Hydrogen is a source of clean energy. When used in fuel cells, it combines with oxygen to produce electricity, and the only chemical by-product is water.
To produce the environmentally friendly fuel, one must do the reverse: split water into hydrogen and oxygen. And that requires a lot of electricity, which can make hydrogen much less green. Now researchers in Australia have come up with a way to make hydrogen efficiently by harnessing the contaminants in wastewater streams (ACS Electrochem. 2025, DOI: 10.1021/acselectrochem.5c00064).
To make green hydrogen at scale, you need a few things: a source of renewable energy, good catalysts to lower energy costs, and electrodes that are cost effective and durable. The research team found that electrodes made from modified biochar—a porous charcoal made from agricultural waste—could combine with dissolved metal pollutants in wastewater to catalyze the reaction.
“We tune the properties of the biochar to make it effective for harvesting active materials from the wastewater,” says Nasir Mahmood, a materials scientist at RMIT University, the lead investigator of the study. The material creates active sites for the splitting of water molecules, he says.
The researchers sourced wastewater from Sydney and Melbourne water corporations, which collect a mix of domestic sewage, industrial waste, rainfall runoff, and other waste products. They treated the wastewater to remove solid waste, organic matter, and nutrients and then poured it into their experimental setup. When they connected the electrodes to a solar panel, they achieved continuous hydrogen generation for over 18 days at high efficiency.
Metals and fluorinated pollutants in the wastewater are the key components for the reaction. Iron, platinum, and nickel help catalyze water splitting. At the same time, chromium and fluorinated compounds help avoid side reactions that might produce toxic products.
All of these pollutants seep into the biochar, deposit inside its network of pores, and create an extensive catalytic surface on the electrodes that’s even more efficient than catalysts made from precious metals, according to the study. This method not only removes heavy metals from wastewater; it uses them as active catalysts, benefiting both the environment and the energy sector, Mahmood says.
The green hydrogen can be collected for use as needed. As for the oxygen, one of the best applications would be to funnel it back into other parts of the wastewater treatment system, Mahmood says.
The team is still working on the system to make it commercially viable. “The biggest challenge is the integration of the wastewater into the electrolyzer system,” Mahmood says. “Wastewater has a lot of other stuff in it,” and he still is not sure whether those contaminants could have an impact on the electrolyzer’s stability. Plus, components not involved in the reaction could cause other effects, like blockages.
Shubra Singh, a researcher from Anna University, Chennai, who was not involved in the study, says that while there have been earlier studies leveraging wastewater for hydrogen production, this work is significant in terms of achieving uninterrupted water splitting for several weeks. The method is promising for use in water-stressed situations as both a water source and chemical feedstock for electrodes, she adds. “It replaces expensive catalysts like platinum and has the potential to be used off grid.”
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