On the importance of the electric double layer structure in aqueous electrocatalysis

Abstract

To design electrochemical interfaces for efficient electric-chemical energy interconversion, it is critical to reveal the electric double layer (EDL) structure and relate it with electrochemical activity; nonetheless, this has been a long-standing challenge. Of particular, no molecular-level theories have fully explained the characteristic two peaks arising in the potential-dependence of the EDL capacitance, which is sensitively dependent on the EDL structure. We herein demonstrate that our first-principles-based molecular simulation reproduces the experimental capacitance peaks. The origin of two peaks emerging at anodic and cathodic potentials is unveiled to be an electrosorption of ions and a structural phase transition, respectively. We further find a cation complexation gradually modifies the EDL structure and the field strength, which linearly scales the carbon dioxide reduction activity. This study deciphers the complex structural response of the EDL and highlights its catalytic importance, which bridges the mechanistic gap between the EDL structure and electrocatalysis.

A unifying mechanism for cation effect modulating C1 and C2 productions from CO2 electroreduction

“…The availability of simulations at full length- and time-scales is critical to unbiasedly confirm the possible coordinating ability of electrolyte constituents to the intermediate species since it can provide the full equilibrium-dynamic structure of the electrolyte phase without the influence of initial conditions. Most importantly, we note that the DFT-CES succeeded in unraveling the atomic origin of the famous camel-shaped behavior of the EDL capacitance, confirming its accuracy in describing the EDL structural details 30 .…”

“…chemisorbed water, Helmholtz ions, etc.) at the buried nanoscale region, which can affect the catalytic reactions under the actual electrochemical conditions 30 , 38 – 44 . Compared with the AIMD simulation, often used for modeling the electrochemical interfaces, the DFT-CES enables to investigate electrolyte phase dynamics with many more atoms over a more extended time-scale; multi-thousands of atoms over a few nanoseconds using the DFT-CES vs .…”

“…Herein, we investigate the cation-controlled mechanism by reflecting more practical electrolysis conditions via full-equilibrium simulations and flow-type-electrolyzer experiments with gas diffusion electrodes (GDE). Using a quantum-mechanics-based multiscale simulation, offering an accurate description on the EDL structure at atom-scale 30 , we mapped out the cation-coordinating ability to all possible intermediates and established corresponding reaction energy profiles for CO, CH 4 , and C 2 H 4 productions. The suggested different nature of RDSs, either a cation-coupled electron transfer (CCET) step for CO and C 2 H 4 productions or a PCET for CH 4 production, was corroborated by our experiments widely varying the M + concentrations and identities.…”

Modelling of Electrocatalytic Double Layers with Refined Treatment of Metal-Water Interactions and Chemisorption

“…There is a wave of renewed interest in the double layer structure in electrocatalysis, [1][2][3][4] probably due to two reasons. First, a multitude of electrolyte effects, such as the cation effect [5][6][7][8][9] and the pH effect [10][11][12][13], emerge recently in electrocatalysis, and there is growing consensus that demystifying these electrolyte effects requires fundamental knowledge of the double layer structure.…”

“…First, a multitude of electrolyte effects, such as the cation effect [5][6][7][8][9] and the pH effect [10][11][12][13], emerge recently in electrocatalysis, and there is growing consensus that demystifying these electrolyte effects requires fundamental knowledge of the double layer structure. [3,14] Several review articles on electrolyte effects in electrocatalysis have been published recently. [14][15][16][17] Second, a growing body of experimental data related to the double layer structure of single crystals of transition metals, notably platinum, have been reported recently.…”