Light driven charging turns gold nanorods into nanocapacitors

by Robert Schreiber
Berlin, Germany (SPX) Jan 19, 2026

Gold nanorods can act as tiny light powered devices that accumulate electrical charge and drive chemical reactions, according to new work by researchers at the University of Potsdam. The study shows in real time how these nanoscopic structures become electrically charged under illumination and introduces a physical model that describes the process as a form of capacitive photocharging.

In photocatalysis with nanoscale metal particles, light can generate excess charge that strongly affects catalytic performance, but the details of this process have been difficult to access experimentally. In an in situ investigation, the Potsdam team tracked how gold nanorods charge up when they are exposed to light and demonstrated that they behave like photochemical capacitors that store electrons on their surface.

The researchers report that illuminating the nanorods creates electron hole pairs in the metal. The holes transfer to surrounding molecules, such as ethanol, while the electrons remain on the particle, leading to a net negative charge on the nanorod surface. As a result, the particles develop electric potentials relative to their environment using light alone, without any external voltage source.

Because the nanorods have a large surface to volume ratio, a substantial amount of charge can accumulate in a very small volume. This high local charge density produces pronounced changes in the optical and chemical properties of the particles, which in turn influence how efficiently they can catalyze reactions such as carbon dioxide reduction or water splitting.

"We were able to directly demonstrate that light alone is sufficient to generate electric potentials between a single nanoparticle and its environment," says lead author Dr. Felix Stete of the University of Potsdam. When the particle absorbs light, the resulting charge separation drives oxidation reactions in the surrounding ethanol and water, while electrons build up on the gold surface.

According to group leader Dr. Wouter Koopman, the nanorods act in a way that is comparable to miniature electrolyzers that split water into hydrogen and oxygen using electricity, but here the driving force is the photovoltage created within each particle. "Our particles essentially behave like nanometer-sized electrolyzers, devices that split water into H2 and O2 with the help of electricity," he explains, "except that they do not require an external electric voltage source."

The team developed a model that treats the illuminated nanoparticles as capacitors, linking the observed changes in optical response to the amount of charge stored on their surface. This capacitive description provides a quantitative framework for understanding how light induced charging proceeds and how it can be manipulated through particle geometry, surrounding media and illumination conditions.

The findings open new possibilities for deliberately tuning photocatalytic systems based on metal nanoparticles. By controlling how and where charge accumulates on gold nanorods, researchers aim to steer key steps in reactions such as CO2 conversion to fuels, hydrogen generation from water and other light driven transformations.

In the longer term, capacitive photocharging at nanoscale metals could support solar powered chemical reactors and new concepts for energy storage that rely on storing charge in catalytic particles dispersed in liquids. The work forms part of the Collaborative Research Center SFB 1636 "Elementary Processes of Light-Driven Reactions at Nanoscale Metals," funded by the German Research Foundation, which focuses on the fundamental physics of such light induced processes.

Research Report: Capacitive photocharging of gold nanorods