Energy-efficient faradaic desalination with scalable MnOx-coated carbon nanofoam papers validated by automated batch testing

Abstract

Electrochemical approaches to water desalination show promise for processing brackish water, but continued progress relies on developing scalable electrode architectures with competitive capacity and uptake dynamics for ion capture. Binder-free, device-ready carbon nanofoam papers (CNFPs) are one such candidate, where intermingled nanoscale networks of conductive carbon and pores balance the transport of electrons and ions throughout the electrified interior. Microwave-assisted electroless deposition of conformal nanoscale manganese oxide (MnOx) at the CNFP surface amplifies the ion-capture capacity to technologically relevant levels via faradaic pseudocapacitance. We take advantage of the design flexibility of these electrode architectures to vary CNFP pore size (5 to >100 nm) and thickness (100–300 μm), and then characterize the resulting MnOx@CNFP electrode series for their respective desalination performance in 20 mM NaCl using automated recirculating-batch protocols. The combination of CNFP conductivity and facile ion/electrolyte transport through the pore network with the faradaic ion-capture capability of the MnOx coating enables effective desalination. Using 0.3 mm-thick electrodes and MnOx loadings over 16 mg cm−2, we obtain desalination productivity of 6.8 L m−2 at 4.4 L m−2 h−1 for 90 % salt removal at only 0.13 Wh L−1 energy consumption.