Engineering topics

Ringe, Stefan

Publications and source records attributed to Ringe, Stefan.

7 records

DOE OSTI2020

Atomistic Insight into Cation Effects on Binding Energies in Cu-Catalyzed Carbon Dioxide Reduction

Electrolyte properties in general and electrolyte ions in particular have been shown to have significant effects on the kinetics of electrochemical CO 2 and CO reduction at metal electrodes, but these effects have not yet been fully understood. Here, we investigate the effects of cations at the aqueous electrolyte–Cu(211) interface on adsorbate binding energies and the electrolyte structure using density functional theory (DFT). Charging the interface via explicit Na + has systematic effects on adsorbate–electrolyte interactions and conformations. We describe specific local adsorbate–ion interactions, including direct alkali ion–adsorbate coordination and hydrogen bonding via ion-coordinated water molecules. The relative importance of these specific interactions and purely electrostatic field–adsorbate interactions is investigated by comparing the DFT-calculated ion effects to those predicted by purely electrostatic models of the interface and the adsorbates. We find that the trend in ion effects among different adsorbates at constant surface charge density is well explained by a purely electrostatic interaction model. The binding energy of OCCHO is found to depend strongly on the surface charge density as well as the spatial distribution of ions at constant surface charge density. These effects are also explained by a purely electrostatic local electrostatic field–adsorbate model. This indicates that alkali ion effects can be mainly attributed to purely electrostatic field interactions and that the local field at ion-stabilized active sites can depend significantly on both the overall charge density and on the spatial distribution of ions at constant charge density. This work provides new insight on alkali ion effects on a variety of adsorbates relevant to the CO 2 and CO reduction reactions by describing specific local ion–adsorbate interactions, systematic changes in adsorbate–electrolyte interactions induced by explicit surface charge, and comparisons of the calculated effects on binding energies to simple electrostatic field–adsorbate models to explain trends among various adsorbates and at varying surface charge densities and supercell configurations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Unified Approach to Implicit and Explicit Solvent Simulations of Electrochemical Reaction Energetics

One of the major open challenges in ab initio simulations of the electrochemical interface is the determination of electrochemical barriers under a constant driving force. Existing methods to do so include extrapolation techniques based on fully explicit treatments of the electrolyte, as well as implicit solvent models which allow for a continuous variation in electrolyte charge. Emerging hybrid continuum models have the potential to revolutionize the field, since they account for the electrolyte with little computational cost while retaining some explicit electrolyte, representing a “best of both worlds” method. In this work, we present a unified approach to determine reaction energetics from fully explicit, implicit, and hybrid treatments of the electrolyte based on a new multicapacitor model of the electrochemical interface. A given electrode potential can be achieved by a variety of interfacial structures; a crucial insight from this work is that the effective surface charge gives a good proxy of the local potential, the true driving force of electrochemical processes. In contrast, we show that the traditionally considered work function gives rise to multivalued functions depending on the simulation cell size. Furthermore, we show that the reaction energetics are largely insensitive to the countercharge distribution chosen in hybrid implicit/explicit models, which means that any of the myriad implicit electrolyte models can be equivalently applied. Furthermore, this work thus paves the way for the accurate treatment of ab initio reaction energetics of general surface electrochemical processes using both implicit and explicit electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

A Two-Dimensional MoS 2 Catalysis Transistor by Solid-State Ion Gating Manipulation and Adjustment (SIGMA)

A variety of methods including tuning chemical compositions, structures, crystallinity, defects and strain, and electrochemical intercalation have been demonstrated to enhance the catalytic activity. However, none of these tuning methods provide direct dynamical control during catalytic reactions. Here we propose a new method to tune the activity of catalysts through solid-state ion gating manipulation and adjustment (SIGMA) using a catalysis transistor. SIGMA can electrostatically dope the surface of catalysts with a high electron concentration over 5 × 10 13 cm –2 and thus modulate both the chemical potential of the reaction intermediates and their electrical conductivity. The hydrogen evolution reaction (HER) on both pristine and defective MoS 2 were investigated as model reactions. Furthermore, our theoretical and experimental results show that the overpotential at 10 mA/cm 2 and Tafel slope can be in situ, continuously, dynamically, and reversibly tuned over 100 mV and around 100 mV/dec, respectively.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Practical Considerations for Continuum Models Applied to Surface Electrochemistry

We report that modelling the electrolyte at the electrochemical interface remains a major challenge in ab initio simulations of charge transfer processes at surfaces. Recently, the development of hybrid polarizable continuum models/ab initio models have allowed for the treatment of solvation and electrolyte charge in a computationally efficient way. However, challenges remain in its application. Recent literature has reported that large cell heights are required to reach convergence, which presents a serious computational cost. Furthermore, calculations of reaction energetics require costly iterations to tune the surface charge to the desired potential. In this work, we present a simple capacitor model of the interface that illuminates how to circumvent both of these challenges. We derive a correction to the energy for finite cell heights to obtain the large cell energies at no additional computational expense. We furthermore demonstrate that the reaction energetics determined at constant charge are easily mapped to those at constant potential, which eliminates the need to apply iterative schemes to tune the system to a constant potential. Lastly, these developments together represent more than an order of magnitude reduction of the computational overhead required for the application of polarizable continuum models to surface electrochemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Understanding cation effects in electrochemical CO 2 reduction

Solid–liquid interface engineering has recently emerged as a promising technique to optimize the activity and product selectivity of the electrochemical reduction of CO 2 . In particular, the cation identity and the interfacial electric field have been shown to have a particularly significant impact on the activity of desired products. Using a combination of theoretical and experimental investigations, we show the cation size and its resultant impact on the interfacial electric field to be the critical factor behind the ion specificity of electrochemical CO 2 reduction. We present a multi-scale modeling approach that combines size-modified Poisson–Boltzmann theory with ab initio simulations of field effects on critical reaction intermediates. The model shows an unprecedented quantitative agreement with experimental trends in cation effects on CO production on Ag, C 2 production on Cu, CO vibrational signatures on Pt and Cu as well as Au(111) single crystal experimental double layer capacitances. The insights obtained represent quantitative evidence for the impact of cations on the interfacial electric field. Lastly, we present design principles to increase the activity and selectivity of any field-sensitive electrochemical process based on the surface charging properties: the potential of zero charge, the ion size, and the double layer capacitance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Influence of Atomic Surface Structure on the Activity of Ag for the Electrochemical Reduction of CO 2 to CO

This work was undertaken to elucidate the facet-dependent activity of Ag for the electrochemical reduction of CO 2 to CO. To this end, CO2 reduction was investigated over Ag thin films with (111), (100), and (110) orientations prepared via epitaxial growth on single-crystal Si wafers with the same crystallographic orientations. Thus, this preparation technique yielded larger area electrodes than can be achieved using single-crystals, which enabled the electrocatalytic activity of the corresponding Ag surfaces to be quantified in the Tafel regime. The Ag(110) thin films exhibited higher CO evolution activity compared to the Ag(111) and Ag(100) thin films, consistent with previous single-crystal studies. Density functional theory calculations suggest that CO 2 reduction to CO is strongly facet-dependent, and that steps are more active than highly coordinated terraces. This is the result of both a higher binding energy of the key intermediate COOH as well as an enhanced double-layer electric field stabilization over undercoordinated surface atoms located at step edge defects. As a consequence, step edge defects likely dominate the CO 2 reduction activity observed over the Ag(111) and Ag(100) thin films. The higher activity observed over the Ag(110) thin film is then related to the larger density of undercoordinated sites compared to the Ag(111) and Ag(100) thin films. Our conclusion that undercoordinated sites dominate the CO 2 reduction activity observed over close-packed surfaces highlights the need to consider the contribution of such defects in studies of single-crystal electrodes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Solvent–Adsorbate Interactions and Adsorbate-Specific Solvent Structure in Carbon Dioxide Reduction on a Stepped Cu Surface

In this work, the structure of water and its interactions with various carbon dioxide reduction intermediates adsorbed on a Cu(211) surface is investigated using density functional theory. We find that the presence of adsorbates has a significant and adsorbate-specific effect on the local water structure and that solvation can stabilize adsorbate conformations different from those found in vacuum. We describe relationships between the hydrogen bonding capability of an adsorbate, the dipole moment of the adsorbate, the energetic strength of water–adsorbate interactions, and the change induced in the local water orientation by the adsorbate. Mechanistic implications are discussed. Here, we investigate and quantify the error associated with using arbitrary locally optimized solvent structures in calculations of relevant physical quantities, such as solvated binding energies and work functions. Possible effects of thermal motion on calculations of the work function are investigated using ab initio molecular dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗