Efficient Electroreduction of Low Nitrate Concentration via Nitrate Self-Enrichment and Active Hydrogen Inducement on the Ce(IV)-Co 3 O 4 Cathode.

Low concentrations of nitrate (NO 3 - ) widely exist in wastewater, post-treated wastewater, and natural environments; its further disposal is a challenge but meaningful for its discharge goals. Electroreduction of NO 3 - is a promising method that allows to eliminate NO 3 - and even generate higher-value NH 3 . However, the massive side reaction of hydrogen evolution has raised great obstacles in the electroreduction of low concentrations of NO 3 - . Herein, we present an efficient electroreduction method for low or even ultralow concentrations of NO 3 - via NO 3 - self-enrichment and active hydrogen (H*) inducement on the Ce(IV)-Co 3 O 4 cathode. The key mechanism is that the strong oxytropism of Ce(IV) in Co 3 O 4 resulted in two changes in structures, including loose nanoporous structures with copious dual adsorption sites of Ce-Co showing strong self-enrichment of NO 3 - and abundant oxygen vacancies (O vs ) inducing substantial H*. Ultimately, the bifunctional role synergistically promoted the selective conversion of NH 3 rather than H 2 . As a result, Ce(IV)-Co 3 O 4 demonstrated a NO 3 - self-enrichment with a 4.3-fold up-adsorption, a 7.5-fold enhancement of NH 3 Faradic efficiency, and a 93.1% diminution of energy consumption when compared to Co 3 O 4 , substantially exceeding other reported electroreduction cathodes for NO 3 - concentrations lower than 100 mg·L -1 . This work provides an effective treatment method for low or even ultralow concentrations of NO 3 - .