Exploring the Interface of Porous Cathode/Bipolar Membrane for Mitigation of Inorganic Precipitates in Direct Seawater Electrolysis

• Published in: ChemSusChem 2022-06, Vol.15 (11), p.e202200372-n/a
• Main Author: Han, Ji‐Hyung
• Format: Article
• Language: English
• Subjects: Acidification; bipolar membrane; Cathodes; Cation exchanging; Chemical reduction; direct seawater electrolysis; Electric potential; Electrodes; Electrolysis; Electron transfer; Hydrogen evolution reactions; Hydrogen production; Inorganic compounds; inorganic precipitation; Membranes; Precipitates; Protons; renewable hydrogen; Seawater; Separators; Voltage; water splitting
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.202200372

Direct seawater electrolysis utilizes natural seawater as the electrolyte. Hydroxide ions generated from the hydrogen evolution reaction at the cathode induce the precipitation of inorganic compounds, which block the active sites of the catalysts, leading to high cell voltage. To mitigate inorganic scaling, herein, an optimized interface between a porous electrode and a bipolar membrane (BPM, as a separator) was suggested in zero‐gap seawater electrolyzers. Despite the formation of inorganic deposits at the front side (facing bulk seawater) of the porous cathode due to the water reduction reaction, the back side facing the cation exchange layer of the BPM remained free from thick inorganic deposits. This was ascribed to the locally acidic environment generated by proton flux from water dissociation at the BPM, enabling stable hydrogen production via the proton reduction at low overpotential. This asymmetric hydrogen evolution reaction at the porous cathode led to a considerably lower cell voltage and higher stability than that achieved with the mesh electrode. Moreover, precipitation at the front side of the porous cathode was further mitigated through acidification of the seawater by introducing an open area of the BPM that was not in contact with the porous cathode, allowing free protons that were not involved in the electron transfer reaction to diffuse out into the bulk seawater. These findings may provide critical guidance for the investigation of interfacial phenomena for the complete mitigation of inorganic scaling in the direct electrolytic splitting of seawater. H2 from seawater: To mitigate inorganic scaling in direct seawater electrolysis, an optimized interface is proposed between a porous cathode with an open area and a bipolar membrane (BPM, as a separator) that generates protons via water dissociation. The proton reduction reaction at the back side, facing the cation exchange layer (CEL) of the BPM, and the passage of free protons through the open area minimize inorganic scaling and acidify the seawater.