Molecular cobalt photocatalyst for high-turnover visible-light hydrogen evolution in alkaline water
A cobalt-based molecular photocatalyst uses visible light to split water in a single alkaline solution, efficiently producing hydrogen with high turnover numbers.
Background
The development of sustainable hydrogen production via photocatalytic water splitting has attracted intense interest as a route to carbon-neutral energy storage. Visible-light-driven hydrogen evolution reactions (HER) using molecular transition-metal complexes aim to harness abundant sunlight and water, generating clean hydrogen fuel under mild conditions. Current commercial electrolyzers rely on high-energy input and precious-metal electrocatalysts, driving the search for cost-effective, earth-abundant molecular catalysts. A central challenge remains achieving efficient HER in aqueous environments without resorting to corrosive acidic media or organic co-solvents, which complicate reactor design and increase operational costs.
Most molecular HER systems operate optimally in strongly acidic solutions or mixed organic/aqueous solvents, necessitating acid additives or organic co-solvents to stabilize low-valent metal intermediates. This pH incompatibility forces separate compartments for the hydrogen- and oxygen-evolving half-reactions, adding complexity and membrane crossover risks. Additionally, many catalysts display limited turnover numbers and rapid deactivation under purely alkaline conditions, where proton availability is lower and competitive side reactions are pronounced. These constraints hinder the integration of both half-reactions in a single basic electrolyte and limit overall solar-to-hydrogen conversion efficiencies.
Technology
A cobalt complex featuring a tetrapyridyl-amine ligand undergoes reversible Co(II)/Co(I) redox cycling under visible-light irradiation to drive photolytic hydrogen evolution in purely aqueous solutions at pH 9.0. The ligand framework stabilizes the low-valent cobalt center, facilitating efficient proton reduction without the need for organic cosolvents or acid additives. Operating in a basic electrolyte enables both hydrogen- and oxygen-evolving half-reactions to proceed in the same solution, simplifying reactor design. Under these conditions, the system achieves turnover numbers up to 218,000, outperforming comparable molecular catalysts reported for visible-light-driven hydrogen evolution.
This approach is differentiated by its exclusive use of alkaline aqueous media, eliminating the traditional requirement for separate acidic and basic compartments or mixed solvent systems. The molecular catalyst’s stability in basic conditions and high activity under visible light set it apart from conventional proton-reduction catalysts that typically rely on acidic environments or organic solvent mixtures. By combining a robust ligand design with exceptional catalytic longevity and integration of both half-reactions in one chamber, this technology offers a streamlined pathway for scalable, solar-driven water splitting.
Benefits
- High catalytic efficiency with turnover numbers up to 218 000
- Operates in purely aqueous alkaline (pH 9.0) solutions without organic cosolvents or acid additives
- Enables both hydrogen- and oxygen-evolving half-reactions in the same electrolyte, eliminating separate compartments
- Visible-light-driven photolytic hydrogen evolution for solar energy utilization
- Higher reaction rates than existing molecular HER systems under comparable conditions
- Ligand-stabilized Co(I/II) redox couple for enhanced catalyst stability and durability
Applications
- Solar-driven hydrogen generation
- Alkaline electrolyzer catalyst
- On-site industrial hydrogen production
- Distributed renewable hydrogen production
- Fuel cell refueling stations
Additional info
A cobalt–tetrapyridyl-amine complex functions as a visible-light-driven molecular catalyst in purely aqueous pH 9 solutions, achieving reversible Co(I/II) redox cycling and driving photolytic hydrogen evolution with turnover numbers up to 218 000. The ligand stabilizes low-valent cobalt, promotes proton reduction without organic cosolvents or acids, and allows both hydrogen- and oxygen-evolving half-reactions to proceed in a single alkaline electrolyte.