Expanded Negative Electrostatic Network-Assisted Seawater Oxidation and High-Salinity Seawater Reutilization

Coastal/offshore renewable energy sources combined with seawater splitting offer an attractive means for large-scale H2 electrosynthesis in the future. However, designing anodes proves rather challenging, as surface chlorine chemistry must be blocked, particularly at high current densities (J). Additionally, waste seawater with increased salinity produced after long-term electrolysis would impair the whole process sustainability. Here, we convert seawater to O2 selectively, on hydroxides, by building phytate-based expanded negative electrostatic networks (ENENs) with electrostatically repulsive capacities and higher negative charge coverage ranges than those of common inorganic polyatomic anions. With surface ENENs, even typically unstable CoFe hydroxides perform nicely toward alkaline seawater oxidation at activities of >1 A cm–2. CoFe hydroxides with phytate-based ENENs exhibit prolonged lifespans of 1000 h at J of 1 A cm–2 and 900 h at J of 2 A cm–2 and thus rival the best seawater oxidation anodes. Direct introduction of trace phytates to seawater weakens corrosion tendency on conventional CoFe hydroxides as well, extending the life of hydroxides by ∼28 times at J of 2 A cm–2. A wide range of materials all obtain prolonged lifetimes in the presence of ENENs, validating universal applicability. Mechanisms are studied using theoretical computations under working conditions and ex situ/in situ characterizations. We demonstrate a potentially viable way to sustainably reutilize high-salinity wastewater, which is a long-standing but neglected issue. Series-connected devices exhibit good resistance to low temperature operation and are more eco-friendly than current organic electrolyte-based energy storage devices.