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S. Luo et al.
target will be sputtered out with certain kinetic energy, shooting toward the substrate
in a certain direction, and then achieving the formation of films. According to its
characteristics, it can be divided into five categories: DC sputtering, AC sputtering,
reactive sputtering, magnetron sputtering and ion beam sputtering. Sputtering method
is facile and effective in preparing films with high melting point, preparing uniform
films on large continuous substrates, controlling the composition of films easily,
preparing alloy films with different components, and preparing multilayered films.
Metal efficient catalysts with various structures such as nanoparticles, films and
wires have been successfully prepared by sputtering. Stamenkovic et al. prepared
the multimetallic mesostructured thin-film catalysts on a glassy carbon substrate
with a diameter of 6 nm by magnetron sputtering. The carbon-free catalysts possess
tunable composition and surface morphology, and exhibit 20-fold more active than
commercial Pt/C catalyst for oxygen reduction reaction [68]. Debe et al. presented
nanostructured thin film catalysts (NSTF) with widely varying compositions of Pt x M y
and Pt x M y N z by sputtering, where M and N are Ni, Co, Zr, Hf, Fe, Mn, 0 ≤ x,
y, z < 1. When measured in 50 cm
2 fuel cells, the whisker-like Pt 3 Ni 7 nano-film
catalyst showed a mass activity exceeds 350 mA mg Pt
−1 at 0.9 V [69]. Sputtering can
fabricate catalysts that cannot be prepared by traditional chemical methods, which
is of great significance in experimental research. Compared with other preparation
methods, sputtering has higher requirements in instrument and produces catalysts in
low yield. Nevertheless, sputtering shows a certain industrial application prospect
due to its advantages on easy realization of continuity and automation.
5.3.2 Sonochemical Synthesis Method
Sonochemical synthesis method, known as sonochemistry, uses ultrasound to accelerate chemical reactions and improve chemical yields. It mainly studies the changes
of chemical reactions or chemical reaction processes aroused by ultrasound. Ultrasound is a kind of high frequency mechanical wave, which has the characteristics of
concentrated energy, strong penetration, etc. When sound energy is high enough, the
attraction between liquid molecules is broken and the cavitation nuclei are formed.
Cavitation nucleus possesses a lifetime of about 0.1 µs, and it can produce local high
temperature of about 4000–6000 K and high pressure of 100 MPa at the moment
of explosion, and generate powerful micro jets with velocity of about 110 m s
−1 ,
and those processes are called ultrasonic cavitation. These conditions are sufficient
to induce chemical bond fracture, aqueous phase combustion, pyrolysis and free
radical reaction of organics within the cavitation bubbles.
Ultrasound can boost the crystal growth, promote the formation of new phase,
manipulate the particle morphology, improve dispersion and reaction selectivity,
increase nucleation and chemical reaction rate, and shorten the reaction time. Besides,
it can stimulate the chemical reactions that cannot occur in the absence of ultrasound.
The device used for sonochemical synthesis method is shown in Fig. 5.8a, which has
S. Luo et al.
target will be sputtered out with certain kinetic energy, shooting toward the substrate
in a certain direction, and then achieving the formation of films. According to its
characteristics, it can be divided into five categories: DC sputtering, AC sputtering,
reactive sputtering, magnetron sputtering and ion beam sputtering. Sputtering method
is facile and effective in preparing films with high melting point, preparing uniform
films on large continuous substrates, controlling the composition of films easily,
preparing alloy films with different components, and preparing multilayered films.
Metal efficient catalysts with various structures such as nanoparticles, films and
wires have been successfully prepared by sputtering. Stamenkovic et al. prepared
the multimetallic mesostructured thin-film catalysts on a glassy carbon substrate
with a diameter of 6 nm by magnetron sputtering. The carbon-free catalysts possess
tunable composition and surface morphology, and exhibit 20-fold more active than
commercial Pt/C catalyst for oxygen reduction reaction [68]. Debe et al. presented
nanostructured thin film catalysts (NSTF) with widely varying compositions of Pt x M y
and Pt x M y N z by sputtering, where M and N are Ni, Co, Zr, Hf, Fe, Mn, 0 ≤ x,
y, z < 1. When measured in 50 cm
2 fuel cells, the whisker-like Pt 3 Ni 7 nano-film
catalyst showed a mass activity exceeds 350 mA mg Pt
−1 at 0.9 V [69]. Sputtering can
fabricate catalysts that cannot be prepared by traditional chemical methods, which
is of great significance in experimental research. Compared with other preparation
methods, sputtering has higher requirements in instrument and produces catalysts in
low yield. Nevertheless, sputtering shows a certain industrial application prospect
due to its advantages on easy realization of continuity and automation.
5.3.2 Sonochemical Synthesis Method
Sonochemical synthesis method, known as sonochemistry, uses ultrasound to accelerate chemical reactions and improve chemical yields. It mainly studies the changes
of chemical reactions or chemical reaction processes aroused by ultrasound. Ultrasound is a kind of high frequency mechanical wave, which has the characteristics of
concentrated energy, strong penetration, etc. When sound energy is high enough, the
attraction between liquid molecules is broken and the cavitation nuclei are formed.
Cavitation nucleus possesses a lifetime of about 0.1 µs, and it can produce local high
temperature of about 4000–6000 K and high pressure of 100 MPa at the moment
of explosion, and generate powerful micro jets with velocity of about 110 m s
−1 ,
and those processes are called ultrasonic cavitation. These conditions are sufficient
to induce chemical bond fracture, aqueous phase combustion, pyrolysis and free
radical reaction of organics within the cavitation bubbles.
Ultrasound can boost the crystal growth, promote the formation of new phase,
manipulate the particle morphology, improve dispersion and reaction selectivity,
increase nucleation and chemical reaction rate, and shorten the reaction time. Besides,
it can stimulate the chemical reactions that cannot occur in the absence of ultrasound.
The device used for sonochemical synthesis method is shown in Fig. 5.8a, which has