Selective light absorber-assisted single nickel atom catalysts for ambient sunlight-driven CO2 methanation

Abstract

Ambient sunlight-driven CO₂ methanation cannot be realized due to the temperature being less than 80 °C upon irradiation with dispersed solar energy. In this work, a selective light absorber was used to construct a photothermal system to generate a high temperature (up to 288 °C) under weak solar irradiation (1 kW m^-2), and this temperature is three times higher than that in traditional photothermal catalysis systems. Moreover, ultrathin amorphous Y₂O₃ nanosheets with confined single nickel atoms (SA Ni/Y₂O₃) were synthesized, and they exhibited superior CO₂ methanation activity. As a result, 80% CO₂ conversion efficiency and a CH₄ production rate of 7.5 L m^-2 h^-1 were achieved through SA Ni/Y₂O₃ under solar irradiation (from 0.52 to 0.7 kW m^-2) when assisted by a selective light absorber, demonstrating that this system can serve as a platform for directly harnessing dispersed solar energy to convert CO₂ to valuable chemicals.

Fig. 1

Traditional and selective light absorber-assisted photothermal systems. a Photograph of the Ni/Y₂O₃ nanosheets powder. b Normalized UV–Vis–IR absorption spectrum of the Ni/Y₂O₃ nanosheets. c Solar energy absorption and thermal radiation diagram for the Ni/Y₂O₃ nanosheets at 200 °C. The ambient solar flux of 1 kW m⁻² is not enough to sustain the thermal radiation; thus, an equilibrium temperature of 200 °C cannot be obtained. d Cross-sectional SEM image and e normalized UV–Vis–IR absorption spectrum of the selective light absorber (AlN_x/Al foil). f Solar energy absorption and thermal radiation diagram of the selective light absorber at 200 °C. The thermal radiation was far below the absorbed energy from ambient solar flux. g Schematic of the new photothermal system used for photothermal CO₂ methanation with the selective absorber and the catalysts. h, i The light-driven temperature and CO₂ conversion rates of the Ni/Y₂O₃ nanosheets with (Ni/Y₂O₃ + S red) and without (Ni/Y₂O₃ green) the selective light absorber-assisted photothermal system, respectively, under different intensities of sunlight irradiation. The scale bar in d is 2000 nm

Fig. 2

Preparation and characterization of the SA Ni/Y₂O₃ nanosheets. a Schematic of the preparation process for Y₂O₃ nanosheets decorated with single Ni atoms (SA Ni/Y₂O₃). b XRD pattern, c N₂ adsorption–desorption isotherm, d SEM image, e TEM image, f HRTEM image, g STEM image, and EDS mapping images of Ni, Y, and O of the SA Ni/Y₂O₃ nanosheets. The inset in f is the corresponding electron diffraction pattern. The scale bars in d, e, f, and g are 1000, 200, 2, and 20 nm, respectively

Fig. 3

Characterization of the Ni in the SA Ni/Y₂O₃ nanosheets. a Aberration-corrected TEM image of the SA Ni/Y₂O₃ nanosheets. b EXAFS spectra of the Ni K-edge of the SA Ni/Y₂O₃ nanosheets, NiO and Ni foil. c Fourier transform (FT) of the Ni K-edge of the SA Ni/Y₂O₃ nanosheets, NiO and Ni foil. d Schematic model of the SA Ni/Y₂O₃ nanosheets and the corresponding FT-EXAFS fitting curves for the SA Ni/Y₂O₃ nanosheets. The scale bar in a is 2 nm

Fig. 4

Thermocatalytic CO₂ hydrogenation experiments. a Thermal CO₂ conversion using the SA Ni/Y₂O₃ nanosheets (SA Ni/Y₂O₃) and Ni nanoparticles/Y₂O₃ nanosheets (Ni/Y₂O₃) as a function of temperature. b CH₄ and CO yields from the CO₂ hydrogenation over the SA Ni/Y₂O₃ nanosheets as a function of temperature. c CO₂ hydrogenation versus reaction time over the SA Ni/Y₂O₃ nanosheets at 240 °C. d Aberration-corrected TEM image of the SA Ni/Y₂O₃ nanosheets after the stability test shown in Fig. 4c. Reaction conditions: 100 ml min⁻¹ of reaction gas (2.5% CO₂+ 10% H₂+ 87.5% N₂), 100 mg of catalyst. The scale bar in d is 2 nm

Fig. 5

Photothermal CO₂ methanation performance of the SA Ni/Y₂O₃ nanosheets with a selective light absorber-assisted photothermal system. a Spatial temperature mapping of the selective light absorber-assisted quartz tube coated with the SA Ni/Y₂O₃ nanosheets under 1.0 kW m⁻² of simulated solar irradiation obtained by an infrared camera. b The temperature and CO₂ conversion achieved by the SA Ni/Y₂O₃ nanosheets with the selective light absorber-assisted photothermal system under different intensities of simulated solar light. c The solar flux over time on June 30, 2018 from 8:00 to 18:00 in Baoding, Hebei, China. d The corresponding photothermal CO₂ conversion over the SA Ni/Y₂O₃ nanosheets with the selective light absorber-assisted photothermal system as a function of time. Reaction conditions: 100 ml min⁻¹ of reaction gas (2.5% CO₂+ 10% H₂+ 87.5% N₂), 100 mg of catalyst