Toward Scalable Nanofluidic Osmotic Power Generation from Hypersaline Water Sources with a Metal–Organic Framework Membrane

We demonstrate a strategy toward scalable nanofluidic osmotic power generation by using PSS/HKUST-1 membrane with subnanometer pores and using hypersaline water sources. The hypersaline water sources provide high ionic conductivity and the subnanometer pores guarantee charge selectivity under high salinity. The power density stabilized at 1.7 W m⁻² when the membrane area increased to 7 mm², the highest for macro-sized nanofluidic membranes.

Abstract

Nanofluidic membranes have shown great promise in harvesting osmotic energy but its scalablity remains challenging since most studies only tested with a membrane area of ≈10⁻² mm² or smaller. We demonstrate that metal-organic-framework membranes with subnanometer pores can be used for scalable osmotic power generation from hypersaline water sources. Our membrane can be scaled up to a few mm², and the power density can be stabilized at 1.7 W m⁻². We reveal that the key is to improve the out-of-membrane conductance while keeping the membrane's charge selectivity, contradicting the previous conception that the ionic conductivity of the membrane plays the dominating role. We highlight that subnanometer pores are essential to ensure the charge selectivity in hypersaline water sources. Our results suggest the importance to engineer the interplay between the in-membrane and out-of-membrane ion transport properties for scalable osmotic power generation.

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