily hydrogen output of 0.5 kg using TiO2-based photocatalysts. The system incorporated Al2O3 coatings and MoS2 co-catalysts to mitigate chloride effects, demonstrating feasibility for larger deployments. However, challenges such as fouling from marine organisms and fluctuating sunlight intensity require further optimization.

Environmental implications must also be considered. While hydrogen production from seawater is carbon-neutral, the potential release of chlorine or other byproducts necessitates careful management. Advanced photocatalytic systems integrate selective membranes or scavengers to minimize unwanted emissions. Life cycle assessments indicate that seawater-based hydrogen production could reduce freshwater consumption by up to 95% compared to conventional electrolysis, making it an attractive option for water-scarce regions.

In summary, the development of corrosion-resistant photocatalytic materials for seawater splitting has made significant progress, with TiO2/MoS2 and BiVO4-based systems leading the way. Protective coatings, selective catalysts, and nanostructuring strategies have improved stability and efficiency, enabling pilot-scale implementations. However, further research is needed to address fouling, scalability, and environmental impacts. As these technologies mature, they could play a pivotal role in the global transition to sustainable hydrogen economies.