Methane, which has a high energy storage density and is safely stored and transported in our existing infrastructure, can be produced through conversion of the undesired energy carrier H 2 with CO 2 . Methane production with standard transition-metal catalysts requires high-temperature activation (300–500 °C). Alternatively, semiconductor metal oxide photocatalysts can be used, but they require high-intensity UV light. Here, we report a Ru metal catalyst that facilitates methanation below 250 °C using sunlight as an energy source. Although at low solar intensity (1 sun) the activity of the Ru catalyst is mainly attributed to thermal effects, we identified a large nonthermal 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. Our highly efficient conversion of H 2 to methane is a promising technology to simultaneously accelerate the energy transition and reduce CO 2 emissions.

Plasmon catalysis is an interesting technology concept for powering chemical processes with light. Here, we report the use of various Al2O3‐supported Ru spheroidal nanoparticles as catalyst for the low‐temperature conversion of CO2 and H2 to CH4 (Sabatier reaction), using sunlight as energy source. At high loadings of Ru spheroidal nanoparticles (5.9 % w/w), we observe a sharp increase in the rate of the sunlight powered reaction when compared to the reaction in dark at the same catalyst bed temperature. Based on our results we exclude plasmon coupling as cause, and attribute the rate enhancement to collective photothermal heating of the Al2O3‐supported Ru nanoparticles.

For the preparation of electrically conductive composites, various combinations of cellulose and conducting materials such as polymers, metals, metal oxides and carbon have been reported. The conductivity of these cellulose composites reported to date ranges from 10-6 to 10 3 S cm-1. Cellulose nanocrystals (CNCs) are excellent building blocks for the production of high added value coatings. The essential process steps for preparing such coatings, i.e. surface modification of CNCs dispersed in water and/or alcohol followed by application of the dispersion to substrate samples using dip coating, are low cost and easily scalable. Here, we present coatings consisting of Ag modified CNCs that form a percolated network upon solvent evaporation. After photonic sintering, the resulting coatings are electrically conductive with an unprecedented high conductivity of 2.9 9 10 4 S cm-1. Furthermore, we report the first colloidal synthesis that yields CNCs with a high degree of Ag coverage on the surface, which is a prerequisite for obtaining coatings with high electrical conductivity.

Distinguishing between photothermal and non‐thermal contributions is essential in plasmon catalysis. Use of a tailored optical temperature sensor based on fiber Bragg gratings enabled us to obtain an accurate temperature map of an illuminated plasmonic catalyst bed with high spatiotemporal resolution. Its importance for quantification of the photothermal and non‐thermal contributions to plasmon catalysis is demonstrated using a Ru/Al2O3 catalyst. Upon illumination with LEDs, we measured temperature differences exceeding 50 °C in the top 0.5 mm of the catalyst bed. Furthermore, we discovered differences between the surface temperature and the temperature obtained via conventional thermocouple measurements underneath the catalyst bed exceeding 200 °C at 2.6 W cm−2 light intensity. This demonstrates that accurate multi‐point temperature measurements are a prerequisite for a correct interpretation of catalysis results of light‐powered chemical reactions obtained with plasmonic catalysts.

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