50
S. Li and R. Jin
Fig. 2.7 a High-resolution Co 2p XPS spectra of CoSe 2 and Au 25 /CoSe 2 composites, b Raman
spectra of CoSe 2 and Au 25 /CoSe 2 composites. Adapted from Ref. [37]. Copyright 2017 American
Chemical Society
2.4.2 Au n NC Size Effect in OER
The size of gold nanoclusters is also important for the catalytic activity. To study the
potential size dependence of Au n NCs for OER, Zhao et al. compared gold nanoclusters of Au 10 (SPht Bu) 10 , Au 25 (SR) 18 , Au 144 (SR) 60 and Au 333 (SR) 79 , with the latter
three being protected by the same phenylethanethiolate ligand. These NCs were
loaded onto CoSe 2 (all at 2.0 wt%, denoted as Au n /CoSe 2 ). The OER polarization
curves show a moderate increase of OER activity with an increase in cluster size. The
Au 333 /CoSe 2 catalyst possesses the smallest overpotential (~0.41 V for 10 mA cm
−2 )
and the largest current density (15.44 mA cm
−2 at the overpotential of 0.45 V).
2.5 Oxygen Reduction Reaction with Au NCs
The ORR is the rate-determining step of the fuel cell system because of its sluggish
kinetics [38, 39]. In both acidic and alkaline electrolyte, different mechanisms have
been documented for ORR. These processes can be described as follows:
Acidic: O 2 + 4 H
+
+ 4 e
−
→ 2 H 2 O
(2.8)
O 2 + 2 H
+
+ 2 e
−
→ H 2 O 2
(2.9)
H 2 O 2 + 2 H + 2 e
−
→ 2 H 2 O
(2.10)
Alkaline: O 2 + H 2 O + 4 e
−
→ 4 OH
−
(2.11)
S. Li and R. Jin
Fig. 2.7 a High-resolution Co 2p XPS spectra of CoSe 2 and Au 25 /CoSe 2 composites, b Raman
spectra of CoSe 2 and Au 25 /CoSe 2 composites. Adapted from Ref. [37]. Copyright 2017 American
Chemical Society
2.4.2 Au n NC Size Effect in OER
The size of gold nanoclusters is also important for the catalytic activity. To study the
potential size dependence of Au n NCs for OER, Zhao et al. compared gold nanoclusters of Au 10 (SPht Bu) 10 , Au 25 (SR) 18 , Au 144 (SR) 60 and Au 333 (SR) 79 , with the latter
three being protected by the same phenylethanethiolate ligand. These NCs were
loaded onto CoSe 2 (all at 2.0 wt%, denoted as Au n /CoSe 2 ). The OER polarization
curves show a moderate increase of OER activity with an increase in cluster size. The
Au 333 /CoSe 2 catalyst possesses the smallest overpotential (~0.41 V for 10 mA cm
−2 )
and the largest current density (15.44 mA cm
−2 at the overpotential of 0.45 V).
2.5 Oxygen Reduction Reaction with Au NCs
The ORR is the rate-determining step of the fuel cell system because of its sluggish
kinetics [38, 39]. In both acidic and alkaline electrolyte, different mechanisms have
been documented for ORR. These processes can be described as follows:
Acidic: O 2 + 4 H
+
+ 4 e
−
→ 2 H 2 O
(2.8)
O 2 + 2 H
+
+ 2 e
−
→ H 2 O 2
(2.9)
H 2 O 2 + 2 H + 2 e
−
→ 2 H 2 O
(2.10)
Alkaline: O 2 + H 2 O + 4 e
−
→ 4 OH
−
(2.11)