Structure-Dependent Electrical Double-Layer Capacitances of the Basal Plane Pd(hkl) Electrodes in HClO₄

Abstract

Electrical double-layer capacitance (C DL) measurements are among the key experiments in physical electrochemistry aimed to understand the properties of electrified solid/liquid interfaces. C DL serves as a critical parameter for developing physical models of electrochemical interfaces. Palladium (Pd) electrodes are among the most widely used functional materials in many applications, including (electro)­catalysis. In this work, we report on double-layer capacitances of the basal plane Pd(111), Pd(100), and Pd(110) electrodes in aqueous HClO4 electrolytes measured using electrochemical impedance spectroscopy. Importantly, we find that the C DL values estimated at the minima of the capacitance vs electrode potential curves can be correlated with the density-functional-theory (DFT)-calculated adsorption energies for water molecules and the coordination of electrode surface atoms. Our results thus suggest that it might be possible to find simple descriptors of the electrical double layer (EDL) analogous to those used for functional electrode materials. Taken together, such descriptors could be employed for efficient high-throughput screening of various electrode/electrolyte interfaces, such as in supercapacitor and electrocatalytic systems.

Subsurface Hydride Formation Leads to Slow Surface Adsorption Processes on a Pd(111) Single-Crystal Electrode in Acidic Electrolytes

“…Figure shows the dependence of the parameters R S , R ads,CT , R abs,CT , C DL , and C ads on the electrode potential in 0.05 M H 2 SO 4 . Figures and S7 show the solution resistance, R S , is independent of the applied potential and is 130 and 185 Ω in 0.05 M H 2 SO 4 and 0.1 HF, respectively The double layer capacitance, C DL , varies little around 10 ± 2 and 30 ± 5 μF cm –2 for 0.05 M H 2 SO 4 and 0.1 M HF solutions, respectively, in rather good agreement with recent studies on double layer capacitances of Pd(111) electrodes . Consistent with the blank voltammogram result in Figures a and S6a, Figures and S7 show the adsorption capacitance, C ads , increases to 189 μF cm –2 in the (bi)­sulfate/hydrogen adsorption region (0.27 V RHE ) and 215 μF cm –2 in the fluoride/hydrogen adsorption region (0.33 V RHE ), respectively.…”

“…Figures 6 and S7 show the solution resistance, R S , is independent of the applied potential and is 130 and 185 Ω in 0.05 M H 2 SO 4 and 0.1 HF, respectively The double layer capacitance, C DL , varies little around 10 ± 2 and 30 ± 5 μF cm −2 for 0.05 M H 2 SO 4 and 0.1 M HF solutions, respectively, in rather good agreement with recent studies on double layer capacitances of Pd(111) electrodes. 39 Consistent with the blank voltammogram result in Figures 5a and S6a, Figures 6 and S7 show the adsorption capacitance, C ads , increases to 189 μF cm −2 in the (bi)sulfate/hydrogen adsorption region (0.27 V RHE ) and 215 μF cm −2 in the fluoride/hydrogen adsorption region (0.33 V RHE ), respectively. Figure 6 shows a broad relatively potential independent plateau on the curve of the hydrogen absorption resistance, R abs,CT , and increase of sulfate anion adsorption charge transfer resistance, R ads,CT , with potential, respectively, in the potential region of (bi)sulfate S9c), close to the value of 0.5 corresponding to a diffusion process.…”

“…A great deal of knowledge has been gathered about the chemical species responsible for the well-defined and reproducible voltammetric profile of single-crystal Pt-group metal electrodes . However, there are very few detailed studies on the reversible H upd and anion adsorption processes on Pd single-crystal electrodes . These studies often assume that perchlorate electrolytes are nonadsorbing, as for Pt.…”

Impact of Pt(hkl) Electrode Surface Structure on the Electrical Double Layer Capacitance

“…In other words, one can use GCNs to characterize and quantify the affinity of the surface for electrolyte components. In Figure 3, the C DL, min ′ values extracted from Figure 2A are plotted versus the special parameter explained as follows (see the description for this parameter and its meaning in the SI, Figure S1, and ref 17). Consider that the GCN can be understood as a measure of "nonsaturated electron density" at the surface.…”

“…For instance, it is necessary to maximize the EDL capacitances in supercapacitors or to normalize the electrocatalytic activity for energy conversion and storage devices. 12−16 Among other groups, we have recently reported that model Pt, Pd, Cu, and Au electrodes demonstrate a somewhat counterintuitive dependence of EDL capacitances on the structure of the electrode surface, 17 its chemical nature, and the nature of the alkali metal cations present in the electrolyte. 18,19 For example, we demonstrated that for both Pt(111) and Au(111) in 0.05 M AMClO 4 (AM = Li + , Na + , K + , Rb + , Cs + ), the EDL capacitance depends linearly on the hydration energy of the alkali metal cation, with the higher hydration energies corresponding to the lower EDL capacitances close to the potential of zero charge (PZC).…”