Magnetic field-driven enhancement of hydrogen production in water electrolysis

能源生产的最新发展旨在增加可再生资源的应用。从这个角度来看，水电解制氢是一项有趣的技术，因为它可以将太阳能电池或风力发电厂提供的能量转化为可储存的化学燃料，进而可能被用来驱动环境友好型燃料电池设备。然而，为了达到这一目的，必须提高电解水的效率，目前碱性水的电解率约为65%。电解水效率低的一个主要原因是电解液中的高欧姆降，这是由产生的不导电氢气泡引起的。氢泡仍然附着在电极上，质子的还原会产生氢泡，阻碍电极，从而通过减少有效电极面积而额外降低效率。在这个项目中，我们的目标是通过施加磁场来减少形成的氢气泡的负面影响，从而提高水的电解效率。它们将由简单的商用NdFeB永磁体产生，众所周知，这种永磁体会在每个气泡周围诱导洛伦兹力驱动的磁流体(MHD)流动。这种流动作用于不同的长度尺度，并可增强电极上气泡的去除。本项目将通过精心设计的系统实验研究来研究这一点。不同电催化和磁性(金、铂、镍)和可变设计的电极将通过循环伏安、噪声谱和电阻抗谱从根本上研究气泡的成核、生长和合并的电化学行为。借助光学显微镜，可以通过测量气泡直径和接触角随时间的变化来表征氢气泡的生长，直到气泡脱离。同时，磁流体在气泡周围的旋转流动将通过粒子图像测速仪进行测量。与单个气泡相比，氢气泡及其相关流动系统之间的相互作用将如何改变脱离现象，这一点将受到特别关注。此外，还将在电解液中添加表面张力降低的添加剂，以进一步改善电极的气泡释放。此外，本项目还将分析磁梯度场对气泡管理可能产生的有利影响。电化学和光学测量的结果将在共同的背景下考虑，以全面了解磁场对水电解的影响。

Recent developments in energy production aim to increase the application of renewable resources. In this perspective, hydrogen production by water electrolysis is an interesting technology, as it may convert the energy supplied by solar cells or wind mills to a storable chemical fuel, which in turn might be utilized to drive environmentally friendly fuel cell devices. However, for this purpose the efficiency of water electrolysis, which is currently about 65 % for alkaline water electrolysis, has to be improved. A main reason for this low efficiency of water electrolysis, is the high ohmic drop in the electrolyte, which is caused by the produced non-conductive hydrogen gas bubbles. Hydrogen bubbles that remain attached to the electrode, where the reduction of protons generates them, block the electrode and thus additionally decrease the efficiency by reducing the effective electrode area. In this project, we aim to increase the water electrolysis efficiency by reducing the negative effects of the formed hydrogen bubbles via application of magnetic fields. These will be generated by simple commercial NdFeB permanent magnets which are known to induce a Lorentz-force-driven Magnetohydrodynamic (MHD) flow around each bubble. This flow acts on different length scales and may enhance the bubble removal from the electrode. This will be studied in this project by means of carefully designed systematic experimental investigations.Electrodes of different electrocatalytic and magnetic properties (Au, Pt, Ni) and variable design will be used to study the electrochemical behavior fundamentally by means of cyclovoltammetry, noise spectra and electrical impedance spectroscopy with respect to nucleation, growth and coalescence of the bubbles. By means of optical microscopy, the growth of hydrogen bubbles will be characterized by measuring e.g. bubble diameter and contact angle versus time until the bubble detaches. In parallel, the MHD swirling flows around the bubbles, will be measured by particle image velocimetry. Particular attention will be paid on how the interaction between the hydrogen bubbles and their associated flow systems will change the detachment compared to single bubbles. Additionally, surface-tension-lowering additives will be added to the electrolyte to further improve the bubble release from the electrode. Also the presumably beneficical impact of magnetic gradient fields on the bubble management will be analysed within this project. The results of electrochemical and optical measurement will be considered in a common context to gain a comprehensive understanding of the magnetic fields effects on water electrolysis.