Macedo David S, Vepsäläinen Mikko, Rodopoulos Theo, Peacock Stephen, Hogan Conor F
Mineral Resources, CSIRO, Melbourne, Victoria 3168, Australia.
Department of Biochemistry and Chemistry, La Trobe University, Melbourne, Victoria 3086, Australia.
Analyst. 2024 Oct 21;149(21):5225-5231. doi: 10.1039/d4an01076k.
Reference electrodes which demonstrate long-term potential stability are essential for many continuous monitoring applications and are commonly based on Ag|AgCl electrodes; however, these electrodes are susceptible to poisoning from aqueous sulphide species which are commonly present in wastewater and natural groundwater. This work presents a sulphide resistant solid-state reference electrode (SSRE) based on a composite material using suspended KCl electrolyte and sacrificial AgCl in a cross-linked polyvinyl acetate polymer matrix. Sulphidation of the sacrificial AgCl produces a stable AgS precipitate and prevents further ingress of the poisoning sulphide species through the composite material. A novel SSRE using this material is compared to a control SSRE without suspended AgCl and a typical liquid filled reference electrode. These three reference electrodes are studied using electrochemical impedance spectroscopy (EIS), and their application is also studied in potentiometric pH sensing and cyclic voltammetry (CV). The long-term sulphide resistance of the two SSREs is also studied with potentiometry, and cross-sections of these electrodes were examined using micro X-ray fluorescence (μXRF). Both SSREs demonstrated higher impedance than the liquid reference electrode but were similar to other SSREs reported in the literature. This impedance did not result a meaningful difference in potentiometric pH sensing or CV experiments done using typical scan rates. The KCl/AgCl SSRE exhibited remarkable sulphide resistance, with all samples demonstrating a stable potential without maintenance after . 120 days of continuous immersion in 1 g L NaS solution, whereas KCl SSRE samples all demonstrated significant drift before this time. μXRF sulphur maps revealed that suspended AgCl prevented sulphide ingress, thus protecting the embedded Ag|AgCl electrode. This work presents a reference electrode that could enable long-term monitoring in challenging sulphide solutions, and also highlights a novel approach for preventing reference electrode poisoning which could be more widely explored.
对于许多连续监测应用而言，具有长期电位稳定性的参比电极至关重要，且通常基于Ag|AgCl电极；然而，这些电极易受废水中和天然地下水中常见的含硫水性物质的毒害。这项工作展示了一种基于复合材料的抗硫化固态参比电极（SSRE），该复合材料在交联聚醋酸乙烯酯聚合物基质中使用悬浮的KCl电解质和牺牲性AgCl。牺牲性AgCl的硫化产生稳定的AgS沉淀，并防止毒害性硫化物通过复合材料进一步侵入。将使用这种材料的新型SSRE与不含悬浮AgCl的对照SSRE以及典型的液填充参比电极进行比较。使用电化学阻抗谱（EIS）研究这三种参比电极，并在电位pH传感和循环伏安法（CV）中研究它们的应用。还用电位法研究了两种SSRE的长期抗硫化性能，并使用微X射线荧光（μXRF）检查了这些电极的横截面。两种SSRE的阻抗均高于液体参比电极，但与文献中报道的其他SSRE相似。在使用典型扫描速率进行的电位pH传感或CV实验中，这种阻抗并未导致有意义的差异。KCl/AgCl SSRE表现出显著的抗硫化性能，所有样品在连续浸泡于1 g/L NaS溶液中120天后，无需维护即可显示出稳定的电位，而KCl SSRE样品在此之前均表现出明显的漂移。μXRF硫分布图显示，悬浮的AgCl可防止硫化物侵入，从而保护嵌入式Ag|AgCl电极。这项工作展示了一种能够在具有挑战性的硫化物溶液中进行长期监测的参比电极，同时也突出了一种可更广泛探索的防止参比电极中毒的新方法。
