The Role of the Double Layer for the Pseudocapacitance of the Hydrogen Adsorption on Platinum

Abstract

Pseudocapacitances such as the hydrogen adsorption on platinum (HAoPt) are associated with faradaic chemical processes that appear as capacitive in their potentiodynamic response, which was reported to result from the kinetics of adsorption processes. This study discusses an alternative interpretation of the partly capacitive response of the HAoPt that is based on the proton transport of ad- or desorbed hydrogen in the double layer. Potentiodynamic perturbations of equilibrated surface states of the HAoPt lead to typical double layer responses with the characteristic resistive-capacitive relaxations that overshadow the fast adsorption kinetics. A potential-dependent double layer representation by a dynamic transmission line model incorporates the HAoPt in terms of capacitive contributions and can computationally reconstruct the charge exchanged in full range cyclic voltammetry data. The coupling of charge transfer with double layer dynamics displays a novel physicochemical theory to explain the phenomenon of pseudocapacitance and the mechanisms in thereon based supercapacitors.

How microstructures, oxide layers, and charge transfer reactions influence double layer capacitances. Part 1: impedance spectroscopy and cyclic voltammetry to estimate electrochemically active surface areas (ECSAs)

“…26 After evaluating the physicochemical mechanisms of the double layer (DL) responses with the EIS measurements, the CV data is exemplarily compared to EIS data. A more detailed analysis of the CV response follows in the second part of this study, 51 while a full collection of the total CV data of all examined electrodes is given in the ESI, † including full range CVs of the examined electrodes between 0 and 0.6 V. The EIS data are displayed in Bode plots. Nyquist plots on the EIS data of all examined electrodes are supplied in the ESI † for more interested readers.…”

“…47,52,64 Towards increasing hole-depth and longer transmission lines the response becomes more resistive, as examined in detail in the second part of this article. 51 The graphite plate shows an approximately 190 times larger value for C À451 than that of the polished gold electrode, showing that the electrolyte uptake of the graphite plate significantly increases the ECSA. Like the type 1 glassy carbon specimen, the graphite plate shows a prominent increase of the capacitance below 1 Hz, which is attributed to capacitances of resistively damped microstructures.…”

“…However, this ECM is an oversimplification, as the DL shows a CPE characteristic and oxide layers leakage current, which is considered in the second part of this study in more detail. 51 Hence, the serial resistance of two capacitances described by eqn (10) shall here rather qualitatively describe that non-conducting oxide layers are expected to decrease the measured capacitances at the electrodes.…”

“…Such diffusion limitations of charge transfer reactions are typically described by CPEs, [57][58][59] as further evaluated in the second part of this study. 51 After the measurements of the gold electrode were completed in perchloric acid, the same electrode is subsequently examined with EIS and CV in nitrogen purged 1 M sodium hydroxide electrolyte without any polishing in between. With reference to Table 1, the value of the serial resistance R s,fit is approximately 2-times larger while that of C À451 is 1.6-times larger in the alkaline electrolyte than that in the acidic electrolyte.…”

“…The CPE-based ECM for the DL can be transformed from the frequency domain into the time domain or vice versa, [25][26][27][68][69][70][71] as discussed in the second part of this study in more detail. 51 The maximum frequency that is obtainable during CV is limited by the smallest possible amplitude and the highest possible scan rate of the used potentiostat, as visualized in Fig. 1B.…”