An official website of the United States government
Abstract Low temperature plasmas (LTP) are a unique class of open‐driven systems in which chemical reactions are unpredictable using established concepts. The terminal state of chemical reactions in LTP, termed thesuperlocalequilibrium state, is hypothesized to be defined by a proposed set of state variables. Using a LTP reactor wherein the state variables have been measured, it is shown that CO2spontaneously splits and the effluent speciation is independent of the influent speciation if the state variables are held constant and the residence time is long. CO2conversion at long residence times, which is expected to be nominally zero from equilibrium thermodynamics, can be as high as 70% in the LTP. The employed low pressure plasma reactor (P= 10 mbar) had a similar volume, productivity, and energy efficiency compared to an atmospheric pressure dielectric barrier discharge reactor, thanks to reaction rates that were three orders of magnitude faster.
more »
« less
Entropy production and chemical reactions in nonequilibrium plasma
Abstract In this work, methods based upon nonequilibrium thermodynamics are elucidated to predict stationary states of chemical reactions in nonequilibrium plasma, and limits for energy conversion efficiency. CO2splitting is used as an example reaction. Expectations from the theoretical framework are compared to experimental results, and reasonable agreement is obtained. The key conclusion is that the probability of observing either reactants or products increases with the amount of energy dissipated by that side of the reaction as heat through collisions with hot electrons. The side of the reaction that dissipates more energy as heat has a higher probability of occurrence. Furthermore, endergonic chemical reactions in nonequilibrium plasma, such as CO2splitting at low temperature, require an intrinsic energy dissipation to satisfy the second law of thermodynamics—a sufficient and necessary waste. This intrinsic dissipation limits the maximum theoretical energy conversion efficiency.
more »
« less
- Award ID(s):
- 1847469
- PAR ID:
- 10449322
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- AIChE Journal
- Volume:
- 67
- Issue:
- 9
- ISSN:
- 0001-1541
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Dielectric barrier discharge (DBD) plasma is a promising technology for catalysis due to its low‐temperature operation, cost‐effectiveness, and silent operation. This review comprehensively analyzes the design and operational parameters of DBD plasma reactors for three key catalytic applications: CH4conversion, CO2splitting, and dry reforming of methane (DRM). While catalyst selection is crucial for achieving desired product selectivity, reactor design and reaction parameters such as discharge power, electrode gap, reactor length, frequency, dielectric material thickness, and feed gas flow rate, significantly influence discharge characteristics and reaction mechanisms. This review also explores the influence of less prominent factors, such as electrode shape and applied voltage waveforms. Additionally, this review addresses the challenges of DBD plasma catalysis, including heat loss, temperature effects on discharge characteristics, and strategies for enhancing overall efficiency.more » « less
-
Abstract Carbon nanomaterials are promising metal‐free catalysts for energy conversion and storage, but the catalysts are usually developed via traditional trial‐and‐error methods. To rationally design and accelerate the search for the highly efficient catalysts, it is necessary to establish design principles for the carbon‐based catalysts. Here, theoretical analysis and material design of metal‐free carbon nanomaterials as efficient photo‐/electrocatalysts to facilitate the critical chemical reactions in clean and sustainable energy technologies are reviewed. These reactions include the oxygen reduction reaction in fuel cells, the oxygen evolution reaction in metal–air batteries, the iodine reduction reaction in dye‐sensitized solar cells, the hydrogen evolution reaction in water splitting, and the carbon dioxide reduction in artificial photosynthesis. Basic catalytic principles, computationally guided design approaches and intrinsic descriptors, catalytic material design strategies, and future directions are discussed for the rational design and synthesis of highly efficient carbon‐based catalysts for clean energy technologies.more » « less
-
Abstract Sn‐based materials are identified as promising catalysts for the CO2electroreduction (CO2RR) to formate (HCOO−). However, their insufficient selectivity and activity remain grand challenges. A new type of SnO2nanosheet with simultaneous N dopants and oxygen vacancies (VO‐rich N‐SnO2NS) for promoting CO2conversion to HCOO−is reported. Due to the likely synergistic effect of N dopant andVO, theVO‐rich N‐SnO2NS exhibits high catalytic selectivity featured by an HCOO−Faradaic efficiency (FE) of 83% at−0.9 V and an FE of>90% for all C1 products (HCOO−and CO) at a wide potential range from −0.9 to−1.2 V. Low coordination Sn–N moieties are the active sites with optimal electronic and geometric structures regulated byVOand N dopants. Theoretical calculations elucidate that the reaction free energy of HCOO* protonation is decreased on theVO‐rich N‐SnO2NS, thus enhancing HCOO−selectivity. The weakened H* adsorption energy also inhibits the hydrogen evolution reaction, a dominant side reaction during the CO2RR. Furthermore, using the catalyst as the cathode, a spontaneous Galvanic Zn‐CO2cell and a solar‐powered electrolysis process successfully demonstrated the efficient HCOO−generation through CO2conversion and storage.more » « less
-
Abstract Chemical reactions induced by plasmons achieve effective solar‐to‐chemical energy conversion. However, the mechanism of these reactions, which generate a strong electric field, hot carriers, and heat through the excitation and decay processes, is still controversial. In addition, it is not fully understood which factor governs the mechanism. To obtain mechanistic knowledge, we investigated the plasmon‐induced dissociation of a single‐molecule strongly chemisorbed on a metal surface, two O2species chemisorbed on Ag(110) with different orientations and electronic structures, using a scanning tunneling microscope (STM) combined with light irradiation at 5 K. A combination of quantitative analysis by the STM and density functional theory calculations revealed that the hot carriers are transferred to the antibonding (π*) orbitals of O2strongly hybridized with the metal states and that the dominant pathway and reaction yield are determined by the electronic structures formed by the molecule–metal chemical interaction.more » « less
