Cho Kang Rae, Kim Minhye, Kim Bupmo, Shin Gahye, Lee Sangkyu, Kim Wooyul
Department of Energy Engineering/KENTECH Institute for Environmental and Climate Technology, Korea Institute of Energy Technology (KENTECH), Naju 58330, Republic of Korea.
Department of Chemical Engineering & Division of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, Republic of Korea.
ACS Omega. 2022 Jun 24;7(29):25110-25121. doi: 10.1021/acsomega.2c01481. eCollection 2022 Jul 26.
One of the most widely used electric field sensors for low-frequency electric field detection (LFEFD) in seawater uses the Ag/AgCl electrode. The surface structure of the electrode including AgCl layers plays a critical role in the electrode's electrochemical performance required for the sensor. In this study, the sequential AgCl formation process under the constant current was examined on the Ag wire in an electrode size for actual applications, and an optimal electrode surface structure was suggested for the LFEFD Ag/AgCl sensor. Upon mild anodization (0.2 mA/cm) in 3.3 M KCl solution that permits us to follow the AgCl formation process manageably, Ag dissolution from the wire surface begins leaving cavities on the surface, with the accompanied growth of initial Ag grains. During this period, AgCl deposits in sizes of about several micrometers to 10 μm with crystal planes also form primarily along scratch lines on the wire surface, but in a partial scale. Then, with further anodization, the assumed thin AgCl deposits start to form, covering a large portion of the wire surface. They grow to become deposits in sizes of about several micrometers to 10 μm with no clear facet planes next to one another and are connected to form the network structure, representing the main developing mode of the AgCl deposits. While they cover all the surface, AgCl deposits also form on the surface of the already formed ones, making multiple AgCl layers. All these deposits develop through the nucleation process with a relatively high surface energy barrier, and their formation rate is solely controlled by the release rate of Ag from the wire, thus by the applied current magnitude. The Ag/AgCl electrode with a thick AgCl layer and many holes in the AgCl surface structure like microchannels is considered to work effectively for the LFEFD sensor in terms of both detection sensitivity and service lifetime.
用于海水中低频电场检测（LFEFD）的最广泛使用的电场传感器之一采用Ag/AgCl电极。包括AgCl层在内的电极表面结构对传感器所需的电极电化学性能起着关键作用。在本研究中，在实际应用的电极尺寸的银线上研究了恒流下连续AgCl的形成过程，并为LFEFD Ag/AgCl传感器提出了最佳电极表面结构。在3.3 M KCl溶液中进行温和阳极氧化（0.2 mA/cm），这使我们能够可控地跟踪AgCl的形成过程，银从导线表面溶解开始在表面留下空洞，同时初始银晶粒生长。在此期间，尺寸约为几微米到10μm的AgCl沉积物也主要沿着导线表面的划痕线形成，但只是部分形成。然后，随着进一步阳极氧化，假定的薄AgCl沉积物开始形成，覆盖导线表面的大部分。它们生长成为尺寸约为几微米到10μm的沉积物，彼此之间没有清晰的晶面，并连接形成网络结构，这代表了AgCl沉积物的主要发展模式。当它们覆盖所有表面时，AgCl沉积物也在已经形成的沉积物表面形成，形成多个AgCl层。所有这些沉积物都通过具有相对较高表面能垒的成核过程形成，它们的形成速率仅由银从导线中的释放速率控制，从而由施加的电流大小控制。具有厚AgCl层且AgCl表面结构中有许多如微通道般孔洞的Ag/AgCl电极，在检测灵敏度和使用寿命方面被认为对LFEFD传感器有效工作。
