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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Evolution of Bonding and Magnetism via Changes in Valence Electron Count in CuFe 2– x Co x Ge 2

A series of solid solutions, CuFe 2–x Co x Ge 2 (x = 0, 0.2, 0.4, 0.8, and 1.0), have been synthesized by arc-melting and characterized by powder X-ray and neutron diffraction, magnetic measurements, Mössbauer spectroscopy, and electronic band structure calculations. All compounds crystallize in the CuFe 2 Ge 2 structure type, which can be considered as a three-dimensional framework built of fused MGe6 octahedra and MGe 5 trigonal bipyramids (M = Fe and Co), with channels filled by rows of Cu atoms. As the Co content (x) increases, the unit cell volume decreases in an anisotropic fashion: the b and c lattice parameters decrease while the a parameter increases. The changes in all the parameters are nearly linear, thus following Vegard’s law. CuFe 2 Ge 2 exhibits two successive antiferromagnetic (AFM) orderings, corresponding to the formation of a commensurate AFM structure, followed by an incommensurate AFM structure observed at lower temperatures. Additionally, as the Co content increases, the AFM ordering temperature (TN) gradually decreases, and only one AFM transition is observed for x ≥ 0.2. The magnetic behavior of unsubstituted CuFe 2 Ge 2 was found to be sensitive to the preparation method. The temperature-dependent zero-field 57 Fe Mössbauer spectra reveal two hyperfine split components that evolve in agreement with the two consecutive AFM orderings observed in magnetic measurements. In contrast, the field-dependent spectra obtained for fields ≥ 2 T reveal a parallel arrangement of the moments associated with the two crystallographically unique metal sites. Electronic band structure calculations and chemical bonding analysis reveal a mix of strong M–M antibonding and non-bonding states at the Fermi level, in support of the overall AFM ordering observed in zero field. The substitution of Co for Fe reduces the population of the M–M antibonding states and the overall density of states at the Fermi level, thus suppressing the T N value.

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

Photochemical CO 2 Reduction by a Postsynthetically Modified Zr-MOF

Metal–organic frameworks are an excellent platform for photochemical CO 2 reduction into valuable chemicals. Herein, we report the synthesis and photocatalytic behavior of Ru@MOF-808, a Zr-based MOF, modified with a Ru-polypyridyl complex. The postsynthetic modification was achieved using solvent-assisted incorporation of bipyridine–carboxylate ligands onto the nodes of the MOF-808, followed by the coordination of Ru­(II)-terpyridine moiety. A thorough characterization including 1 H NMR, diffuse reflectance UV/vis, X-ray absorption spectroscopy and gas adsorption studies, combined with DFT calculations, provides strong support for efficient incorporation of the molecular Ru-complex at the loading of one Ru center per node. In the presence of a strong sacrificial reductant BIH, Ru@MOF-808 was found to catalyze the photochemical reduction of CO 2 into a mixture of CO and formate ion. When compared to the homogeneous model catalyst Ru­(tpy)­(bpy) 2+ , Ru@MOF-808 was found to exhibit higher formate yields. Additionally, to explain these formate enhancements, we propose a mechanism that involves CO 2 capture at the MOF nodes to form Zr-bicarbonate species, which further react in a hydride transfer reaction with photogenerated Ru–H donor, thereby outperforming molecular catalysts in HCOO – production. Overall, the results presented in this work indicate the potential of Zr-based MOFs in integrating CO 2 capture with its photochemical conversion to desired products.

CO2 reduction↗
DOE OSTI2020

Revisiting Competing Paths in Electrochemical CO 2 Reduction on Copper via Embedded Correlated Wavefunction Theory

We re-evaluate two key steps in the mechanism of CO 2 reduction on copper at a higher level of theory capable of correcting inherent errors in density functional theory (DFT) approximations, namely, embedded correlated wavefunction (ECW) theory. Here, we consider the CO reduction step on Cu(111), which is critical to understanding reaction selectivity. Here, we optimize embedding potentials at the periodic plane-wave DFT level using density functional embedding theory (DFET). All possible adsorption sites (adsites) for each adsorbate then are screened with ECW theory at the catalytically active site to refine the local electronic structure. Unsurprisingly, DFT and ECW theory predict different adsite preferences, largely because of DFT’s inability to properly situate the CO 2π* level. Differing preferred adsites suggest that different reaction pathways could emerge from DFT versus ECW theory. Starting from these preferred ECW theory adsites, we then obtain reaction pathways at the plane-wave DFT level using the climbing-image nudged elastic band method to determine minimum energy paths. Thereafter, we perform ECW calculations at the catalytically active site to correct the energetics at each interpolated structure (image) along the reaction pathways. Via this approach, we confirm that the first step in CO reduction via hydrogen transfer on Cu(111) is to form hydroxymethylidyne (*COH) instead of formyl (*CHO). Although the prediction to preferentially form *COH is consistent with that of DFT, the two theories predict quite different structural and mechanistic behaviors, suggesting that verification is needed for other parts of the mechanism of CO 2 reduction, which is the subject of ongoing work.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Catalytic CO Oxidation on MgAl 2 O 4 -Supported Iridium Single Atoms: Ligand Configuration and Site Geometry

Probing and understanding the local chemical environment of an active site is essential for designing high-performance single-atom catalysts (SACs). Density functional theory (DFT) calculations were performed to investigate the ligand configuration and site geometry of MgAl 2 O 4 -supported iridium single atoms (Ir-1) toward catalytic carbon monoxide (CO) oxidation. We employed MgAl 2 O 4 (111) and MgAl 2 O 4 (211) as the model substrates with adsorbed Ir single atoms of different site geometries. DFT calculations revealed that the Mg-site on MgAl 2 O 4 (111) and the step site on MgAl 2 O 4 (211) are the most stable adsorption sites for Ir single atoms. Irrespective of site choices, CO oxidation on supported Ir single atoms follows the Eley-Rideal (E-R) mechanism, in which the surface oxygen vacancies close to the Ir single atoms activate molecular O 2 with a negligible barrier and the rate-limiting step is the gas-phase CO directly attacking the O-Ir species that is modulated by a CO ligand. Furthermore, first-principles X-ray absorption near-edge spectra of reaction intermediates along with in situ/operando X-ray absorption spectroscopy (XAS) suggest that Ir single atoms adsorb primarily on the step sites of MgAl 2 O 4 . However, microkinetic modeling predicts that a higher activity can be attained on the equally stable Mg-site, maximizing the population of which in catalyst synthesis might prove fruitful in future studies. Electronic structure analysis indicates that the CO ligand increases the reactivity of adsorbed oxygen atoms bound to Ir single atoms by increasing the antibonding nature of the O-Ir bond.

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

Mechanistic Study of the Li–Air Battery with a Co 3 O 4 Cathode and Dimethyl Sulfoxide Electrolyte

The lithium–air battery, a powerful competitor to replace the traditional lithium-ion battery, has attracted increasing attention due to its extremely high theoretical energy density. However, its development is limited by the cathode and electrolyte properties, which should include high stability, conductivity, and electrocatalytic properties in oxygen-rich environments. Here, we employ a systematic first-principles study of Li–O 2 discharge and charge reactions on the Co 3 O 4 -based cathode with the assistance of dimethyl sulfoxide (DMSO) electrolyte. The structure, stability, and electronic properties of different surface reconstructions of the Co 3 O 4 (100) facet are investigated. In addition, the mechanisms and thermodynamic overpotentials of multi-step reactions between Li + /e – and O 2 are provided, where lithium suboxide products (Li 2 O 2 or Li 3 O 2 ) are formed on the different Co 3 O 4 (100) terminations. The solvation shell of Li + components in explicit DMSO solvent is investigated through ab initio molecular dynamics simulations. In general, we find that the Co 3 O 4 (100)-O (oxidized) surface is the most stable one under standard conditions, and the stable Li + solvation structure is found in a tetrahedral Li(DMSO) 4 + shell in the DMSO-based electrolyte. Moreover, in the system of the Co 3 O 4 (100)-O cathode and DMSO electrolyte, the solution model pathway is energetically favorable for the Li–O 2 discharge reaction. It provides a low constant overpotential of 0.17 V during a long-term discharging process, thus causing the final toroid Li 2 O 2 formation on the cathode. During the charging process, an overpotential of 0.36 V is required to rapidly decompose Li 2 O 2 .

25 ENERGY STORAGE↗
DOE OSTI2022

Volatile Products of the Autoxidation of Poly(ethylenimine) in CO 2 Sorbents

Poly(ethyleneimine) (PEI)-based CO 2 sorbents are a promising material class for use in CO 2 capture applications, particularly direct air capture (DAC), due to their high amine content and CO 2 capacities. The sorbent lifetime is a key uncertainty in the deployment of these materials in such applications, as they oxidize under conditions relevant to candidate DAC process cycles. Here, in this study, we utilize thermogravimetric analysis/differential scanning calorimetry/FTIR spectroscopy to characterize the nature, rate, and quantity of volatile species formed from the oxidation of PEI when supported on mesoporous Al 2 O 3 . We show that NH 3 , CO 2 , and H 2 O are primary volatile species formed from PEI oxidation and that their production rate matches the overall oxidation rate as measured via heat flow from a differential scanning calorimeter. We show that the total quantity of NH 3 evolved is consistent with terminal primary amines being cleaved from the polymer chain and that approximately one hydrogen atom per PEI repeat unit reacts to form H 2 O during the reaction. Finally, metadynamics and quantum chemical simulations performed on a simplified system are used to highlight the likely importance of radicals in the elementary reactions that comprise the oxidation reaction set. The findings here represent the first characterization of the volatile products from the oxidation of PEI in CO 2 sorbents and lead to a greater understanding of the mechanisms behind the oxidative degradation of these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Probing the Morphology and Mobility of Amines in Porous Silica CO 2 Sorbents by 1 H T 1 – T 2 Relaxation Correlation NMR

Molecular and oligomeric amines supported in porous oxide supports are a promising class of CO 2 sorbent materials studied for CO 2 removal from diverse streams such as flue gas and ambient air. Among the various amines investigated, low molecular weight, hyperbranched poly(ethyleneimine) (PEI), and tetraethylenepentamine (TEPA) are among the most extensively studied. While macroscopic structure–performance relationships relating the support structure, amine loading, and other factors affecting CO 2 sorption capacities and kinetics have been developed, structural and dynamic information about the organic amine phase in the porous support is less plentiful. The structure and mobility of amines impregnated in the pores of porous supports directly impact gas sorption, as the accessibility of amine sites in the pores directly relates to amine distribution in the pores and overall pore filling as well as the dynamics of the amine chains. Here, we prepare a family of mesoporous silica SBA-15 materials containing varying loadings of oligomeric (PEI) and molecular (TEPA) amines. 1 H T 1 –T 2 relaxation correlation solid-state NMR experiments are used to characterize the structural and dynamic properties of the confined amines. Both TEPA and PEI are shown to form multiple different domains in the pores, each with distinguishable dynamic properties. TEPA and PEI form more rigid layers around the silica support walls at lower organic loading fractions, characterized by lower mobilities, followed by the formation of more mobile domains less engaged in pore wall interactions at higher loadings. TEPA shows faster mobilities than PEI because of its lower molecular weight. TEPA also appears to more easily transfer between domains within the pores, leading to generally faster CO 2 uptake rates with higher sorption capacities, while PEI located closer to the pore walls remained much less mobile and is thus less engaged in CO 2 capture.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

MgO Nanostructures on Cu(111): Understanding Size- and Morphology-Dependent CO 2 Binding and Hydrogenation

To design and optimize cost-effective technologies for the capture, utilization, and storage of carbon dioxide (CO 2 ), we need a fundamental knowledge and control of chemical interactions associated with the capture and conversion of the molecule into high-value chemicals, minerals, and all kinds of materials. Bulk magnesium oxide (MgO) is frequently used for the trapping and storage of CO 2 by generation of magnesium carbonates. In this study, the growth and reactivity of MgO nanostructures on a Cu 2 O/Cu(111) substrate were investigated using scanning tunneling microscopy (STM) and synchrotron-based ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). For extremely small concentrations of Mg (~ 0.01 monolayer (ML)), a well-ordered film of copper oxide with small clusters (0.2-0.5 nm in width, 0.4-0.6 Å in height) of embedded MgO was seen. At a coverage of 0.1 ML, MgO nanoparticles with a width of 0.4 to 1 nm and a height of ~ 1.5 Å were randomly distributed on the copper oxide. Further, random distribution was also observed when the MgO coverage was raised to 0.25 ML, with the width of the MgO particles increasing to 2-2.5 nm and the height reaching 2 Å. These oxide nanostructures displayed a high reactivity towards CO 2 and H 2 that is not seen for bulk MgO. Dissociation of H 2 was observed at room temperature with reaction of the H adatoms with CuO x and C-containing groups. On the small MgO nanostructures (< 1 nm in width), instead of plain carbonate formation, there was dissociation of CO 2 into CO and C species, opening reaction channels for the conversion of this harmful molecule into oxygenates and light alkanes.

03 NATURAL GAS↗
DOE OSTI2025

CO 2 Hydrogenation on Pd(111): The Role of Subsurface Hydrogen and Surface Defects

Palladium-based catalysts are often used in carbon dioxide (CO 2 ) hydrogenation reactions with different possible reaction pathways producing methanol, methane, formic acid, or carbon monoxide. We used ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to understand the surface reaction mechanism of CO 2 hydrogenation on Pd(111). AP-XPS results show that the order in which the reactants are introduced yields different initial surface species. In a CO 2 and H 2 mixture, carbonaceous species (CH x , C*, PdC x ) are formed upon heating Pd(111) at 400 K and above. In addition, a Pd(111) sample pre-exposed to an elevated pressure of H 2 followed by evacuation to ultrahigh vacuum (UHV) can store enough hydrogen atoms in the subsurface and bulk to provide a hydrogen source for the CO 2 hydrogenation reaction to occur when exposed to CO 2 gas alone. In conclusion, the formation of carbonaceous species likely occurs through the decomposition of a transient CH x O intermediate facilitated by low-coordinated sites and surface defects.

36 MATERIALS SCIENCE↗
DOE OSTI2020

High-Performance Pt–Co Nanoframes for Fuel-Cell Electrocatalysis

Pt-based alloy catalysts are promising candidates for fuel-cell applications, especially for cathodic oxygen reduction reaction (ORR) and anodic methanol oxidation reaction (MOR). The rational design of composition and morphology is crucial to promoting catalytic performances. Here, we report the synthesis of Pt–Co nanoframes via chemical etching of Co from solid rhombic dodecahedra. The obtained Pt–Co nanoframes exhibit excellent ORR mass activity in acidic electrolyte, which is as high as 0.40 A mg Pt –1 initially and 0.34 A mg Pt –1 after 10 000 potential cycles at 0.95 V RHE . Furthermore, their MOR mass activity in alkaline media is up to 4.28 A mg Pt –1 and is 4-fold higher than that of commercial Pt/C catalyst. Furthermore, experimental studies indicate that the weakened binding of intermediate carbonaceous poison contributes to the enhanced MOR behavior. More impressively, the Pt–Co nanoframes also demonstrate remarkable stability under long-term testing, which could be attributed to the negligible electrochemical Co dissolution.

25 ENERGY STORAGE↗
DOE OSTI2021

Access to Perfluorometallacyclopentane Complexes of Cobalt through the [(MeCN) 4 Co(C 4 F 8 )][PF 6 ] Precursor

Here, the acetonitrile ligands in [(MeCN) 4 Co(C 4 F 8 )][PF 6 ] were found to be labile toward ligand substitution reactions, allowing for the preparation of [(MeCN)(tpy)Co(C 4 F 8 )][PF 6 ], [(tpy)CoBr(C 4 F 8 )], [(bpy) 2 Co(C 4 F 8 )][PF 6 ], and [(cis-κ 2 -pym-PPh 2 ) 2 Co(C 4 F 8 )][PF 6 ] (tpy = 2,2':6',2"-terpyridine, bpy = 2,2'-bipyridine, and pym-PPh 2 = diphenyl(2-pyrimidyl)phosphine). All of the aforementioned complexes have been structurally characterized by X-ray diffraction. Additionally, an improved procedure for the preparation of [(MeCN) 4 Co(C 4 F 8 )][X] (X = PF 6 or BF 4 ) is reported.

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

Surface-Enhanced Raman Detection of the CO 2 Moisture Swing

The development of scalable, energy-efficient carbon dioxide (CO 2 ) capture technologies is critical for achieving net-zero emissions. Moisture swing (MS) sorbents offer a promising alternative to traditional thermal regeneration methods by enabling reversible CO 2 binding through humidity-driven ion hydrolysis. In this study, we investigate the anion speciation dynamics in two classes of MS materials─an anion-exchange resin with a bicarbonate anion and activated carbon impregnated with potassium bicarbonate salt─using both sorption measurements and in situ surface-enhanced Raman spectroscopy (SERS). Ni-coated Ag nanowires were employed as SERS substrates to enhance signal intensity and enable the real-time detection of carbonate (CO 3 2– ), bicarbonate (HCO 3 – ), and hydroxide (OH – ) species under controlled humidity conditions in both air and nitrogen atmospheres. The results reveal humidity-dependent interconversion between anionic species with significant spectral shifts confirming the reversible hydrolysis reactions that drive the MS mechanism. Under humid conditions, we observed the depletion of bicarbonate signals and a concurrent increase in carbonate species, consistent with moisture-induced desorption of CO 2 . With the activated carbon samples, we further observed the formation of hydroxide. These findings not only validate the mechanistic models of humidity-driven anion exchange in MS sorbents but also demonstrate the practical potential of SERS as an operando diagnostic tool for monitoring CO 2 capture media. The ability to resolve and semiquantitatively evaluate the reversible transformation of carbonate, bicarbonate, and hydroxide ions under realistic environmental conditions provides valuable insight for the rational design, performance optimization, and quality control of next-generation sorbent materials for direct air capture applications.

CO2 capture↗
DOE OSTI2024

Low-Temperature Molten Salt Electrochemical CO 2 Upcycling for Advanced Energy Materials

One strategy for addressing the climate crisis caused by CO 2 emissions is to efficiently convert CO 2 to advanced materials suited for green and clean energy technology applications. Porous carbon is widely used as an advanced energy storage material because of its enhanced energy storage capabilities as an anode. Herein, we report electrochemical CO 2 upcycling to solid carbon with a controlled microstructure and porosity in a ternary molten carbonate melt at 450 °C. Controlling the electrochemical parameters (voltage, temperature, cathode material) enabled the conversion of CO 2 to porous carbon with a tunable morphology and porosity for the first time at such a low temperature. Additionally, a well-controlled morphology and porosity are beneficial for reversible energy storage. In fact, these carbon materials delivered high specific capacity, stable cycling performances, and exceptional rate capability even under extremely fast charging conditions when integrated as an anode in lithium-ion batteries (LIBs). In conclusion, the present approach not only demonstrated efficient upcycling of CO 2 into porous carbon suitable for enhanced energy storage but can also contribute to a clean and green energy technology that can reduce carbon emissions to achieve sustainable energy goals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Synergistic Assembly of Charged Oligomers and Amino Acids at the Air–Water Interface: An Avenue toward Surface-Directed CO 2 Capture

Interfaces are considered a major bottleneck in the capture of CO 2 from air. Efforts to design surfaces to enhance CO 2 capture probabilities are challenging due to the remarkably poor understanding of chemistry and self-assembly taking place at these interfaces. In this report we leverage surface-specific vibrational spectroscopy, Langmuir trough techniques, and simulations to mechanistically elucidate how cationic oligomers can drive surface localization of amino acids (AAs) that serve as CO 2 capture agents speeding up the apparent rate of absorption. We demonstrate how tuning these interfaces provides a means to facilitate CO 2 capture chemistry to occur at the interface, while lowering surface tension and improving transport/reaction probabilities. We show that in the presence of interfacial AA-rich aggregates, one can improve capture probabilities vs that of a bare interface, which holds promise in addressing climate change through the removal of CO 2 via tailored interfaces and associated chemistries.

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

Electrically Conductive Amine Functionalized Reduced Graphite Oxide Foam for CO 2 Removal from the Air

Rapid regeneration of CO 2 adsorbents is critical to improving the productivity of direct air capture (DAC) systems. In this study, we codesigned a material to have appropriate electrical conductivity and CO 2 adsorption properties to enable efficient CO 2 capture from air. Specifically, we present a poly(ethylenimine) (PEI)-impregnated thermally annealed graphite oxide (TAGO900) foam adsorbent tailored for vacuum-assisted electrically driven thermal swing adsorption (V-ETSA). This structured adsorbent leverages the high electrical conductivity of the reduced graphite oxide framework to enable fast and direct heating of the adsorbent material by electrical resistance heating (Joule heating). An optimal sample, 40 wt % PEI (molecular weight 25k) impregnated TAGO900, shows the best balance between adsorption capacity (1.54 mmol g –1 ) and adsorption rates (0.016 mmol g –1 min –1 ) using fixed bed breakthrough experiments at 25 °C and 70% RH using 50 sccm 400 ppm of CO 2 /N 2 flow. Compared to conventional temperature vacuum swing adsorption (TVSA), the V-ETSA approach achieves substantially faster CO 2 desorption, achieving average desorption rates (including cooling time) of 0.09 mmol g –1 min –1 ─approximately 2.5 times faster than TVSA under similar operating conditions. The maximum desorption rate reaches 0.23 mmol/g/min during the desorption stage. These results underscore the importance of the direct heating strategy, such as Joule heating, for fast and highly productive vacuum swing adsorption in DAC systems.

amines↗
DOE OSTI2025

Potential-Controlled Deposition of Multilayer CO 2 Reduction Catalyst Films onto Silicon Photoelectrodes Demonstrates Thickness-Dependent Catalytic Rates

Covalently attaching molecular catalysts to semiconductor surfaces yields promising hybrid photoelectrode architectures for reducing CO 2 to higher-value carbon products. Polymeric molecular catalyst films have higher loading densities than their monolayer counterparts, promising greater rates of solar fuel production. Using photoassisted diazonium electrografting, multilayered films of a Re(apbpy)(CO) 3 Cl CO 2 -reduction catalyst were attached to low-doped p-type Si (pSi). Parallel characterization of the newly formed films with ellipsometry, XPS, and ICP-MS revealed that catalyst loading increased with increasingly negative applied grafting potentials (Vgraft), providing us an experimental test bed to study the effects of film thickness on photocatalytic performance. Controlled-potential electrolysis experiments showed enhanced CO evolution rates on all photoelectrodes with increasingly negative applied potentials (V app ), with thicker films exhibiting the greatest rates of enhancement. Competitive proton reduction reactions at the Si surface were not strongly linked to V app but dependent on film thickness, with thicker films showing increased CO-to-H 2 production ratios.

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

Hydrogenation of CO 2 to Methanol on a Au δ+ –In 2 O 3–x Catalyst

CO 2 hydrogenation to methanol has attracted increasing attention with the development of renewable hydrogen. A big challenge is to identify catalysts able to achieve high conversion and selectivity. In this work, we report an In 2 O 3 -supported Au catalyst that exhibits excellent performance for hydrogenation of CO 2 selectively to methanol. In situ characterizations using time-resolved X-ray diffraction, ambient-pressure X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy confirm that a strong metal–support interaction leads to a reactive Au δ+ –In 2 O 3– x interface for activation and hydrogenation of CO 2 to methanol. An effective gold-indium oxide bonding favors the dispersion of the noble metal and prevents its sintering under reaction conditions. The methanol selectivity reaches 100% at temperatures below 225 °C and is more than 70% at 275 °C over the Au δ+ –In 2 O 3– x catalyst. It is even 67.8% with a space time yield of methanol of 0.47 g MeOH /(h·g cat ) at 300 °C, 5 MPa, and 21,000 cm 3 h –1 g cat –1 . The results obtained here represent the highest selectivity and activity ever reported for CO 2 hydrogenation over supported gold catalysts. Our study shows that the strong Au/In 2 O 3 interaction and the intrinsic chemical activity of In 2 O 3 can be used to significantly improve the catalytic performance of Au catalysts, providing promising routes for the rational design and application of Au catalysts beyond CO 2 hydrogenation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Liquid–Solid Boundaries Dominate Activity of CO 2 Reduction on Gas-Diffusion Electrodes

Electrochemical CO 2 electrolysis to produce hydrocarbon fuels or material feedstocks offers a renewable alternative to fossilized carbon sources. Gas-diffusion electrodes (GDEs), composed of solid electrocatalysts on porous supports positioned near the interface of a conducting electrolyte and CO 2 gas, have been able to demonstrate the substantial current densities needed for future commercialization. These higher reaction rates have often been ascribed to the presence of a three-phase interface, where solid, liquid, and gas provide electrons, water, and CO 2 , respectively. Conversely, mechanistic work on electrochemical reactions implicates a fully two-phase reaction interface, where gas molecules reach the electrocatalyst’s surface by dissolution and diffusion through the electrolyte. Because the discrepancy between an atomistic three-phase versus two-phase reaction has substantial implications for the design of catalysts, gas-diffusion layers, and cell architectures, the nuances of nomenclatures and governing phenomena surrounding the three-phase-region require clarification. In this paper we outline the macro, micro, and atomistic phenomena occurring within a gas-diffusion electrode to provide a focused discussion on the architecture of the often-discussed three-phase region for CO 2 electrolysis. From this information, we comment on the outlook for the broader CO 2 electroreduction GDE cell architecture.

CO2 reduction↗