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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Coordination of copper within a crystalline carbon nitride and its catalytic reduction of CO 2

Inherently disordered structures of carbon nitrides have hindered an atomic level tunability and understanding of their catalytic reactivity. Starting from a crystalline carbon nitride, poly(triazine imide) or PTI/LiCl, the coordination of copper cations to its intralayer N-triazine groups was investigated using molten salt reactions. The reaction of PTI/LiCl within CuCl or eutectic KCl/CuCl 2 molten salt mixtures at 280 to 450 °C could be used to yield three partially disordered and ordered structures, wherein the Cu cations are found to coordinate within the intralayer cavities. Local structural differences and the copper content, i.e., whether full or partial occupancy of the intralayer cavity occurs, were found to be dependent on the reaction temperature and Cu-containing salt. Crystallites of Cu-coordinated PTI were also found to electrophoretically deposit from aqueous particle suspensions onto either graphite or FTO electrodes. As a result, electrocatalytic current densities for the reduction of CO 2 and H 2 O reached as high as ∼10 to 50 mA cm −2 , and remained stable for >2 days. Selectivity for the reduction of CO 2 to CO vs. H 2 increases for thinner crystals as well as for when two Cu cations coordinate within the intralayer cavities of PTI. Mechanistic calculations have also revealed the electrocatalytic activity for CO 2 reduction requires a smaller thermodynamic driving force with two neighboring Cu atoms per cavity as compared to a single Cu atom. These results thus establish a useful synthetic pathway to metal-coordination in a crystalline carbon nitride and show great potential for mediating stable CO 2 reduction at sizable current densities.

Chemistry↗
DOE OSTI2025

Systematic computational study of oxide adsorption properties for applications in photocatalytic CO 2 reduction

While the adsorption properties of transition metal catalysts have been widely studied, leading to the discovery of various scaling relations, descriptors of catalytic activity, and well-established computational models, a similar understanding of semiconductor catalysts has not yet been achieved. In this work, we present a high-throughput density functional theory investigation into the adsorption properties of 5 oxides of interest to the photocatalytic CO 2 reduction reaction: TiO 2 (rutile and anatase), SrTiO 3 , NaTaO 3 , and CeO 2 . Using a systematic approach, we exhaustively identify unique surfaces and construct adsorption structures to undergo geometry optimizations. We then perform a data-driven analysis, which reveals the presence of weak adsorption energy scaling relations, the propensity of adsorbates of interest to interact with oxygen surface sites, and the importance of slab deformation upon adsorption. Our findings are presented in the context of experimental observations and in comparison to previously studied classes of catalysts, such as pure metals and tellurium-containing semiconductors, and reinforce the need for a comprehensive approach to the study of site-specific surface phenomena on semiconductors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Water-Dispersible CsPbBr 3 Perovskite Nanocrystals with Ultra-Stability and its Application in Electrochemical CO 2 Reduction

Thanks to the excellent optoelectronic properties, lead halide perovskites (LHPs) have been widely employed in high-performance optoelectronic devices such as solar cells and light-emitting diodes. However, overcoming their poor stability against water has been one of the biggest challenges for most applications. Herein, we report a novel hot-injection method in a Pb-poor environment combined with a well-designed purification process to synthesize water-dispersible CsPbBr 3 nanocrystals (NCs). The as-prepared NCs sustain their superior photoluminescence (91% quantum yield in water) for more than 200 days in an aqueous environment, which is attributed to a passivation effect induced by excess CsBr salts. Thanks to the ultra-stability of these LHP NCs, for the first time, we report a new application of LHP NCs, in which they are applied to electrocatalysis of CO 2 reduction reaction. Noticeably, they show significant electrocatalytic activity (faradaic yield: 32% for CH 4 , 40% for CO) and operation stability (> 350 h).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Molecular Coatings Improve the Selectivity and Durability of CO 2 Reduction Chalcogenide Photocathodes

The quest for solar-driven conversion of carbon dioxide to chemicals and fuels hinges upon the identification of an efficient, durable, and selective photocathode. Chalcogenide p-type semiconductors exemplified by chalcopyrite Cu(In,Ga)Se 2 (CIGS) have been effectively deployed as photocathodes. However, selectivity toward CO 2 reduction and durability of the commonly used CdS adlayer remain primary challenges. Here, we demonstrate that for the wide band gap CuGa 3 Se 5 chalcopyrite absorber these challenges are well addressed by an organic coating generated in situ from an N,N'-(1,4-phenylene)bispyridinium ditriflate salt in the electrolyte. The molecular additive provides a 30-fold increase in selectivity toward CO2R products compared to the unmodified system and lowers Cd corrosion at least 10-fold. This dual functionality highlights the promise of hybrid solid-state-molecular photocathodes for enabling durable and efficient solar fuel systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Operando X-ray Absorption Spectroscopy Study of SnO 2 Nanoparticles for Electrochemical Reduction of CO 2 to Formate

Tin–based electrocatalysts exhibit a remarkable ability to catalyze CO 2 to formate selectively. Understanding the size-property relationships and exploring the evolutions of active size still lack complete understanding. Herein, we prepared SnO 2 nanoparticles (NPs) with controllable size supported on commercial carbon spheres (SnO 2 /C–n, n=1,2,3) by a simple low-temperature annealing method. The transmission electron microscopy(TEM)/scanning transmission electron microscope (STEM) images and fitting results of the small angle X-ray scattering (SAXS) profile confirm the increased size of SnO 2 NPs as the increase of SnO 2 loading. The catalytic performance of SnO 2 has proved the size-dependent effect during CO 2 reduction reaction process. The as-prepared SnO 2 /C–1 displayed the maximum Faradic efficiency of formate (FE HCOO– ) of 82.7% at –1.0 V vs. RHE. In contrast, SnO 2 /C–2 and SnO 2 /C–3 with larger particle sizes achieved lower maximum FE HCOO– and larger overpotential. Moreover, we employed operando XAS to study the evolution of the oxidation state and local coordination environment of SnO 2 under working conditions. In addition to the observed the shifts of rising edge of Sn K-edge X-ray absorption near edge structure (XANES) spectra to lower energy side as the applied voltage decreases, the decreased coordination number of Sn in the Sn-O scattering path and the presence of Sn mental contribution in extended X-ray absorption fine structure (EXAFS) spectra verify the reduction of SnO 2 to SnO x and metallic Sn.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

The Conventional Gas Diffusion Electrode May Not Be Resistant to Flooding during CO 2 /CO Reduction

The electrochemical CO 2 or CO reduction to chemicals and fuels using renewable energy is a promising way to reduce anthropogenic carbon emissions. The gas diffusion electrode (GDE) design enables low-carbon manufacturing of target products at a current density (e.g., 500 mA cm –2 ) relevant to industrial requirements. However, the long-term stability of the GDE is restricted by poor water management and flooding, resulting in a significant hydrogen evolution reaction (HER) within almost an hour. The optimization of water management in the GDE demands a thorough understanding of the role of the gas diffusion layer (GDL) and the catalyst layer (CL) distinctively. In this work, the hydrophobicity of the GDL and CL is independently adjusted to investigate their influence on gas transport efficiency and water management. The gas transport efficiency is more enhanced with the increase in hydrophobicity of the GDL than the CL. Direct visualization of water distribution by optical microscope and micro-computed tomography demonstrates that the water flow pattern transfers from the stable displacement to capillary fingering as GDL hydrophobicity increases. Unfortunately, only increasing the hydrophobicity is not sufficient to prevent flooding. A revolutionary change in the design of the GDE structure is essential to maintain the long-term stability of CO 2 /CO reduction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The quest for improved air quality may push China to continue its CO 2 reduction beyond the Paris Commitment

China is challenged with the simultaneous goals of improving air quality and mitigating climate change. The “Beautiful China” strategy, launched by the Chinese government in 2020, requires that all cities in China attain 35 μg/m 3 or below for annual mean concentration of PM 2.5 (particulate matter with aerodynamic diameter less than 2.5 μm) by 2035. Meanwhile, China adopts a portfolio of low-carbon policies to meet its Nationally Determined Contribution (NDC) pledged in the Paris Agreement. Previous studies demonstrated the co-benefits to air pollution reduction from implementing low-carbon energy policies. Pathways for China to achieve dual targets of both air quality and CO 2 mitigation, however, have not been comprehensively explored. Here, we couple an integrated assessment model and an air quality model to evaluate air quality in China through 2035 under the NDC scenario and an alternative scenario (Co-Benefit Energy [CBE]) with enhanced low-carbon policies. Results indicate that some Chinese cities cannot meet the PM 2.5 target under the NDC scenario by 2035, even with the strictest end-of-pipe controls. Achieving the air quality target would require further reduction in emissions of multiple air pollutants by 6 to 32%, driving additional 22% reduction in CO 2 emissions relative to the NDC scenario. Results show that the incremental health benefit from improved air quality of CBE exceeds 8 times the additional costs of CO 2 mitigation, attributed particularly to the cost-effective reduction in household PM 2.5 exposure. The additional low-carbon energy polices required for China’s air quality targets would lay an important foundation for its deep decarbonization aligned with the 2 °C global temperature target.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Fluorine-Tuned Carbon-Based Nickel Single-Atom Catalysts for Scalable and Highly Efficient CO 2 Electrocatalytic Reduction

Electrocatalytic CO 2 reduction is garnering significant interest due to its potential applications in mitigating CO 2 and producing fuel. However, the scaling up of related catalysis is still hindered by several challenges, including the cost of the catalytic materials, low selectivity, small current densities to maintain desirable selectivity. In this study, Fluorine (F) atoms were introduced into an N-doped carbon-supported single nickel (Ni) atom catalyst via facile polymer-assisted pyrolysis. This method not only maintains the high atom utilization efficiency of Ni in a cost-effective and sustainable manner but also effectively manipulates the electronic structure of the active Ni-N 4 site through F doping. The catalyst has also been further optimized by controlling the F states, including convalent and semi-ionic states, by adjusting the fluorine sources involved. Consequently, this catalyst with unique structure exhibited comparable electrocatalytic performance for CO 2 -to-CO conversion, achieving a Faradaic efficiency (FE) of over 99% across a wide potential range and an exceptional CO evolution rate of 9.5 x 10 4 h -1 at -1.16 V vs reversible hydrogen electrode (RHE). It also delivered a practical current of 400 mA cm -2 while maintaining more than 95% CO FE. Experimental analysis combined with density functional theory (DFT) calculations have also shown that F-doping modifies the electron configuration at the central Ni-N 4 sites. In conclusion, this modification lowers the energy barrier for CO 2 activation, thereby facilitating the production of the crucial *COOH intermediate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Production of C 2 /C 3 Oxygenates from Planar Copper Nitride-Derived Mesoporous Copper via Electrochemical Reduction of CO 2

Electrochemical reduction of CO 2 provides an opportunity to produce fuels and chemicals in a carbon-neutral manner, assuming that CO 2 can be captured from the atmosphere. To do so requires efficient, selective, and stable catalysts. In this study, we report a highly mesoporous metallic Cu catalyst prepared by electrochemical reduction of thermally nitrided Cu foil. Under aqueous saturated CO 2 reduction conditions, the Cu 3 N-derived Cu electrocatalyst produces virtually no CH 4 , very little CO, and exhibits a faradaic efficiency of 68% in C 2+ products (C 2 H 4 , C 2 H 5 OH, and C 3 H 7 OH) at a current density of ~18.5 mA cm –2 and a cathode potential of -1.0 V versus the reversible hydrogen electrode. Under these conditions, the catalyst produces more oxygenated products than hydrocarbons. We show that surface roughness is a good descriptor of catalytic performance. The roughest surface reached 98% CO utilization efficiency for C 2+ product formation from CO 2 reduction and the ratio of oxygenated to hydrocarbon products correlates with the degree of surface roughness. These effects of surface roughness are attributed to the high population of undercoordinated sites as well as a high pH environment within the mesopores and adjacent to the surface of the catalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Exploiting heat transfer to achieve efficient photoelectrochemical CO 2 reduction under light concentration

Photoelectrochemical (PEC) conversion of carbon dioxide into valuable chemicals and fuels represents a promising path towards combating anthropogenic CO 2 emissions. However, the limited conversion efficiencies, operation lifetimes and CO 2 utilization efficiencies of PEC devices currently prohibit their application beyond the laboratory scale. Here, a wireless device converting CO 2 and water into carbon monoxide and hydrogen at a peak solar conversion efficiency exceeding 16% under an illumination intensity of 5 suns is demonstrated. A CO/H 2 product ratio between 10–20 is measured during a 17 h stability test. Fluctuations in device performance are rigorously analyzed via deconvolution of electrochemical and photoabsorber contributions. Furthermore, it is demonstrated that beneficial heat dissipation is enabled by wireless integration of the photoabsorber and electrocatalyst components, accounting for roughly 10% of the achieved conversion efficiency, an achievement unattainable with physically separated photoabsorber and electrolyzer components.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Monolithic Photoelectrochemical CO 2 Reduction Producing Syngas at 10% Efficiency

We report increasing anthropogenic carbon dioxide emissions have prompted the search for photoelectrochemical (PEC) methods of converting CO 2 to useful commodity products, including fuels. Ideally, such PEC approaches will be sustained using only sunlight, water, and CO 2 as energetic and reactant inputs. However, low peak conversion efficiencies (< 5%) have made commercialization of fully-integrated PEC devices prohibitive. Here, a 4 cm 2 monolithic PEC device exceeding 10% solar-to-fuel efficiency with principal fuel products of carbon monoxide and hydrogen is reported. The corresponding solar-to-CO and solar-to-H 2 efficiencies are 7% and 3.5%, respectively. Screening of a range of operating conditions reveals a tunable product mixture of H 2 and CO using a gold electrocatalyst. Accordingly, it is shown that device optimization yields a H 2 -to-CO ratio of 1:2 commonly present in synthesis gas (syngas). Notably, the modularity and facile fabrication of this device permit the incorporation of a broad array of materials for various applications. For example, the electrocatalyst may easily be swapped to target a different set of products.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Environment of Metal–O–Fe Bonds Enabling High Activity in CO 2 Reduction on Single Metal Atoms and on Supported Nanoparticles

Single-atom catalysts are often reported to have catalytic properties that surpass those of nanoparticles, while a direct comparison of sites common and different for both is lacking. In this work, we show that single atoms of the Pt-group embedded into the surface of Fe 3 O 4 have a greatly enhanced interaction strength with CO 2 compared with Fe 3 O 4 surface. The strong CO 2 adsorption on single Rh atoms and corresponding low activation energies lead to two-orders-of-magnitude higher conversion rates of CO 2 compared to Rh nanoparticles. This high activity of single atoms stems from the partially oxidic state imposed by their coordination to the support. Fe 3 O 4 -supported Rh nanoparticles follow the behavior of single atoms for CO 2 interaction and reduction, which is attributed to the dominating role of partially oxidic sites at the Fe 3 O 4 -Rh interface. Thus, we show a likely common catalytic chemistry for two kinds of materials thought to be different, and we show that single atoms of Pt-group metals on Fe 3 O 4 are an especially successful material for catalyzed reactions that depend primarily upon sites with the metal-O-Fe environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

A Phenazine‐Based Two‐Dimensional Covalent Organic Framework for Photochemical CO 2 Reduction with Increased Selectivity for Two‐Carbon Products

Abstract The reduction of carbon dioxide (CO₂) into valuable products will contribute to sustainable carbon use. Here we report the photocatalytic reduction of CO₂ to carbon monoxide, formate, and oxalate ions using a redox‐active phenazine‐based 2D covalent organic framework (Phen‐COF) and its phenazine monomer. Under similar irradiation conditions,Phen‐COFproduced 2.9 times more CO, 11 times more formate, and 13 times more oxalate compared to equimolar amounts of the monomeric phenazine, demonstrating that the COF architecture enhances catalytic performance (TOF COF : 10 −7 s −1 CO, 10 −8 s −1 formate, and 10 −11 s −1 oxalate). Structural analysis, including X‐ray diffraction and N₂ porosimetry, confirmed the COF's long‐range order and porosity. Mechanistic studies suggest a sequential formate‐to‐oxalate pathway, with CO and formate acting as intermediates. These results demonstrate the potential of the COF architecture to improve the performance of metal‐free, redox‐active aromatic systems such as phenazines to facilitate efficient and selective CO₂ conversion under mild conditions.

Chemistry↗
DOE OSTI2024

Radiation-assisted electrochemical reduction of CO 2 to CO

Carbon monoxide (CO) is a versatile intermediate feedstock for many applications and can be produced through the electrochemical reduction of carbon dioxide (CO 2 ). However, current electrochemical CO production is hindered by high overall costs, primarily due to low conversion efficiencies and significant energy requirements. Herein, we report a unique way of enhancing the electrochemical reduction of CO 2 to CO using gamma (γ) photons. The γ-irradiation applied to the electrochemical cell setup induces the production of e˙ - , which results in an increased CO 2 ionization and production of excited CO 2 (CO$^{*}_{2}$) molecules via lower energy barrier. The ionized CO 2 ˙ - is quickly stabilized over a silver catalyst, providing an alternative low activation energy route for CO 2 reduction. In conclusion, a decrease in the overpotential barrier enhanced the electrochemical reduction of CO 2 to CO by 25%.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Tuning Internal Strain in Metal–Organic Frameworks via Vapor Phase Infiltration for CO 2 Reduction

Abstract A gas‐phase approach to form Zn coordination sites on metal–organic frameworks (MOFs) by vapor‐phase infiltration (VPI) was developed. Compared to Zn sites synthesized by the solution‐phase method, VPI samples revealed approximately 2.8 % internal strain. Faradaic efficiency towards conversion of CO 2 to CO was enhanced by up to a factor of four, and the initial potential was positively shifted by 200–300 mV. Using element‐specific X‐ray absorption spectroscopy, the local coordination environment of the Zn center was determined to have square‐pyramidal geometry with four Zn−N bonds in the equatorial plane and one Zn‐OH 2 bond in the axial plane. The fine‐tuned internal strain was further supported by monitoring changes in XRD and UV/Visible absorption spectra across a range of infiltration cycles. The ability to use internal strain to increase catalytic activity of MOFs suggests that applying this strategy will enhance intrinsic catalytic capabilities of a variety of porous materials.

Yang, Fan↗