Electrolyte-Dependent Oxygen Evolution Reactions in Alkaline Media: Electrical Double Layer and Interfacial Interactions

Abstract

Traditional understanding of electrocatalytic reactions generally focuses on either covalent interactions between adsorbates and the reaction interface (i.e., electrical double layer, EDL) or electrostatic interactions between electrolyte ions. Here, our work provides valuable insights into interfacial structure and ionic interactions during alkaline oxygen evolution reaction (OER). The importance of inner-sphere OH − adsorption is demonstrated as the IrO x activity in 4.0 M KOH is 6.5 times higher than that in 0.1 M KOH. Adding NaNO 3 as a supporting electrolyte, which is found to be inert for long-term stability, complicates the electrocatalytic reaction in a half cell. The nonspecially adsorbed Na + in the outer compact interfacial layer is suggested to form a stronger noncovalent interaction with OH − through hydrogen bond than adsorbed K + , leading to the decrease of interfacial OH − mobility. This hypothesis highlights the importance of outer-sphere adsorption for the OER, which is generally recognized as a pure inner-sphere process. Meanwhile, based on our experimental observations, the pseudocapacitive behavior of solid-state redox might be more reliable in quantifying active sites for OER than that measured from the conventional EDL charging capacitive process. The interfacial oxygen transport is observed to improve with increasing electrolyte conductivity, ascribing to the increased accessible active sites. The durability results in a liquid alkaline electrolyzer which shows that adding NaNO 3 into KOH solution leads to additional degradation of OER activity and long-term stability. These findings provide an improved understanding of the mechanistic details and structural motifs required for efficient and robust electrocatalysis.

Electrolyte Effects on the Electrocatalytic Performance of Iridium‐Based Nanoparticles for Oxygen Evolution in Rotating Disc Electrodes

“…For the OER, previous studies have shown that the presence of different cations in the electrolyte can have an important effect in the catalytic performance of different transition oxide materials including IrO x. …”

Comprehensive impedance investigation of low-cost anion exchange membrane electrolysis for large-scale hydrogen production

“…Upon the application of higher voltage, the electrons try to flow through the external circuit and the OHions attempt to cross the AEM. However, due to internal barriers, the electrons and OHions are not able to transfer at lower voltages 24 . Hence, there is a decrease in hydrogen production due to the voltage drop-this is referred to as the activation overpotential or charge transfer resistance (R CT ).…”

Elucidating the Performance Limitations of Alkaline Electrolyte Membrane Electrolysis: Dominance of Anion Concentration in Membrane Electrode Assembly

“…In the assignment of the charge transfer resistances this indicates a decreased activity of OER with increasing KOH concentration. However, it is to be supposed that both HER and OER kinetic improve with increasing the KOH concertation, which should result in a reduction in activation loss . This surprising observation for the OER can be explained when considering that increasing concentration of KOH also leads to an increased viscosity, which influences hydrodynamic transport properties, like diffusion, convection, but also bubble formation and bubble detachment .…”