Oregon State’s new MOF turns light and water into hydrogen with no added metal catalyst

Researchers at Oregon State University have created a new class of light-activated materials that can produce hydrogen from water, offering a potentially cleaner route from sunlight to fuel. Their photocatalyst produces hydrogen quickly and efficiently, and the material needs no additional expensive metal catalyst.

The team, led by Kyriakos Stylianou of the university’s College of Science worked on this research. The findings could give researchers another tool for reducing greenhouse gas emissions and addressing climate change, Stylianou said.

Hydrogen is widely used in fuel cells for vehicles, and in making ammonia, refining metals and manufacturing plastics.

How photocatalyst works

A catalyst speeds up a chemical reaction without being permanently changed, and a photocatalyst does the same when activated by light. After absorbing light, the material reaches a higher energy state and can use that energy to drive reactions more quickly, Stylianou said.

The work centers on metal-organic frameworks, or MOFs, crystalline porous materials built from positively charged metal ions surrounded by organic linker molecules. Their tiny pores and adjustable structures let scientists fine-tune properties for different uses. Millions of different MOF structures are theoretically possible, Stylianou said. Chemists have already synthesized nearly 100,000 MOFs, and the properties of roughly 500,000 more have been predicted.

An unusual sulfur bond

The team focused on a MOF called BVR-19. It contains an unusual sulfide-to-sulfide bond that temporarily breaks when exposed to light, producing highly reactive sulfur species.

“The organic component does the important work,” Stylianou said. Instead of leaning mainly on metal atoms, the material uses its sulfur-containing organic building blocks to capture light energy and shuttle electrons toward hydrogen production. He called the approach a different way of thinking about how such materials should be designed.

That design means BVR-19 needs no additional expensive metal catalyst, which could simplify future light-driven hydrogen systems. It also forms spontaneously in water-based solutions at room temperature, lowering the energy needed to make it.

Cleaner than natural gas

Splitting water with a catalyst can be cleaner than the dominant industrial method, methane-steam reforming, which uses natural gas and releases carbon dioxide while producing hydrogen. Existing water-splitting methods often rely on electrocatalysis, whose environmental benefit depends on where the electricity comes from. To stay both sustainable and economically competitive, that power must come from low-cost renewable sources.

Cost remains a hurdle: methane-steam reforming yields hydrogen at about $1.50 per kilogram ($0.68 per pound), while green hydrogen runs roughly $5 per kilogram ($2.27 per pound).

New design rules

Stylianou, who directs Oregon State’s Materials Discovery Laboratory, said the work offers a blueprint for designing materials that bring down the cost of green hydrogen. By changing the metal while keeping the rest of the material essentially the same, his team learned why some versions of the MOF work much better than others. Those findings provide new design rules for creating more effective materials for solar fuel production, he said.

The Murdock Charitable Trust, the National Science Foundation and Oregon State’s College of Science supported the study. The paper is titled “Intraligand Charge Transfer in Metal-Organic Frameworks Facilitates Radical Anion-Mediated Hydrogen Evolution.” Emmanuel Musa and other members of the lab, along with several other Oregon State researchers, contributed to the work.

The research was published in the Journal of the American Chemical Society.

Source: https://interestingengineering.com/science/light-activated-mof-hydrogen-from-water