Improving the Thermodynamic Energy Efficiency of Battery Electrode Deionization Using Flow-Through Electrodes

Abstract

1415 Abstract 16 Ion intercalation electrodes are being investigated for use in mixed capacitive deionization (CDI) 17 and battery electrode deionization (BDI) systems because they can achieve selective ion removal 18 and low energy deionization. To improve the thermodynamic energy efficiency (TEE) of these 19 systems, flow-through electrodes were developed by coating porous carbon felt electrodes with a 20 copper hexacyanoferrate composite mixture. The TEE for ion separation using flow-through 21 electrodes was compared to a system using flow-by electrodes with the same materials. The 22 flow-through BDI system increased the recoverable energy nearly threefold (0.009 kWh m −3 , 23 compared to a 0.003 kWh m −3 ), which increased the TEE from ~6% to 8% (NaCl concentration 24 reduction from 50 mM to 42 mM; 10 A m −2 , 50% water recovery, and 0.5 mL min −1 ). The TEE 25 was further increased to 12% by decreasing the flow rate from 0.50 mL min −1 to 0.25 mL min −1 .26 These findings suggest that under similar operational conditions and materials, flow-through 27 battery electrodes could achieve better energy recovery and TEE for desalination than flow-by 28 electrodes.

Membrane and Electrochemical Processes for Water Desalination: A Short Perspective and the Role of Nanotechnology

“…To convert Faradaic reactions—which are problematic reactions in the CDI process [ 72 ]—to the useful reactions, a Faradaic deionization process was developed to directly exchange the flux of electrons and ions [ 81 ]. This is also commonly referred to as the cation intercalation desalination [ 82 , 83 , 84 ] or BDI process [ 10 , 85 , 86 , 87 ] and primarily uses electrodes that can intercalate sodium ions (similar to that of battery electrodes for lithium-ion intercalation) ( Figure 3 a).…”

“…Unlike typical CDI that utilizes EDL for ion storage, cations and anions can be directly intercalated into the electrode in the BDI system. Thus, the BDI system often showed superior salt adsorption capacity (>50 mg-Na + /g [ 10 , 87 ]) compared to that of the CDI system (<30 mg-Na + /g [ 67 ]) depending on the electrode geometry and the selection of materials.…”

“…Fundamental organic and inorganic fouling experiments have been reported for CDI and ED [ 112 , 113 , 114 , 115 , 116 ], but fouling phenomena are not yet fully understood, as electrochemical processes are in the early stages of research compared to membrane processes. Moreover, a limited number of operations with relatively short cycles (mostly <100) have been reported for electrochemical processes [ 80 , 85 , 86 , 87 ]. Finally, high-performance electrodes are often challenging to mass-produce because of the use of expensive materials and technical difficulties in synthesis.…”

Low porosity, high areal-capacity Prussian blue analogue electrodes enhance salt removal and thermodynamic efficiency in symmetric Faradaic deionization with automated fluid control

“…In FDI, saltwater can flow through a gap between electrodes in a flow-by configuration or directly through the porous structure of electrodes sandwiched within a cell in a flow-through configuration. Flow-through electrodes incorporating Prussian blue analogue (PBA) CIMs, which we first demonstrated ( Reale et al., 2019 ), have shown improved salt removal ( Smith, 2017 ), charge utilization ( Liu and Smith, 2018 ; Smith, 2017 ; Son et al., 2020 ), and specific energy consumption ( Smith, 2017 ; Son et al., 2020 ) compared to flow-by PBA electrodes due to charge-efficiency loss at electrode/channel interfaces in flow-by ( Liu and Smith, 2018 ; Smith, 2017 ) and smaller ohmic drop in flow-through ( Son et al., 2020 ). Further, our experiments introducing flow-through FDI achieved rapid salt removal with one order of magnitude lower specific energy consumption, as provided by judicious choice of electronically conductive additives ( Reale et al., 2019 ) and inspired by our earlier work demonstrating that nanoparticle agglomeration limits transport in electrodes containing PBAs ( Shrivastava and Smith, 2018 ).…”

“…The configuration of electrolyte flow through porous electrodes ( Liu and Smith, 2018 ; Reale et al., 2019 ; Smith, 2017 ; Son et al., 2020 ) and charge transport within porous electrodes ( Reale et al., 2019 ; Shrivastava and Smith, 2018 ) are known to affect rate capability and energy consumption in FDI when using symmetric CIM electrodes, but past results suggest that unknown mechanisms remain and prevent the salt-removal potential of CIMs from being accessed. In FDI, saltwater can flow through a gap between electrodes in a flow-by configuration or directly through the porous structure of electrodes sandwiched within a cell in a flow-through configuration.…”