Highly Efficient Power Conversion from Salinity Gradients with Ion-Selective Polymeric Nanopores

Abstract

A polymeric nanopore membrane with selective ionic transport has been proposed as a potential device to convert the chemical potential energy in salinity gradients to electrical power. However, its energy conversion efficiency and power density are often limited due to the challenge in reliably controlling the size of the nanopores with the conventional chemical etching method. Here we report that without chemical etching, polyimide (PI) membranes irradiated with GeV heavy ions have negatively charged nanopores, showing nearly perfect selectivity for cations over anions, and they can generate electrical power from salinity gradients. We further demonstrate that the power generation efficiency of the PI membrane approaches the theoretical limit, and the maximum power density reaches 130 mW/m 2 with a modified etching method, outperforming the previous energy conversion device that was made of polymeric nanopore membranes.

Ultrafast ion sieving using nanoporous polymeric membranes

“…On the one hand, compared to 12-μm-thick PET Hostaphan® films, the permeability of K + ions through the PET Lumirror® films improves by 1000 times because the dehydration barrier is significantly lowered due to increased pore size 33 – 35 . Also, the shorter length of the pores helps to increase permeability 36 , 37 . On the other hand, the observed high selectivity between the alkali metal ions and alkali earth metal ions or heavy metal ions could be contributed significantly by the following two factors: one is the electrostatic interaction between the ions and the negatively charged pore wall, and the other is the partial dehydration of the transported ions.…”

Fabrication and application of nanoporous polymer ion-track membranes

“…Achieving this condition has been challenging for tracketching nanopores in high-concentration electrolyte solutions. In contrast, the power generation efficiency η of a track-UV PI membrane was found to approach the theoretical limit because the nanopore size approaches the molecular scale [61]. The maximum power output P max is highly sensitive to the surface charge density of the nanopore and the concentration difference of the salinity gradients.…”

“…The radii of these nanochannels are as small as 0.3 nm, and their density is as high as 5×10 10 cm −2 [12]. If needed, these nanochannels can be further enlarged by heat treatment or chemical etching [61].…”

Carboxylated PIM‐1 incorporating sulfonated graphene oxide effectively improves the ion transport properties of the membrane

“…The selectivity of ions in membranes is determined by the transfer number (t), which quantifies the contribution of cations and anions to the transmembrane current. 43,44 A transfer number of t + = 1 indicates that the membrane completely rejects anions, and vice versa. The transfer values can be obtained using the drift-diffusion method by analyzing the current-voltage characteristic curves (I-V curves) according to the GHK equation in a two-chamber electrolytic cell setup with solutions of varying concentrations.…”