A Cornell University-led research team has developed a sustainable and low-cost method to produce carbon-free green hydrogen using just sunlight and seawater as inputs.

The team devised a prototype by leveraging one of the drawbacks of photovoltaics —relatively low efficiency.

Most solar cells can only convert up to 30% of solar energy into electricity, and the remaining is dissipated as waste heat. The team was able to harness the waste heat to warm the seawater until it evaporated. Once the seawater evaporates and the desalinated vapor condenses into clean water, it is passed through an electrolyzer. The electrolyzer splits the water molecules into hydrogen and oxygen.

“The short-wavelength sunlight interacts with the solar cell to generate electricity, and the longer wavelength light generates the waste heat to power the seawater distillation. This way, all the solar energy can be fully used. Nothing is wasted,” said Lenan Zhang,  lead researcher and assistant professor in the Sibley School of Mechanical and Aerospace Engineering at Cornell Engineering.

The device also uses a capillary wick that traps the water in direct contact with the solar panel into a thin film. This boosts the evaporation efficiency to more than 90%, allowing for the heating of large volumes of water.

Solar-powered water electrolysis holds significant promise for the mass production of green hydrogen. However, to produce one kilogram of hydrogen, at least nine kilograms of water is required. The huge quantities of water consumed increase the cost of green hydrogen and raise conservation concerns.

The manufacturing costs of green hydrogen production can be roughly 10 times higher than those of regular hydrogen due to the large amounts of water needed for the process.

On the other hand, seawater is an abundant resource for water, but generating green hydrogen from seawater can be challenging.

Zhang was at the Massachusetts Institute of Technology exploring ways to use solar power to convert seawater into potable water through thermal desalination. After arriving at Cornell University, Zhang and his team started working on expanding the technology to produce green hydrogen.

In June 2024, engineers from the University of Illinois, Chicago, developed a novel method to produce hydrogen from water utilizing only solar power and agricultural waste such as manure or husks. This novel technique claimed to reduce the energy required to extract hydrogen from water by 600%.

In 2023, engineers at the Massachusetts Institute of Technology developed a conceptual design to produce totally green, carbon-free hydrogen fuel with a trainlike system of reactors that is driven solely by solar energy.