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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ag(CO)2 by Materials Project

AgO2C2 crystallizes in the monoclinic C2/c space group. The structure is one-dimensional and consists of four AgO2C2 clusters and two AgO2C2 ribbons oriented in the (0, 0, 1) direction. In each AgO2C2 cluster, Ag2+ is bonded in a 3-coordinate geometry to three O2- atoms. There are a spread of Ag–O bond distances ranging from 2.24–2.55 Å. There are two inequivalent C1+ sites. In the first C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the second C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ag2+ and one C1+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Ag2+ and one C1+ atom. In each AgO2C2 ribbon, Ag2+ is bonded in a distorted rectangular see-saw-like geometry to four O2- atoms. There are a spread of Ag–O bond distances ranging from 2.25–2.58 Å. There are two inequivalent C1+ sites. In the first C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the second C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ag2+ and one C1+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ag2+ and one C1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ag(CO)2 by Materials Project

AgO2C2 crystallizes in the triclinic P1 space group. The structure is two-dimensional and consists of one AgO2C2 ribbon oriented in the (0, 1, 0) direction and one AgO2C2 sheet oriented in the (0, 0, 1) direction. In the AgO2C2 ribbon, there are four inequivalent Ag2+ sites. In the first Ag2+ site, Ag2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Ag–O bond distances ranging from 2.26–2.53 Å. In the second Ag2+ site, Ag2+ is bonded in a distorted rectangular see-saw-like geometry to four O2- atoms. There are a spread of Ag–O bond distances ranging from 2.29–2.49 Å. In the third Ag2+ site, Ag2+ is bonded in a distorted rectangular see-saw-like geometry to four O2- atoms. There are a spread of Ag–O bond distances ranging from 2.26–2.50 Å. In the fourth Ag2+ site, Ag2+ is bonded in a distorted rectangular see-saw-like geometry to four O2- atoms. There are a spread of Ag–O bond distances ranging from 2.28–2.53 Å. There are eight inequivalent C1+ sites. In the first C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the second C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the third C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.27 Å. In the fourth C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.27 Å. In the fifth C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.27 Å. In the sixth C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.27 Å. In the seventh C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.27 Å. In the eighth C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.27 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two Ag2+ and one C1+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to two Ag2+ and one C1+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to two Ag2+ and one C1+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to two Ag2+ and one C1+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to two Ag2+ and one C1+ atom. In the sixth O2- site, O2- is bonded in a distorted single-bond geometry to two Ag2+ and one C1+ atom. In the seventh O2- site, O2- is bonded in a distorted single-bond geometry to two Ag2+ and one C1+ atom. In the eighth O2- site, O2- is bonded in a distorted single-bond geometry to two Ag2+ and one C1+ atom. In the AgO2C2 sheet, there are four inequivalent Ag2+ sites. In the first Ag2+ site, Ag2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Ag–O bond distances ranging from 2.36–2.74 Å. In the second Ag2+ site, Ag2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Ag–O bond distances ranging from 2.37–2.73 Å. In the third Ag2+ site, Ag2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Ag–O bond distances ranging from 2.36–2.74 Å. In the fourth Ag2+ site, Ag2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Ag–O bond distances ranging from 2.36–2.77 Å. There are eight inequivalent C1+ sites. In the first C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the second C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the third C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the fourth C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the fifth C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the sixth C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the seventh C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the eighth C1+ site, C1+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to two Ag2+ and one C1+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to two Ag2+ and one C1+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to two Ag2+ and one C1+ atom. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to two Ag2+ and one C1+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to two Ag2+ and one C1+ atom. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to two Ag2+ and one C1+ atom. In the seventh O2- site, O2- is bonded in a 1-coordinate geometry to two Ag2+ and one C1+ atom. In the eighth O2- site, O2- is bonded in a 1-coordinate geometry to two Ag2+ and one C1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Membrane‐electrode assembly design parameters for optimal CO 2 reduction

Commercial-scale generation of carbon-containing chemicals and fuels by means of electrochemical CO 2 reduction (CO 2 R) requires electrolyzers operating at high current densities and product selectivities. Membrane-electrode assemblies (MEAs) have been shown to be suitable for this purpose. In such devices, the cathode catalyst layer controls both the rate of CO 2 R and the distribution of products. In this study, we investigate how the ionomer-to-catalyst ratio (I:Cat), catalyst loading, and catalyst-layer thickness influence the performance of a cathode catalyst layer containing Ag nanoparticles supported on carbon. In this paper, we explore how these parameters affect the cell performance and establish the role of the exchange solution (water vs. CsHCO 3 ) behind the anode catalyst layer in cell performance. We show that a high total current density is best achieved using an I:Cat ratio of 3 at a Ag loading of 0.01–0.1 mg Ag /cm 2 and with a 1.0 M solution of CsHCO 3 circulated behind the anode catalyst layer. For these conditions, the optimal CO partial current density depends on the voltage applied to the MEA. The work also reveals that the performance of the cathode catalyst layer is limited by a combination of the electrochemically active surface area and the degree to which mass transfer of CO 2 to the surface of the Ag nanoparticles and the transport of OH – anions away from it limit the overall catalyst activity. Hydration of the ionomer in the cathode catalyst layer is found not to be an issue when using an exchange solution. The insights gained allowed for a Ag CO 2 R MEA that operates between 200 mA/cm 2 and 1 A/cm 2 with CO faradaic efficiencies of 78–91%, and the findings and understanding gained herein should be applicable to a broad range of CO 2 R MEA-based devices.

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

Electrocatalytic Reduction of CO 2 to CO over Ag(110) and Cu(211) Modeled by Grand-Canonical Density Functional Theory

We report the results of modeling CO 2 reduction (CO 2 R) to CO over Ag(110) and Cu(211) surfaces at different applied potentials using grand-canonical density functional theory (GC-DFT), a method specifically designed to accurately model electrochemical systems. In addition to demonstrating GC-DFT’s ability to accurately model electrochemical processes, we also compare it with the computational hydrogen electrode (CHE) approach. GC-DFT predicts that the geometries of these reacting systems strongly depend on the applied potential and the Helmholtz free energies vary nonlinearly with the applied potential, which contradicts a central assumption of the CHE approach. The CHE approach neglects the change in the number of electrons on the electrode surface at different applied potentials, which reduces its accuracy as the potential changes from the potential of zero charge. Our results further demonstrate that the grand free energies of the reaction intermediates not only depend on the value of the applied potential but also on the metal surface type, adsorption site, and adsorbate. GC-DFT’s ability to predict the effect of the applied potential on adsorbate geometry enables it to evaluate different possible reaction mechanisms at different applied potentials. For instance, GC-DFT predicts that the first step of CO2R likely switches from proton-coupled electron transfer to sequential electron transfer and then proton transfer at more reducing potentials, a result that cannot be determined by the CHE because it assumes that all electron transfers are coupled to proton transfers and neglects the effect of the applied potential on the adsorbate geometry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Optimized Tandem Catalyst Patterning for CO 2 Reduction Flow Reactors

Tandem catalysis involves two or more catalysts arranged in proximity within a single reaction vessel, with the aim of synergistically aligning the catalysts’ reaction pathways to maximize overall system performance. This study presents a proof of concept showing the integration of continuum transport modeling with design optimization in a simplified two-dimensional flow reactor setup for electrochemical CO 2 reduction. Ag catalysts provide the CO 2 ⟶ CO reaction capability, and Cu catalysts provide the CO ⟶ high-value products reaction capability. Given a set of input parameters, the optimization algorithm uses adjoint methods to modify the Ag/Cu surface patterning in order to maximize the current density toward high-value products, such as ethylene. The optimized designs yield significant performance enhancement especially at more negative applied voltages (i.e., stronger surface reactions) and for larger numbers of patterning sections. For an applied voltage of −1.7 V vs. SHE, the 12-section optimized design increases the current density toward ethylene by up to 65% compared to the unoptimized 2-section design. For the optimized cases, observed differences in the production and consumption of CO (the key intermediate species) and minimized zones of low CO reactant surface concentration on Cu sections explain the improved reactor performance.

CO2 reduction↗
DOE OSTI2023

Surface‐modified Ag@Ru‐P25 for photocatalytic CO 2 conversion with high selectivity over CH 4 formation at the solid–gas interface

Systematic optimization of the photocatalyst and investigation of the role of each component is important to maximizing catalytic activity and comprehending the photocatalytic conversion of CO 2 reduction to solar fuels. A surface-modified Ag@Ru-P25 photocatalyst with H 2 O 2 treatment was designed in this study to convert CO 2 and H 2 O vapor into highly selective CH 4 . Ru doping followed by Ag nanoparticles (NPs) cocatalyst deposition on P25 (TiO 2 ) enhances visible light absorption and charge separation, whereas H 2 O 2 treatment modifies the surface of the photocatalyst with hydroxyl (–OH) groups and promotes CO 2 adsorption. High-resonance transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and extended X-ray absorption fine structure techniques were used to analyze the surface and chemical composition of the photocatalyst, while thermogravimetric analysis, CO 2 adsorption isotherm, and temperature programmed desorption study were performed to examine the significance of H 2 O 2 treatment in increasing CO 2 reduction activity. The optimized Ag 1.0 @Ru 1.0 -P25 photocatalyst performed excellent CO 2 reduction activity into CO, CH 4 , and C 2 H 6 with a ~95% selectivity of CH 4 , where the activity was ~135 times higher than that of pristine TiO 2 (P25). For the first time, this work explored the effect of H 2 O 2 treatment on the photocatalyst that dramatically increases CO 2 reduction activity.

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

Engineering Catalyst–Electrolyte Microenvironments to Optimize the Activity and Selectivity for the Electrochemical Reduction of CO 2 on Cu and Ag

We report the electrochemical reduction of carbon dioxide (CO 2 R) driven by renewably generated electricity (e.g., solar and wind) offers a promising means for reusing the CO 2 released during the production of cement, steel, and aluminum as well as the production of ammonia and methanol. If CO 2 could be removed from the atmosphere at acceptable costs (i.e., <$100/t of CO 2 ), then CO 2 R could be used to produce carbon-containing chemicals and fuels in a fully sustainable manner. Economic considerations dictate that CO 2 R current densities must be in the range of 0.1 to 1 A/cm 2 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 CO 2 and H 2 O, and the identities of the cations in the double layer adjacent to the catalyst surface).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Cascade electrocatalysis via AgCu single-atom alloy and Ag nanoparticles in CO 2 electroreduction toward multicarbon products

Electrocatalytic CO 2 reduction into value-added multicarbon products offers a means to close the anthropogenic carbon cycle using renewable electricity. However, the unsatisfactory catalytic selectivity for multicarbon products severely hinders the practical application of this technology. In this paper, we report a cascade AgCu single-atom and nanoparticle electrocatalyst, in which Ag nanoparticles produce CO and AgCu single-atom alloys promote C-C coupling kinetics. As a result, a Faradaic efficiency (FE) of 94 ± 4% toward multicarbon products is achieved with the as-prepared AgCu single-atom and nanoparticle catalyst under ~720 mA cm -2 working current density at -0.65 V in a flow cell with alkaline electrolyte. Density functional theory calculations further demonstrate that the high multicarbon product selectivity results from cooperation between AgCu single-atom alloys and Ag nanoparticles, wherein the Ag single-atom doping of Cu nanoparticles increases the adsorption energy of *CO on Cu sites due to the asymmetric bonding of the Cu atom to the adjacent Ag atom with a compressive strain.

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

Chemical Modifications of Ag Catalyst Surfaces with Imidazolium Ionomers Modulate H 2 Evolution Rates during Electrochemical CO 2 Reduction

Bridging polymer design with catalyst surface science is a promising direction for tuning and optimizing electrochemical reactors that could impact long-term goals in energy and sustainability. Particularly, the interaction between inorganic catalyst surfaces and organic-based ionomers provides an avenue to both steer reaction selectivity and promote activity. In this work, we studied the role of imidazolium-based ionomers for electrocatalytic CO 2 reduction to CO (CO 2 R) on Ag surfaces and found that they produce no effect on CO 2 R activity yet strongly promote the competing hydrogen evolution reaction (HER). By examining the dependence of HER and CO 2 R rates on concentrations of CO 2 and HCO 3 –, we developed a kinetic model that attributes HER promotion to intrinsic promotion of HCO 3 – reduction by imidazolium ionomers. We also show that varying the ionomer structure by changing substituents on the imidazolium ring modulates the HER promotion. This ionomer-structure dependence was analyzed via Taft steric parameters and density functional theory calculations, which suggest that steric bulk from functionalities on the imidazolium ring reduces access of the ionomer to both HCO 3 – and the Ag surface, thus limiting the promotional effect. Our results help develop design rules for ionomer–catalyst interactions in CO 2 R and motivate further work into precisely uncovering the interplay between primary and secondary coordination in determining electrocatalytic behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Static and dynamic spin properties in the quantum triangular lattice antiferromagnet Ag 2 CoO 2

In Ag 2 CoO 2 , Co forms triangular lattice layers, which are separated by the metallic (Ag 2 ) block. The magnetic susceptibility and heat capacity measurements show that this material exhibits an antiferromagnetic transition at T N =17.5 K and the Weiss temperature (T Θ ) and the effective moment are -274 K and 1.62μ B , respectively, indicating that the Co ion carries spin (S) 1/2 and has a strongly frustrated state with T Θ /T N =15.7. A density functional theory calculation confirmed that the valence state of the Co ions is 2+ and the low-spin state with S=1/2 is realized at reduced on-site Coulomb interaction on Co. We performed elastic and inelastic neutron scattering experiments in a powder sample of Ag 2 CoO 2 . Although no noticeable magnetic Bragg peaks were observed below T N , distinct magnetic excitations were observed in the inelastic neutron scattering experiments. The excitations are consistent with those expected for the S=1/2 Heisenberg triangular lattice antiferromagnet. These results suggest that the ordered moment is reduced due to the quantum effect, which explains the absence of the magnetic Bragg peaks. Our results thus suggest that Ag 2 CoO 2 is a good candidate to realize a quantum Heisenberg triangular lattice antiferromagnet.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Operando NRIXS and XAFS Investigation of Segregation Phenomena in Fe-Cu and Fe-Ag Nanoparticle Catalysts during CO 2 Electroreduction

Operando nuclear resonant inelastic X-ray scattering (NRIXS) and X-ray absorption fine-structure spectroscopy (XAFS) measurements were used to gain insight into the structure and surface composition of FeCu and FeAg nanoparticles (NPs) during the electrochemical CO 2 reduction (CO 2 RR) and to extract correlations with their catalytic activity and selectivity. The formation of a core–shell structure during CO 2 RR for FeAg NPs was inferred from the analysis of the operando NRIXS data (phonon density of states, PDOS) and XAFS measurements. Electrochemical analysis of the FeAg NPs revealed a faradaic selectivity of 36 % for CO in 0.1 M KHCO 3 at -1.1 V vs. RHE, similar to that of pure Ag NPs. In contrast, a predominant selectivity towards H 2 evolution is obtained in the case of the FeCu NPs, analogous to the results obtained for pure Fe NPs, although small Cu NPs have also been shown to favor H 2 production.

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

The AUREX cell: a versatile operando electrochemical cell for studying catalytic materials using X-ray diffraction, total scattering and X-ray absorption spectroscopy under working conditions

Understanding the structure–property relationship in electrocatalysts under working conditions is crucial for the rational design of novel and improved catalytic materials. This paper presents the Aarhus University reactor for electrochemical studies using X-rays (AUREX) operando electrocatalytic flow cell, designed as an easy-to-use versatile setup with a minimal background contribution and a uniform flow field to limit concentration polarization and handle gas formation. The cell has been employed to measure operando total scattering, diffraction and absorption spectroscopy as well as simultaneous combinations thereof on a commercial silver electrocatalyst for proof of concept. This combination of operando techniques allows for monitoring of the short-, medium- and long-range structure under working conditions, including an applied potential, liquid electrolyte and local reaction environment. The structural transformations of the Ag electrocatalyst are monitored with non-negative matrix factorization, linear combination analysis, the Pearson correlation coefficient matrix, and refinements in both real and reciprocal space. Upon application of an oxidative potential in an Ar-saturated aqueous 0.1 M KHCO 3 /K 2 CO 3 electrolyte, the face-centered cubic (f.c.c.) Ag gradually transforms first to a trigonal Ag 2 CO 3 phase, followed by the formation of a monoclinic Ag 2 CO 3 phase. A reducing potential immediately reverts the structure to the Ag (f.c.c.) phase. Following the electrochemical-reaction-induced phase transitions is of fundamental interest and necessary for understanding and improving the stability of electrocatalysts, and the operando cell proves a versatile setup for probing this. In addition, it is demonstrated that, when studying electrochemical reactions, a high energy or short exposure time is needed to circumvent beam-induced effects.

Frank, Sara (ORCID:0000000163218363)↗
DOE OSTI2025

Electro-activated indigos intensify ampere-level CO 2 reduction to CO on silver catalysts

The electrochemical reduction of carbon dioxide (CO 2 ) to carbon monoxide (CO) is challenged by a selectivity decline at high current densities. Here we report a class of indigo-based molecular promoters with redox-active CO 2 binding sites to enhance the high-rate conversion of CO 2 to CO on silver (Ag) catalysts. Theoretical calculations and in situ spectroscopy analyses demonstrate that the synergistic effect at the interface of indigo-derived compounds and Ag nanoparticles could activate CO 2 molecules and accelerate the formation of key intermediates (*CO 2 – and *COOH) in the CO pathway. Indigo derivatives with electron-withdrawing groups further reduce the overpotential for CO production upon optimizing the interfacial CO 2 binding affinity. By integrating the molecular design of redox-active centres with the defect engineering of Ag structures, we achieve a Faradaic efficiency for CO exceeding 90% across a current density range of 0.10 − 1.20 A cm –2 . The Ag mass activity toward CO increases to 174 A mg –1 Ag . This work showcases that employing redox-active CO 2 sorbents as surface modification agents is a highly effective strategy to intensify the reactivity of electrochemical CO 2 reduction.

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

Bulk Layering Effects of Ag and Cu for Tandem CO 2 Electrolysis

The electrochemical reduction of carbon dioxide (CO 2 ) presents an opportunity to close the carbon cycle and obtain sustainably sourced carbon compounds. In recent years, copper has received widespread attention as the only catalyst capable of meaningfully producing multi-carbon (C 2+ ) species. Notably carbon monoxide (CO) can also be reduced to C 2+ compounds on copper, motivating tandem systems that combine copper and CO-producing species, like silver, to enhance overall C 2+ selectivities. In this work, we examine the impact of layered-combinations of bulk Cu and Ag by varying the location and proportion of the CO-producing Ag layer. We report an effective increase in the C 2+ oxygenate selectivity from 23 % with a 100 nm Cu to 38 % for a 100: 15 nm Cu : Ag layer. Notably, however, for all co-catalyst cases there is an overproduction of CO vs Cu alone, even for 5 nm Ag layers. Lastly, due to restructuring and interlayer mobility of the copper layer it is clear that the stability of copper limits the locational advantages of such tandem solutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗