Scrutinizing the Basis of Pd Electrochemistry: An Accurate Assessment of the Electrochemically Active Surface Area

Abstract

Palladium nanoparticles supported on a pretreated carbon substrate (Pd/C) were synthesized from a surfactant-free microwave-heated ethylene glycol without any external reducing agent and characterized by high-resolution electron transmission microscopy, thermogravimetric analysis, and X-ray diffraction analysis. Cyclic voltammetry was effectively employed to scrutinize the electrochemical processes such as Pd hydrogen interactions including hydrogen adsorption, absorption, desorption, and hydrogen evolution as well as Pd–oxygen interactions like the oxide formation and the subsequent reduction of the oxide layer. The electrochemical oxidation of palladium was clearly indicated at the potential ranging from 0.78 to 1.20 V versus reversible hydrogen electrode (RHE) in the anodic scan direction whereas the corresponding reduction peak was observed with a broad peak centered at 0.79 V versus RHE in the reverse scan. Therefore, an accurate evaluation of the EASA measurements on ultrathin film palladium (Pd/C) electrodes in acidic (0.5 mol L⁻¹ H₂SO₄, pH ∼ 1) media was successfully conducted. Moreover, the steady-state cyclic voltammetry (CV) measurements have been conducted at the lowest scan rate of 1 mV s⁻¹, enabling obtaining of hydrogen adsorption, absorption, and desorption reaction features without concurrent. Besides, Pd/C electrocatalyst exhibited 129 mV overpotential yielding a cathodic current density of 10 mA cm⁻² toward hydrogen evolution reaction. This study outlines the description of practical experimental conditions essential for accurately determining the EASA that facilitates a comprehensive evaluation of their electrochemical performance.