| Mar 13, 2026 |
Atomic-level simulations and electrochemical experiments reveal how charge centers called polarons form on semiconductor surfaces to activate green hydrogen production.
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(Nanowerk News) Electrocatalysis and photoelectrocatalysis play a central role in facilitating clean energy conversion and numerous other sustainable processes and technologies. However, the most effective catalysts currently available are based on noble metals, particularly platinum. The high price and limited availability of these materials slow down the expansion of hydrogen production and drive up the costs. Therefore, the development of new, less expensive but still highly effective catalyst materials is crucial for achieving cost-effective and large-scale hydrogen production. Here, semiconductor materials are one possible but relatively little explored alternatives for hydrogen evolution.
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“Unlike traditional metal-based catalysts, semiconductor materials can utilize more common and less expensive elements. However, the development of semiconductor electrodes has been slowed down by the fact that their electrochemical and catalytic properties are not well understood”, explain Professor Karoliina Honkala and Senior Lecturer, Academy Research Fellow, Marko Melander from University of Jyväskylä, who led the research (Nature Communications, “Potential-dependent polaron formation activates TiO2 for the hydrogen evolution reaction”).
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| Lowering the electrode potential charges a single Ti atom (purple) negatively. The forming polarons enable hydrogen (yellow) to bind to the surface and activate the hydrogen evolution reaction on the TiO2 surface. (Image: University of Jyväskylä)
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Semiconductor electrochemistry has been studied less extensively than the electrochemistry of metals, largely due to limitations in available research methods. In particular, computational studies have been challenging because the effect of an external electrode potential has been difficult to model in atomic and electron level calculations. Melander and Honkala have, however, recently overcome this limitation by developing a new approach, the constant inner potential density functional theory, which enables the inclusion of the electrode potential in the simulation of semiconductor electrochemistry.
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“We developed this method two years ago, and it opens new possibilities for modeling semiconductor electrodes. In the present study, we applied the method to the study of the hydrogen evolution reaction on a TiO2 semiconductor electrode. Our simulations showed how and why changing the electrode potential achieves hydrogen production on TiO2. Through the calculations made in collaboration with our partners, we predicted that local charge centers, polarons, form on the TiO2 surface and catalyze the hydrogen evolution,” explains Melander.
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Accurate experiments confirmed the computational predictions
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Experimental testing and validation of the computational results was a significant challenge that needed the application of highly advanced experimental methods. For example, state-of-the-art photoelectrochemical Raman measurements, in situ electron resonance spectroscopy, and operando photoelectron spectroscopy were used to verify the computational results.
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“The experiments carried out by our collaborators were extremely demanding and time-consuming. Nevertheless, they directly demonstrated and confirmed that changing the electrode potential can be used to create polarons on the TiO2 surface. These charge centers then drive the hydrogen evolution reaction on TiO2 electrodes and probably also on other semiconductors,” explains Honkala.
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New approaches and opportunities for catalyst development
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The discovered electrode potential -controlled polaron formation is a previously unknown phenomenon in electrochemistry and does not occur on conventional metal electrodes. The JYU researchers believe that this phenomenon could be utilized in future catalyst design and materials development.
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“We found that the formation of polarons enables semiconductor electrodes to avoid the so-called scaling relations. On metallic electrodes, these laws limit and constrain the achievable catalytic activity. Our discovery of the potential-dependent polaron formation may lead to new approaches to avoid the scaling relations and thereby improvement in catalyst design,” predict Honkala and Melander.
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