Molecular origin of negative component of Helmholtz capacitance at electrified Pt(111)/water interface

Abstract

Electrified solid/liquid interfaces are the key to many physicochemical processes in a myriad of areas including electrochemistry and colloid science. With tremendous efforts devoted to this topic, it is unexpected that molecular-level understanding of electric double layers is still lacking. Particularly, it is perplexing why compact Helmholtz layers often show bell-shaped differential capacitances on metal electrodes, as this would suggest a negative capacitance in some layer of interface water. Here, we report state-of-the-art ab initio molecular dynamics simulations of electrified Pt(111)/water interfaces, aiming at unraveling the structure and capacitive behavior of interface water. Our calculation reproduces the bell-shaped differential Helmholtz capacitance and shows that the interface water follows the Frumkin adsorption isotherm when varying the electrode potential, leading to a peculiar negative capacitive response. Our work provides valuable insight into the structure and capacitance of interface water, which can help understand important processes in electrocatalysis and energy storage in supercapacitors.

Modeling Electrified Pt(111)-Had/Water Interfaces from Ab Initio Molecular Dynamics

“…The red curve is taken from the recent work. 29 The insets show the change of the structure of interface water in response to the electrode potential on the Pt(111) and Pt(111)-H ad surface. The red, white, and orange balls represent the O, H w , and H ad atom, respectively.…”

“…Similar EDL models have been successfully used to simulate the Au(111) and Pt(111)/water interfaces. 5 , 29 …”

Probing Interfacial Electronic Effects on Single‐Molecule Adsorption Geometry and Electron Transport at Atomically Flat Surfaces

“…Chemisorbed water can induce significant interfacial electronic structural changes, [17] thus,w eu sed ah ybrid ILbased electrolyte with varied concentrations of added water to modulate the adsorption geometry of 4,4'-BPY.F irst, we performed SM measurements of 4,4'-BPY SAMs on Au(111) in pure BMIPF 6 with STM-BJ.T hen different amounts of water were added to the electrolyte in situ to study interfacial effects on the 4,4'-BPY binding configuration in the molecular junction. As shown in Figure 2a,I Le lectrolytes with added water volume ratios (V H 2 O %) of less than 10 %o nly have one distinct conductance peak, while two peaks appear at 10 À3.3 G 0 (H), and 10 À3.9 G 0 (L)w hen V H 2 O %i ncreases to 20 %a nd above (Figure S5).…”

Origin of Asymmetric Electric Double Layers at Electrified Oxide/Electrolyte Interfaces

“… 15 , 16 Nevertheless, the analysis and extraction of this microscopic interfacial information on EDL is rather difficult if not impossible. 17 − 19 …”