# A Bipolar Membrane Containing Core–Shell Structured Fe3O4-Chitosan Nanoparticles for Direct Seawater Electrolysis

## TL;DR

A new bipolar membrane with Fe3O4-chitosan nanoparticles improves direct seawater electrolysis efficiency by reducing precipitate formation and enhancing performance.

## Contribution

A core–shell structured Fe3O4–chitosan nanoparticle catalyst is developed to enhance bipolar membrane performance in direct seawater electrolysis.

## Key findings

- The BPM with Fe3O4–chitosan nanoparticles achieved a water-splitting flux of 26.2 μmol cm−2 min−1, 18.6% higher than a commercial membrane.
- The membrane showed lower cell voltage and stable catholyte acidification over 100 hours in seawater electrolysis tests.

## Abstract

Seawater has attracted increasing attention as a promising resource for hydrogen production via electrolysis. However, multivalent ions present in seawater can reduce the efficiency of direct seawater electrolysis (DSWE) by forming inorganic precipitates at the cathode. Bipolar membranes (BPMs) can mitigate precipitate formation by regulating local pH, thereby enhancing DSWE efficiency. Accordingly, this study focuses on the fabrication of a high-performance BPM for DSWE applications. The water-splitting performance of BPMs is strongly dependent on the properties of the catalyst at the bipolar junction. Herein, iron oxide (Fe3O4) nanoparticles were coated with cross-linked chitosan to improve solvent dispersibility and catalytic activity. The resulting core–shell catalyst exhibited excellent dispersibility, facilitating uniform incorporation into the BPM. Water-splitting flux measurements identified an optimal catalyst loading of approximately 3 μg cm−2. The BPM containing Fe3O4–chitosan nanoparticles achieved a water-splitting flux of 26.2 μmol cm−2 min−1, which is 18.6% higher than that of a commercial BPM (BP-1E, Astom Corp., Tokyo, Japan). DSWE tests using artificial seawater as the catholyte and NaOH as the anolyte demonstrated lower cell voltage and stable catholyte acidification over 100 h compared to the commercial membrane.