ABSTRACT
Engineered asymmetric heterogeneous ion-selective membranes have become a focal point for their improved efficiency in harnessing osmotic energy from ionic solutions with varying salinity. However, achieving both energy conversion efficiency and excellent chemical stability necessitates effectively mitigating the formation of detrimental interface cracks between two different layers. We develop a charge-gradient sulfonated poly(ether ether ketone) (SPEEK) membrane (CG-SPEEK) on a large-scale using a straightforward coating method. As an osmotic energy generator, CG-SPEEK membrane achieves an impressive output power density of 9.2 W m-2 and exhibits ultrahigh cation selectivity (0.99), with an energy conversion efficiency of 48% at a 50-fold NaCl concentration gradient. The results highlight the ion diode effects of CG-SPEEK, driven by a charge density gradient that accelerates cation transport while suppressing ion concentration polarization. Density functional theory simulations provide further insights, revealing that the energy barrier for Na+ ion transport through CG-SPEEK membrane is lower than that through a homogeneous SPEEK membrane. This work not only enhances our understanding of ion transport dynamics but also establishes the CG-SPEEK membrane as a promising candidate for efficient osmotic energy conversion applications.
ABSTRACT
Formate, as an important chemical raw material, is considered to be one of the most promising products for industrialization among CO2 electroreduction reaction (CO2RR) products, but it still suffers from poor selectivity and a low formation rate at a high current density on account of the competitory hydrogen evolution reaction. Herein, the heterogeneous nanostructure was constructed by anchoring In2O3 nanoparticles on poly(3,4-ethylenedioxythiophene) (PEDOT)-modified carbon black (In2O3/PC), in which the PEDOT polymer interface layer could immobilize In2O3 nanoparticles and obtain a notable reduction in electron transfer resistance among the In2O3 particles, showing a 27% increase in the total electron transfer rate. The optimized In2O3/PC with rich heterogeneous interfaces selectively reduced CO2 to formate with a high FE of 95.4% and a current density of 251.4 mA cm-2 under -1.18 V vs RHE. Also, the formate production rate for In2O3/PC was up to 7025.1 µmol h-1 cm-2, surpassing most previously reported CO2RR catalysts. The in situ XRD results revealed that In2O3 particles were reduced to metallic indium (In) as catalytic active sites during CO2RR. DFT calculations verified that a strong interface interaction between In sites and PC induced electron transfer from In sites to PC, which could optimize the charge distribution of active sites, accelerate electron transfer, and elevate the p-band center of In sites toward the Fermi level, thereby lowering the adsorption energy of *OCHO intermediates for CO2 conversion to formate.
ABSTRACT
By closing and opening ion channels, electric eels are able to convert ion concentration gradients into electricity. Inspired by electric eels, considerable artificial sub-nanoscale ion channels with high ion selectivity and transportation efficiency have been designed for harvesting the osmotic energy between ionic solutions of different salinities, but constructing smart ion-gated sub-nanochannels for effective ion transport is still a huge challenge. Herein, photo-controllable sub-nanochannels of metal-organic framework (MOF) NH2-MIL-53 encapsulated with spiropyrans (SP-MIL-53) were fabricated by a facile in situ growth strategy. Interestingly, the highly ordered sub-nanochannels of SP-MIL-53 were switched on and off to efficiently regulate the ion flux by the light-driven isomerization of SP, which made it a smart ionic gate with a high on-off ratio of 16.2 in 10 mM KCl aqueous solution via UV irradiation. Moreover, the ion-gated sub-nanochannel membrane yielded a high power density of 8.3 W m-2 under a 50-fold KCl concentration gradient in the open state. Density functional theory calculations revealed that K+ ions in SP-MIL-53 sub-nanochannels had a higher mobility constant (3.61 × 10-2) with UV irradiation than without UV illumination (2.33 × 10-22). This work provides an effective way to develop smart ion-gating sub-nanochannels for capturing salinity gradient power.
ABSTRACT
The waste organic solvents containing inorganic salts have been considered sustainable resources, which can effectively capture salinity gradient energy using ion-selective membranes. However, it still remains a great challenge to fabricate the ion-selective membranes with high conversion efficiency and stability in an organic system. Here, the bioinspired nacre-like layered MXene/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) (MP) composite membranes for capturing salinity gradient energy from an organic solvent are fabricated via filtration method, in which PEDOT:PSS molecules are introduced into MXene interlayers. Accordingly, the MP membrane exhibits high mechanical property and wonderful stability in common organic solvents. As expected, the power generation of the MP membrane reaches up to 3216 ± 603 nW in a 2/0.001 M methanol (Met)-LiCl solution and a record high power generation of 6926 ± 959 nW after adding NaOH into the Met-LiCl solution, which is superior to the previous report. Both experimental and theoretical studies confirm that the MP membrane has excellent cation selectivity and fast ion transport performance. The results are attributable to an increased interlayer spacing between MXene layers and an improved cation selectivity due to the insertion of PEDOT:PSS chains and the enhanced dissociation of negative charges by NaOH. The ultrastable two-dimensional (2D) nanochannel membrane provides practical application for harvesting energy from waste organic solvents.
