A direct urea microfluidic fuel cell with flow-through Ni-supported-carbon- nanotube-coated sponge as porous electrode

A direct urea microfluidic fuel cell (UMFC) is demonstrated using a Ni-supported-carbon-nanotube-coated sponge (Ni/CNT@Sponge) as the flow-through porous anode. Ni/CNT@Sponge electrode is prepared through Ni/CNT composite synthesis followed by sponge dipping-drying process. Ni/CNT catalyst shows better performance to urea electrooxidation than Ni/C. The three-dimensional architecture of Ni/CNT@Sponge can provide high effective active area, which enhances the UMFC cell performance. The UMFC works in an alkaline and an acid environment at the anode and cathode respectively, achieving a high theoretical OCV of 1.976 V. With 3 M urea in 3 M KOH as anolyte, 1.5 M H₂SO₄ as the catholyte, an OCV of 0.92 V at 20 °C can be obtained. Peak power density and maximum current density of 3.9 mW cm⁻² and 23 mA cm⁻² can be achieved, respectively, which increase to 6.6 mW cm⁻² and 33 mA cm⁻², respectively when the temperature is increased to 45 °C. This work develops a new type of urea microfluidic fuel cell, also opens up a promising approach for urea-rich wastewater treatment.