Department of Environmental Engineering, Inha University, Incheon, 22212, Republic of Korea.
School of Environmental Engineering, University of Seoul, Dongdaemun-gu, Seoul 02504, South Korea.
Environ Res. 2019 Jun;173:549-555. doi: 10.1016/j.envres.2019.03.069. Epub 2019 Mar 30.
For water electrolysis, a rare earth material (eg., platinum) is often used as an electrode, but because of the high cost and toxicity of chemicals, researchers are searching for cost effective and eco-friendly alternative materials. Various alloys and metals have been long explored for use as electrode materials in different media. Stainless steel (SS 304) electrodes are cost effective and have a large surface area; further their catalytic performance is comparable to that of carbon coated noble metals cathodes. Stainless steel has good mechanical properties and durability so it is widely used in desalination plants, oil and gas industries, ship building, etc. However, over a period of time it corrodes very quickly in saline water. To improve the stability and durability of the electrodes (i.e., to minimize corrosion), we anneal the samples under two different sets of conditions and test the electrodes in 3.5% NaCl solution. The anodic peak (-0.25 V) observed for bare stainless steel result from the formation of iron (II) hydroxide [Fe(OH)]. The Raman bands observed at 210 and 274 cm for bare stainless steel result from the formation of α-FeO owing to partial, anodic, and cathodic reactions occurring on the electrode which disrupts the surface layers. High intensity X-ray diffraction (XRD) and Raman peaks of CrO and MnCrO observed in argon and hydrogen annealed sample after cyclic voltammetry reveal that this sample is more stable than bare and air annealed samples. XRD reveals mixed oxide phases in addition to eskolaite and magnetite phases. Scanning electron microscope (SEM) images show that although the air-annealed sample has a soft, spongy structure, Na and Cl ions are adsorbed in the voids on the outer surface of the electrode leading to quick degradation. For the air-annealed sample the oxide appears to adhere poorly to the stainless steel. Oxygen (ie., oxide composition) may play a key role in adherence and growth of CrO formed at high temperature. X-ray photoelectron spectroscopy (XPS) reveals that large amounts of Cr and Mn are dissolved/corroded into the electrolyte for air annealed sample which is in good agreement with the Raman and SEM results.
对于水电解，通常使用稀土材料（例如铂）作为电极，但由于化学物质的成本和毒性较高，研究人员正在寻找具有成本效益和环保的替代材料。各种合金和金属已被长期探索用于不同介质中的电极材料。不锈钢（SS 304）电极具有成本效益且表面积大；此外，其催化性能可与涂覆碳的贵金属阴极相媲美。不锈钢具有良好的机械性能和耐用性，因此广泛用于海水淡化厂、石油和天然气行业、造船等领域。然而，在一段时间内，它在盐水中会迅速腐蚀。为了提高电极的稳定性和耐久性（即最大限度地减少腐蚀），我们在两组不同的条件下对样品进行退火，并在 3.5%NaCl 溶液中测试电极。裸不锈钢观察到的阳极峰（-0.25 V）是由于铁（II）氢氧化物[Fe(OH)]的形成。裸不锈钢的 210 和 274 cm 处的 Raman 带归因于α-FeO 的形成，这是由于电极上发生的部分阳极和阴极反应破坏了表面层。循环伏安法后氩气和氢气退火样品中观察到的 CrO 和 MnCrO 的高强度 X 射线衍射（XRD）和 Raman 峰表明，该样品比裸样和空气退火样更稳定。XRD 除了发现 Eskolaite 和磁铁矿相外，还揭示了混合氧化物相。扫描电子显微镜（SEM）图像表明，尽管空气退火样品具有柔软的海绵状结构，但 Na 和 Cl 离子会吸附在电极外表面的空隙中，导致快速降解。对于空气退火的样品，氧化物似乎与不锈钢的结合不良。氧（即氧化物组成）可能在高温下形成的 CrO 的附着和生长中起关键作用。X 射线光电子能谱（XPS）表明，大量的 Cr 和 Mn 溶解/腐蚀到空气退火样品的电解质中，这与 Raman 和 SEM 结果非常吻合。
