Selective ammonium enrichment in stopped-flow discharge operation of capacitive deionization (CDI) using a NiHCF/CNT electrode
Journal
Desalination
Journal Volume
629
Start Page
120119
ISSN
00119164
Date Issued
2026-07-01
Author(s)
Abstract
Selective ammonium (NH4+) enrichment from wastewater is increasingly important, while practical recovery remains challenging due to competing ions and limited product purity. In this work, we demonstrate a synergistic strategy that couples a carbon nanotube bridged nickel hexacyanoferrate (NiHCF/CNT) intercalation electrode with a stopped flow discharge operation in capacitive deionization (CDI) to achieve selective and energy efficient NH4+ enrichment. NiHCF provides an intrinsic preference for NH4+ intercalation over Na+ and Ca2+, while CNT incorporation forms conductive pathways that markedly enhance charge transfer and ion transport. As a result, the NiHCF/CNT electrode exhibits a high specific capacitance of 248.62 F/g in NH4Cl, exceeding that in NaCl and CaCl2, and a low charge-transfer resistance of 0.75 Ω. Notably, in single-pass CDI, the NiHCF/CNT electrode achieved NH4+/Ca2+ and NH4+/Na+ selectivity coefficients of 26.33 and 8.49, respectively. Introducing a 10 min stopped-flow step further increased NH4+ enrichment by 1.5-fold relative to no stopped flow and enabled rapid recovery, reaching 21.48 mg/g within 2 min after pump restart. Moreover, the NiHCF/CNT electrode maintained stable CDI performance over 10 consecutive cycles. Overall, this work highlights a practical route in which material enabled selectivity and process level brine minimization work synergistically to produce a higher purity, more concentrated NH₄+ stream for resource recovery from complex waters.
Subjects
Ammonium enrichment
Capacitive deionization
Nickel hexacyanoferrate
Selective intercalation
Stopped-flow discharge
Publisher
Elsevier B.V.
Type
journal article