Brightlands Science Lecture: Sunlight as fuel for sustainable chemical processes

Driven by the global aspiration to achieve a CO₂-neutral society, the conversion of CO₂ to CH₄ via the Sabatier reaction (CO₂ + 4 H₂ -> CH₄ + 2 H₂O) has recently grown into a significant research field. Besides the reduction of anthropogenic CO₂ emissions, it offers the prospect of long-term storage of renewable energy, producing an easy-to-handle energy carrier with a high gravimetric storage density. Conventionally, the Sabatier reaction is performed in dark, catalyzed by supported metal nanoparticles, and requires thermal activation at temperatures between 300°C and 500°C. Instead of conventional heating, we successfully applied sunlight as sustainable energy source. We reported a Ru metal catalyst that facilitates methanation below 250 °C using sunlight as energy source. Although at low solar intensity (1 sun) the activity of the Ru catalyst is mainly attributed to photothermal effects, we identified a large non-thermal contribution at slightly elevated intensities (5.7 and 8.5 sun) resulting in a high photon-to-methane efficiency of up to 55% over the whole solar spectrum. We attribute the excellent sunlight-harvesting ability of the catalyst and the high photon-to-methane efficiency to its UV–vis–NIR plasmonic absorption. Plasmon-enhanced chemical reactions could pave the way to shift from conventional thermally activated processes to sustainable, solely sunlight-fueled ones.