DOI: 10.1002/ente.201600069

Ordered Mesoporous Carbon/Titanium CarbideComposites as Support Materials for Platinum CatalystsGang Zhao, Tianshou Zhao,* Xiaohui Yan, Lin Zeng, and Jianbo Xu[a]

Introduction

New carbon materials, including carbon nanofibers,[1] carbonnanotubes,[2] carbon aerogels,[3] and mesoporous carbons,[4]

have been studied as support materials for platinum (Pt) cat-alysts in fuel cells owing to their good electrical conductivi-ties, high corrosion resistances, and high specific surfaceareas. Among these materials, ordered mesoporous carbon(OMC) is one of the most promising because of its high spe-cific surface area, unique textural structure, and narrow poresize distribution.

OMC was first synthesized by Ryoo et al. in 1999,[5] usinga mesoporous silica molecular sieve (MCM-48) as the hard-template agent and sucrose as the carbon source. After that,Joo et al. used a similar method to prepare OMC by employ-ing another mesoporous silica molecular sieve (SBA-15) asthe template and furfuryl alcohol as the carbon source.[6]

Platinum supported on OMC showed a much higher activitythan platinum on carbon black. In 2006, Meng et al. reportedthe synthesis of OMC from an organic–organic assembly oftriblock copolymers with phenolic resin precursors by anevaporation induced self-assembly (EISA) strategy.[7] Differ-ent from the hard-template methods above, this so-calledsoft-template method does not involve the extra step of re-moving the hard template, making it more economical. Sincethen, OMC has been receiving increasing attention as a sup-port material in proton exchange membrane fuel cells(PEMFCs) and direct methanol fuel cells (DMFCs).[4a,c,8]

However, despite the advantageous ordered mesoporousstructure of OMC, there are some disadvantages to useOMC as the support material for platinum catalysts. Firstly,OMC prepared by either soft- or hard-template methodscontains few oxygen-containing groups to act as the anchor-ing sites for platinum catalysts. Although functionalizationcan furnish OMC with these groups, the textural structure ofthe OMC is prone to collapse as well.[9] Secondly, the nor-mally low carbonization temperature (<1000 8C) of OMC

would inevitably lead to low degrees of graphitization, result-ing in low electrical conductivity and low resistance to thecorrosion.[10]

Titanium carbide (TiC) is reported to have a high electri-cal conductivity and good resistance to corrosion, and the po-tential of using TiC as a support material has been demon-strated.[11] Nevertheless, the specific surface area of TiC israther low, due to its large molecular weight.[12] In this sense,if the titanium carbide is formed in the skeleton of OMC,the electrical conductivity and corrosion resistance of thiscomposite may improve significantly, while the high specificsurface area and the pore structure are still maintained. Fur-thermore, titanium atoms can work as the anchoring sites forplatinum particles, so that the functionalization step onOMC can be avoided.

Herein, we describe the synthesis of ordered mesoporouscarbon/titanium carbide (OMC/TiC) composites with a highspecific surface area and narrow pore size distribution bya soft-template method. After that, platinum catalysts areprepared by reducing platinum particles in the pores of theOMC/TiC composite by an impregnation method, using eth-ylene glycol (EG) as the reducing agent. Compared to plati-num supported on pure OMC (Pt/OMC) and commercial Pt/C, platinum supported on OMC/TiC (Pt/OMC/TiC) showshigher activity towards the oxygen reduction reaction (ORR)and the methanol oxidization reaction (MOR), as well asbetter stability.

Ordered mesoporous carbon/titanium carbide composites(OMC/TiC) are synthesized by using Pluronic F127 and tita-nium isoproxide as the structure-directing agent and titaniumprecursor. Characterizations confirm the formation of an or-dered mesoporous textural structure and the formation ofnanocrystals of TiC in the framework of carbon. By using theresultant OMC/TiC as the support material, a platinum cata-lyst (Pt/OMC/TiC) is then prepared. Electrochemical meas-

urements show that a higher activity for the methanol oxidi-zation reaction and oxygen reduction reaction can be ob-served for the Pt/OMC/TiC, compared to Pt/OMC anda commercial Pt/C catalyst. The results obtained in the pres-ent work suggest that the synthesized OMC/TiC is a promis-ing support material for platinum catalysts in proton ex-change membrane fuel cells and direct methanol fuel cells.

[a] G. Zhao, T. Zhao, X. Yan, L. Zeng, J. XuDepartment of Mechanical and Aerospace EngineeringThe Hong Kong University of Science and TechnologyClear Water Bay, Kowloon, Hong Kong SAR (PR China)E-mail: metzhao@ust.hk

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Results and Discussion

Characterization of OMC and OMC/TiC composites

X-ray diffraction (XRD) patterns of the OMC/TiC compo-site and pure OMC are shown in Figure 1 a. As can be seen,a broad diffraction peak centered at 2q�43.808 of the pureOMC corresponds to the [100] reflection of graphitic carbon.For the as-prepared OMC/TiC composite, five resolved dif-fraction peaks are observed at 2q�36.208, 42.008, 60.708,72.608, and 76.708, indexed to the [111], [200], [220], [311],and [222] reflections of the cubic titanium carbide phase, ac-cording to the standard powder diffraction file (PDF) 38-1420, which confirms the formation of nanocrystals of TiC.

To determine the relative amount of TiC in the OMC/TiCcomposite, thermogravimetric (TG) measurements were con-ducted in air.[13] As illustrated in Figure 1 b. a significantweight loss of the pure OMC occurs at around 400 8C, indi-cating a collapsed carbon framework caused by burning outin air. However, the collapsed temperature of the as-pre-pared OMC/TiC lags by several tens of degrees. Further-more, a small increase in the weight of the as-preparedOMC/TiC is observed at the beginning of the collapse atabout 400 8C. This is caused by the oxidation of TiC intoTiO2 under air flow. Because the molecular weight of TiO2 ishigher than that of the TiC, the oxidation of TiC increasesthe weight. The residue weight (12.4 %) of the OMC/TiCcomposite obtained from TG measurements is actually theweight of TiO2, not the TiC. By calculation, the actual weightratio of TiC in the OMC/TiC composite is about 9.3 %. Forthe pure OMC, there is almost no residue weight when thetemperature is above 500 8C.

Nitrogen sorption isotherms were measured for the pureOMC and OMC/TiC composites to characterize features ofthe pore structures of the OMC and OMC/TiC composite.As shown in Figure 1 c, both samples illustrated a combina-

tion of type I and IV curves, with an obvious condensationstep at PS/P0 range of 0.3–0.7 and a large amount of nitrogenadsorption at very low PS/P0 values, indicating that the twosamples have a typical mesoporous structure with a narrowparticle size distribution and a large number of microsporesin the framework. Table 1 concludes that the specific surface

area of the as-prepared OMC/TiC composite is 535.6 m2 g�1,lower than that of the OMC (693.05 m2 g�1), suggesting thatthe introduction of TiC decreases the specific surface areaowing to its large molar weight. However, the carbothermalreaction at high temperature not only produces titanium car-bide, but also forms large numbers of micropores, resultingfrom the consumption of carbon in the carbon framework,which mitigates the decrease of the specific surface area.Therefore, the specific surface area of OMC/TiC still main-tains a rather high value. Pore size distributions (Figure 1 d)show that similar average pore sizes are attained: 4.2 nm and4.0 nm for OMC/TiC and OMC, respectively.

The electrical conductivity was tested, similar to the litera-ture,[11a, 14] and the result is shown in Table 2. The OMC/TiCcomposites had the highest value of 7.87 Scm�1, much higherthan that of XC-72 (4.42 Scm�1) and OMC (4.46 S cm�1). A

possible reason is the formation of TiC in the carbon frame-work, which improves electrical conductivity. It should benoted that the experimentally determined electrical conduc-tivity does not only depend on the sample properties, butalso on other parameters (e.g., pressure and the amount ofthe sample). Therefore it is not straightforward to compareconductivity data from different laboratories.[11a,14] The struc-ture and morphologies of the as-prepared OMC and OMC/TiC composite were characterized by transmission electronmicroscopy (TEM). As shown in Figure 2, for the pureOMC, large domains of ordered hexagonal arrays are well-shaped in the [110] and [001] directions (Figure 2 a, b), indi-cating a high degree of regularity for the ordered mesopo-rous structure. For the OMC/TiC composite, the orderedstructure can also be observed in the two directions (Fig-

Figure 1. Characterizations of XRD (a), TG (b), nitrogen sorption isotherms(c), and pore size distribution (d) of the as-prepared OMC and OMC/TiCcomposite.

Table 1. Physicochemical parameters of OMC and OMC/TiC composite.

Sample SBET

[m2 g�1]Vt

[Lg�1]Smic

[m2 g�1]Vmic

[mL g�1]d[nm]

OMC 693.1 0.4885 327.3 0.1486 4.0OMC/TiC 535.6 0.3352 315.3 0.1458 4.2

Table 2. Electrical conductivity measurements of OMC and OMC/TiC com-posites.

Sample s [S cm�1]

XC-72 4.42OMC 4.46OMC/TiC 7.87

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ure 2 c,d), and the TiC nanocrystals with sharp contrast arewell demonstrated. It is noted that some TiC particles are solarge that the ordered mesoporous structure undergoesa severe distortion, which explains the inferior regularity ofthe OMC/TiC. The lattice fringes of the nanocrystals ob-served in the inset high-resolution TEM (HRTEM) image(Figure 2 d) further confirms the formation of a TiC cubicphase in the carbon framework.

Characterization of Pt/OMC and Pt/OMC/TiC

XRD patterns of platinum catalysts supported on the OMCand OMC/TiC composite are illustrated in Figure 3 a. Fourresolved diffraction peaks can be clearly observed in bothsamples at 2 q�39.88, 46.28, 68.38, and 81.38, indexed to the[111], [200], [220], and [311] reflections of the typical faced-centered cubic platinum. For the Pt/OMC/TiC, the reflec-tions of the nanocrystal of TiC seem to be covered by thesignals of platinum; however, a small diffraction peak of Pt/OMC/TiC could be seen at 2q�61.08, corresponding to the[220] reflection of crystalized TiC, implying the existence ofTiC nanocrystals. To calculate the average particle size ofplatinum by Scherrer equation, we choose the [220] reflec-tion peaks of platinum at 2q�68.38, in order to avoid the in-fluence of carbon and TiC. The average platinum particlesize of Pt/OMC/TiC composite is 2.8 nm, much smaller thanthat of Pt/OMC (3.5 nm).

In order to determine the amount of platinum, TG meas-urements for the as-prepared Pt/OMC and Pt/OMC/TiC inair are illustrated in Figure 3 b. In the first stage. when thetemperature is below 300 8C, both samples show a smallweight loss, which can be ascribed to some residue of organicmaterials, such as ethylene glycol, glycolic acid, and so on.

The significant weight losses occur at around 400 8C, indicat-ing a collapsed carbon framework caused by burning out inair. The different behaviors of Pt/OMC and Pt/OMC/TiCmanifest exactly the same trend as shown in Figure 1 b.Therefore, combined with Figure 1 b, the weight ratios ofplatinum in Pt/OMC and Pt/OMC/TiC are 13.5 % and18.2 %, respectively. The actual weight ratios of platinum inPt/OMC and Pt/OMC/TiC may get a little higher, if theweight losses in the beginning stage are considered.

From the above XRD and TG results, it is found that theplatinum catalyst supported on OMC/TiC has a smaller aver-age particle size and higher weight ratio than that supportedon OMC. This can be explained by the fact that the oxygen-containing groups of OMC after heat treatment are so fewthat not enough anchoring sites are provided for platinum.As to the Pt/OMC/TiC, titanium atoms in the framework ofOMC can act as the anchoring points for platinum. Further-more, the molar ratio between titanium and platinum islarger than 3:2, implying that sufficient anchoring sites areprovided.

TEM images of the as-prepared Pt/OMC and Pt/OMC/TiCare illustrated in Figure 3 c,d. Domains of ordered hexagonalarrays can be observed in both samples, suggesting that theunique pore structure is preserved after supporting platinumcatalysts. Platinum particles are mostly deposited inside thepores of the supporting materials, including OMC and OMC/TiC composite, but not on the outside surface, indicatinghigh utilization of the surface area of the supporting materi-als. However, the agglomeration of platinum particles seemsmore severe in Pt/OMC than in Pt/OMC/TiC, despite thefact that TG curves show the amount of platinum in Pt/OMCis much lower than in Pt/OMC/TiC. The reason is that TiCcan offer anchoring sites for platinum particles, which helpsthe dispersion and deposition of platinum particles on thesurface of OMC/TiC. However, in Pt/OMC, due to insuffi-cient anchoring sites, platinum particles are liable to agglom-

Figure 2. TEM images of the as-prepared OMC in [110] (a) and [001] (b) di-rections, and OMC/TiC in [110] (c) and [001] (d) directions, and inset high-resolution TEM of TiC nano-crystal in OMC/TiC composite.

Figure 3. Characterizations of XRD (a), TG (b) of the as-prepared Pt/OMCand Pt/OMC/TiC, and TEM images of the Pt/OMC (c) and Pt/OMC/TiC (d).

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eration. This observation otherwise confirms the results ofXRD and TG measurements in the previous paragraph. Theagglomeration of platinum particles in Pt/OMC is so severe,that it is hard to calculate the particle size in TEM images(Figure 3 c). In addition, in a TEM image of Pt/OMC/TiC(Figure 3 d), it is difficult to distinguish TiC particles fromplatinum particles, which also makes it impossible to definethe average size of platinum particles.

Electrochemical measurements

Cyclic voltammetry (CV) experiments were performed to in-vestigate the electrocatalytic behavior of the as-prepared Pt/OMC and Pt/OMC/TiC in nitrogen-saturated 0.5m HClO4

solution, compared to a commercial 20 % Pt/C sample onVulcan XC-72 from E-TEK. All the samples demonstratea behavior typical of platinum catalysts in an acid environ-ment, with hydrogen adsorption/desorption in the potentialrange of 0–0.35 V (vs. RHE, the same as following), as indi-cated in Figure 4 a. The double electric layers of the Pt/OMC

and Pt/OMC/TiC in the potential range of 0.35–0.6 V aremuch thicker than that of the commercial 20 % Pt/C, imply-ing much higher specific surface areas of the two home-madeplatinum catalysts than that of the commercial Pt/C, causedby the high specific surface areas of the OMC and OMC/TiCcomposite, used as the support materials for platinum cata-lysts. By integrating the charge (QH) in the hydrogen desorp-tion region ranging from 0–0.35 V, deducting the effect ofdouble-layer charging, the electrochemical surface area(SECSA) can be obtained using Equation (1):

SECSA ¼ QH=QHref ð1Þ

where QHref is a constant and assumed to be 0.21 mC cm�2.By calculation, the value of SECSA of the Pt/OMC/TiC is100.5 m2 g�1, larger than that of the Pt/OMC (79.9 m2 g�1) andthe commercial Pt/C (75.0 m2 g�1), as indicated in Figure 4 b.The probable reason is that the average platinum particlesize of Pt/OMC/TiC may be smaller than that of the Pt/OMC, in addition to the platinum particles being well-dis-persed in the pore structures, according to the Figure 3 c,d,implying an approved efficiency with respect to platinum uti-lization. Compared to the commercial Pt/C, the unique pore

structure of OMC seems to improve the value of SECSA, byfacilitating the transportation.

Linear sweeping voltammograms (LSVs) were conductedto further understand the ORR performance of the as-pre-pared Pt/OMC and Pt/OMC/TiC, which was performed in anoxygen-saturated 0.5 m HClO4 solution with a flow rate of20 mL min�1 and at a rotation speed of 1600 rpm and a scanrate of 10 mV s�1. As shown in Figure 5 a, all the as-prepared

platinum catalysts demonstrate an activity for ORR per-formance. Specifically, the onset potentials for the Pt/OMC/TiC and Pt/OMC are 1.01 V and 0.99 V, slightly more posi-tive compared to that of the commercial Pt/C (0.98 V). Toevaluate the mass activity of the platinum catalyst for ORR,the kinetics current density (jk) at the potential of 0.9 V vs.RHE is widely accepted as a standard for comparison, whichcan be calculated from the Koutecky–Levich (K–L) Equa-tion (2):

j�1 ¼ j�1k þ j�1

d ð2Þ

where j, jk, and jd are the measured, kinetic-limiting, and dif-fusion-limiting current density, respectively. By calculation,the Pt/OMC/TiC had the highest value of jk (260 mA mg�1

Pt),much larger than that of Pt/OMC (196 mA mg�1

Pt) and com-mercial Pt/C (186 mA mg�1

Pt), as shown in Figure 5 b, imply-ing the best mass activity of Pt/OMC/TiC for ORR. Thisresult is consistent with the comparison of SECSA for the threeplatinum catalysts, indicating that the improvement for ORRcan be ascribed to the enlargement of the value of SECSA.

Other than the ORR, a CV measurement of the methanoloxidization reaction (MOR) was also conducted in a mixtureof 1 m methanol and 0.5 m HClO4 solution. Figure 6 a revealsthat for all samples, methanol oxidation produces anodicpeaks at around 0.8 V in the positive scan, while in the nega-tive one, anodic peaks appear at around 0.7 V, due to the oxi-dation of the incompletely oxidized carbonaceous speciesdissociated from methanol molecules formed in the positivesscan. For the as-prepared Pt/OMC and the commercial Pt/C,the onset potentials for MOR are similar. However, the peakMOR current densities are different. By calculation, we cor-rect peak current density in the CV curves by the amount ofplatinum used (jp,mass). As seen in Figure 6 b, the value of

Figure 4. CV curves in nitrogen-saturated 0.5 m HClO4 solution (a), and calcu-lated values of SECSA for the as-prepared Pt/OMC and Pt/OMC/TiC, comparedwith the commercial 20 % Pt/C.

Figure 5. LSV curves s in oxygen-saturated 0.5 m HClO4 solution (a), and cal-culated values of jk @ 0.9 V vs. RHE (b) for the as-prepared Pt/OMC and Pt/OMC/TiC, compared with commercial 20 % Pt/C.

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jp,mass for Pt/OMC (358 mA mg�1Pt) is a litter larger than that

of the commercial Pt/C (452 mA mg�1Pt). While for the as-

prepared Pt/OMC/TiC, the onset potential is the more nega-tive than that of the Pt/OMC and the commercial Pt/C. Fur-thermore, the value of jp,mass for the Pt/OMC/TiC is780 mA mg�1

Pt, which is the largest of the three samples. Thiscould be ascribed to not only the smaller particle size andthe highly ordered pore structure, but also a synergetic effectof TiC on platinum.[15] Platinum is easily poisoned by CO-like intermediate products of the MOR process. However,this poisonous effect could be significantly alleviated by thesynergetic effect of TiC, due to the formation of �OH fromwater on the TiC surface, which improves the CO toleranceof the platinum nanoparticles, which is also confirmed in theCO stripping voltammetry measurement. As shown in Fig-ure 7 a, a distinct peak, referred to as the CO oxidation reac-tion, could be observed for all of the samples. However, themost notable difference between Pt/OMC and the Pt/OMC/TiC composite is the negative shift of the CO oxidation peakin the latter. The peak potential of CO oxidation on Pt/OMC/TiC is shifted negatively by about 80 mV, compared to

that on Pt/OMC, indicating that the formation of TiC in theOMC framework reduced the overpotential for CO oxida-tion. Therefore, the Pt/OMC/TiC has an improved CO toler-ance.

The stability of the platinum catalysts was examined by anaccelerated degradation test (ADT), as depicted in the Ex-perimental section. As Figure 7 b shows, all the platinum cat-alysts demonstrate a decreasing trend of SECSA with an in-crease of the number of cycles. For the commercial Pt/C andthe Pt/OMC, the decreasing rates of SECSA are similar, whichreduce by half after 6000 cycles. While that for Pt/OMC/TiCis only about 28 % reduction, indicating a better stability.ORR and MOR performances after the ADT further con-firm the improvement of the corrosion resistance of Pt/OMC/TiC (Figure 7 c,d). Notably, the commercial Pt/C andPt/OMC illustrate similar slopes in the ORR tests, showingthe similar degradation rates after 6000 cycles (about 50 %reduction of jk for both the commercial 20 % Pt/C and thePt/OMC). A slower corrosion rate could be observed for thePt/OMC/TiC on ORR performance after 6000 cycles (24 %reduction). For MOR, the value of jp,mass decreases by about52 %, 47 %, and 14 % for the commercial Pt/C, the Pt/OMC,and the Pt/OMC/TiC, respectively. Overall, the above dataimply that the commercial Pt/C and the Pt/OMC have a simi-lar degradation rate. However, the Pt/OMC/TiC has a slowerdegradation rate. As we know, the degradation of Pt/C cata-lysts is mainly caused by carbon corrosion, leading to the ag-glomeration of platinum particles and a reduction in plati-num utilization, resulting in performance degradation.[16] Forthis reason, the formation of TiC in the OMC frameworkcan improve the corrosion resistance of the OMC/TiC com-posite, and platinum catalysts supported on a OMC/TiC com-posite shows an enhanced stability.

Conclusions

Ordered mesoporous carbon/titanium carbide composite(OMC/TiC) has been successfully synthesized by using Plur-onic F127 and titanium isoproxide as the structure-directingagent and the titanium precursor. The as-prepared OMC/TiCexhibits a large surface area of 535.55 m2 g�1 and a narrowpore size distribution, and the weight ratio of TiC is as highas 9.3 %. Platinum supported on the as-prepared OMC/TiCcomposite demonstrates a smaller average particle size andhigher loading. In addition, Pt/OMC/TiC shows superiormass activities for MOR and ORR to those of the Pt/OMCand commercial Pt/C. For ORR, the mass activity of the as-prepared Pt/OMC/TiC is 260 mA mg-1

Pt, much higher thanthat of the Pt/OMC (196 mAmg�1

Pt) and the commercial Pt/C (186 mA mg�1

Pt). For MOR, the as-prepared Pt/OMC/TiChas a more negative onset potential and higher value of jp,mass

(780 mA mg�1Pt), compared to that of the Pt/OMC

(452 mA mg�1Pt) and the commercial Pt/C (358 mA mg�1

Pt).Furthermore, the ADT test demonstrated that the formationof TiC in the composites improves the corrosion resistanceof the support material. Therefore, OMC/TiC has a great po-

Figure 6. CV curves for MOR in nitrogen saturated 1 m CH3OH+0.5 m

HClO4 solution (a), and calculated values of jp,mass (b) for the as-prepared Pt/OMC and Pt/OMC/TiC, compared with commercial 20% Pt/C.

Figure 7. CO stripping voltammetry of Pt/OMC and Pt/OMC/TiC (a), and thenormalized SECSA (b), jk@0.9 V on ORR (c), and jp, mass (d) on MOR for the twoas-prepared Pt catalysts in the stability test, compared with those of the com-mercial 20% Pt/C.

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tential to be used as a support material for platinum catalystsin PEMFCs and DMFCs.

Experimental Section

Preparation of OMC/TiC composite

A resol solution, obtained from phenol and formaldehyde ac-cording to the previously reported procedures,[7] was used as thecarbon precursor. For a typical preparation, 1.0 g of phenol and0.21 g of NaOH (20 wt %) were mixed and stirred, then 1.7 g offormaldehyde solution (37 wt %) was dropped into this solution.The mixture was heated at 75 8C for 1 h and cooled. The pHvalue of the mixture was adjusted to 7.0 by using dilute HCl so-lution, and water in the mixture was reduced through vacuumdistillation. Ethanol was added to form a resol solution(20 wt %).When preparing OMC/TiC, triblock copolymer Pluronic F127,the resol solution, and titanium isoproxide were dissolved in eth-anol to form a solution. The solution was transferred to dishesand evaporated at room temperature for 8 h to remove the sol-vent, followed by heating at 100 8C for 24 h for thermopolymeri-zation. The product was heated at 350 8C for 3 h to remove F127and 1200 8C for 2 h for the carbothermal reaction in argon flow.The heating rate was 1 8C min�1 below 600 8C and then increasedto 5 8C min�1 above 600 8C.For comparison, OMC was prepared, and the preparation proce-dure was similar to that of the OMC/TiC composite withoutadding titanium isoproxide.

Preparation of supported platinum catalysts

Platinum catalysts supported on OMC/TiC composite and pureOMC were prepared by impregnation with ethylene glycol (EG)as the reducing agent,[17] and platinum loadings were both set at20 wt %.In a typical preparation of Pt/OMC/TiC, 3.38 mL of chloroplatin-ic acid EG solution (7.4 mgPt mL�1) and 100 mg of OMC/TiCwere mixed in a certain amount of EG. The pH value of the mix-ture was adjusted to about 12 by using 1m NaOH EG solution.The mixture was heated to 140 8C for 3 h, and then cooled. Thefinal catalyst (Pt/OMC/TiC) was obtained after filtering, washing,and drying at 80 8C for 10 h in a vacuum oven. For comparison,Pt/OMC was also synthesized in the same procedure, with thedifference that pure OMC was used instead of the OMC/TiCcomposite. Commercial 20% Pt/C on Vulcan XC-72 was alsoused for comparison.

Physical characterization

X-ray diffraction (XRD) patterns were recorded with an X’pertPro (PANalytical) with nickel-filtered CuKa radiation. Thermog-ravimetric (TG) analyses were measured on a TGAQ5000 fromroom temperature to 900 8C under air flow with a ramp rate of5 8C min�1. Nitrogen sorption isotherms were measured witha Beckman Coulter SA3100 Surface Area Analyzer. The Bruna-uer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH)methods were utilized to calculate the specific surface area(SBET) and the pore size distribution. Transmission electron mi-croscopy (TEM) experiments were conducted on a TEM 2010F(JEOL). The samples for TEM measurements were suspended inethanol and dropped onto a holey carbon film supported ona copper grid. The electrical conductivity measurements were

done according to literature reports.[11a, 14] Briefly, the sample waspressed to a pellet, and then placed between two gold plates.The electrical conductivity was measured by impedance spectros-copy. For comparison, the electrical conductivity of Vulcan XC-72 carbon was also measured.

Electrochemical measurement

All electrochemical measurements were carried out using an Au-tolab instrument. A three-electrode system was used, in whicha platinum mesh was used as the counter electrode and a saturat-ed calomel electrode (SCE) as the reference electrode. Theworking electrode was made as follows: 2.0 mg of catalyst wasdispersed in 2 mL of ethanol and ultrasonicated for 20 min, andthen 20% Nafion solution was added and ultrasonicated for an-other 20 min. 20 mL of the above-prepared catalyst ink was in-jected onto a polished glassy carbon electrode by a microsyringeand dried at ambient conditions. Cyclic voltammetry (CV) meas-urements were conducted under nitrogen saturated 0.5m HClO4

solution. Linear sweep voltammetry (LSV) measurements wereconducted under oxygen saturated 0.5 m HClO4 solution witha rotating speed of 1600 rpm to examine the oxygen reductionreaction (ORR) performance, and CV measurements were con-ducted under nitrogen saturated 0.5m HClO4 +1m CH3OH solu-tion for methanol oxidization reaction (MOR). CO stripping vol-tammetry were measured to examine the CO tolerance for theas-prepared samples in 0.5 m HClO4 solution. Accelerated degra-dation test (ADT) was conducted to evaluate the stability of thecatalysts, by continuous cycling for 6000 cycles between 0 V and1.2 V vs. RHE at 100 mVs�1 in 0.5 m HClO4 solution at roomtemperature. The SECSA, the jp,mass for MOR, and the jk for ORRwere measured and calculated every 2000 cycles during ADT.

Acknowledgements

The work described in this paper was fully supported bya grant from the Research Grants Council of the Hong KongSpecial Administrative Region, China (project 622712).

Keywords: carbons · composites · fuel cells · platinum ·titanium carbide

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Received: January 29, 2016Revised: March 10, 2016Published online on && &&, 0000

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FULL PAPERS

G. Zhao, T. Zhao,* X. Yan, L. Zeng,J. Xu

&& –&&

Ordered Mesoporous Carbon/Titanium Carbide Composites asSupport Materials for PlatinumCatalysts

In need of some TiC: Composites ofordered mesoporous carbon and titani-um carbide (OMC/TiC) are prepared,and used as support material for plati-num catalysts (Pt/OMC/TiC). Electro-chemical measurements reveal that Pt/OMC/TiC has superior activity to-wards the oxygen reduction reaction(ORR) and methanol oxidation reac-tion (MOR), which confirms thatOMC/TiC composite offers great po-tential as a support material for plati-num catalysts in fuel cells.

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