Direct seawater electrolysis via synergistic acidification by inorganic precipitation and proton flux from bipolar membrane

Han, Ji-Hyung; Jwa, Eunjin; Lee, Hongjun; Kim, Eun Joong; Nam, Joo-Youn; Hwang, Kyo Sik; Jeong, Namjo; Choi, Jiyeon; Kim, Han−Ki; Jeung, Youn-Cheul; Chung, Taek Dong

doi:10.1016/j.cej.2021.132383

Cited by 30 publications

(42 citation statements)

References 44 publications

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“…Although acidification of seawater in BPM-DSWE is very effective in suppressing the dispersed inorganic precipitates, as described in a previous report, [20] the inorganic deposits formed at the surface of the mesh-type cathode continue to grow over a long period of time (Figure 1). This indicates that the inorganic precipitation induced by hydroxide ions from the water reduction is faster than dissolution of the deposits in the acidified seawater.…”

Section: Resultsmentioning

confidence: 50%

“…Interestingly, the pH of the bulk catholyte changed significantly depending on the electrode structure (Figure 3a). With the mesh cathode, the pH of the seawater was lowered to 3 in 2 h, as described in a previous paper, [20] whereas with the porous electrode, the initial pH (pH � 8.5) of the seawater was maintained. In contrast, 0.5 m NaCl solution underwent rapid alkalization (pH � 10) in 2 h, which definitively confirms the precipitation of inorganics at the porous cathode in seawater; this process captures the hydroxide ions generated by the electroreduction of water, suppressing the pH rise.…”

Section: Resultsmentioning

confidence: 99%

“…Recently, Han et al proposed a DSWE with a bipolar membrane (BPM) as a separator for controlling inorganic precipitates. [20] This is the first report of a combination of BPM and real seawater (as a catholyte) for hydrogen production. It was confirmed that seawater was acidified to pH 2 despite the significant generation of hydroxide ions in the HER.…”

Section: Introductionmentioning

confidence: 94%

“…A batch-type cell, as described in a previous paper, [20] consisting of two chambers (acryl, internal dimension: 5 × 5 × 5 cm 3 ) with a BPM (Astom, Corp. Japan) as a separator, was used for electrolysis. Each chamber contained 120 mL of electrolyte.…”

Section: Experimental Section Direct Seawater Electrolyzermentioning

confidence: 99%

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

Han

2022

ChemSusChem

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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.

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Section: Resultsmentioning

confidence: 50%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 94%

Section: Experimental Section Direct Seawater Electrolyzermentioning

confidence: 99%

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

Han

2022

ChemSusChem

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“…Recently, I reported the acidification of seawater as a catholyte in direct seawater electrolysis with a bipolar membrane (BPM) as a separator. 18 A BPM comprises a cation exchange layer (CEL) and an anion exchange layer (AEL). Water dissociation (WD: H 2 O → H + + OH − ) occurs at the interfacial layer between the CEL and AEL under reverse bias, producing protons and hydroxide ions that migrate out of the respective layer in opposite directions.…”

Section: ■ Introductionmentioning

confidence: 99%

Complete Suppression of Dispersed Inorganic Precipitates in Reverse Electrodialysis via Seawater Acidification

Han

2022

Ind. Eng. Chem. Res.

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A large-scale reverse electrodialysis (RED) system consists of several hundred cell pairs, resulting in a stack voltage of tens of volts at the ends of the electrodes. Under this high voltage condition, water reduction/oxidation inevitably occurs despite the presence of redox couples, which means that a continuous supply of redox couples is required for long-term operation due to their instability under sudden changes in pH around the electrodes. On the other hand, water electrolysis can be used as an electrode reaction in natural seawater, without chemical reagents. However, inorganic precipitation by hydroxide ions produced in the water reduction reaction is a persistent problem that hampers cathode operation in seawater, because the deposits decrease the electrochemically active surface area of the cathode and hinder ionic flow across the ion exchange membranes. It has recently been demonstrated that seawater acidifies to pH 3 via a cooperative effect between proton flux from a bipolar membrane and inorganic precipitation at the cathode interface. In this study, seawater acidification was applied to the RED system to completely suppress dispersed inorganic deposits, enabling the stable operation of large-scale RED stacks without clogging problems. This result opens the possibility of developing an environmentally friendly RED system that does not use any chemical reagents.

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Recent Advances in Hybrid Seawater Electrolysis for Hydrogen Production

Yu,

Liu

2023

Advanced Materials

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Seawater electrolysis (SWE) is a promising and potentially cost‐effective approach to hydrogen production, considering that seawater is vastly abundant and SWE is able to combine with offshore renewables producing green hydrogen. However, SWE has long been suffering from technical challenges including the high energy demand and interference of chlorine chemistry, leading electrolyzers to a low efficiency and short lifespan. In this context, hybrid SWE, operated by replacing the energy‐demanding oxygen evolution reaction and interfering chlorine evolution reaction (CER) with a thermodynamically more favorable anodic oxidation reaction (AOR) or by designing innovative electrolyzer cells, has recently emerged as a better alternative, which not only allows SWE to occur in a safe and energy‐saving manner without the notorious CER, but also enables co‐production of value‐added chemicals or elimination of environmental pollutants. This review provides a first account of recent advances in hybrid SWE for hydrogen production. The substitutional AOR of various small molecules or redox mediators, in couple with hydrogen evolution from seawater, is comprehensively summarized. Moreover, how the electrolyzer cell design helps in hybrid SWE is briefly discussed. Last, the current challenges and future outlook about the development of the hybrid SWE technology are outlined.

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Direct seawater electrolysis via synergistic acidification by inorganic precipitation and proton flux from bipolar membrane

Cited by 30 publications

References 44 publications

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

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

Complete Suppression of Dispersed Inorganic Precipitates in Reverse Electrodialysis via Seawater Acidification

Recent Advances in Hybrid Seawater Electrolysis for Hydrogen Production

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