The increase of energy demand added to the concern for environmental pollution linked to energy generation based on the combustion of fossil fuels has motivated the study and development of new sustainable ways for energy harvesting. Among the different alternatives, the opportunity to generate energy by exploiting the osmotic pressure difference between water sources of different salinities has attracted considerable attention. It is well-known that this objective can be accomplished by employing ion-selective dense membranes. However, so far, the current state of this technology has shown limited performance which hinders its real application. In this context, advanced nanostructured membranes (nanoporous membranes) with high ion flux and selectivity enabling the enhancement of the output power are perceived as a promising strategy to overcome the existing barriers in this technology. While the utilization of nanoporous membranes for osmotic power generation is a relatively new field and therefore, its application for large-scale production is still uncertain, there have been major developments at the laboratory scale in recent years that demonstrate its huge potential. In this review, we introduce a comprehensive analysis of the main fundamental concepts behind osmotic energy generation and how the utilization of nanoporous membranes with tailored ion transport can be a key to the development of high-efficiency blue energy harvesting systems. Also, the document discusses experimental issues related to the different ways to fabricate this new generation of membranes and the different experimental set-ups for the energy-conversion measurements. We highlight the importance of optimizing the experimental variables through the detailed analysis of the influence on the energy capability of geometrical features related to the nanoporous membranes, surface charge density, concentration gradient, temperature, building block integration, and others. Finally, we summarize some representative studies in up-scaled membranes and discuss the main challenges and perspectives of this emerging field.

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Nanofluidic osmotic power generators – advanced nanoporous membranes and nanochannels for blue energy harvesting

We theoretically investigate the feasibility of enhancing the reverse electrodialysis power generation in nanochannels by covering the surface with a polyelectrolyte layer (PEL). Along these lines, two conical nanochannels are considered that differ in the extent of the covering. Each nanochannel connects two large reservoirs filled with KCl electrolytes of different ionic concentrations. Considering the Poisson–Nernst–Planck and Navier–Brinkman equations, finite-element-based numerical simulations are performed under a steady-state. The influences of the PEL properties and the salinity gradient on the reverse electrodialysis characteristics are examined in detail via a thorough parametric study. It is shown that the maximum power generated is an increasing function of the charge density and the thickness of the PEL. This means that the maximum power generated may be theoretically increased to any desired degree by covering the nanochannel surface with a sufficiently dense and thick PEL. Considering a typical PEL with a charge density of 100 mol m−3 and a thickness of 8 nm along with a high-to-low concentration ratio of 1000, we demonstrate that it is possible to extract a power density of 51.5 W m−2, which is nearly three times the maximum achievable value employing bare conical nanochannels at the same salinity gradient.

Tripling the reverse electrodialysis power generation in conical nanochannels utilizing soft surfaces.

Impacts of the shape of soft nanochannels on their ion selectivity and current rectification

A Comprehensive Review on the Applications of Boron Nitride Nanomaterials in Membrane Fabrication and Modification

Augmentation of the reverse electrodialysis power generation in soft nanochannels via tailoring the soft layer properties

Covering the conical nanochannels with dense polyelectrolyte layers significantly improves the ionic current rectification.

https://link.springer.com/content/pdf/10.1007/s10404-021-02501-3.pdf

Mahdi Khatibi

Papers

Covering the conical nanochannels with dense polyelectrolyte layers significantly improves the ionic current rectification.

Tripling the reverse electrodialysis power generation in conical nanochannels utilizing soft surfaces.

Impacts of the shape of soft nanochannels on their ion selectivity and current rectification

Augmentation of the reverse electrodialysis power generation in soft nanochannels via tailoring the soft layer properties

A variational approach applied to reduce fouling with the electroosmotic flow in porous-wall microchannels