Ni-Fe Layered Double Hydroxide Nanosheets Supported on Exfoliated Graphite for Efficient Urea Oxidation in Direct Urea Fuel Cells.

Abstract

Urea-rich wastewater can cause serious eutrophication problem to the water environment. On the other hand, urea is a potential fuel with high energy density, which can be effectively utilized by direct urea fuel cell. In this work, exfoliated graphite (EG) with high surface area and electrical conductivity was obtained by microwave irradiation, which was used to support the Ni-Fe layered double hydroxide (LDH), leading to a highly efficient and low-cost urea oxidation catalyst. Compared with commercial RuO2 , the as-prepared Ni-Fe LDH/EG exhibited a lower onset potential of 1.25 V vs. reversible hydrogen electrode as well as a lower Tafel slope of 44 mV dec-1 . The catalyst durability was also proved to be excellent. The optimized Ni/Fe molar ratio was confirmed to be 3 : 1, while the most suitable catalyst/EG ratio was 3 : 50. When applied in a dual-electrolyte direct urea fuel cell, the peak power density reached 12 mW cm-2 , and the long-term discharge was also stable with negligible voltage loss at 10 mA cm-2 for 3 h. Such a low-cost and efficient urea oxidation catalyst can be widely utilized in future direct urea fuel cells, which achieve wastewater treatment and renewable electricity generation at the same time.