  Flowing electrode capacitive deionization systems (FE-CDI) have recently
garnered attention because of their ability to prevent cross contamination and
operate in uninterrupted cycles ad infinitum. Typically, FE-CDI electrodes
suffer from low conductivity, reducing deionization performance. Utilization of
higher mass loadings to combat this leads to poor rheological properties.
Herein, Ti$_3$C$_2$T$_x$ MXene was introduced as 1 mg/mL slurry electrodes in
an FE-CDI system for the removal and recovery of ammonia from simulated
agricultural wastewater. The electrode performance was evaluated by operating
the FE-CDI system with a feed solution of 500 mg/L NH$_4$Cl running in batch
mode at a constant voltage of 1.20 V and -1.20 V in charging and discharging
modes, respectively. Despite the low loading, Ti$_3$C$_2$T$_x$ flowing
electrodes showed markedly improved performance, achieving 60% ion removal
efficiency in a saturation time of 115 minutes with an adsorption capacity of
460 mg/g. To understand the high adsorption performance of the electrodes,
physiochemical and structural analysis was done via a variety of
characterization techniques such as SEM, TEM, XRD, DLS, and Raman Spectroscopy.
Cyclic Voltammetry and Galvanostatic charge/discharge profiles were obtained to
evaluate the electrochemical properties of the electrodes. The system proved to
be an energy-saving technology by exhibiting a charge efficiency of 58-70%
while operating at an energy consumption of 0.45 kWh/kg. A 92% regeneration
efficiency showed that the electrodes were stable and suitable for long term
and scalable usage. The results demonstrate that MXenes have the potential to
improve the FE-CDI process for energy-efficient removal and recovery of
ammonia.
