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Defective Antifluorite MnO2-Layered RuO2 for Direct Seawater Electrolysis at Circum-Neutral pH
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Date
2025-09-04
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Abstract
The direct electrolysis of unbuffered seawater at pH 8.2 remains challenging. This study synthesizes RuO<inf>2</inf> electrodes with electrodeposited polymorphs of MnO<inf>2</inf> (δ-, ε-, γ-, and defective antifluorite [DA]-MnO<inf>2</inf>) as a semipermeable overlayer that selectively allows water transport while blocking chloride diffusion. Whereas the oxygen evolution reaction (OER) and chlorine evolution reaction occur simultaneously with the bare RuO<inf>2</inf> electrode, only the former is observed with the MnO<inf>2</inf>-coated RuO<inf>2</inf> electrodes. Compared to the crystalline δ-, ε-, and γ-MnO<inf>2</inf> polymorphs, the DA-MnO<inf>2</inf>/RuO<inf>2</inf> electrode drives the OER at a Faradaic efficiency (FE) of ≈100% for over 100 h in unbuffered seawater, with an OER-FE of ≈98.7% and 90.0% in 1 M and 5 M NaCl, respectively. Based on theoretical calculations, the excellent electrocatalytic behavior of DA-MnO<inf>2</inf> is attributed to the steric structure of the staggered, narrower Mn-O polyhedron channels, inhibiting the diffusion of Cl<sup>−</sup> through the MnO<inf>2</inf> overlayer.