Dynamic potential–pH diagrams application to electrocatalysts for wateroxidation

Abstract

The construction and use of ''dynamic potential-pH diagrams'' (DPPDs), that are intended to extend the usefulness of thermodynamic Pourbaix diagrams to include kinetic considerations is described. As an example, DPPDs are presented for the comparison of electrocatalysts for water oxidation, i.e., the oxygen evolution reaction (OER), an important electrochemical reaction because of its key role in energy conversion devices and biological systems (water electrolyses, photoelectrochemical water splitting, plant photosynthesis). The criteria for obtaining kinetic data are discussed and a 3-D diagram, which shows the heterogeneous electron transfer kinetics of an electrochemical system as a function of pH and applied potential is presented. DPPDs are given for four catalysts: IrO 2 , Co 3 O 4 , Co 3 O 4 electrodeposited in a phosphate medium (Co-Pi) and Pt, allowing a direct comparison of the activity of different electrode materials over a broad range of experimental conditions (pH, potential, current density). In addition, the experimental setup and the factors affecting the accurate collection and presentation of data (e.g., reference electrode system, correction of ohmic drops, bubble formation) are discussed.

Water Oxidation at Electrodes Modified with Earth‐Abundant Transition‐Metal Catalysts

“…Bard et al compared Co3O4 and CoPi using dynamic potential-pH diagrams. [ 60 ] The overall higher activity of CoPi was attributed to higher hydration, leading to an increase in the number of accessible sites. [61] On the other hand, CoPi showed a significant decrease of current at high current densities.…”

Template synthesis of 3-DOM IrO2 powder catalysts: temperature-dependent pore structure and electrocatalytic performance

“…The good common practice in electrocatalysis requests that all potentials are referred to the reversible hydrogen electrode (RHE). This is even more important in the case of OER since its equilibrium potential (referred to the standard hydrogen electrode, SHE) depends on the pH with a slope equal to 0.059 V/pH at 25°C, while the potential (referred to RHE) is independent of the pH of the supporting electrolyte [27]. So the potentials mentioned herein are all adjusted relative to the potential of RHE.…”

The cavity-microelectrode as a tip for scanning electrochemical microscopy

“…for screening of oxygen reduction catalysts) we tested a Co 3 O 4 -filled C-ME tip for the oxygen evolution reaction (OER). The choice of Co 3 O 4 comes from its well-recognized activity towards water oxidation in alkaline media [18].…”