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Enhanced Catalytic Activity and Stability of Pt/CeO2/PANI Hybrid Hollow Nanorod Arrays for Methanol Electrooxidation Han Xu, An-Liang Wang, Yexiang Tong, and Gao-Ren Li ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b01010 • Publication Date (Web): 24 Jun 2016 Downloaded from http://pubs.acs.org on June 28, 2016

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Enhanced Catalytic Activity and Stability of Pt/CeO2/PANI Hybrid Hollow Nanorod Arrays for Methanol Electrooxidation Han Xu, An-Liang Wang, Ye-Xiang Tong, and Gao-Ren Li* MOE Laboratory of Bioinorganic and Synthetic Chemistry, KLGHEI of Environment and Energy Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, China

E-mail: [email protected]

ABSTRACT

Here we designed and fabricated novel Pt/CeO2/PANI three-layered hollow nanorod arrays (THNRAs) as advanced electrocatalysts for methanol oxidation by combining the merits of CeO2, PANI, multilayered structure and hollow nanorod arrays. The synthesized Pt/CeO2/PANI THNRAs exhibit higher electrocatalytic activity and better stability toward the oxidation of methanol than Pt/PANI HNRAs, Pt/CeO2 HNRAs and commercial Pt/C catalysts. The enhanced electrocatalytic performance of the Pt/CeO2/PANI THNRAs may be due to the synergistic effects among Pt, CeO2 and PANI and the special three-layered hollow nanorod arrays, which can provide short diffusion paths for electroactive species and high-availability of electrocatalysts. The facile synthesis method can be considered as a promising strategy to design the high-performance electrocatalysts with low-cost for fuel cells.

Keywords: Multi-layered structure; hollow nanorod array; electrocatalyst; electroactivity; durability

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The direct methanol fuel cells (DMFCs) have been thought as one of the effective energy-conversion devices for growing attention to air pollution and global warming due to their high volumetric energy density, abundant sources of methanol and environmentally friendly.1-3 Currently, Pt is still considered as the most efficient anode electrocatalyst for the DMFCs. Nonetheless, its high cost, scarcity, poor reaction kinetics and poisoning have hindered their large-scale commercial applications.4-6 Therefore, increasing Pt utilization rate and decreasing Pt loading while improving electrocatalytic activity and stability are extremely important for the development of anode catalysts for DMFCs. The electrochemical performance of Pt electrocatalysts usually suffers from obviously deterioration due to the intermediates, for instance CO, which poison Pt surfaces.7-12 Recently, many attentions to reduce the adsorbed CO on the surfaces of Pt have been paid to the addition of co-catalysts such as transition metal to promote the oxidation of CO.13-17 Up to now, the incorporation of Ru into Pt catalysts has achieved the best electrocatalytic performance, but the Ru is expensive. Recently, some studies have focused on the unique electrocatalytic activity of dispersed Pt nanoparticles supported on metal oxides and the Pt/metal oxide interface boundary sites have provided evidences for the enhancement of electroactivity and stability.18-20 Among the various metal oxide supports, CeO2 has received widespread attention because of high oxygen storage capacity of CeO2, high anticorrosion ability in acidic media, and the alterable valence of Ce cations, which may efficiently inhibit the sintering of Pt nanoparticles and make sufficient OHads species available to electro-oxidize the majority of intermediates (for instance CO) on Pt surface during the methanol oxidation.21-28 Therefore, the exploration of the possibility of CeO2 as a high efficient co-catalyst for methanol oxidation is necessary. In addition, conducting polymer, especially polyaniline (PANI), as a support has attracted much interest for catalysts due to its good adhesion, low cost, friendly environmental effect, high electrochemical stability and high hydrophilic performance.29-30 The PANI as a support can obviously enhance the ability of CO antipoisoning and the dispersion of Pt.31-32 Recently, the hollow and array nanostructures are highly attractive for the electrocatalysts and they can obviously enhance the catalyst utilization and transmission of electroactive species and can efficiently resist the aggregation, dissolution and Ostwald 2 Plus Environment ACS Paragon

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ripening of catalysts.33-36 Based on the above considerations, the Pt/CeO2/PANI composite hollow arrays are promising candicates for methanol oxidation. However, up to now, few studies have focused on the structure design of Pt/CeO2/PANI composite electrocatalysts and their synergistic effects for the enhancement of electroactivity and durability for DMFCs. Here the novel Pt/CeO2/PANI three-layered hollow nanorod arrays (THNRAs) were fabricated as the advanced electrocatalysts for methanol oxidation for DMFCs. Besides the merits of THNRAs that can provide high utilization rate of catalysts, large surface area, and fast electrolyte diffusion/penetration, the fabricated Pt/CeO2/PANI THNRAs also exhibit strong synergistic effects coupling among Pt, CeO2 and PANI, which will result in electron delocalization among PANI π-conjugated ligands, Ce 3d orbitals and Pt 4f orbitals. The electrochemical measurements showed these fabricated Pt/CeO2/PANI THNRAs exhibited high electrocatalytic performance and high CO poisoning tolerance. This study represents a new method to design the electrocatalysts with high electrocatalytic activity, high long-term stability, and low-cost for DMFCs. Figure 1 shows the schematic illustration of the method used to fabricate Pt/CeO2/PANI THNRAs, and the procedures are described in detail in supporting information. SEM images of ZnO, ZnO/PANI, ZnO/PANI/CeO2 and ZnO/Pt/CeO2/PANI NRAs are shown in Figure 2a-d, respectively. It is clearly seen that the continuous and uniform PANI, CeO2 and Pt coating layers are obtained on the nanorod surfaces. The Pt/CeO2/PANI THNRAs were fabricated after removing ZnO nanorods and their SEM images are shown in Figure 3a. It is clearly seen that the nanorods are separated from each other, the lengths of Pt/CeO2/PANI nanorods are ~1.5 µm and their diameters are ~400 nm. The hollow structure of Pt/CeO2/PANI nanorods is studied by TEM as shown in Figure 3b, which clearly shows hollow structure with a wall thickness of about about 40 nm to 60 nm and inner diameter of about 300 nm. Figure 3c shows the magnified TEM image of the area marked with green line in Figure 3b, which shows the outersurface of Pt/CeO2/PANI hollow nanorod consists of the homogeneous overlapped Pt nanocrystals. The HRTEM image of the area marked with red line in Figure 3c is shown in Figure 3d, which shows the size of Pt nanocrystals is about 5 nm, and the interplanar distance of Pt nanocrystals is 3 Plus Environment ACS Paragon

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0.22 nm (inset on the top left corner of Figure 3d ), which corresponds to Pt (111). The selected area electron diffraction (SAED) pattern of the outer surface of the Pt/CeO2/PANI hollow nanorod (inset on the top right corner of Figure 3d) clearly shows the polycrystalline texture of Pt nanocrystals. To investigate the three-layered structures in the Pt/CeO2/PANI THNRAs, the wall of the Pt/CeO2/PANI hollow nanorod of marked with a red arrow in Figure 3e was measured by EDX line scan and the result is shown in Figure 3f, which clearly shows the distributions of the elements of N (coming from PANI), Ce (coming from CeO2) and Pt in the hollow nanorod wall. To further identify the stucture of the wall of Pt/CeO2/PANI hollow nanorod, EDX mapping of the area marked with a green frame in Figure 3e was measured, and the results are clearly shown in Figure 3g-j, which indicate that the three-layered structure is clearly observed and the thicknesses of PANI, CeO2, and Pt layers are about 20, 20, and 20 nm, respectively. For comparison study, the Pt/PANI HNRAs and Pt/CeO2 HNRAs were also fabricated via the similar method and their SEM images are exhibited in Figure S1a and S1b, respectively. The Pt loadings of Pt/CeO2/PANI THNRAs, Pt/PANI HNRAs and Pt/CeO2 HNRAs all are 15.8 µg cm-2. The crystallographic structure of Pt/CeO2/PANI THNRAs is examined by XRD as shown in Figure 4a, which shows the peaks of CeO2 and Ti substrate and no peak for Pt and PANI. Based on the diffraction peaks of CeO2, the CeO2 was crystalline in a cubic fluorite structure.28 In addition, no peak is seen for Pt and PANI, and this may be attributed to low Pt content in the catalyst and the amorphous PANI layer, respectively. FT-IR spectra of Pt/CeO2/PANI THNRAs and PANI films are exhibited in Figure 4b. For the PANI films, the broad bands at 3500~3000 cm-1 represent the N-H and C-H stretching modes of PANI.37 The band at 1633 cm-1 is due to C=C stretching of quinonoid, and the peaks at 1444 and 1064 cm-1 is due to the benzene ring and aromatic C-H in-plane bending,30,38-39 respectively. As shown in Figure 4b, the Pt/CeO2/PANI THNRAs show a similar FT-IR spectrum to that of PANI films, indicating that the existence of PANI in the Pt/CeO2/PANI THNRAs. To investigate the electron interactions in Pt/CeO2/PANI THNRAs, XPS spectra of Pt/CeO2/PANI THNRAs, PANI films, CeO2 films and Pt films were measured. For PANI films, the high resolution N 1s spectrum is fitted with three peaks as shown in Figure 5b, and the binding energy (BE) at about 4 Plus Environment ACS Paragon

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399.72 eV corresponds to benzenoid amine (-NH-), that at about 398.88 eV corresponds to quinoid amine (=N‒) and that at 400.36 eV corresponds to nitrogen cationic radical (‒N·+‒).40-41 The Pt/CeO2/PANI THNRAs display a similar N 1s spectrum to that of PANI films at the binding energy of 397~403 eV (see Figure 5a), which further demonstrates the existence of PANI in the Pt/CeO2/PANI THNRAs. Compared with PANI films, the Pt/CeO2/PANI THNRAs show a positive shift of about 0.19 eV in the BE of N 1s peak, indicating the electronic state change of N atoms in Pt/CeO2/PANI THNRAs. XPS spectra of Pt/CeO2/PANI THNRAs and CeO2 films in Ce 3d region are exhibited in Figure 5c-d, respectively. The analysis of the spectra shown in Figure 5d is illustrated as following: the peaks at 898.54 and 917.26 eV correspond to CeIV 3d5/2 and CeIV 3d3/2, respectively. The peaks at 883.21 and 901.47 eV can be attributed to CeIII 3d5/2 and CeIII 3d3/2, respectively. The SD, SU1 and SU2 correspond to the satellite peaks of CeIII, where SD and SU mean ‘shake-down’ and ‘shake-up’, respectively.42-43 A comparison of the integrated intensities of CeIII and CeIV peaks in Figure 5c can indicate the approximative ratio of CeIII/CeIV in Pt/CeO2/PANI THNRAs and it is about 50%. The high content of CeIII shows high concentration of surface oxygen vacancies, which will induce the significant enhancement of CO poisoning tolerance activity for the Pt/CeO2/PANI THNRAs.44-46 The CeIII 3d5/2 (883.00 eV) and CeIV 3d5/2 (898.47 eV) peaks of Pt/CeO2/ PANI THNRAs present 0.12 and 0.29 eV shifts compared with pure CeO2 films as shown in Figure S2, indicating the electronic state changes of element Ce in Pt/CeO2/PANI THNRAs. Figure 5e-f shows Pt 4f regions of Pt/CeO2/PANI THNRAs and pure Pt films, and each Pt 4f spectrum is deconvolved into four peaks. A comparison of the integrated intensities of Pt0 and PtII peaks in Figure 5e-f shows that Pt exists as Pt0 (~81 at%) in the Pt/CeO2/PANI THNRAs, whereas much less Pt0 (~65 at%) exists in Pt films, indicating that the addition of PANI and CeO2 can obviously increase the relative Pt0 content in Pt/CeO2/PANI THNRAs. Furthermore, we also observed a definite negative shift of 0.36 eV in the BE of Pt0 4f7/2 for Pt/CeO2/PANI THNRAs relative to Pt films. the above shift in BE of N 1s, Ce 3d and Pt 4f peaks of the Pt/CeO2/PANI THNRAs result from the electron interactions among the PANI, CeO2 and Pt, thus resulting in a high content of metallic Pt in electrocatalyst and synergistic effects for electrocatalytic reactions. In addition, Raman spectra of 5 Plus Environment ACS Paragon

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Pt/CeO2/PANI THNRAs, PANI films and CeO2 films in Figure S3 also indicate the electron interactions among Pt, PANI and CeO2 in the Pt/CeO2/PANI THNRAs. The electrochemically active surface areas (ECSAs) of Pt/CeO2/PANI THNRAs, Pt/CeO2 HNRAs, Pt/PANI HNRAs and commercial Pt/C catalysts were studied by calculating the areas of hydrogen desorption after the deduction of the double layer region. CVs of the above various catalysts in the solution of 0.5 M H2SO4 at 100 mV s-1 are shown in Figure 6a. The ECSA (m2/gPt) of electrocatalysts is estimated via following equation:47 ECSA=QH/(210×WPt), where QH represents the total charge (µC) for hydrogen desorption, WPt is Pt loading (µg·cm-2) on the electrode, and 210 represents the charge (µC·cm-2Pt) needed to oxidize a monolayer of hydrogen on a bright Pt surface. The ECSA of Pt/CeO2/PANI THNRAs is calculated to be 43.26 m2·(g, Pt)-1, which is much larger than 10.42 m2·(g, Pt)-1 of Pt/CeO2 HNRAs and 26.49 m2·(g, Pt)-1 of Pt/PANI HNRAs and is similar to 45.08 m2·(g, Pt)-1 of commercial Pt/C catalysts. Enhancement of the ECSA for Pt/CeO2/PANI THNRAs compared with Pt/CeO2 HNRAs and Pt/PANI HNRAs may be ascribed to highly uniform dispersion of Pt nanoparticles, high content of metallic Pt, and synergistic effects among PANI, CeO2 and Pt in the Pt/CeO2/PANI THNRAs. Electrocatalytic activities of Pt/CeO2/PANI THNRAs, Pt/CeO2 HNRAs, Pt/PANI HNRAs and commercial Pt/C electrocatalysts for methanol oxidation were studied in solution of 0.5 M H2SO4+0.5 M CH3OH at the scan rate of 100 mV s-1, and the representative CVs after activation are exhibited in Figure 6b. The specific peak current density of Pt/CeO2/PANI THNRAs is about 2.0, 1.6 and 2.3 times higher than that of Pt/CeO2 HNRAs, Pt/PANI HNRAs, and commercial Pt/C catalysts, respectively, indicating that the Pt/CeO2/PANI THNRAs own much higher electrocatalytic activity toward methanol oxidation than Pt/CeO2 HNRAs, Pt/PANI HNRAs and commercial Pt/C catalysts (the current densities all are normali-zed to the mass of Pt in catalysts). In addition, as shown in Figure 6b, the Pt/CeO2/PANI THNRAs show a clearly lower onset potential of the forward anodic peak than those of Pt/CeO2 HNRAs, Pt/PANI HNRAs, and commercial Pt/C catalysts, indicating that the Pt/CeO2/PANI THNRAs are more favorable to electrooxidation of methanol. Figure 7a shows CVs of Pt/CeO2/PANI THNRAs with 1000 cycles, and Figure 7b shows the 6 Plus Environment ACS Paragon

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corresponding change of specific peak current density. During the initial cycles, the specific peak current density of Pt/CeO2/PANI THNRAs drastically increases. After 200 cycles, the specific peak current density almost remains unchangeable with increasing cycle number and the highest peak current density appears at about 910th cycle. After 1000 cycles, the conservation rate of peak current density is about 97.89% of the highest value, indicating that Pt/CeO2/PANI THNRAs have superior cycling stability for the oxidation of methanol. However, Pt/CeO2 HNRAs, Pt/PANI HNRAs and commercial Pt/C exhibit much lower conservation rates of the highest peak current densities after 1000 cycles as shown in Figure 7b. Therefore, the Pt/CeO2/PANI THNRAs own much enhanced cycling stability compared with Pt/CeO2 HNRAs, Pt/PANI HNRAs and commercial Pt/C catalysts. In addition, Figure 7b also shows the Pt/CeO2/PANI THNRAs own much higher electrocatalytic activity than Pt/CeO2 HNRAs, Pt/PANI HNRAs and commercial Pt/C catalysts. After 1000 cycles, the surface morphologies of Pt/CeO2/PANI THNRAs are still kept well as shown in Figure 7c, indicating high structure-stability of the Pt/CeO2/PANI THNRAs. Moreover, both specific peak current density and durability of Pt/CeO2/PANI THNRAs are superior to those of the reported Pt-based catalysts such as Pt nanosheets,48 Mesoporous Pt/Pd/Pt,49 Nano-PtPd/RGO50 and Pt-CNT-Pt51 (please see Table S1 for details). As we all know, the intensity ratio of peak current density of forward to backward scans (If /Ib) is often used to evalute the poisoning resistance of catalysts for application in methanol oxidation.47,51,52 Traditionally, a higher ratio means stronger resistance to poisoning of carbonaceous species. In this study, we find that the If /Ib value of the Pt/CeO2/PANI THNRAs is about 0.96, which is higher than those of Pt/PANI HNRAs (0.84) and Pt/C catalysts (0.80) and is close to that of Pt/CeO2 HNRAs (1.0) as shown in Figure 6b. The above results show that the introduction of CeO2 can effectively relieve the poisoning of carbonaceous species and the Pt/CeO2/PANI THNRAs own higher poisoning resistance than Pt/PANI HNRAs and commercial Pt/C electrocatalysts. To further study the surface poisoning rate of Pt/CeO2/PANI THNRAs, the chronoamperometry curves of Pt/CeO2/PANI THNRAs, Pt/CeO2 HNRAs, Pt/PANI HNRAs and Pt/C electrocatalysts were carried out at at 0.65 V in 0.5 M H2SO4+0.5 M CH3OH solution as shown in Figure 7d. It is obvious that the Pt/CeO2/PANI THNRAs reveal a much 7 Plus Environment ACS Paragon

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higher specific current density and a much slower current decay than Pt/CeO2 HNRAs, Pt/PANI HNRAs and commercial Pt/C catalysts. For example, the specific current density of Pt/CeO2/PANI THNRAs, Pt/CeO2 HNRAs, Pt/PANI HNRAs and Pt/C electrocatalysts after 3000s are 111.5, 23.9, 19.4 and 5.0 mA mg-1Pt, indicating that the Pt/CeO2/PANI THNRAs own much higher electrocatalytic activity and higher tolerance to intermediates generated during the oxidation of methanol. Here the high electrocatalytic activity and excellent long-term cycling stability of Pt/CeO2/PANI THNRAs were demonstrated, and Pt/CeO2/PANI THNRAs as electrocatalysts exhibit following advantages as illustrated in Figure 8: (i) The hollow nanorod array structures of the designed Pt/CeO2/PANI THNRAs can facilitate the transportion of electroactive species; (ii) Due to hollow nanotube array, the large specific surface area and anisotropic morphology of Pt/CeO2/PANI THNRAs and the thin Pt shells coated on hollow nanorods will obviously enhance the utilization rate of Pt and can efficiently prevent Ostwald ripening and aggregation of Pt during methanol oxidation; (iii) Pt/CeO2/PANI THNRAs supported on conductive substrate would enhance the structural stability and provide the straightway path for electron transport, resulting in an excellent electrical contact with current collectors, thus will let each hollow nanorod to effectively participate in electrochemical reactions; (iv) The electron delocalization among PANI π-conjugated ligands, Ce 3d orbitals and Pt 4f orbitals will alter electronic structure and d-band center of Pt and result in synergistic effects among Pt, CeO2, and PANI, which will weaken the adsorption energy of carbonaceous intermediates (e.g., COads) on the Pt surfaces, and thus will make it more efficiently to remove surface adsorbed carbonaceous intermediates; (v) CeO2 in catalyst can well promote the dispersion of Pt and provide the labile OH species for electrooxidation of surface adsorbed carbonaceous intermediates to produce CO2 during methanol oxidation.25-26,44,53 Herein, high CO tolerance of the Pt/CeO2/PANI THNRAs was also demonstrated by CO stripping voltammetry. The catalytic activity of Pt/CeO2/PANI THNRAs toward CO oxidation in solution of 0.5 M H2SO4 was compared with Pt/CeO2 HNRAs, Pt/PANI HNRAs and commercial Pt/C catalysts. Figure 9 exhibits two continuous CVs of Pt/CeO2/PANI THNRAs, Pt/CeO2 HNRAs, Pt/PANI HNRAs and Pt/C electrocatalysts recorded among -0.2~1.0 V at 100 mV s-1. In the first anodic scan of CO stripping 8 Plus Environment ACS Paragon

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CVs, a much higher CO oxidation peak on Pt/CeO2/PANI THNRAs than those on Pt/CeO2 HNRAs, Pt/PANI HNRAs and commercial Pt/C catalysts is clearly observed, In addition, Pt/CeO2/PANI THNRAs show more negative onset potential of CO electrooxidation (~0.50 V) than Pt/CeO2 HNRAs (~0.55 V), Pt/PANI HNRAs (~0.62 V) and Pt/C catalysts (~ 0.60 V), indicating that the Pt/CeO2/PANI THNRAs can obviously reduce the adsorption strength of CO on catalyst and accordingly will facilitate the removal of CO. The reappearance of hydrogen desorption peaks and the disappearance of CO stripping peaks at second anodic scan CO stripping CVs indicate the Pt/CeO2/PANI THNRAs are free of dissolved CO and own high CO tolerance. In summary, the novel low-cost Pt/CeO2/PANI THNRAs catalysts were designed and syntheszied for methanol oxidation. The Pt/CeO2/PANI THNRAs exhibited significantly improved catalytic activity and stability compared with Pt/CeO2 HNRAs, Pt/PANI HNRAs and Pt/C electrocatalysts. Besides the strong points of THNRAs, the improved activity and durability of Pt/CeO2/PANI THNRAs can be attributed to the electron delocalization among Pt, CeO2 and PANI, which leads to high conent of metallic Pt and synergistic effects for methanol oxidation. Moreover, Pt/CeO2/PANI THNRAs have the advantage of CeO2 that can provide the labile OH species for electrooxidation of surface adsorbed carbonaceous intermediates, leading to high CO tolerance of catalysts. Here the certified perfect inosculations of compositional and geometrical advantages provide a new route to synthesize Pt-based catalysts with high electrocatalytic activity and stability for DMFCs.

ASSOCIATED CONTENT Supporting Information Experimental section, XPS spectra, SEM images, CVs and Raman spectra. This material is available free of charge via the Internet at http://pubs.rsc.org.

AUTHOR INFORMATION Corresponding Author [email protected] 9 Plus Environment ACS Paragon

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Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by National Natural Science Foundation of China (51173212), National Basic Research Program of China (2015CB932304), Natural Science Foundation of Guangdong Province (S2013020012833 and 2016A010104004), and Fundamental Research Fund for the Central Universities (16lgjc67).

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Figure 1. Schematic illustration of the fabrication process of the Pt/CeO2/PANI THNRAs.


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Figure 2. SEM images of the fabricated (a) ZnO NRAs, (b) PANI/ZnO NRAs, (c) CeO2/PANI/ZnO NRAs and (d) Pt/CeO2/PANI/ZnO NRAs.


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Figure 3. (a) SEM image of Pt/CeO2/PANI HNRAs; (b) TEM image of a typical Pt/CeO2/PANI hollow nanorod; (c) TEM image of the area marked with green circle in (b); (d) HRTEM image and SAED (inset on the top right corner) of the area marked with red circle in (c); (e) TEM image of a frontal Pt/CeO2/PANI hollow nanorod; (f) EDX line scans along the red arrow in (e); (g) STEM-HAADF image, and (h-j) STEM-EDX-mappings of a part of wall of Pt/CeO2/PANI hollow nanorod marked with a green frame in figure 3e. 15 Plus Environment ACS Paragon

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Figure 4. (a) XRD patterns of Pt/CeO2/PANI THNRAs, Pt HNRAs, CeO2 HNRAs, and Ti substrate; (b) FT-IR spectra of Pt/CeO2/PANI THNRAs and PANI HNRAs.


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Figure 5. XPS spectra of N 1s of (a) Pt/CeO2/PANI THNRAs and (b) PANI films; XPS spectra of Ce 3d of (c) Pt/CeO2/PANI THNRAs and (d) CeO2 films; XPS spectra of Pt 4f of (e) Pt/CeO2/PANI THNRAs and (f) Pt films.


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Figure 6. (a) CVs of Pt/CeO2/PANI THNRAs, Pt/PANI HNRAs, Pt/CeO2 HNRAs and commercial Pt/C catalysts in the solution of 0.5 M H2SO4 at 100 mV s-1; (b) CVs of Pt/CeO2/PANI THNRAs, Pt/PANI HNRAs, Pt/CeO2 HNRAs and commercial Pt/C catalysts in the solution of 0.5 M H2SO4+0.5 M CH3OH at 100 mV s-1 after activation.


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Figure 7. (a) CVs of Pt/CeO2/PANI THNRAs from 1st to 1000th cycle in the solution of 0.5 M CH3OH +0.5 M H2SO4 at 100 mV s-1; (b) The changes of specific peak current densities of the Pt/CeO2/PANI THNRAs, Pt/PANI HNRAs, Pt/CeO2 HNRAs and commercial Pt/C catalysts with increasing cycle number; (c) SEM image of the Pt/CeO2/PANI THNRAs after 1000 cycles. (d) Chronoamperometry curves of the Pt/CeO2/PANI THNRAs, Pt/PANI HNRAs, Pt/CeO2 HNRAs and commercial Pt/C catalysts in the solution of 0.5 M CH3OH+0.5 M H2SO4 at 100 mV s-1.


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Figure 8. Schematic illustration for the advantages of Pt/CeO2/PANI THNRAs.


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Figure 9. CO stripping measurements of Pt/CeO2/PANI THNRAs, Pt/PANI HNRAs, Pt/CeO2 HNRAs and commercial Pt/C catalysts in the solution of 0.5 M H2SO4 at 100 mV s-1.


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Enhanced Catalytic Activity and Stability of Pt ... - ACS Publications

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