28 research outputs found
Quantifying Confidence in DFT Predicted Surface Pourbaix Diagrams of Transition Metal Electrode-Electrolyte Interfaces
Density Functional Theory (DFT) calculations have been widely used to predict
the activity of catalysts based on the free energies of reaction intermediates.
The incorporation of the state of the catalyst surface under the
electrochemical operating conditions while constructing the free energy diagram
is crucial, without which even trends in activity predictions could be
imprecisely captured. Surface Pourbaix diagrams indicate the surface state as a
function of the pH and the potential. In this work, we utilize error-estimation
capabilities within the BEEF-vdW exchange correlation functional as an ensemble
approach to propagate the uncertainty associated with the adsorption energetics
in the construction of Pourbaix diagrams. Within this approach,
surface-transition phase boundaries are no longer sharp and are therefore
associated with a finite width. We determine the surface phase diagram for
several transition metals under reaction conditions and electrode potentials
relevant for the Oxygen Reduction Reaction (ORR). We observe that our surface
phase predictions for most predominant species are in good agreement with
cyclic voltammetry experiments and prior DFT studies. We use the OH
intermediate for comparing adsorption characteristics on Pt(111), Pt(100),
Pd(111), Ir(111), Rh(111), and Ru(0001) since it has been shown to have a
higher prediction efficiency relative to O, and find the trend
Ru>Rh>Ir>Pt>Pd for (111) metal facets, where Ru binds OH the strongest. We
robustly predict the likely surface phase as a function of reaction conditions
by associating c-values to quantifying the confidence in predictions within the
Pourbaix diagram. We define a confidence quantifying metric using which certain
experimentally observed surface phases and peak assignments can be better
rationalized.Comment: 21 pages, 8 figures and Supporting Informatio
Enhancing electrochemical intermediate solvation through electrolyte anion selection to increase nonaqueous Li-O battery capacity
Among the 'beyond Li-ion' battery chemistries, nonaqueous Li-O batteries
have the highest theoretical specific energy and as a result have attracted
significant research attention over the past decade. A critical scientific
challenge facing nonaqueous Li-O batteries is the electronically insulating
nature of the primary discharge product, lithium peroxide, which passivates the
battery cathode as it is formed, leading to low ultimate cell capacities.
Recently, strategies to enhance solubility to circumvent this issue have been
reported, but rely upon electrolyte formulations that further decrease the
overall electrochemical stability of the system, thereby deleteriously
affecting battery rechargeability. In this study, we report that a significant
enhancement (greater than four-fold) in Li-O cell capacity is possible by
appropriately selecting the salt anion in the electrolyte solution. Using
Li nuclear magnetic resonance and modeling, we confirm that this
improvement is a result of enhanced Li stability in solution, which in turn
induces solubility of the intermediate to LiO formation. Using this
strategy, the challenging task of identifying an electrolyte solvent that
possesses the anti-correlated properties of high intermediate solubility and
solvent stability is alleviated, potentially providing a pathway to develop an
electrolyte that affords both high capacity and rechargeability. We believe the
model and strategy presented here will be generally useful to enhance Coulombic
efficiency in many electrochemical systems (e.g. Li-S batteries) where
improving intermediate stability in solution could induce desired mechanisms of
product formation.Comment: 22 pages, 5 figures and Supporting Informatio
Design Principles for Self-forming Interfaces Enabling Stable Lithium Metal Anodes
The path toward Li-ion batteries with higher energy-densities will likely
involve use of thin lithium metal (Li) anode (<50 m in thickness), whose
cyclability today remains limited by dendrite formation and low Coulombic
efficiency. Previous studies have shown that the solid-electrolyte-interface
(SEI) of Li metal plays a crucial role in Li electrodeposition and stripping.
However, design rules for optimal SEIs on lithium metal are not
well-established. Here, using integrated experimental and modeling studies on a
series of structurally-similar SEI-modifying compounds as model systems, we
reveal the relationship between SEI compositions, Li deposition morphology and
coulombic efficiency, and identify two key descriptors (ionicity and
compactness) for high performance SEIs through integrated experimental and
modeling studies. Using this understanding, we design a highly ionic and
compact SEI that shows excellent cycling performance in LiCoO-Li full cells
at practical current densities. Our results provide guidance for the rational
selection and optimization of SEI modifiers to further improve Li metal anodes.Comment: 21 pages, 6 figures and Supplementary Informatio