Experimental Measurement of Overpotential Sources during Anodic Gas Evolution in Aqueous and Molten Salt Systems

Abstract

Current interrupt and galvanostatic EIS techniques were utilized in a complementary fashion to characterize the different sources of overpotential during anodic gas evolution. Room temperature anodic evolution of oxygen at a nickel working electrode in aqueous potassium hydroxide and the high temperature (348°C) anodic evolution of chlorine at a glassy carbon working electrode in molten (LiCl) 57.5 -(KCl) 13.3 -(CsCl) 29.2 where investigatd. Combining of the two techniques enables to separate the total measured overpotential into its ohmic, charge transfer, and mass transfer components. Potential decay curves indicated that natural convection (due to both bubble evolution and density driven flow) was a major driving force in reestablishing equilibrium conditions at the working electrode surface. During oxygen evolution, charge transfer resistance dominated the total overpotential at low current densities, but as the current density approached ∼100mA/cm 2 , mass transfer overpotentials and ohmic overpotential became non-negligible. The mass transfer overpotential during chlorine evolution was found to be half that found during oxygen evolution.

Potential response of single successive constant-current-driven electrolytic hydrogen bubbles spatially separated from the electrode

“…On the contrary, it has been recently shown that bubbles growing directly on electrode surfaces (note that this is not the case in the system used in this study) can act as ion conduction pathways themselves [48][49][50]. Although the separation of the concentration and hyperpolarization overpotentials has been quantified for other electrochemical systems with larger electrodes and stochastic bubble generation [51,52], the effect of single bubbles on the individual overpotential components still remains elusive. In this study, we aim to bridge this gap by observing successive electrolytic bubbles in a recent cell design where the site of bubble nucleation is separated from the site of gas generation.…”

Structural Evolution and Durability of Ultrafine NiFe Phosphide Nanoparticle/Carbon Composite Films in Water Oxidation at High Current Densities

“…The attachment of gas bubbles on the electrode surface is known to cause an additional overpotential on top of the prediction by electrochemical kinetics due to the reduced accessible surface . Such an effect has been proven significant above j ≈ 100 mA cm –2 in alkaline OER, and at these current densities, the Ohmic potential drop also increases as ion conduction near the electrode surface is restricted . The bubble coverage is negatively correlated to the hydrophilicity of the surface.…”

“…51 Such an effect has been proven significant above j ≈ 100 mA cm −2 in alkaline OER, and at these current densities, the Ohmic potential drop also increases as ion conduction near the electrode surface is restricted. 52 The bubble coverage is negatively correlated to the hydrophilicity of the surface. For the NiFe-P films, the carbonaceous matrix formed at higher ϕ is hydrophobic, as shown by the water contact angle of the films in Figure S22.…”

Coordination Chemistry Engineered Polymeric Carbon Nitride Photoanode with Ultralow Onset Potential for Water Splitting

“…For a given semiconductor‐based photoanode with a certain electronic band structure, the E onset is solely dependent on the overpotential in PEC process, [14] which includes ohmic, kinetic, and mass transfer overpotentials [15] . Reducing the ohmic overpotential (i.e.…”