High-Performance Alkaline Seawater Electrolysis with Anomalous Chloride Promoted Oxygen Evolution Reaction

A highly selective and durable oxygen evolution reaction (OER) electrocatalyst is the bottleneck for direct seawater splitting because of side reactions primarily caused by chloride ions (Cl-). Most studies about OER catalysts in seawater focus on the repulsion of the Cl- to reduce its negative effects. Herein, we demonstrate that the absorption of Cl- on the specific site of a popular OER electrocatalyst, nickel-iron layered double hydroxide (NiFe LDH), does not have a significant negative impact; rather, it is beneficial for its activity and stability enhancement in natural seawater. A set of in situ characterization techniques reveals that the adsorption of Cl- on the desired Fe site suppresses Fe leaching, and creates more OER-active Ni sites, improving the catalyst's long-term stability and activity simultaneously. Therefore, we achieve direct alkaline seawater electrolysis for the very first time on a commercial-scale alkaline electrolyser (AE, 120 cm2 electrode area) using the NiFe LDH anode. The new alkaline seawater electrolyser exhibits a reduction in electricity consumption by 20.7 % compared to the alkaline purified water-based AE using commercial Ni catalyst, achieving excellent durability for 100 h at 200 mA cm-2. An anomalous Cl--promoted oxygen evolution reaction (OER) mechanism with a typical catalyst, nickel-iron layered double hydroxide (NiFe-LDH), is proposed. First, both Fe leaching and active lattice oxygen are suppressed by the adsorption of Cl- on desired Fe sites, which improves the catalyst's long-term stability. Second, more high-valency OER-active Ni sites are created, thus increasing the activity.+image

Automated summary

This study demonstrates the beneficial effect of chloride ions (Cl-) on the activity and stability of a popular oxygen evolution reaction (OER) catalyst, nickel-iron layered double hydroxide (NiFe LDH), in natural seawater. The adsorption of Cl- on the desired Fe sites suppresses Fe leaching and creates more OER-active Ni sites, improving the catalyst's long-term stability and activity simultaneously.