Energy-efficient CO2 hydrogenation with fast response using photoexcitation of CO2 adsorbed on metal catalysts.

Many heterogeneous catalytic reactions occur at high temperatures, which may cause large energy costs, poor safety, and thermal degradation of catalysts. Here, we propose a light-assisted surface reaction, which catalyze the surface reaction using both light and heat as an energy source. Conventional metal catalysts such as ruthenium, rhodium, platinum, nickel, and copper were tested for CO2 hydrogenation, and ruthenium showed the most distinct change upon light irradiation. CO2 was strongly adsorbed onto ruthenium surface, forming hybrid orbitals. The band gap energy was reduced significantly upon hybridization, enhancing CO2 dissociation. The light-assisted CO2 hydrogenation used only 37% of the total energy with which the CO2 hydrogenation occurred using only thermal energy. The CO2 conversion could be turned on and off completely with a response time of only 3 min, whereas conventional thermal reaction required hours. These unique features can be potentially used for on-demand fuel production with minimal energy input

Theoretical insights into selective electrochemical conversion of carbon dioxide.

Electrochemical conversion of CO2 and water to valuable chemicals and fuels is one of the promising alternatives to replace fossil fuel-based processes in realizing a carbon-neutral cycle. For practical application of such technologies, suppressing hydrogen evolution reaction and facilitating the activation of stable CO2 molecules still remain major challenges. Furthermore, high production selectivity toward high-value chemicals such as ethylene, ethanol, and even n-propanol is also not easy task to achieve. To settle these challenges, deeper understanding on underlying basis of reactions such as how intermediate binding affinities can be engineered at catalyst surfaces need to be discussed. In this review, we briefly outline recent strategies to modulate the binding energies of key intermediates for CO2 reduction reactions, based on theoretical insights from density functional theory calculation studies. In addition, important design principles of catalysts and electrolytes are also provided, which would contribute to the development of highly active catalysts for CO2 electroreduction

Theoretical insights into selective electrochemical conversion of carbon dioxide

Abstract Electrochemical conversion of CO2 and water to valuable chemicals and fuels is one of the promising alternatives to replace fossil fuel-based processes in realizing a carbon–neutral cycle. For practical application of such technologies, suppressing hydrogen evolution reaction and facilitating the activation of stable CO2 molecules still remain major challenges. Furthermore, high production selectivity toward high-value chemicals such as ethylene, ethanol, and even n-propanol is also not easy task to achieve. To settle these challenges, deeper understanding on underlying basis of reactions such as how intermediate binding affinities can be engineered at catalyst surfaces need to be discussed. In this review, we briefly outline recent strategies to modulate the binding energies of key intermediates for CO2 reduction reactions, based on theoretical insights from density functional theory calculation studies. In addition, important design principles of catalysts and electrolytes are also provided, which would contribute to the development of highly active catalysts for CO2 electroreduction

Surface Plasmon Aided Ethanol Dehydrogenation Using Ag–Ni Binary Nanoparticles

Plasmonic metal nanoparticles absorb light energy and release the energy through radiative or nonradiative channels. Surface catalytic reactions take advantage of the nonradiative energy relaxation of plasmons with enhanced activity. Particularly, binary nanoparticles are interesting because diverse integration is possible, consisting of a plasmonic part and a catalytic part. Herein, we demonstrated ethanol dehydrogenation under light irradiation using Ag–Ni binary nanoparticles with different shapes, snowman and core–shell, as plasmonic catalysts. The surface plasmon formed in the Ag part enhanced the surface catalytic reaction that occurred at the Ni part, and the shape of the nanoparticles affected the extent of the enhancement. The surface plasmon compensated the thermal energy required to trigger the catalytic reaction. The absorbed light energy was transferred to the catalytic part by the surface plasmon through the nonradiative hot electrons. The effective energy barrier was greatly reduced from 41.6 kJ/mol for the Ni catalyst to 25.5 kJ/mol for the core–shell nanoparticles and 22.3 kJ/mol for the snowman-shaped nanoparticles. These findings can be helpful in designing effective plasmonic catalysts for other thermally driven surface reactions

Codesign of an integrated metal-insulator-semiconductor photocathode for photoelectrochemical reduction of CO2 to ethylene

Photoelectrochemical carbon-dioxide reduction (PEC CO2R) is a potentially attractive means for producing chemicals and fuels using sunlight, water, and carbon dioxide; however, this technology is in its infancy. To date, most studies of PEC CO2R have reported products containing one carbon atom (C1 products) but the production of valuable products containing two or more carbons (C2+ products), such as ethylene, ethanol, etc., is rarely demonstrated. Metal-semiconductor-insulator (MIS) photocathode/catalyst structures offer a promising approach for this purpose, since they integrate the functions of light absorption, charge separation, and catalysis. In this study, we have investigated a Cu/TiO2/p-Si photocathode/catalyst structure with the aim of establishing the effects of semiconductor-insulator interactions on the performance of the photocathode and the influence of the direction of illumination of the MIS structure on the total current density and the distribution of products formed by on the Cu catalyst. We have also examined the influence of ionomer coatings deposited on the Cu surface on the total current density and the distribution of products formed. A major finding is that for a fixed Cu potential the distribution of products formed by PEC CO2R are the same, irrespective of the direction of illumination, and are identical to those obtained by electrochemical reduction of CO2 (EC CO2R). Another important finding is that the total current density and the faradaic efficiency to ethylene are enhanced significantly by deposition of a thin bilayer of Sustainion/Nafion onto the surface of the Cu. © 2023 The Royal Society of Chemistry.FALS

Codesign of an integrated metal–insulator–semiconductor photocathode for photoelectrochemical reduction of CO 2 to ethylene

Photoelectrochemical carbon-dioxide reduction (PEC CO2R) is a potentially attractive means for producing chemicals and fuels using sunlight, water, and carbon dioxide; however, this technology is in its infancy. To date, most studies of PEC CO2R have reported products containing one carbon atom (C1 products) but the production of valuable products containing two or more carbons (C2+ products), such as ethylene, ethanol, etc., is rarely demonstrated. Metal-semiconductor-insulator (MIS) photocathode/catalyst structures offer a promising approach for this purpose, since they integrate the functions of light absorption, charge separation, and catalysis. In this study, we have investigated a Cu/TiO2/p-Si photocathode/catalyst structure with the aim of establishing the effects of semiconductor-insulator interactions on the performance of the photocathode and the influence of the direction of illumination of the MIS structure on the total current density and the distribution of products formed by on the Cu catalyst. We have also examined the influence of ionomer coatings deposited on the Cu surface on the total current density and the distribution of products formed. A major finding is that for a fixed Cu potential the distribution of products formed by PEC CO2R are the same, irrespective of the direction of illumination, and are identical to those obtained by electrochemical reduction of CO2 (EC CO2R). Another important finding is that the total current density and the faradaic efficiency to ethylene are enhanced significantly by deposition of a thin bilayer of Sustainion/Nafion onto the surface of the Cu

Engineering Catalyst-Electrolyte Microenvironments to Optimize the Activity and Selectivity for the Electrochemical Reduction of CO2 on Cu and Ag.

The electrochemical reduction of carbon dioxide (CO2R) driven by renewably generated electricity (e.g., solar and wind) offers a promising means for reusing the CO2 released during the production of cement, steel, and aluminum as well as the production of ammonia and methanol. If CO2 could be removed from the atmosphere at acceptable costs (i.e., <$100/t of CO2), then CO2R could be used to produce carbon-containing chemicals and fuels in a fully sustainable manner. Economic considerations dictate that CO2R current densities must be in the range of 0.1 to 1 A/cm2 and selectivity toward the targeted product must be high in order to minimize separation costs. Industrially relevant operating conditions can be achieved by using gas diffusion electrodes (GDEs) to maximize the transport of species to and from the cathode and combining such electrodes with a solid-electrolyte membrane by eliminating the ohmic losses associated with liquid electrolytes. Additionally, high product selectivity can be attained by careful tuning of the microenvironment near the catalyst surface (e.g., the pH, the concentrations of CO2 and H2O, and the identities of the cations in the double layer adjacent to the catalyst surface).We begin this Account with a discussion of our experimental and theoretical work aimed at optimizing catalyst microenvironments for CO2R. We first examine the effects of catalyst morphology on the production of multicarbon (C2+) products over Cu-based catalysts and then explore the role of mass transfer combined with the kinetics of buffer reactions in the local concentration of CO2 and pH at the catalyst surface. This is followed by a discussion of the dependence of the local CO2 concentration and pH on the dynamics of CO2R and the formation of specific products over both Cu and Ag catalysts. Next, we explore the impact of electrolyte cation identity on the rate of CO2R and the distribution of products. Subsequently, we look at utilizing pulsed electrolysis to tune the local pH and CO2 concentration at the catalyst surface. The last part of the discussion demonstrates that ionomer-coated catalysts in combination with pulsed electrolysis can enable the attainment of very high (>90%) selectivity to C2+ products over Cu in an aqueous electrolyte. This part of the Account is then extended to consider the difference in the catalyst-nanoparticle microenvironment, present in the catalyst layer of a membrane electrode assembly (MEA), with respect to that of a planar electrode immersed in an aqueous electrolyte