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Potential response of single successive constant-current-driven electrolytic hydrogen bubbles spatially separated from the electrode
Electrochimica Acta ( IF 6.6 ) Pub Date : 2022-06-11 , DOI: 10.1016/j.electacta.2022.140691
Akash Raman, Pablo Peñas, Devaraj van der Meer, Detlef Lohse, Han Gardeniers, David Fernández Rivas

The presence of bubbles in gas-evolving electrolytic processes can heavily alter the mass transport of gaseous products and can induce severe overpotential penalties at the electrode through the action of bubble coverage (hyperpolarization) and electrolyte constriction (Ohmic shielding). However, bubble formation can also alleviate the overpotential by lowering the concentration of dissolved gas in the vicinity of the electrode. In this study, we investigate the latter by considering the growth of successive hydrogen bubbles driven by a constant current in alkaline-water electrolysis and their impact on the half-cell potential in the absence of hyperpolarization. The bubbles nucleate on a hydrophobic cavity surrounded by a ring microelectrode which remains free of bubble coverage. The dynamics of bubble growth does not adhere to one particular scaling law in time, but undergoes a smooth transition from pressure-driven towards supply-limited growth. The contributions of the different bubble-induced phenomena leading to the rich behaviour of the periodic fluctuations of the overpotential are identified throughout the different stages of the bubble lifetime, and the influence of bubble size and applied current on the concentration and Ohmic overpotential components is quantified. We find that the efficiency of gas absorption, and hence the concentration-lowering effect, increases with increasing bubble size and also with increasing current. However, the concentration-lowering effect is always eventually countered and overcome by the effect of Ohmic shielding as the bubble size outgrows and eclipses the electrode ring beneath.



中文翻译:

与电极空间分离的单个连续恒流驱动电解氢气泡的电位响应

气体演化电解过程中气泡的存在会严重改变气态产物的质量传输,并通过气泡覆盖(超极化)和电解质收缩(欧姆屏蔽)的作用在电极处引起严重的过电位损失。然而,气泡的形成也可以通过降低电极附近溶解气体的浓度来缓解过电位。在本研究中,我们通过考虑碱性水电解中由恒定电流驱动的连续氢气泡的生长及其在没有超极化的情况下对半电池电位的影响来研究后者。气泡在被保持无气泡覆盖的环形微电极包围的疏水空腔上成核。泡沫增长的动态不会及时遵循特定的比例定律,而是经历了从压力驱动向供应受限增长的平稳过渡。在气泡寿命的不同阶段确定了导致过电位周期性波动的丰富行为的不同气泡诱导现象的贡献,并量化了气泡尺寸和施加电流对浓度和欧姆过电位分量的影响. 我们发现,气体吸收的效率,因此降低浓度的效果,随着气泡尺寸的增加和电流的增加而增加。然而,随着气泡尺寸过大并遮盖下方的电极环,欧姆屏蔽效应最终会抵消和克服浓度降低效应。

更新日期:2022-06-13
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