[论文解读] Coalescence induced late departure of bubbles improves water electrolysis efficiency

Tao Wu, Bo Liu+5 more|arXiv (Cornell University)|Feb 9, 2024

Minerals Flotation and Separation TechniquesEnvironmental Science被引用 3

一句话总结

本研究证明，在水电解中促进气泡聚结可使效率提高30%以上，通过持续与微气泡合并来延迟气泡脱离。该过程将电极上的气泡尺寸减小至10 μm以下，并引发强烈且局部的扰动（最高达1 m/s），持续约10 ms，显著改善传质与传热，同时释放出活性催化位点。

ABSTRACT

In water electrolysis, bubbles form on the electrode and interact through processes such as collision and coalescence. However, the impact of bubble coalescence a fundamental process governing electrolytic bubble behaviour-on electrolysis efficiency remains unclear. Here, we show that enhancing bubble coalescence improves electrolysis efficiency by more than 30% compared to systems where coalescence is inhibited. One key feature is the continuous coalescence of a newly detached bubble with microbubbles on the electrode, which delays the former from departing. Experimental observations and numerical simulations reveal two key benefits of bubble coalescence for electrolysis efficiency: (1) it liberates surface bubbles from the electrode at much smaller sizes, reducing their diameter from approximately 60-80 um to less than 10 um, thus freeing the active sites of the electrode from bubble coverage; (2) it induces strong agitation, with velocities reaching 1m/s in a small region near the electrode (at a depth of 10-5 m), thereby significantly improving the heat/mass transfer locally. Importantly, the chaotic agitation effect lasts for approximately 10 ms, two orders of magnitude longer than the coalescence process, which occurs in around 0.2 ms. This work provides valuable insight into bubble management in water electrolysis and other gas-evolution electrochemical reactions.

研究动机与目标

• 研究气泡聚结对水电解效率的影响。
• 理解气泡动力学（尤其是聚结）如何影响电极表面覆盖率与传质。
• 探讨气泡诱导的扰动在增强电极表面附近局部传热与传质中的作用。
• 通过调控气泡聚结行为，开发提升电解效率的策略。

提出的方法

• 在受控电解装置中开展实验，观察电极上气泡的生成、聚结与脱离动力学。
• 采用高速成像技术捕捉气泡行为，并量化脱离时间与气泡尺寸。
• 进行数值模拟，以模拟电极表面附近的气泡聚结与流场分布。
• 分析流速场，评估聚结引发的扰动强度与持续时间。
• 对比聚结增强与聚结抑制的系统，以分离其对效率的影响。
• 在模拟中使用表面张力与流体动力学力，预测气泡脱离行为。

实验结果

研究问题

• RQ1 在水电解中，气泡聚结如何影响气泡从电极表面脱离的尺寸与时间？
• RQ2 聚结引发的扰动对电极附近电解质中局部传热与传质有何影响？
• RQ3 聚结如何通过减少气泡覆盖度来影响电极上活性位点的可及性？
• RQ4 气泡聚结引发的流体扰动的持续时间与强度如何？
• RQ5 与抑制聚结的系统相比，促进聚结在多大程度上提升了整体电解效率？

主要发现

• 增强气泡聚结使电解效率相比聚结被抑制的系统提高了30%以上。
• 气泡聚结将表面气泡直径从约60–80 μm降低至10 μm以下，显著减少了电极覆盖度。
• 聚结引发的扰动在电极表面附近10–5 m深度区域达到最高1 m/s的流速。
• 混沌扰动效应持续约10 ms，比聚结过程本身（约0.2 ms）长两个数量级。
• 由于聚结导致气泡脱离延迟，电极上的活性催化位点得以更有效地释放，从而改善反应动力学。
• 数值模拟证实，聚结通过产生瞬态的高速流体流动，增强了局部传质。