Impacts of multi-foulings on salinity gradient energy conversion process in negatively charged conical nanochannels

Membrane fouling inevitably occurs during nanofluidic reverse electrodialysis.Herein,the impact of multi-fouling on the energy conversion performance of negatively charged conical nanochannels under asymmetrical configurations is systematically investigated.The results reveal that in Configuration I,where a high-concentration solution is applied at the tip side,at small concentration ratios,multiple foulings reduce the electric power.In Configuration II,where a low-concentration solution is applied at the tip side,multiple foulings near the base side contribute to the electric power.Any fouling that formed near the lowconcentration entrance diminished the electric power and energy conversion efficiency.Multi-fouling lowered the electrical power consumption by 69.27%and 99.94%in Configurations I and II,respectively.In Configuration I,the electric power first increased with increasing fouling surface charge density,reached its maximum value,and thereafter decreased.In Configuration II,the electric power first decreased with increasing fouling surface charge density,reached its minimum value,and thereafter increased.Large negative or positive charge densities of fouling contribute to the electric power and energy conversion efficiency.

Tracing the impact of stack configuration on interface resistances in reverse electrodialysis by in situ electrochemical impedance spectroscopy

Reverse electrodialysis(RED)is an emerging membrane-based technology for the production of renewable energy from mixing waters with different salinities.Herein,the impact of the stack configuration on the Ohmic and non-Ohmic resistances as well as the performance of RED were systematically studied by using in situ electrochemical impedance spectroscopy(EIS).Three different parameters(membrane type,number of cell pairs and spacer design)were controlled.The Ohmic and non-Ohmic resistances were evaluated for RED stacks equipped with two types of commercial membranes(Type I and Type II)supplied by Fujifilm Manufacturing Europe B.V:Type I Fuji membranes displayed higher Ohmic and non-Ohmic resistances than Type II membranes,which was mainly attributed to the difference in fixed charge density.The output power of the stack was observed to decrease with the increasing number of cell pairs mainly due to the increase in ionic shortcut currents.With the reduction in spacer thickness from 750 to 200μm,the permselectivity of membranes in the stack decreased from 0.86 to 0.79 whereas the energy efificiency losses increased from 31%to 49%.Overall,the output of the present study provides a basis for understanding the impact of stack design on internal losses during the scaling-up of RED.

Progress and prospects of two-dimensional materials for membrane-based osmotic power generation

The electrical energy that can be harnessed from the salinity difference across the sea water and river water interface can be one of the sustainable and clean energy resources of the future.This energy can be harnessed via the nanofluidic channels that selectively permeate ions.The selective diffusion of cations and anions can produce electricity through reverse electrodialysis.Two-dimensional(2D)materials are a class of nanomaterials that hold great promise in this field.Several breakthrough works have been previously published which demonstrate the high electrical power densities of 2D membranes.The ion transportation can be either through the nano-sized in-plane pores or interlayer spacings of 2D materials.This review article highlights the progress in 2D materials for salinity gradient power generation.Several types of 2D membranes with various nano-architectures are discussed in this review article.These include atom-thick 2D membranes with nanopores,2D lamellar membranes,2D lamellar membranes with nanopores,2D/one-dimensional(1D),and 2D/2D hybrid membranes.The fabrication techniques,physical characteristics,ion transportation properties,and the osmotic power generation of these 2D membranes are elaborated in this review article.Finally,we overview the future research direction in this area.It is envisioned that the research on 2D materials can make practical salinity gradient power generation one step closer to reality.