Determination of Electroactive Surface Area of Ni-, Co-, Fe-, and Ir-Based Oxide Electrocatalysts

Abstract

Metal oxides are important functional materials with a wide range of applications, especially in the field of electrocatalysis. However, quick and accurate assessment of their real electroactive surface area (ECSA), which is of paramount importance for the evaluation of their performance, remains a challenging task. Herein, we present a relatively simple strategy for an accurate in situ determination of the ECSA of commonly used metal oxide catalysts, namely Ni-, Co-, Fe-, Pt-, and Ir-based oxides. Similar to the well-established practice in electrocatalysis, the method is based on the phenomenon of specific adsorption. It uses the fact that at electrode potentials close to the onset of the oxygen evolution reaction, specifically adsorbed reaction intermediates manifest themselves through so called adsorption capacitance, which is unambiguously detectable using electrochemical impedance spectroscopy. We determined and calibrated these capacitances for common catalyst metal oxides using model thin films. Therefore, with simple impedance measurements, experimentalists can acquire the adsorption capacitance values and accurately estimate the real electroactive surface area of the above-mentioned oxide materials, including nanostructured electrocatalysts. Additionally, as illustrative examples, we demonstrate the application of the method for the determination of the ECSA of oxide catalyst nanoparticles.

Intrinsic Electrocatalytic Activity for Oxygen Evolution of Crystalline 3d‐Transition Metal Layered Double Hydroxides

“…Specific activities obtained by normalizing the current to the electrochemically active surface area (ECSA) can be used as alternative methods if the TOFs cannot be accurately calculated. For LDHs, the evaluation of the ECSA is not straightforward, due to 1) potential dependent changes of the electrical conductivity of LDHs, [33] 2) a narrow or non‐existing potential window that is free of faradaic current in the conductive regime, 3) metal oxidation peaks in cyclic voltammograms that overlap with the OER faradaic current, and 4) difficulties in obtaining model catalysts with smooth planar surfaces for the conversion of the calculated values, that is, capacitances, in the unit of an area [34] . Among the various methods to estimate the ECSA, we used the capacitance of the adsorbed OER intermediates ( C a ) that was calculated by electrochemical impedance spectroscopy (EIS) at 1.6 V RHE .…”

Intrinsic Electrocatalytic Activity for Oxygen Evolution of Crystalline 3d‐Transition Metal Layered Double Hydroxides

“…ForL DHs,t he evaluation of the ECSA is not straightforward, due to 1) potential dependent changes of the electrical conductivity of LDHs, [33] 2) anarrow or non-existing potential window that is free of faradaic current in the conductive regime,3 )m etal oxidation peaks in cyclic voltammograms that overlap with the OER faradaic current, and 4) difficulties in obtaining model catalysts with smooth planar surfaces for the conversion of the calculated values, that is,c apacitances,i nt he unit of an area. [34] Among the various methods to estimate the ECSA, we used the capacitance of the adsorbed OER intermediates (C a )t hat was calculated by electrochemical impedance spectroscopy (EIS) at 1.6 V RHE .T his potential is more anodic than the oxidation peak associated to the oxidation of Ni II and Co II ,in which NiM and CoM LDH become conductive. [11] The equivalent circuit which was used to fit the impedance data was adapted from Watzele and Bandarenka, [26] and previously introduced and discussed by Lyons and Brandon.…”

Recent Advances in the Understanding of Nickel-Based Catalysts for the Oxidation of Hydrogen-Containing Fuels in Alkaline Media

“…Recently, Watzele et al 125 proposed a yet another strategy to determine the ECSA of metal oxide catalysts…”