Plasmon-enhanced catalytic reactions for renewable fuels

Viktoria Golovanova

Prof. Joan Ramón Morante Lleonart Dra. Teresa Andreu Arbella

IREC UB

The depletion of fossil fuels and global warming caused by excessive carbon emissions have led to an urgent transition to renewable energy sources, of which only solar energy is capable of meeting the growing global energy demand. In this context, the utilization of sunlight in catalytic reactions for the production of renewable fuels is a great challenge. The hot field of plasmon-assisted catalysis requires inexpensive materials with excellent optical and catalytic properties at the same time. So far, few works have highlighted the importance of plasmon heating as the main consequence of plasmon. Due to the above reasoning, nickel (Ni) is an excellent candidate for plasmon-enhanced catalytic applications, as it is an abundant transition metal with a beneficial combination of excellent catalytic and photothermal properties. The main objectives of this work are i) the design of Ni-based plasmonic catalysts for renewable fuel reactions (CO₂ methanation and hydrogen evolution reaction -HER-), ii) their structural, optical and functional study to identify the optimal reaction conditions and quantify the gain in the light-assisted reaction, and iii) define the mechanisms of reaction improvement. The first chapter of the thesis presents an overview of the problem, includes the description of the fundamental concepts and provides a state of the art in plasmon-enhanced CO2 methanation and HER. The second chapter is dedicated to the development of the highly active Ni/CeO2 catalyst (80% CO₂ conversion and 95% methane selectivity) for light-assisted CO2 methanation. A 2.4-fold increase in the reaction rate was demonstrated, which led to a 20% decrease in energy consumption. In situ characterization techniques revealed a dual effect of solar radiation on the Ni/CeO2 catalyst, confirming the presence of photothermal and electronic effects. The third chapter presents a study on plasmonic Ni nanoparticles with enhanced absorption in the visible light range and their application as a photocathode for HER. The strong photothermal effect of the nanoparticles on the reaction rate allowed to increase the hydrogen production by 27% after finding the optimal conditions. Light-dark and pressed illumination measurements were used to identify the mechanism of the light-induced overpotential drop. The fourth chapter is dedicated to the optical study of Ni nanophore (NHA) arrays and the use of their surface plasmon in the iodate reduction reaction. The tunable hollow mask lithography method used in the fabrication of NHA involved precise adjustment of its geometric parameters and optimization of its optical properties. The study of wavelength-dependent photocurrent under pulsed laser irradiation of planar and structured photocathodes with respect to their optical spectrum demonstrated the photothermal plasmonic nature of the reaction enhancement.

The plasmonic Ni-based catalysts, developed during my PhD thesis, allow to improve the currently developing power-to-gas technology by implementing solar light into the process. The universal catalyst can be applied to enhance both cathodic and anodic reactions in water electrolysis, improving the yield of hydrogen, and thus having a huge impact on the decarbonization of the energy sector. Moreover, the Ni-based catalysts were proven to significantly improve the CO2 methanation rate under weakly concentrated solar light, leading to significant gain in power consumption. Further steps will be focused on optimizing the reactor design for high conversion values without the need the lower the flow rate and optimization of proper light and heat management of the reactor, which will be implemented in the ongoing Producte19 project (AGAUR, 2019 PROD 00091), and in IREC methanation pilot plant that will be commissioned by Naturgy Energy Group by 2023. The plasmonic catalyst will be also combined with the state-of-the-art photoanodes to mitigate the bottleneck reaction of water oxidation by means of solar light. Finally, the photothermal catalyst will be applied in the plasmonic seawater desalination, leading to facile freshwater collection under outdoor conditions.

Fossil Fuel Depletion; Global Warming; Carbon Emissions; Renewable Energy Sources; Solar Energy; Sunlight Utilization; Catalytic Reactions; Renewable Fuels; Plasmon-Assisted Catalysis; Inexpensive Materials; Optical Properties; Catalytic Properties; Plasmon Heating; Abundant Transition Metal; Nickel (Ni); Plasmon-Enhanced Catalytic Applications; Photothermal Properties; Ni-based Plasmonic Catalysts; CO₂ Methanation; Hydrogen Evolution Reaction (HER); Structural Study; Optical Study; Functional Study; Optimal Reaction Conditions; Light-Assisted Reaction Gain; Reaction Improvement Mechanisms; Ni/CeO2 Catalyst; High Activity; CO₂ Conversion; Methane Selectivity; Reaction Rate Increase; Energy Consumption Decrease; In situ Characterization; Dual Effect; Solar Radiation; Photothermal Effects; Electronic Effects; Plasmonic Ni Nanoparticles; Enhanced Visible Light Absorption; Photocathode; Hydrogen Production; Optimal Conditions; Light-Dark Measurements; Pressed Illumination Measurements; Light-Induced Overpotential Drop; Ni Nanophore (NHA) Arrays; Surface Plasmon; Iodate Reduction Reaction; Tunable Hollow Mask Lithography; NHA Fabrication; Geometric Parameters; Optical Properties Optimization; Wavelength-Dependent Photocurrent; Pulsed Laser Irradiation; Planar Photocathodes; Structured Photocathodes; Optical Spectrum; Photothermal Plasmonic Nature; Reaction Enhancement.