As the chlorine evolution reaction (ClER) is a competing side process of the oxygen evolution reaction (OER) during alkaline seawater splitting, the monitoring of ClER is very important for efficient and environmental-friendly electrocatalytic seawater splitting. However, fast and quantitative detection of anodically produced hypochlorite (ClO^-) ions during alkaline seawater splitting is still a challenge due to the highly active nature of ClO^- and the complex chemical environment in seawater. Here we report the quantitative detection of anodically produced ClO^- by online sample collection and offline UV–vis analysis. The starch-iodide solution was employed to capture ClO^- in the electrolyte sample, and the resulting solution has a high UV–vis absorption that can be used to quantify the concentration of ClO^-. The proposed method exhibits a strong anti-interference ability and has a detection limit of 5 μM in both simulated and real seawater. As a proof-of-concept example, we monitor ClER during anodic OER in simulated alkaline seawater, and detect the potential- and time-dependent production of ClO^-. We demonstrate that the detection limit of ClO^- is sensitive enough to monitor ClER in practical seawater electrolysis. The quantitative detection of ClO^- also allows the calculation of the Faradaic efficiency of OER (FE_OER) and ClER (FE_ClER), and we found that the total Faradaic efficiency (FE_OER + FE_ClER) at different potentials are all quite close to 100%, providing strong evidence for the precision and reliability of this detection method. This work presents a sensitive, precise and convenient method for monitoring the ClER during alkaline seawater splitting.

由于析氯反应 (ClER) 是碱性海水分解过程中析氧反应 (OER) 的竞争副过程，因此监测 ClER 对于高效和环保的电催化海水分解非常重要。然而，由于 ClO ^-的高活性性质和海水中复杂的化学环境，在碱性海水分解过程中快速定量检测阳极产生的次氯酸根 (ClO ^{- ) 离子仍然是一个挑战。}在这里，我们报告了阳极产生的二氧化氯的定量检测^——通过在线样品采集和离线紫外-可见分析。淀粉-碘化物溶液用于捕获 ClO ^-在电解质样品中，所得溶液具有高紫外-可见吸收，可用于量化 ClO ^-的浓度。该方法具有很强的抗干扰能力，在模拟海水和真实海水中的检测限均为 5 μM。作为概念验证示例，我们在模拟碱性海水中的阳极 OER 期间监测 ClER，并检测 ClO - 的电位和时间依赖性^产生。^{我们证明了 ClO -}的检测极限足够灵敏，可以在实际海水电解中监测 ClER。ClO 的定量检测^-还允许计算 OER ( FE _OER ) 和 ClER ( FE _{ClER)的法拉第效率})，我们发现不同电位下的总法拉第效率（FE _OER  +  FE _ClER）都非常接近100%，为该检测方法的精度和可靠性提供了有力的证据。这项工作提出了一种灵敏、精确和方便的方法来监测碱性海水分解过程中的 ClER。