A charge-free and membrane-free hybrid capacitive mixing system for salinity gradient energy harvesting

Yang, Boguang; Yu, Jian; Li, Zhenning

doi:10.1039/d2ta08213f

Cited by 7 publications

(3 citation statements)

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“…The power density values of existing EDL-based membrane-free systems are below 65 mW/m 2 [ 29 , 32 , 42 ]. Other technologies, such as battery mixing and hybrid mixing, have been reported to achieve a maximum power density of about 98 mW/m 2 under a 0.6 M to 0.01 M salinity gradient for membrane-free and charge-free operations [ 58 , 59 ] (Table S5 ). In contrast, our research has demonstrated that proper surface modifications can increase the power density to 166 mW/m 2 for a 0.6 M to 0.01 M gradient.…”

Section: Discussionmentioning

confidence: 99%

Tuning Surface Molecular Design of Porous Carbon for Blue Energy Harvesting

Wang

2023

Research

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Capacitive mixing is a promising blue energy technology due to its membrane-free electricity generation and long electrode life cycle. However, because of limited performance, existing systems do not lend themselves to practical implementation. Although it is a crucial factor directly influencing electrode behavior, surface chemistry has largely been overlooked in capacitive mixing. Here, we show that manipulating surface functionalization alone can tune the responses of electrodes to produce a high voltage rise without altering the pore structure of the electrodes. Our findings reveal that the spontaneous electrode potential of a surface-modified carbon electrode shifts negatively proportional to the surface charge due to the surface groups, which explains why and how manipulating the surface chemistry can improve the power generation capacity. Using electrodes fabricated with identical activated carbon material but with different surface treatments, we have achieved a remarkably high power density of 166 mW/m 2 delivered to an electrical load under a 0.6 M to 0.01 M salinity gradient, with the total power generated of 225 mW/m 2 . The corresponding volumetric power densities were 0.88 kW/m 3 net and 1.17 kW/m 3 total. The volumetric power density of our prototype is comparable to or better than those of prevailing membrane technologies, such as pressure retarded osmosis and reverse electrolysis, whose volumetric power density values are 1.1 kW/m 3 and 0.16 kW/m 3 , respectively. In the seawater stage, the net power density reached 432 mW/m 2 or 2.3 kW/m 3 . Such performance far exceeds existing membrane-free systems, with the highest reported power density of 65 mW/m 2 under a 0.5 M to 0.02 M salinity gradient (121 mW/m 2 in this work). The device demonstrated unparalleled durability, maintaining 90% of the maximum energy capacity after 54,000 charge–discharge cycles.

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Section: Discussionmentioning

confidence: 99%

Tuning Surface Molecular Design of Porous Carbon for Blue Energy Harvesting

Wang

2023

Research

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“…7,8 Capacitive mixing (CapMix) represents one of the popular technologies to harvest blue energy. 9 The CapMix method is based on capacitive double-layer expansion (CDLE), which involves two electrodes submerged alternatively in the stream of seawater (SW) or freshwater (FW), forming a capacitor. By elaborately mixing SW and FW within the double layers continuously, we can collect the salinity gradient energy.…”

Section: Introductionmentioning

confidence: 99%

Unraveling Flow Effect on Capacitive Energy Extraction from Salinity Gradients

Zhou,

Jing,

Zhao

et al. 2024

ACS Appl. Mater. Interfaces

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The harvesting of salinity gradient energy through a capacitive double-layer expansion (CDLE) technique is directly associated with ion adsorption and desorption in electrodes. Herein, we show that energy extraction can be modulated by regulating ion adsorption/desorption through water flow. The flow effects on the output energy, capacitance, and energy density under practical conditions are systematically investigated from a theoretical perspective, upon which the optimal operating condition is identified for energy extraction. We demonstrate that the net charge accumulation displays a negative correlation with the water flow velocity and so does the surface charge density, and this causes a nontrivial variation in the magnitude of output energy when water flows are introduced. When high water flows are introduced in both the charging and discharging processes, the energy extraction can be significantly reduced by 47.69–49.32%. However, when a high flow is solely exerted in the discharging process, the energy extraction can be enhanced by 12.94–14.49% even at low operation voltages. This study not only offers a comprehensive understanding of the microscopic mechanisms of surface-engineered energy extraction with water flows but also provides a novel direction for energy extraction enhancement.

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“…Once the electrode is saturated (or approaching saturation), the absorbed ions in the EDL are desorbed and released back into the process stream. 20,21 This step is known as the discharge process. An alternative platform to CDI is membrane capacitive deionization (MCDI).…”

Section: Introductionmentioning

confidence: 99%

Selective phosphate removal with manganese oxide composite anion exchange membranes in membrane capacitive deionization

Yang,

Zhang,

Shrimant

et al. 2024

Preprint

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The discharge of excessive phosphorous into water bodies can lead to serious eutrophication threatening aquatic ecosystem. Membrane capacitive deionization (MCDI) is an effective platform for deionizing aqueous streams; however, conventional MCDI is unable to selectively remove targeted ions from a liquid mixture. In this work, we fabricated manganese oxide composite anion exchange membranes (AEMs) for MCDI to enhance phosphate removal selectivity from sodium chloride-sodium dihydrogen phosphate (10:1 molar ratio) aqueous mixtures. We systematically investigated several critical factors, such as constant current or voltage operation, applied voltage amount, process stream pH, and manganese oxide content in the AEM, on phosphate removal efficiency and phosphate selectivity. A trade-off was observed between phosphate removal and selectivity when increasing the cell voltage. Under the best conditions, an MCDI unit with a 20 wt% Mn2O3 composite AEM and a bipolar membrane facilitated high phosphate removal efficiency of ≥ 31.8 % and a phosphate over chloride selectivity of 1.1 while showing stability for at least 30 cycles. To help understand how manganese oxide particles boost AEM selectivity, static electronic structure calculations were performed, and they revelated that hydrogen phosphate absorption on Mn2O3 composite AEM was 314 kcal/mol more exothermic than that on pristine AEM while chloride adsorption on Mn2O3 composite AEM was 2.2 kcal/mol less exothermic than that on a pristine AEM. Overall, this work presents an effective strategy for selectively removing phosphate from model wastewater solutions and the mechanistic understanding that governs ion selectivity in composite ion-exchange membranes used in MCDI.

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A charge-free and membrane-free hybrid capacitive mixing system for salinity gradient energy harvesting

Abstract: Capacitive mixing (CapMix) is a promising technology to harvest the salinity gradient energy (SGE) by generating electricity through the potential difference owing to electrolyte salinity change at the electrode/electrolyte interface....

Cited by 7 publications

References 50 publications

Tuning Surface Molecular Design of Porous Carbon for Blue Energy Harvesting

Tuning Surface Molecular Design of Porous Carbon for Blue Energy Harvesting

Unraveling Flow Effect on Capacitive Energy Extraction from Salinity Gradients

Selective phosphate removal with manganese oxide composite anion exchange membranes in membrane capacitive deionization

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