Topics in Current Chemistry (2018) 376:42
1 3
and exit of reactant and product. Continuingly, nickel nanoparticles were electro-deposited on the CS surface to form Ni@CS anode, which had a large surface area (Fig. 20b). The calculated EASA of Ni@CS anode was 18 times that
of the Ni/Ti flat anode. The entire fabrication process avoided the introduction of
binders and therefore exhibited a high catalytic activity, stability, and durability.
Specifically, in the 0.1 M urea and 1 M NaOH, Ni@CS catalyst reached a peak
current density of 290 mA cm
−2
, which was 18 times that of the flat Ni/Ti catalyst. During the 20-min chronoamperometric test, the value of current density at
the four applied potentials (0.45, 0.40, 0.35, and 0.30 V) demonstrated almost no
attenuation owing to the robustness of the carbon sponge skeleton and deposited
Ni catalyst [126].
5 Conclusions
A review of recent advances in the electro-oxidation of urea for DUFCs and urea
electrolysis is presented. When urea is used for anodic fuel in DUFCs, the device
can purify waste water as well as generate power in the meantime. In addition, as a
hydrogen-rich chemical fuel, urea can also be electrolyzed to produce hydrogen for
energy storage in the near future. The exact mechanisms of urea decomposition are
pretty different in alkaline and neutral mediums and therefore separately discussed
in detail. More importantly, the development of anodic electro-catalysts is significant for optimizing the electrochemical properties of both DUFCs and urea electrolysis cell, which is primarily summarized in our review (as shown in Table 5). Pure
nickel, nickel oxides, or hydroxides still suffer from obstacles such as poor conductivity, inadequate stability, and lack of resistance to CO poisoning at present, which
lead to high onset oxidant potential, poor cycling, or severe polarization. Therefore,
future research on the nickel-based catalysts may be focused on solving the above
challenges from several aspects: On the one hand, improving catalyst preparation
methods is necessary to synthesize the nanostructured catalysts with controllable
morphologies. The rapid development of nanotechnology provides a great technical
support for fabricating catalysts with higher performance. On the other hand, novel
nickel-based compounds such as phosphides and selenides show a competitive catalytic current density and relatively low over-potential. Moreover, the incorporation
of other transition metals into these compounds is expected to satisfy the demands
of bi-functional catalysts for both production of hydrogen and electrolysis of urea
in the overall water spitting systems. The introduction of novel and promising catalyst supports manifests a great potential in improving the conductivity, stability, and
electrochemical activity of the catalysts.
Reprinted from the journal
70
1 3
and exit of reactant and product. Continuingly, nickel nanoparticles were electro-deposited on the CS surface to form Ni@CS anode, which had a large surface area (Fig. 20b). The calculated EASA of Ni@CS anode was 18 times that
of the Ni/Ti flat anode. The entire fabrication process avoided the introduction of
binders and therefore exhibited a high catalytic activity, stability, and durability.
Specifically, in the 0.1 M urea and 1 M NaOH, Ni@CS catalyst reached a peak
current density of 290 mA cm
−2
, which was 18 times that of the flat Ni/Ti catalyst. During the 20-min chronoamperometric test, the value of current density at
the four applied potentials (0.45, 0.40, 0.35, and 0.30 V) demonstrated almost no
attenuation owing to the robustness of the carbon sponge skeleton and deposited
Ni catalyst [126].
5 Conclusions
A review of recent advances in the electro-oxidation of urea for DUFCs and urea
electrolysis is presented. When urea is used for anodic fuel in DUFCs, the device
can purify waste water as well as generate power in the meantime. In addition, as a
hydrogen-rich chemical fuel, urea can also be electrolyzed to produce hydrogen for
energy storage in the near future. The exact mechanisms of urea decomposition are
pretty different in alkaline and neutral mediums and therefore separately discussed
in detail. More importantly, the development of anodic electro-catalysts is significant for optimizing the electrochemical properties of both DUFCs and urea electrolysis cell, which is primarily summarized in our review (as shown in Table 5). Pure
nickel, nickel oxides, or hydroxides still suffer from obstacles such as poor conductivity, inadequate stability, and lack of resistance to CO poisoning at present, which
lead to high onset oxidant potential, poor cycling, or severe polarization. Therefore,
future research on the nickel-based catalysts may be focused on solving the above
challenges from several aspects: On the one hand, improving catalyst preparation
methods is necessary to synthesize the nanostructured catalysts with controllable
morphologies. The rapid development of nanotechnology provides a great technical
support for fabricating catalysts with higher performance. On the other hand, novel
nickel-based compounds such as phosphides and selenides show a competitive catalytic current density and relatively low over-potential. Moreover, the incorporation
of other transition metals into these compounds is expected to satisfy the demands
of bi-functional catalysts for both production of hydrogen and electrolysis of urea
in the overall water spitting systems. The introduction of novel and promising catalyst supports manifests a great potential in improving the conductivity, stability, and
electrochemical activity of the catalysts.
Reprinted from the journal
70