Nitrate-to-Ammonia Conversion on Ru/Ni Hydroxide Hybrid through Zinc-Nitrate Fuel Cell

The fuel cell is a basic device to generate electricity from chemical fuels. It is often operated with oxygen as the oxidizing agent, but its sluggish reduction has become a key challenge. Herein, a conceptual oxygen-free design is demonstrated, namely a zinc-nitrate fuel cell, which converts nitrate waste into valuable ammonia and generates electricity simultaneously. The cell is constructed with zinc foil as the anode and ruthenium (Ru) nanoparticles loaded on nickel foam as the cathode. Catalyzed by Ru/Ni hydroxide hybrid, the reaction rate of 384 mmol h(-1) mg(Ru)(-1) (1.4 x 10(-6) +/- 0.1 x 10(-6) mol s(-1) cm(-2)) and Faradic efficiency (FENH3 = 97% +/- 2%) at -0.6 V versus reverse hydrogen electrode are achieved for nitrate-to-ammonia conversion. During ammonia production, such zinc-nitrate fuel cell can further deliver a maximum power density of 51.5 mW cm(-2) (0.25 cm(2) electrode) and 23.3 mW cm(-2) (1 cm(2) electrode), keeping ultrahigh Faradic efficiency (97% +/- 4% at 40 mA cm(-2)) after long tests.

Automated summary

The fuel cell is a device that generates electricity from chemical fuels, but its slow reaction rate has been a key challenge. This study demonstrates a novel oxygen-free design of a zinc-nitrate fuel cell that converts nitrate waste into ammonia and generates electricity simultaneously. The cell maintains high chemical conversion efficiency and power density even after long-term testing.