Support Information of the Article Electrochemical and Surface Science Data for Stabilized Pt-Pd-Co Methanol Oxidation Catalysts

Figure 1: The experimental procedure was organized into three main stages. PtNiCo/C nanoparticles were synthesized through an organometallic colloidal method using appropriate metal precursors. The nanoparticles were formed under controlled reaction conditions in the presence of a stabilizing agent and supported in situ on Vulcan XC-72R carbon. After synthesis, residual solvents, ligands, and reaction by-products were removed through vacuum concentration and successive washing steps. the PtPdCo/C catalysts were structurally, morphologically, and chemically characterized using XRD, SEM, HR-TEM, and XPS. The catalyst inks were prepared by dispersing the catalyst powder in a Nafion®/ethanol mixture under ultrasonication. The resulting ink was deposited onto a polished glassy carbon electrode to obtain a uniform catalytic layer. Electrochemical characterization was performed using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. Figure 2 presents the XPS survey spectra obtained for the four as-prepared Pt–Pd–Co/C ternary electrocatalysts with different nominal compositions. The survey spectra were employed to examine the surface elemental composition before detailed high-resolution analysis. The subsequent analysis focused on the O 1s, Co 2p, Pt 4f, and Pd 3d regions to identify the surface chemical states. High-resolution spectra were acquired using a pass energy of 20 eV and a step size of 0.1 eV. The C 1s signal at 284.5 eV was employed for charge correction. This initial XPS examination provides the reference framework for comparing the surface chemistry of the four different ternary compositions Figure 3 shows the high-resolution XPS spectra of the Pt₇₀Co₂₀Pd₁₀/C catalyst in the O 1s, Co 2p, Pt 4f, and Pd 3d regions. Deconvolution of the Pt 4f region indicates that Pt is predominantly present in the metallic Pt⁰ state, accounting for 78.24%, together with a smaller Pt(OH)₂ contribution. Pd is distributed among Pd⁰, PdO, and an assigned PdCl₂ contribution, with metallic Pd representing 57.78%. The Co 2p spectrum is assigned to Co₃O₄ spinel-related contributions. The O 1s spectrum contains components attributed to Pt/Pd–O, Pt/Pd–OH, and H₂O, with the hydroxyl-related contribution being dominant. Collectively, the spectra reveal the coexistence of metallic noble-metal species and oxidized surface components in this catalyst Figure 4 presents the high-resolution O 1s, Co 2p, Pt 4f, and Pd 3d spectra obtained for the Pd₇₀Co₂₀Pt₁₀/C electrocatalyst. Peak fitting indicates contributions from both metallic and oxidized noble-metal species. The Pt 4f region contains 69.43% Pt⁰ and 30.57% Pt(OH)₂ according to the reported fitting results. The Pd 3d region contains contributions assigned to metallic Pd, PdO, and PdCl₂ species. The Co 2p region was fitted with components associated with the Co₃O₄ spinel structure. The O 1s envelope includes metal–oxygen, hydroxyl, water-related, and an additional satellite contribution. These results demonstrate the chemically heterogeneous surface of the Pd-rich ternary catalyst. Figure 5 shows the detailed XPS analysis of the Co₇₀Pt₂₀Pd₁₀/C catalyst through the O 1s, Co 2p, Pt 4f, and Pd 3d core-level regions. The reported fitting results show that the Pt surface contribution is predominantly metallic, with Pt⁰ representing 80.24% and Pt(OH)₂ accounting for 19.76%. The Pd 3d region similarly contains a major metallic Pd⁰ contribution of 58.47%, accompanied by PdO and an assigned PdCl₂ component. The Co 2p envelope contains several contributions attributed to Co₃O₄ spinel species. The O 1s region includes signals associated with Pt/Pd–O, Pt/Pd–OH, and adsorbed water. The combined spectra characterize the oxidation-state distribution of Pt, Pd, Co, and oxygen-containing species at the catalyst surface Figure 6 presents the high-resolution XPS core-level spectra corresponding to O 1s, Co 2p, Pt 4f, and Pd 3d for the Co₇₀Pd₂₀Pt₁₀/C electrocatalyst. The quantitative fitting reported in the document identifies Pt exclusively as metallic Pt⁰ within the fitted Pt 4f contribution. Pd is predominantly present as Pd⁰, representing 70.60%, together with a PdO contribution of 29.40%. The Co 2p signal is represented by several components attributed to the Co₃O₄ spinel phase. The O 1s spectrum contains contributions associated with Pt/Pd–O, Pt/Pd–OH, and H₂O. Among these oxygen components, the Pt/Pd–O contribution has the largest reported percentage. Thus, Figure 6 highlights the coexistence of metallic noble metals with oxidized cobalt and oxygen-containing surface species. Figure 7 displays the Bode phase-angle plots obtained by electrochemical impedance spectroscopy for the Pt–Pd–Co/C ternary electrocatalysts at an overpotential of 0.2 V. The experiments were conducted in an alkaline electrolyte containing 1 M KOH and 2 M CH₃OH. The Bode representation provides electrochemical impedance information for comparison among the different catalyst compositions. According to the accompanying discussion, the high-Co electrode materials presented the lowest overall impedance. The document relates this behaviour to the influence of cobalt on charge-transfer kinetics in the ternary catalytic system. These EIS measurements therefore complement the surface characterization conducted by XPS and SEM/EDS and provide electrochemical information on the response of the catalysts under methanol oxidation conditions. Figure 8 presents the corresponding Bode phase-angle plots measured at an overpotential of 0.3 V in 1 M KOH + 2 M CH₃OH. The measurements allow comparison of the impedance behaviour of the four Pt–Pd–Co/C ternary compositions at a second applied overpotential. Together, Figures 7 and 8 provide the EIS dataset used to evaluate differences in the electrochemical response associated with catalyst stoichiometry. The manuscript reports that compositions with higher cobalt contents show the lowest total impedance. This behaviour is discussed in terms of improved charge-transfer kinetics associated with cobalt-containing ternary systems. The EIS results therefore provide an electrochemical complement to the chemical-state and compositional information obtained by the other characterization techniques. Figure 9 presents the SEM/EDS elemental mapping of the Pt₇₀Co₂₀Pd₁₀/C catalyst following electrochemical measurements. The mapping was used to investigate the spatial distribution of the constituent elements after electrochemical evaluation. The manuscript reports that SEM/EDS observations demonstrate good dispersion and structural stability following the electrochemical experiments. The analysis is relevant for assessing the post-reaction distribution of Pt, Co, and Pd within the carbon-supported material. SEM/EDS furthermore complements XPS because it supplies morphological and elemental-distribution information rather than exclusively surface chemical-state information. Figure 9 therefore contributes to assessing the post-electrochemical characteristics of the Pt-rich catalyst. Figure 10 displays SEM/EDS elemental mapping of the Pd₇₀Co₂₀Pt₁₀/C catalyst after electrochemical measurements. The elemental maps provide spatially resolved information on the distribution of Pd, Co, and Pt associated with the carbon-supported catalyst. The manuscript uses these post-reaction observations to assess dispersion and structural stability after electrochemical evaluation. Comparison with the other compositions makes it possible to examine how the nominal composition is reflected in the SEM/EDS characterization. The EDS information also provides complementary evidence to the surface-sensitive chemical-state analysis obtained by XPS. Together with the corresponding semi-quantitative results in Figure 14, Figure 10 forms part of the post-electrochemical compositional evaluation of the Pd-rich ternary catalyst. Figure 11 shows the SEM/EDS elemental mapping obtained for the Co₇₀Pt₂₀Pd₁₀/C electrocatalyst following electrochemical testing. The analysis examines the spatial distribution of the metallic components within the carbon-supported material after exposure to the electrochemical environment. This catalyst belongs to the high-cobalt group investigated in the study. The manuscript reports that the SEM/EDS mappings demonstrate good dispersion and structural stability following electrochemical evaluation. This characterization is particularly useful when considered together with the Co 2p XPS analysis and the lower impedance reported for high-Co compositions. Figure 11 therefore links post-reaction morphological and compositional characterization with the broader comparison of the four ternary catalyst formulations. Figure 12 presents the post-electrochemical SEM/EDS mapping of the Co₇₀Pd₂₀Pt₁₀/C catalyst. The elemental mapping was obtained after electrochemical measurements and provides information about the distribution of Co, Pd, and Pt within the supported catalyst. As one of the two cobalt-rich compositions, this material provides an important comparison with the Pt- and Pd-rich formulations. The manuscript collectively describes Figures 9–12 as demonstrating good dispersion and structural stability following electrochemical evaluation. The SEM/EDS dataset therefore provides complementary post-reaction information to the surface chemical states identified by XPS. The corresponding semi-quantitative composition is subsequently presented in Figure 16. Figure 13 presents the SEM/EDS semi-quantitative analysis of the Pt₇₀Co₂₀Pd₁₀/C catalyst following electrochemical measurements. The analysis complements the elemental mapping shown in Figure 9 by providing semi-quantitative compositional information for the post-reaction material. The SEM/EDS approach was employed to evaluate morphology, elemental distribution, and composition following electrochemical testing. According to the manuscript, the combined results support good dispersion and structural stability of the catalyst materia