Auto Generative Capacitive Mixing for Power Conversion of Sea and River Water by the Use of Membranes

An enormous dissipation of the order of 2 kJ/L takes place during the natural mixing process of fresh river water entering the salty sea. "Capacitive mixing" is a promising technique to efficiently harvest this energy in an environmentally clean and sustainable fashion. This method has its roots in the ability to store a very large amount of electric charge inside supercapacitor or battery electrodes dipped in a saline solution. Three different schemes have been studied so far, namely, Capacitive Double Layer Expansion (CDLE), Capacitive Donnan Potential (CDP) and Mixing Entropy Battery (MEB), respectively based on the variation upon salinity change of the electric double layer capacity, on the Donnan membrane potential, and on the electrochemical energy of intercalated ions.

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“…Indeed, La Mantia et al report a power production of 105 mW/m 2 , of the same order of those obtained for CDLE and CDP [17,32,33]. …”

Section: Mixing Entropy Batterysupporting

confidence: 61%

“…Relevant investigations along this line of research include the optimization of cycle timing, i.e., the duration of each step of the cycle [44,45,49]; the minimization of the time needed to exchange the solutions [33] and the avoidance of the mixing of the two solutions in the flow channel [31,33,44].…”

Section: Key Parametersmentioning

confidence: 99%

Capacitive Mixing for Harvesting the Free Energy of Solutions at Different Concentrations

Rica

Ziano

Salerno

et al. 2013

Entropy

115

111

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“…Ion-exchange membranes may be utilized between the porous electrodes and electrolyte in an alternative CapMix configuration. ,, In this setup, the concentration difference between the electrode pores and HC or LC solution drives ion permeation across the IEMs. Since IEMs allow the selective passage of counterions and retain co-ions, the porous electrodes adjacent to the AEM and CEM in HC solution accumulate anions and cations, respectively, without the need for an externally imposed voltage.…”

Section: Technologies To Harness Salinity Gradient Energymentioning

confidence: 99%

Salinity Gradients for Sustainable Energy: Primer, Progress, and Prospects

Yip

Brogioli

Hamelers³

et al. 2016

Environ. Sci. Technol.

286

183

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Combining two solutions of different composition releases the Gibbs free energy of mixing. By using engineered processes to control the mixing, chemical energy stored in salinity gradients can be harnessed for useful work. In this critical review, we present an overview of the current progress in salinity gradient power generation, discuss the prospects and challenges of the foremost technologies - pressure retarded osmosis (PRO), reverse electrodialysis (RED), and capacitive mixing (CapMix) and provide perspectives on the outlook of salinity gradient power generation. Momentous strides have been made in technical development of salinity gradient technologies and field demonstrations with natural and anthropogenic salinity gradients (for example, seawater-river water and desalination brine-wastewater, respectively), but fouling persists to be a pivotal operational challenge that can significantly ebb away cost-competitiveness. Natural hypersaline sources (e.g., hypersaline lakes and salt domes) can achieve greater concentration difference and, thus, offer opportunities to overcome some of the limitations inherent to seawater-river water. Technological advances needed to fully exploit the larger salinity gradients are identified. While seawater desalination brine is a seemingly attractive high salinity anthropogenic stream that is otherwise wasted, actual feasibility hinges on the appropriate pairing with a suitable low salinity stream. Engineered solutions are foulant-free and can be thermally regenerative for application in low-temperature heat utilization. Alternatively, PRO, RED, and CapMix can be coupled with their analog separation process (reverse osmosis, electrodialysis, and capacitive deionization, respectively) in salinity gradient flow batteries for energy storage in chemical potential of the engineered solutions. Rigorous techno-economic assessments can more clearly identify the prospects of low-grade heat conversion and large-scale energy storage. While research attention is squarely focused on efficiency and power improvements, efforts to mitigate fouling and lower membrane and electrode cost will be equally important to reduce levelized cost of salinity gradient energy production and, thus, boost PRO, RED, and CapMix power generation to be competitive with other renewable technologies. Cognizance of the recent key developments and technical progress on the different technological fronts can help steer the strategic advancement of salinity gradient as a sustainable energy source.

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“…Hence the system can, as a first-order approximation, be described by RC models such as the one given in Figure Figure 1. 23,35 OCP of the CDP. The open circuit potential of the CDP is defined by the potential difference that can be measured when a pair of CDP electrodes are equilibrated in a solution of concentration A, C A , and subsequently at stationary state in a solution of concentration B, C B .…”

Section: ■ Theorymentioning

confidence: 99%

“…The rest of the system has ohmic resistance as characteristics. Hence the system can, as a first-order approximation, be described by RC models such as the one given in Figure Figure . , …”

Section: Theorymentioning

confidence: 99%

Faster Time Response by the Use of Wire Electrodes in Capacitive Salinity Gradient Energy Systems

et al. 2012

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Capacitive energy extraction based on Donnan potential (CDP) and capacitive energy extraction based on double layer expansion (CDLE) are novel electroctrochemical processes to convert the potential free energy of mixing sea and river water into electric work. This is done by the use of supercapacitor electrodes with and without ion exchange membranes. Currently, these techniques rely on improved mass transport in order to become more efficient and give higher power output. In this paper we evaluate the transport phenomena by diffusion and the electrode geometry when switching between sea and river water at open circuit potential (OCP). By changing the electrode geometry from a flat plate to a cylindrical one, experiments and analytical models in combination show that mass transport by diffusion is increased. This is demonstrated without any changes in the hydrodynamic conditions. Improving mass transport without changing the hydrodynamic conditions breaks with what has been the convention in the scientific community of salinity gradient power. Moreover, in sea water the transport phenomena appear to be controlled by diffusion, and the response time for building open circuit potential in CDP and CDLE under this condition is reduced by a factor of 2 when using wire electrodes instead of flat plate electrodes. In river water, the trend is similar though the response time is generally larger.

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Auto Generative Capacitive Mixing for Power Conversion of Sea and River Water by the Use of Membranes

Cited by 11 publications

References 36 publications

Capacitive Mixing for Harvesting the Free Energy of Solutions at Different Concentrations

Capacitive Mixing for Harvesting the Free Energy of Solutions at Different Concentrations

Salinity Gradients for Sustainable Energy: Primer, Progress, and Prospects

Faster Time Response by the Use of Wire Electrodes in Capacitive Salinity Gradient Energy Systems

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