Monitoring the chlorine evolution reaction during electrochemical alkaline seawater splitting

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 (FEOER) and ClER (FEClER), and we found that the total Faradaic efficiency (FEOER + FEClER) 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.