Coni nanoparticles/cnt composite as effective anode for direct urea fuel cells
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Answer:
Explanation:
1. INTRODUCTION
Besides the human and animal urines, fertilizers industries discharge huge amount of ureacontaminated wastewaters. The urea fertilizer manufacturing plants discharge 0.75 m3 wastewater
containing around 1wt% urea per ton fertilizer produced [1]. Environmentally, the urea-polluted water
should be treated to avoid formation of the ammonia gas from urea hydrolysis [2].
NH2CONH2 + H2O 2NH3 + CO2 (1)
Besides the air pollution which may result in falling the acidic rains, the produced ammonium
can create other environmental problems. The dissolved ammonia is biologically oxidized in water by
two kinds of microorganisms (Nitrobacter and Nitrosomonas ) to nitrate (NO3) in a process called
Int. J. Electrochem. Sci., Vol. 13, 2018 4694
nitrification[3]. The main problem is producing a dangerous unstable compound as an intermediate;
nitrogen dioxide. This process takes place in the oxygen-containing media such as open water surfaces
so the nitrate ion can be reduced to form different kinds of nitrogenous gases. Beside the
aforementioned problems, domoic acid which is deadly toxin can be produced by some kinds of ocean
algae in the urea-polluted media [4].
Owing considerable amount of hydrogen (6.67 wt%) drew the attention of the researchers to
exploit the urea-containing wastewater as a good source of hydrogen gas. Therefore, electrolysis has
been proposed as a treatment process for the urea-containing wastewater and simultaneously producing
H2 gas due to occurring some oxidation reactions which can be explained electrochemically as follow
[5-7]:
Anode: CO(NH2)2 + 6OH¯ N2 + 5H2O + CO2 + 6e E
0
= - 0.746 V (2)
Cathode: 6H2O + 6e 3H2 + 6OH¯ E
0
= - 0.829 V (3)
Overall: CO(NH2)2 + H2O N2 + 3H2 + CO2 E
0
= - 0.083 V (4)
As it might be concluded from the standard potentials, the electrolysis process needs small
energy however, practically, due to the high overpotentials, the real electrode potentials are very far
from the theoretical ones especially the anode potential even with the precious metals anodes[8].
Therefore, the electrolysis process needs high energy and it is economically not preferable.
Developing a proper anode material can lead to operate direct urea fuel cells (DUFC) in which
the urea is oxidized and simultaneously the wastewater will be treated. In the DUFC, the electrodes
reactions will be in these forms [9].
Cathode: 2H2O+O2+4e 4OH¯ E0
= + 0.40 V (5)
Anode: CO(NH2)2+6OH¯ N2+5H2O+CO2+6e E
0
= - 0.746 V (6)
Overall: 2CO(NH2)2+3O2 2N2+4H2O+2CO2 E
0
= + 1.146 V (7)
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Explanation:
