Plasmonic nanoparticles raise the heat on hydrogen production

Pyroelectric catalysis (pyro-catalysis) can convert environmental temperature fluctuations into clean fuels like hydrogen. However, compared with more common forms of catalysis, such as photocatalysis, pyro-catalysis is inefficient, because the temperature of the ambient environment tends to change rather slowly.

Now, a team co-led by researchers at City University of Hong Kong (CityU) has found a way to trigger a significantly faster and more efficient pyro-catalytic reaction. Their approach involves using localized plasmonic heat sources to rapidly and efficiently heat up a pyro-catalytic material, and then allow it to cool down. Their findings, reported in a paper in Nature Communications, open up new avenues for efficient catalysis for biological applications, pollutant treatment and clean energy production.

Pyro-catalysis refers to catalysis triggered by surface charges to pyroelectric materials induced by temperature fluctuations. It is a green, self-powered catalysis technique that harvests waste thermal energy from the environment, and has attracted increasing attention as a way to produce clean energy and generate reactive oxygen species, which can be used for disinfection and dye treatment.

However, most currently available pyroelectric materials are not efficient if the ambient temperature doesn’t change much. As the environmental temperature change is often limited, a more viable way to increase the pyro-catalytic efficiency is to increase the rate, rather than the size, of the temperature changes, causing the temperature to cycle rapidly over time. But achieving multiple thermal cycling in a pyro-catalyst within a short time interval using conventional heating methods has proved very challenging.

A research team co-led by Lei Dangyuan, associate professor in the Department of Materials Science and Engineering (MSE) at CityU, recently overcame this obstacle using a novel strategy of combining pyroelectric materials with the localized thermo-plasmonic effect of noble metal nanomaterials.

These plasmonic nanostructures, which support the collective oscillation of free electrons, can absorb light and convert it quickly into heat. Their nanoscale size allows fast yet effective temperature changes within a confined volume, without significant heat loss to the surrounding environment. This means the localized heat generated by the thermo-plasmonic nanostructures can be easily fine-tuned and turned on or off by external light irradiation within an ultrashort time interval.

In their experiments, the researchers utilized barium titanate (BaTiO₃) nanoparticles as the pyro-catalytic material. They decorated these coral-like BaTiO₃ nanoparticles with gold nanoparticles, which acted as plasmonic heat sources, converting the photons from a pulsed laser into heat. This demonstrated that gold nanoparticles could act as a rapid, dynamic and controllable localized heat source without raising the surrounding temperature, prominently and efficiently increasing the overall pyro-catalytic reaction rate of the BaTiO₃ nanoparticles.

With this strategy, the team achieved a high pyro-catalytic hydrogen production rate. Their plasmonic pyroelectric nano-reactors were able to produce hydrogen at a rate of about 133µmol·g^-1·h^-1 through thermo-plasmonic local heating and cooling under irradiation with a nanosecond laser at a wavelength of 532nm.

Furthermore, the repetition rate of the nanosecond laser used in the experiment was just 10Hz, which meant that 10 pulses of light were irradiated on the catalyst per second to achieve 10 heating and cooling cycles. This implies that, by increasing the laser pulse repetition rate, the pyroelectric catalytic performance could be improved in the future.

The research team believes that their results have opened up a new approach for improving pyro-catalysis by designing innovative pyroelectric composite systems with other photothermal materials. This substantial progress will make the future application of pyro-catalysis in pollutant treatment and clean energy production more feasible.

This story is adapted from material from City University of Hong Kong, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.