89
7.3.2 Synthesis of Pt ML by Surface Mediated Growth
To generate Pt shells with controlled morphology and thickness on a Pd core, viz.,
Pd C Pt n nanoparticles (with n being the number of Pt layers in the shell on Pd cores),
Wang et al. utilized a Cu UPD–mediated electrodeposition method [18]. Figure 7.7
shows the voltammetry curves for Cu UPD on Pd and Pt nanoparticle catalysts,
wherein a full monolayer of Cu is deposited and removed during potential cycles
positive of the Cu bulk’s deposition potential (0.36 V).
An irreversible deposition of Pt under diffusion control takes place at potentials
below its bulk deposition potential (0.67 V) in the solution containing 0.1 mM
K 2 PtCl 4 and 50 mM Cu
2+
. With repeated potential cycles between 0.37 and 0.67 V,
the Cu UPD current gradually increases (green curves in Fig. 7.7b), reflecting the
enlargement of the surface area as the size of the core-shell nanoparticles grows by
irreversibly deposited Pt. The role of Cu UPD and stripping cycle in this electrodeposition process is to lower the rate of Pt deposition and to enhance surface diffusion of Pt adatoms so that a smooth layer forms. At the end of Pt deposition, a
linear potential sweep, up to 1 V, completely removes Cu (Fig. 7.7). The number of
Fig. 7.6 Schematic procedure for obtaining metallic Pd nanoparticles decorated by a monolayer
of Pt synthesized in ethanol (a) and high-angle annular dark-field (HAADF) of the obtained
nanoparticles (b). Reproduced from [12] by permission of Springer Nature
2.0
1.0
0.0
–1.0
–2.0
0.0
0.2
0.4
0.6
0.8
1.0
E vs RHE (V)
E vs RHE (V)
Current density (mA cm –2
)
Current density (mA cm –2
)
0.8
0.4
0.0
–0.4
–0.8
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Cu mediated Pt deposition
Bulk
Cu
Bulk
Pt
Pd
Pt
Cu UPD
30 mV s –1
30 mV s
–1
Fig. 7.7 (a) Voltammetry curves for Cu UPD on Pd (blue) and Pt (red) nanoparticles in Ar-saturated
solutions containing 50 mM H 2 SO 4 and 50 mM CuSO 4 , together with a baseline voltammetry
curve for Pd in a solution without Cu (black). (b) Voltammetry curves before (blue), during (green),
and after (red) Pt ML deposition on Pd in the above solution with additional 0.1 mM K 2 PtCl 4 . From
Ref. [18] by permission of American Chemical Society
7.3 Other Syntheses of Pt Monolayer Electrocatalysts
7.3.2 Synthesis of Pt ML by Surface Mediated Growth
To generate Pt shells with controlled morphology and thickness on a Pd core, viz.,
Pd C Pt n nanoparticles (with n being the number of Pt layers in the shell on Pd cores),
Wang et al. utilized a Cu UPD–mediated electrodeposition method [18]. Figure 7.7
shows the voltammetry curves for Cu UPD on Pd and Pt nanoparticle catalysts,
wherein a full monolayer of Cu is deposited and removed during potential cycles
positive of the Cu bulk’s deposition potential (0.36 V).
An irreversible deposition of Pt under diffusion control takes place at potentials
below its bulk deposition potential (0.67 V) in the solution containing 0.1 mM
K 2 PtCl 4 and 50 mM Cu
2+
. With repeated potential cycles between 0.37 and 0.67 V,
the Cu UPD current gradually increases (green curves in Fig. 7.7b), reflecting the
enlargement of the surface area as the size of the core-shell nanoparticles grows by
irreversibly deposited Pt. The role of Cu UPD and stripping cycle in this electrodeposition process is to lower the rate of Pt deposition and to enhance surface diffusion of Pt adatoms so that a smooth layer forms. At the end of Pt deposition, a
linear potential sweep, up to 1 V, completely removes Cu (Fig. 7.7). The number of
Fig. 7.6 Schematic procedure for obtaining metallic Pd nanoparticles decorated by a monolayer
of Pt synthesized in ethanol (a) and high-angle annular dark-field (HAADF) of the obtained
nanoparticles (b). Reproduced from [12] by permission of Springer Nature
2.0
1.0
0.0
–1.0
–2.0
0.0
0.2
0.4
0.6
0.8
1.0
E vs RHE (V)
E vs RHE (V)
Current density (mA cm –2
)
Current density (mA cm –2
)
0.8
0.4
0.0
–0.4
–0.8
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Cu mediated Pt deposition
Bulk
Cu
Bulk
Pt
Pd
Pt
Cu UPD
30 mV s –1
30 mV s
–1
Fig. 7.7 (a) Voltammetry curves for Cu UPD on Pd (blue) and Pt (red) nanoparticles in Ar-saturated
solutions containing 50 mM H 2 SO 4 and 50 mM CuSO 4 , together with a baseline voltammetry
curve for Pd in a solution without Cu (black). (b) Voltammetry curves before (blue), during (green),
and after (red) Pt ML deposition on Pd in the above solution with additional 0.1 mM K 2 PtCl 4 . From
Ref. [18] by permission of American Chemical Society
7.3 Other Syntheses of Pt Monolayer Electrocatalysts