Effect of metal ion location in reaction medium on formation process and structure of PtCu–CuO nanoparticles supported on carbon and γ-Fe₂O₃

Figures & data

Table 1. Average size and atomic ratios of PtCu nanoparticles measured using TEM, ICP-AES, and XRD. The sample IDs note the pH of the reaction medium and the support used.

Sample ID	Average size (nm)	ICP-AES Pt:Cu atomic ratio	XRD Pt:Cu atomic ratio
pH 5_C	3.0	52:48	57:43
pH 7_C	3.3	52:48	58:42
pH 11_C	3.9	52:46	76:24
pH 12_C	5.0	55:45	83:17
pH 5_γ-Fe2O3	2.9	53:47	59:41
pH 7_γ-Fe2O3	3.0	54:46	64:36
pH 9_γ-Fe2O3	3.2	54:46	68:32
pH 11_γ-Fe2O3	3.2	55:45	76:24

Figure 1. Metal ion ratio in solution as a function of pH of precursor containing (a) carbon support and (b) γ-Fe₂O₃ support (circle denotes Pt ion and square denotes Cu ion).

Figure 2. TEM micrographsaphs of PtCu nanoparticles supported on carbon at (a) pH 5, (b) pH 7, (c) pH 11, and (d) pH 12.

Figure 3. TEM micrographs of PtCu nanoparticles supported on γ-Fe₂O₃ at (a) pH 5, (b) pH 7, (c) pH 9, and (d) pH 11.

Figure 4. XRD patterns of PtCu nanoparticles supported on (a) carbon and (b) γ-Fe₂O₃.

Figure 5. Schematic of supported PtCu nanoparticle.

Table 2. Composition of PtCu nanoparticles determined from results (wt.%).

Sample ID	Pt in alloy^a	Pt ions not reduced	Cu in alloy	CuO	Cu ions not reduced
pH 5_C	6.0	1.5	1.5	0.3	0.7
pH 7_C	5.9	1.6	1.4	0.4	0.7
pH 11_C	6.2	1.3	0.6	1.1	0.8
pH 12_C	6.2	1.3	0.4	1.3	0.8
pH 5_γ-Fe2O3	7.9	–	1.8	0.5	–
pH 7_γ-Fe2O3	7.6	–	1.4	0.8	–
pH 9_γ-Fe2O3	7.5	–	1.2	1.0	–
pH 11_γ-Fe2O3	7.6	–	0.8	1.3	–

^aPt input is 7.5 wt.%.

^bCu input is 2.5 wt.%.

Figure 6. Cu composition in PtCu alloy particle as a function of metal ion content in solution for (a) carbon and (b) γ-Fe₂O₃ supports (circle denotes Pt ion and square denotes Cu ion).

Figure A1. Particle size distribution of PtCu nanoparticles supported on carbon at (a) pH 5, (b) pH 7, (c) pH 11, and (d) pH 12.

Table B1. Chemical states of Pt and Cu calculated from linear combination fit of XANES spectra.

	Pt (%)		Cu (%)
Sample ID	Pt	PtO2	Cu	CuO
pH 5_C	87.3	12.7	33.3	66.7
pH 7_C	82.3	17.7	24.8	75.2
pH 11_C	89.4	10.6	17.4	82.6
pH 12_C	94.4	5.6	21.4	78.6
pH 5_γ-Fe2O3	84.5	15.5	27.6	72.4
pH 7_γ-Fe2O3	83.0	17.0	–	–
pH 9_γ-Fe2O3	80.6	19.4	–	–
pH 11_γ-Fe2O3	83.0	17.0	19.0	81.0

Figure A2. Particle size distribution of PtCu nanoparticles supported on γ-Fe₂O₃ at (a) pH 5, (b) pH 7, (c) pH 9, and (d) pH 11.

Figure B1. XANES spectra of PtCu nanoparticles supported on carbon (a) Pt–L_III and (b) Cu–K edges.

Figure B2. XANES spectra of PtCu nanoparticles supported on γ-Fe₂O₃ (a) Pt–L_III and (b) Cu–K edges.

Figure C. Plot of lattice parameter as a function of Cu content in nanoparticles for (a) carbon and (b) γ-Fe₂O₃ supports.