Researchers from Northwestern University has used advanced optical techniques to observe water molecules in real time forming oxygen by giving up electrons. Their findings shed light on why water splitting, a promising method for hydrogen production, often demands more energy than expected.
Before water molecules transfer electrons to form oxygen, they rotate so that the oxygen “head” faces the electrode. This movement appears to be a key step that consumes extra energy, explaining the gap between theoretical and actual voltage requirements. The research from Northwestern University was published in the journal Science Advances and can be found here:
Speelman, R., Marker, E. J., & Geiger, F. M. (2025). Quantifying Stern layer water alignment before and during the oxygen evolution reaction. Science Advances, 11(10). https://doi.org/10.1126/sciadv.ado8536
Water splitting is an appealing way to generate hydrogen fuel, which many see as a cleaner alternative to fossil fuels. In such a process, water is run over an electrode while a voltage is applied, causing hydrogen and oxygen to separate. The hydrogen can be collected for energy storage or used directly in fuel cells. However, the oxygen-forming portion of the reaction (the oxygen evolution reaction, or OER) is notoriously inefficient. As noted by researchers across multiple institutions, the flipping motion of water molecules is a significant reason for this extra energy requirement.
“When you split water, two half-reactions occur,”
said Northwestern’s Franz Geiger, who led the study. Geiger is the Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern’s Weinberg College of Arts and Sciences and member of the International Institute for Nanotechnology and the Paula M. Trienens Institute for Energy and Sustainability. The study’s co-authors are Northwestern’s Raiden Speelman and Ezra Marker, who are both members of Geiger’s lab. Geiger went onto say:
“One half-reaction produces hydrogen and the other produces oxygen. The half-reaction that produces oxygen is really difficult to perform because everything has to be aligned just right. It ends up taking more energy than theoretically calculated. If you do the math, it should require 1.23 volts. But, in reality, it requires more like 1.5 or 1.6 volts.”
“Providing that extra voltage costs money, and that’s why water splitting hasn’t been implemented at a large scale. We argue that the energy required to flip the water is a significant contributor to needing this extra energy. By designing new catalysts that make water flipping easier, we could make water splitting more practical and cost-effective.”
NASA and other agencies interested in deep-space missions have been tracking these developments too. On future trips to Mars, astronauts could use similar methods to generate oxygen from local ice or water sources. But to make these processes viable off-world (or at large scale here on Earth), engineers need to design catalysts that minimize the energy lost during that pivotal flipping step.
Franz Geiger’s team at Northwestern developed a specialised laser-based method to watch how water molecules behave at a metal electrode. By monitoring how light interacts with the electrode surface, they observed when hydrogen atoms were turned away from or pointed toward the metal. In one orientation, the hydrogen atoms block the path for electron transfer; in another, the oxygen atom is positioned just right to give up its electrons.
“Our technique is the optical equivalent to noise-canceling headphones,” Geiger said. “We can essentially control constructive and deconstructive interference; the photon’s phase, and, from that, we can precisely quantify how many water molecules are pointing to the surface and how many rearrange to point in away from it.”
Although earlier studies had hinted at the need for more accurate measurements of molecular orientation, Geiger’s group reports direct evidence of the flip in real time. This result matches findings from other laboratories—some of which had used computational simulations to predict that water molecules would rotate before oxygen is formed.
Across these recent reports, a common theme emerges: different metals and different pH levels influence the flipping process. Iridium, while efficient, is rare and expensive. Nickel and iron, on the other hand, are more affordable and abundant. Researchers hope to refine these cheaper catalysts to make them as effective as iridium at assisting the OER. Adjusting the pH of the solution can help too, since a more alkaline environment has shown potential for improving water orientation and thus lowering energy costs.
“Iridium only comes to Earth from meteoric impacts, so there’s a limited amount,” he said. “It’s very expensive and certainly not going to help solve the energy crisis any time soon. Researchers are looking at alternatives, like nickel and iron, and we’re hoping to find ways to make these materials just as efficient; if not more efficient, than iridium.”
While the final word on water flipping is far from written, these multi-sourced findings offer a clearer understanding of one of water’s quirks on electrode surfaces. If researchers can use these insights to design better catalysts; and possibly reduce the voltage needed for splitting, then hydrogen’s role in the clean energy landscape could get a boost.
Hassan graduated with a Master’s degree in Chemical Engineering from the University of Chester (UK). He currently works as a design engineering consultant for one of the largest engineering firms in the world along with being an associate member of the Institute of Chemical Engineers (IChemE).
