Facile, Controllable, and Ultrathin NiFe-LDH In Situ Grown on a Ni Foam by Ultrasonic Self-Etching for Highly Efficient Urine Conversion.

Abstract

As the primary source of nitrogen pollutants in domestic sewage, urine is also an alternative for H2 production via electrochemical processes. However, it suffers from sluggish kinetics and noble-metal catalyst requirement. Here, we report a non-precious ultrathin NiFe-layered double hydroxide catalyst for the remarkable conversion of urea into N2 and H2, which is in situ grown on a Ni foam via ultrasonic self-etching in Fe3+/ethylene glycol (EG). EG regulates the etching rate of Fe3+, resulting in an ultrathin nanosheet structure with the aid of ultrasonication. This structure dramatically promotes the dehydrogenation process via decreasing the nanolayer thickness from 120 to 3.4 nm and leads to a 4.8-fold increase in the generation of active sites. It exhibits record urea oxidation kinetics (390.8 mA·cm-2 at 1.5 V vs RHE) with excellent stability (120 h), which is 11.8 times better than that of commercial Pt/C catalyst (33.1 mA·cm-2). Tests with real urine at 20 mA cm-2 achieve 74% total nitrogen removal and 2853 μmol·h-1 of H2 production. This study provides an attractive landscape for producing H2 by consuming urine biowastes.