Electrochemically selective ammonium recovery from wastewater via coupling hydrogen bonding and charge storage

Electrochemical ammonium (NH₄⁺) storage (EAS) has been established as an efficient technology for NH₄⁺ recovery from wastewater. However, there are scientific difficulties unsolved regarding low storage capacity and selectivity, restricting its extensive engineering applications. In this work, electrochemically selective NH₄⁺ recovery from wastewater was achieved by coupling hydrogen bonding and charge storage with self-assembled bi-layer composite electrode (GO/V₂O₅). The NH₄⁺ storage was as high as 234.7 mg N g^-1 (> 10² times higher than conventional activated carbon). Three chains of proof were furnished to elucidate the intrinsic mechanisms for such superior performance. Density functional theory (DFT) showed that an excellent electron-donating ability for NH₄⁺ (0.08) and decrease of diffusion barrier (22.3 %) facilitated NH₄⁺ diffusion onto electrode interface. Physio- and electro-chemical results indicated that an increase of interlamellar spacing (14.3 %) and electrochemical active surface area (ECSA, 388.9 %) after the introduction of GO were responsible for providing greater channels and sites toward NH₄⁺ insertion. Both non-ionic chemical-bonding (V⁵⁺=O‧‧‧H, hydrogen-bonding) and charge storage were contributed to the higher capacity and selectivity for NH₄⁺. This work offers underlying guideline for exploitation a storage manner for NH₄⁺ recovery from wastewater.