Decoupling Gas Evolution from Water-Splitting Electrodes

Abstract

Bubbles are known to hinder electrochemical processes in water-splitting electrodes. In this study, we present a novel method to promote gas evolution away from the electrode surface. We consider a ring microelectrode encircling a hydrophobic microcavity from which a succession of bubbles grows. The ring microelectrode, tested under alkaline water electrolysis conditions, does not suffer from bubble coverage. Consequently, the chronopotentiometric fluctuations of the cell are weaker than those associated with conventional microelectrodes. Herein, we provide fundamental understanding of the mass transfer processes governing the transient behaviour of the cell potential. With the help of numerical transport models, we demonstrate that bubbles forming at the cavity reduce the concentration overpotential by lowering the surrounding concentration of dissolved gas, but may also aggravate the ohmic overpotential by blocking ion-conduction pathways. The theoretical and experimental insight gained have relevant implications in the design of efficient gas-evolving electrodes. File list (2) download file view on ChemRxiv RingElectrodesVSub.pdf (2.04 MiB) download file view on ChemRxiv RingElectrodesSIVSub.pdf (822.57 KiB)

Influence of Bubbles on the Energy Conversion Efficiency of Electrochemical Reactors

“…Bubbles preferentially nucleated on these hydrophobic sites, preventing the masking of the electrocatalytic area and in consequence removing completely their effect on the kinetic overpotential and significantly the ohmic overpotential. 134 In chronoamperometric experiment, periodic overpotential drops were found to correspond to each bubble evolution event, demonstrating the positive effect of bubbles as they act as gas reservoirs and decrease supersaturation levels near the electrode surface.…”

“…In yet another novel design, a ring microelectrode encircling a hydrophobic microcavity under alkaline water electrolysis conditions, was effective in avoiding bubble coverage. 134 The chronopotentiometric fluctuations of the cell were found to be weaker than in conventional microelectrodes. Numerical transport modeling helped explaining how bubbles forming at the cavity reduce the concentration overpotential by lowering the surrounding concentration of dissolved gas.…”

“…123,142 Furthermore, power spectral density (PSD) analysis can be used to estimate the size and rates of detaching bubbles by correlating the electrode area covered by a bubble to potential fluctuations by real-time measurements. 67,134,144 When oper n n ns re s e sys e e ves s " s s r", p en f ns r re r n erv s due the periodic formation, growth and detachment of bubbles. This allows for the study of the bubble dynamics through real time measurements of screening area, contact angle and potential.…”

Real‐Time Monitoring of Hydrogen Production by Water Electrolysis Using a Tapered Polarization‐Maintaining Optical Fiber Mach–Zehnder Interferometer

“…[4][5][6] However, gas bubbles tend to adsorb on the electrodes and occupy the active reaction sites, which seriously restrain the gas-evolving reactions by declining the efficiency of mass transfer and diffusion of the solid-gas-liquid interface. [7,8] Therefore, bubble monitoring and management on the electrode is significant for improving gas production efficiency and has aroused much attention.…”

Electrochemical Generation of Individual Nanobubbles Comprising H2, D2, and HD

“…The formation of bubbles at electrode surfaces during electrochemical gas-evolving reactions blocks the transport of reactants, deleteriously affecting the efficiency of electrochemical conversions. , A number of technologically important electrochemical processes involve gas-evolving reactions, including hydrocarbon and hydrazine fuel cells, − the chloralkali process, and water electrolysis. − Understanding and ultimately controlling the mechanism by which bubbles form is an active area of research. − …”