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

Abstract

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 mgRu–1 (1.4 × 10–6 ± 0.1 × 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 cm2 electrode) and 23.3 mW cm–2 (1 cm2 electrode), keeping ultrahigh Faradic efficiency (97% ± 4% at 40 mA cm–2) after long tests.

Exploring the origin of the high electro-catalytic activity for nitrate-to-ammonia conversion on electrodeposited Ni/Ru hydroxide hybrids

“…S5 and 6 †) indicate the presence of both Ru 0 and Ru-O bonds in the Ru-25CV/pNF and the Ru-LPD, which are considered crucial for efficient nitrate-to-ammonia conversion. 15 Regarding the Ni states, the XPS spectra of Ni 2p for the Ru-LPD/pNF are similar to those of the pristine NF (Fig. 2b), showing characteristic peaks of Ni 0 , NiO and Ni-OH.…”

“…S11. † 15 The products were also analyzed for the presence of nitrite, hydroxylamine and hydrazine, but no significant levels were found.…”

“…13 To address this issue, Ru with oxygen-doped nanoclusters has been demonstrated to have excellent activity for electrochemical nitrate reduction reactions, 14 especially when tensile strains associated with oxygen doping have been introduced, offering ammonia-production rates of 3.25 × 10 −7 mol s −1 cm −2 at −0.8 V vs. RHE. 15 In this study, we conducted further investigations on the catalyst structure to better understand the high efficiency of nitrate-to-ammonia conversion. We compared electrodes prepared by drop-cast Ru nanoparticles onto pristine nickel foam with electrodeposited Ni/Ru hydroxide hybrid.…”

Transition-Metal-Free, Pure p-Block Alloy Electrocatalysts for the Highly Efficient Nitrate Reduction to Ammonia

“…On the other hand, ammonia is a value-added product that has the potential to be used as a raw material for fertilizers and fuel cells . Therefore, transforming nitrate to ammonia is a key process for closing the nitrogen evolution cycle and turning waste into precious goods . Highly efficient and economical catalysts for nitrate reduction to ammonia (NRA) are in urgent demand.…”

“…12 Therefore, transforming nitrate to ammonia is a key process for closing the nitrogen evolution cycle and turning waste into precious goods. 13 Highly efficient and economical catalysts for nitrate reduction to ammonia (NRA) are in urgent demand.…”