Atomistic modeling of electrocatalysis: Are we there yet?

Abstract

Electrified interfaces play a prime role in energy technologies, from batteries and capacitors to heterogeneous electrocatalysis. The atomistic understanding and modelling of these interfaces is challenging due to the structural complexity and the presence of the electrochemical potential. Including the potential explicitly in the quantum mechanical simulations is equivalent to simulating systems with a surface charge. For realistic relationships between the potential and the surface charge (i.e., the capacity), the solvent and counter charge need to be considered. The solvent and electrolyte description are limited by the computational power: either molecules and ions are included explicitly, but the phase-space sampling is at least 10 times too small to reach convergence or implicit solvent and electrolyte descriptions are adopted which suffer from a lack of realism. Both approaches suffer from a lack of validation against directly comparable experimental data. Furthermore, the limitations of density functional theory in terms of accuracy are critical for these metal/liquid interfaces. Nevertheless, the atomistic insight in electrocatalytic interfaces allow insights with unprecedented details. The joint theoretical and experimental efforts to design non-noble hydrogen evolution catalysts are discussed as an example for the success of theory to spur and accelerate experimental discoveries.

The Sabatier Principle in Electrocatalysis: Basics, Limitations, and Extensions

“…Currently, continuum solvation models such as Vaspsol (Mathew et al, 2014(Mathew et al, , 2019, COSMO (Klamt and Schüürmann, 1993), or Jaguar (Bochevarov et al, 2013) are commonly used to describe solvation at the electrode/electrolyte interface (Abidi et al, 2020;Basdogan et al, 2020b;Groß, 2020). However at least in the case of the intermediates relevant to the ORR and CO 2 reduction reactions on Cu, Au, and Pt, the widely used continuum solvation models did not improve the accuracy of binding energies compared to the respective calculations in vacuum (Heenen et al, 2020).…”

“…Experimental conditions, however, correspond to a grand canonical ensemble where the electrode potential is fixed instead of the charge. Recent progress in this field put forth grand canonical models beyond the CHE method (Hansen and Rossmeisl, 2016;Hörmann et al, 2019Hörmann et al, , 2020Abidi et al, 2020), allowing the electrode potential to be explicitly included into the DFT calculations (Govind Rajan et al, 2020;Groß, 2020). Yet, a limitation of this approach is that the outcome may severely depend on the chosen value for the proton/hydrogen work function, for which values between 3.9 eV and 4.7 eV have been reported in the literature (Busch et al, 2020;Bhattacharyya et al, 2021).…”

Room‐Temperature Sodium–Sulfur Batteries and Beyond: Realizing Practical High Energy Systems through Anode, Cathode, and Electrolyte Engineering

“…For instance, DFT calculations are first performed for materials with potential polysulfide confinement and/or catalytic properties. [ 221–223 ] Electrochemical tests are then carried out, with the reaction mechanisms probed in operando using techniques such as in situ Raman spectroscopy and synchrotron X‐ray diffraction (XRD). [ 134,141,142,224 ] The mechanistic insights gleaned then serve as input for improving subsequent iterations.…”

Reversible catalysis

“…From a Tafel plot of η against log(i), extrapolating the current measured at high overpotential down to η=0 gives the exchange current i 0 . Another measurement of the surface's activity is the "onset overpotential" defined as the overpotential above which the current exceeds an arbitrarily chosen threshold (often 10 mA/cm 2 for OER and HER 74,75 ). The exchange current and the onset potential (of e.g.…”