Nitrogen doped carbon coated Mo modified TiO2 nanowires ([email protected]) with functionalized interfacial as advanced PtRu catalyst support for methanol electrooxidation

Electrochimica Acta 331 (2020) 135410

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Nitrogen doped carbon coated Mo modified TiO2 nanowires (NC@MTNWs-FI) with functionalized interfacial as advanced PtRu catalyst support for methanol electrooxidation Yun-Long Zhang 1, Jia-Long Li 1, Lei Zhao**, Xu-Lei Sui, Qing-Yan Zhou, Xiao-Fei Gong, Jia-Jun Cai, Jia-Zhan Li, Da-Ming Gu, Zhen-Bo Wang* MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, State Key Lab of Urban Water Resource and Environment, Harbin Institute of Technology, No.92 West-Da Zhi Street, Harbin, 150001, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 15 August 2019 Received in revised form 18 November 2019 Accepted 29 November 2019 Available online 29 November 2019

A strategy combining hydrothermal in-situ pre-carbonization coating and interfacial functionalization is proposed to prepare the nitrogen doped carbon coated Mo modified one-dimensional TiO2 nanowires (NC@MTNWs-FI) with functionalized interfacial core-shell structure as advanced carriers for PtRu nanoparticles towards methanol electrooxidation. Mo functional doping and chitosan pre-carbonization occur simultaneously on the surface of TiO2 nanowires (TNWs), resulting in a special concentric multilayer one-dimensional (1D) structure with TiO2 core, Mo functionalized interface and an outer N-doped carbon layer. The mass activity of the prepared PtRu/NC@MTNWs-FI catalyst is increased to 1.23 A mg
1 Pt for methanol electrooxidation, which is 2 times higher than that of the unmodified supported catalyst (PtRu/NC@TNWs) and the stability is increased by 15.9%. In addition, it is 2.24 times higher than that of the PtRu/C catalyst and the stability is increased by 23.2%. This excellent catalytic performance is attributed to the synergistic electron donating effect of the Mo functionalized interface and the nitrogen doped carbon layer on the supported PtRu as well as the stronger anchoring effect. This work reveals a new method for designing highly active and stable electrocatalytic support materials for the development of fuel cells. © 2019 Elsevier Ltd. All rights reserved.

Keywords: Nitrogen doped carbon coating Functionalized interfacial TiO2 nanowires PtRu catalyst Methanol electrooxidation

1. Introduction Direct methanol fuel cells (DMFCs) are considered to be alternative energy sources for portable devices in the future and are one of the major sustainable energy sources [1e5]. The fascinating properties exhibited by platinum (Pt)-based catalysts in the field of catalysis have never been ignored by researchers, but researches on their stability and anti-toxic properties have also never stopped [6e9]. For example, CO substances produced by oxidation of methanol tend to poison Pt, which seriously affects its activity and practical application [10e12]. Alloying Pt with a second oxophilic metal such as Ru, can efficiently weaken the poisoning effect

* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (L. Zhao), (Z.-B. Wang). 1 Yun-Long Zhang and Jia-Long Li contributed equally. https://doi.org/10.1016/j.electacta.2019.135410 0013-4686/© 2019 Elsevier Ltd. All rights reserved.

[email protected]

[13e15]. However, the electrochemical instability of Ru causes its dissolution to trigger the re-poisoning of Pt, and the electrocatalytic activity of the PtRu alloy electrocatalyst is drastically reduced [16,17]. In addition, the uniform dispersion of Pt on the support also greatly affects the performance of its electrooxidation of methanol [18e20]. Other requirements for acceptable supports under fuel cell operating conditions are high stability, high electrical conductivity and suitable porosity [21,22]. A major disadvantage of carbon black and other carbon materials is their insufficient corrosion resistance, which has increased a series of research in the past few years [23,24]. In order to overcome the above obstacles, it is imperative to continuously strive to develop new superior support materials and improve their structure and composition to increase MOR activity and lower Pt content. As a widely studied semiconductor, titanium dioxide (TiO2) has high hydrophilicity, surprising chemical stability under harsh conditions and co-catalysis for MOR, thus it is widely applied in the field of methanol electrooxidation [25,26]. YangFan et al. [27] prepared the TiO2eC hybrid material by carbonizing the mixed

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precursor containing TiO2 and urea, which is used to support Pt electrocatalyst for methanol oxidation. The electrocatalyst has a higher electrochemical surface area (ECSA) and significantly improves the catalytic activity and stability for methanol electrooxidation. The excellent properties of TiO2 mainly come from several aspects: (1) TiO2 has the electronic effect, in which titanium ions with hypo-d-electronic properties promote the electrocatalytic performance of noble metal surface atoms with hyper-delectronic, thereby reducing the adsorption energy of CO intermediates and increasing the flow of CO [28,29]. (2) The OH species adsorbed (OHad) on TiO2 can promote the conversion of poisonous CO intermediates into CO2, thereby improving the durability of the Pt catalyst [30,31]. (3) TiO2 can promote the dispersion of noble metal nanoparticles and anchor the nanoparticles [32]. Although TiO2 has the significant effect on the stability and activity of methanol oxidation electrocatalysts, the low conductivity of TiO2 inhibits its application in PEMFC [33,34]. Doping of TiO2 with donor elements does not create anion vacancies in the structure, which can improve the stability of the material to thermal and electrochemical oxidation [35]. Prabhu Ganesan et al. [36] synthesized the pure rutile phase Nb-doped TiO2 support with high conductivity by simple hydrolysis method, the support exhibited disordered pore structure and achieved better stability than Vulcan carbon at higher anode potentials. Although these methods have made significant progress, further breakthroughs are still urgently needed. In this work, we used hydrothermally synthesized TiO2 nanowires (TNWs) as substrates, which were simultaneously modified by Mo-doped interface functionalization and in situ pre-carbonized coated by hydrothermal method using natural polymer chitosan (CTS) as carbon and nitrogen precursor, and then the nitrogen doped carbon coated core-shell structure support (NC@MTNWs-FI) was synthesized by high temperature annealing. In addition, its application as the PtRu electrocatalyst support for electrocatalytic methanol oxidation was investigated. The synergistic effect of the electron donation of Mo functionalized interface and the nitrogen doped carbon shell to the supported PtRu NPs led to a significant enhancement of the electrocatalytic activity and stability for methanol electrooxidation.

added in the hydrothermal reaction solution, and the obtained product was recorded as NC@TNWs. 2.2. Synthesis of PtRu/NC@MTNWs-FI catalyst PtRu/NC@MTNWs-FI was prepared by microwave assisted polyol process (MAPP). Briefly, 40 mg synthesized NC@MTNWs-FI was dissolved into 80 mL mixed solution of isopropyl alcohol and ethylene glycol (1:4) and sonicated for 1 h. The H2PtCl6/EG and RuCl3/EG solution was dropped and stirred for 3 h, then the pH was regulated to 8.0 with 0.5 mol L
1 NaOH/EG solution. The mixed solution was heated in a microwave oven for 50 s under argon protection, and after the solution was gradually cooled, the pH of the solution was regulated to 2 by HNO3/EG and then stirred for 10 h. The product was washed 4 times with ultrapure water and then placed at 60  C under vacuum. The mass fraction of PtRu in the product was 20%, and the molar ratio of Ru/Pt was 1:1. As the comparative experiment, PtRu/NC @ TNWs and PtRu/C were synthesized by the same method except that different supports were used. 2.3. Characterization and electrochemical test X-ray diffraction (XRD) detection was performed on a Rigaku D/ max-2500 diffractometera. X-ray photoelectron spectroscopy (XPS) analysis was performed on an ESCALAB 250Xi. The Raman spectrum of the sample was collected with a Renishaw 2000 Raman spectrometer. Transmission electron microscopy (TEM) and high resolution TEM (HRTEM) was carried out on the FEI Tecnai G2 F20. Energy dispersive X-ray spectroscopy (EDX) was performed using a XL30 ESEM FEG scanning electron microscope (SEM). Standard three-electrode batteries were used for electrochemical testing at 25  C on CHI 650E electrochemical analyzer. A catalyst-carrying glassy carbon disk electrode, Hg/Hg2SO4 (0.68 V, relative to the RHE) and a platinum mesh were used as the working electrode, the reference electrode and the counter electrode, respectively. In this paper, all potential is related to RHE. In addition, please see the support information for more details. 3. Results and discussion

2. Experimental section 2.1. Fabrication of polymer-derived interface functionalized NC@MTNWs Typically, 200 mg hydrothermally synthesized anatase titanium dioxide nanowires (TNWs), 747 mg water-soluble chitosan (CTS, average monomer molecular weight 179.17; theoretical carbon coating amount 60 wt%), 531 mg ammonium molybdate ((NH4)6Mo7O24$4H2O), 720 mg sodium sulfide (Na2S$9H2O) and 435 mg hydroxylamine hydrochloride (NH2OH$HCl) were dissolved in 155 mL deionized water and dispersed by ultrasonication to form a uniform suspension. The suspension was transferred to a 200 mL PTFE-lined autoclave at 180  C for 12 h, which was placed in a reactor with uniform rotation. After naturally returning to room temperature, the product was percolated and washed with deionized water and removed water in a vacuum condition under 75  C for 5 h to obtain the pre-carbonized chitosan-coated interface functionalized PCC@MoxTi1-xO2 core-shell nanowire support, recorded as PCC@MTNWs-FI. The PCC@MTNWs-FI was placed in a tube furnace and annealed at 900  C for 2 h under high-purity Ar gas atmosphere to obtain the fully carbonized NC@MTNWs-FI support. As a comparative experiment, the preparation method of the support without functional interface which is not doped with Mo is similar to the former, except that only TNWs and chitosan are

Scheme 1 described the design synthesis process of NC@MTNWs-FI carrier, which includes 3 simultaneous reactions under hydrothermal conditions: (1) the surface of TNWs was etched and regenerated under weak alkaline hydrothermal treatment; (2) the Mo functionalized layer was formed by the incorporation of Mo dopant into the regrown amorphous shell; (3) chitosan in situ carbonated at the Mo functionalized layer producing the outermost nitrogen-doped carbonated layer. Nitrogendoped carbon layer is completely carbonized after treatment at 900  C in argon atmosphere, which fabricated the special concentric multilayered one-dimensional (1D) conformation with a TNWs core and external with Mo interface functionalization and nitrogendoped carbon bishell. Finally, PtRu NP was loaded onto the prepared NC @MTNWs-FI support by microwave assisted polyol method. X-ray diffraction (XRD) analysis was performed to analyze the crystal structure and phase composition. From the XRD comparison chart in Fig. 1(a), it can be observed that the characteristic diffraction peaks of TNWs prepared by hydrothermal method, the nitrogen doped carbon coated NC@TNCs and the Mo interface functionalized NC@MTNCs-FI are well indexed with the standard peak of anatase structured TiO2 (JCPDS No. 71e1166), and no crystal structure phase transition occurs. It indicates that both NC@TNWs and NC@MTNWs-FI can maintain the crystal structure of TNWs

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Scheme 1. Schematic diagram of synthesis of NC@MTNWs-FI support and PtRu catalyst by simultaneous nitrogen-doped carbon coating and interface functionalization.

before heat treatment after annealing at 900  C for 2 h. From the viewpoint of the diffraction intensity of the diffraction peak, the diffraction intensity of the heat-treated support was significantly increased, which indicates that the crystallinity of the support after the treatment was significantly increased. In addition, the diffraction peaks of molybdenum oxide and molybdenum sulfide were not found in the diffraction pattern of NC@MTNWs-FI, which further indicated that during the process of Mo-doped interfacial functionalization, Mo ions were lattice-substituted at the Ti site of TiO2, which will give rise to a series of doping properties [37,38]. Raman spectroscopy can reflect the carbon layer structure obtained by pre-carbonization of chitosan before and after high temperature annealing. Fig. 1(b) shows the Raman spectra of PCC@MTNWs-FI and NC@MTNWs-FI. The characteristic peaks of carbon materials around 1345 cm
1 and 1584 cm
1 are D and G bands, respectively. The ratio of the integrated peak area of the D band to the G band is called the Tuinstra-Koenig relationship and is an important index for evaluating the degree of graphitization of carbon materials. It is

found that the degree of graphitization of the NC@MTNWs-FI carbonized layer after high temperature annealing is much larger than that of PCC@MTNCs-FI obtained by hydrothermal coating and pre-carbonization. It indicates that the N-doped carbon formed by chitosan after high temperature annealing have been completely carbonized and have a high degree of graphitization. The N-doped electron-rich sites will interact more strongly with the supported catalytic metals, thus enhancing the loading performance and the anchoring effect. The TEM analysis was carried out on the nitrogen doped carbon coated support and the catalyst. The TEM images of PtRu/ NC@MTNWs-FI, PtRu/NC@TNWs and NC@MTNWs-FI are shown in Fig. 2. From Fig. 2(a), the NC@MTNWs-FI exhibits a clear and complete one-dimensional nanowire structure with a diameter of approximately 45 nm. Fig. 2(c) displays a HRTEM image of the PtRu/ NC@MTNCs-FI catalyst. From this figure, clear lattice diffraction fringes of oxide and catalytic metal can be observed. The diffraction fringes with a pitch of 0.35 nm and 0.221 nm correspond to the

Fig. 1. The XRD patterns of TNWs, NC@TNWs, and NC@MTNWs-FI (a); Raman spectra of PCC@MTNWs-FI and NC@MTNWs-FI (b).

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anatase TiO2 (101) plane and the Pt (111) plane, respectively. According to the diffraction fringes of different crystal phases and the contrast of different elements, the positions of PtRu NPs and nitrogen doped carbon coated support were indicated, from which it can be found that PtRu NPs with a diameter of about 2 nm were supported at the outer edge of the one-dimensional nanowires support with core-shell structure. The selected area electron diffraction pattern of the PtRu/NC@MTNCs-FI catalyst given in Fig. 2(e) was used to obtain the specific diffraction ring. By calculating the distance from the (101) and (001) plane diffraction rings to the center, the pitch is 0.36 and 0.24 nm. Fig. 2(b) and (d) show the TEM images of PtRu/NC@MTNWs-FI and PtRu/NC@TNWs, the particle size and distribution of PtRu NPs in PtRu/NC@MTNWs-FI are more uniform than PtRu/NC@TNWs, and the latter shows obvious local agglomeration. In addition, in order to study the material composition of the nitrogen doped carbon coated catalyst and confirm the existence of the auxiliary catalytic element Ru, the modifying elements Mo and N, the Energy dispersive X-ray spectrometry (EDAX) of samples was carried out. The spectrum and surface element content are shown in Fig. S1 and Table S1, respectively. The characteristic peaks of Pt, Ru, Mo and N are presented in the energy spectrum, indicating that PtRu NP was effectively supported on the support, meanwhile the Mo and N elements were successfully doped into NC@MTNW-FIs. From Table S2, the loading of Pt and Ru is approximately 20 wt%, the Mo content of the PtRu/NC@MTNWs-FI catalyst coated with the nitrogen doped carbon is 0.89 at.%, and the doping amount of N is 3.23 at.%. X-ray photoelectron spectroscopy (XPS) was performed to obtain the surface element composition of the catalyst. As demonstrated in Fig. 3(a), Pt, Mo, C, Ti, Ru, O and N elements can be distributed in the wide-scan spectrum. To further analyze the doping elements N and Mo, the Mo 3d characteristic peaks in the PtRu/NC@MTNWs-FI catalyst are fitted as shown in Fig. 3(b), and the binding energy and relative content of Mo(V) and Mo(VI) were calculated as shown in Table S2. The doping element Mo is present in the PtRu/NC@MTNWs-FI catalyst in equilibrium with two mixed valence states (Mo6þ, 46.8% and Mo5þ, 53.2%). This mixed valence state enables the doping element to have an electron donating effect, which can effectively enhance the electronic interaction between the modified support and the catalytic metal [37]. And the reason why there is no Mo4þ may be due to the strong interaction of this doping element with the catalytic metal platinum, which tends Mo to exist in the higher valence state due to this electron donating effect [39e41]. The fitting of the N 1s characteristic peaks in the PtRu/NC@MTNWs-FI and PtRu/NC@TNWs catalysts was depicted in

Fig. 3(c), Fig. S2, respectively, and Table S2 gave the relative amounts of N elements in different chemical states. The relative content of pyridine type N in the catalyst functionalized modified by Mo was 31.6% and 13.6% higher than of the unmodified catalyst. Pyridine type N can provide the main active sites for nucleation of Pt nanoparticles and has a better anchoring effect to prevent migration and agglomeration of Pt nanoparticles during aging [42]. According to Fig. 3(d), the peak position and component calculated of Pt (0), Pt (II) and Pt (IV) calculated from the Pt 4f characteristic peak fitting curve are shown in Table S2. The binding energy of Pt (0) in the core-shell catalyst coated nitrogen doped carbon was negatively shifted, which indicates that N in the carbon shell interacts with the electrons of Pt supported by the composite support. In addition, the binding energy of Pt (0) in Mo-modified PtRu/ NC@MTNWs-FI was more negatively shifted, which indicates that there is a synergistic electron donating effect between Mo and N in the composite support. The negative shift of Pt 4f binding energy is due to the electronic interaction between the modified support and the catalytic nanoparticles, which represents a change in the electronic structure of the Pt affected by the support. In addition, the stronger Mo/N synergistic electron donation effect also increased the relative proportion of the Pt (0) valence in the PtRu/ NC@MTNWs-FI, which was 6.5% and 8.2% higher than the PtRu/ NC@TNWs catalyst and the PtRu/C catalyst, respectively. The higher catalytic activity and stability characteristics of the low-valence Pt are more favorable for the electrocatalytic oxidation of methanol [43]. Methanol electrooxidation (MOR) is a direct means of testing catalyst performance. Fig. 4(a) shows the cyclic voltammograms (CV) curves of PtRu/NC@MTNWs-FI, PtRu/NC@TNWs and PtRu/C catalyst in the 0.5 mol L
1 CH3OH and 0.5 mol L
1 H2SO4 solution and the canning rate is 0.05 V s
1. The forward peak current densities of PtRu/NC@MTNWs-FI catalyst was 1.23 A mg
1 Pt, which was 2.08 times and 2.24 times higher than that of PtRu/NC@TNWs and PtRu/C catalyst, respectively. At the same time, the MOR activity and stability of the catalyst are better than similar catalysts reported in the related literature recently [44e46], and is superior to the previously reported interfacial-functionalized MoxTi1-xO2d nanotubes, which proves that the synergistic electron donating effect of Mo/N modification effectively improves the performance of the catalyst [47]. Furthermore, as indicated by dashed lines in Fig. 4(b), the corresponding potential on PtRu/NC@MTNWs-FI is much lower than that on PtRu/NC@TNWs and PtRu/C catalyst at a given oxidation current density. Further improvement in MOR activity is due to the synergistic electron donating effect of Mo/N

Fig. 2. (a)TEM image of NC@MTNWs-FI; (b,c,e)TEM, HRTEM, and SAED images of PtRu/NC@MTNWs-FI; (d)TEM images of PtRu/NC@TNWs

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Fig. 3. The XPS spectra of PtRu/NC@MTNWs-FI, PtRu/NC@TNWs, and PtRu/C (a), The Mo 3d, N 1s and Pt 4f for the PtRu/NC@MTNWs-FI(b,c and d).

modification. Electrochemical impedance spectroscopy can reflect the impedance of charge transfer during electrochemical reactions and is an important research tool for electrode process dynamics. Fig. 4(c) provides electrochemical impedance plots of PtRu/ NC@MTNWs-FI, PtRu/NC@TNWs, and PtRu/C catalysts in 0.5 mol L
1 CH3OH and 0.5 mol L
1 H2SO4. From the figure, the PtRu/NC@MTNWs-FI catalyst has a smaller capacitive reactance arc diameter than PtRu/NC@TNWs and PtRu/C catalyst, which means that the modified catalyst with nitrogen doped carbon coated onedimensional core-shell structure has faster MOR reaction rate. From the Nyquist diagram of the high frequency region in Fig. 4(d), the internal resistance of the catalyst reflected by the intersection of the arc and the real axis can be obtained. Due to the synergistic electron donating effect of Mo/N, the internal resistance of PtRu/ NC@MTNWs-FI is significantly lower than PtRu/NC@TNWs and PtRu/C catalyst. Fig. 4(e) shows the CV curves of COads stripping for PtRu/NC@MTNWs-FI, PtRu/NC@TNWs, and PtRu/C catalysts. The start-up potential of the COads oxidation peak of the PtRu/ NC@TNWs was negatively shifted by 200 mV relative to the PtRu/C catalyst, while the onset potential of the PtRu/NC@MTNWs-FI catalyst was shifted by 247 mV relative to the PtRu/C catalyst. It indicates that the modification brought by the interface functionalization of Mo can effectively improve the anti-COads poisoning ability of the catalyst, and the catalyst supported by NC@MTNWs with Mo/N synergistic electron donating effect has stronger antiCOads poisoning ability. Fig. 4(f) provides the integrated peak

areas of the COds oxidation peaks of PtRu/NC@MTNWs-FI, PtRu/ NC@TNWs, and PtRu/C catalysts, and the electrochemically active surface area (ECSA) was calculated according to the formula S1, which was 86.8 m2g-1, 59.7 m2g-1 and 88.9 m2g-1, respectively. The surface area specific activity (SA) of PtRu/NC@MTNWs-FI, PtRu/ NC@TNWs and PtRu/C catalysts for methanol oxidation was 14.2, 10.1 and 6.9 A m
2, respectively. Therefore, it can be concluded that PtRu/NC@MTNWs-FI has a significant improvement in the catalytic ability per unit active surface area due to the Mo/N synergistic electron donating effect. The durability of PtRu/NC@MTNWs-FI, PtRu/NC@TNWs, and PtRu/C catalysts was first evaluated by chronoamperometry at the constant potential of 0.6 V. From Fig. 5(a), the current density of the PtRu/NC@MTNWs-FI was always higher than the PtRu/NC@TNWs and PtRu/C catalysts throughout the test period, and the current density after 3600 s was 0.53 A cm
2, which was 4.3 times higher than that of PtRu/NC@TNWs and 8.3 times higher than that of the PtRu/C catalyst, respectively. The aging inactivation behavior of the catalyst during long-term working can be simulated by accelerated potential cycling test. Fig. 5(b)e(d) show the CV curves of PtRu/ NC@MTNWs-FI, PtRu/NC@TNWs, and PtRu/C catalysts before and after aging for 1000 cycles. Fig. 5(e)e(f) provide the corresponding relationship and normalized relationship between the forward peak current density of the three catalysts and the number of scanning cycles, respectively. The three catalysts produced significant performance degradation after the initial 200 cycles of

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Fig. 4. CV cures of PtRu/NC@MTNWs-FI, PtRu/NC@TNWs, and PtRu/C catalyst in a solution of 0.5 mol L
1 CH3OH and 0.5 mol L
1 H2SO4(a), comparison in start-up potential(b); Nyquist plots(c) comparison in high frequency region(d); The COad stripping voltammograms(e), The comparison of mass activity and specific activity(f).

accelerated potential cycling test, whereas the attenuation amplitude of PtRu/NC@MTNWs-FI was significantly less than PtRu/ NC@TNWs and PtRu/C catalyst. The PtRu/NC@MTNWs-FI catalyst maintained an initial activity of 64.2% after 1000 cycles of aging, which was higher than the 48.3% for the PtRu/NC@TNWs catalyst and 41% for the PtRu/C catalyst. In addition, the current density after aging of PtRu/NC@MTNWs-FI was 0.79 A mg
1 Pt, which was 1.32 times higher than the primary activity of PtRu/NC@TNWs and PtRu/C catalyst. A critical reason for the degradation of catalyst performance is the agglomeration of PtRu NPs. Fig. 6 is the TEM image of PtRu/ NC@MTNWs-FI and PtRu/NC@TNWs catalyst before and after accelerated potential cycling test and statistical graph of particle size distribution of PtRu NPs. The average particle size of PtRu NPs in the PtRu/NC@MTNWs-FI catalyst before the aging experiment was 1.87 nm, which was smaller than 2.62 nm in the PtRu/

NC@TNWs catalyst. After 1000 cycles of accelerated potential cycling test aging experiments, the PtRu particle size of PtRu/ NC@MTNWs-FI and PtRu/NC@TNWs catalysts increased significantly, which is the main reason for the decay of catalyst activity. After APCT, the particle size of PtRu NPs in PtRu/NC@MTNWs-FI increased to 2.88 nm without serious agglomeration; while the particle size of PtRu NPs in PtRu/NC@TNWs catalyst increased to 3.79 nm, and the significant agglomeration phenomenon has occurred. This agglomeration is due to the lack of Mo/N synergistic electron donating effect, resulting in the lack of strong electronic interaction and anchoring effect between the non-interface functionalized support and PtRu NPs. 4. Conclusions In summary, we successfully prepared the nitrogen doped

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Fig. 5. iet curves for catalyst (a), CV of PtRu/NC@MTNWs-FI (b), PtRu/NC@TNWs(c), and PtRu/C(d) catalyst before and after APCT. Mass activities corresponding to cycle numbers during APCT (e). The normalization of initial forward peak current density corresponding to cycle numbers during APCT (f).

carbon coated core-shell structure support (NC@MTNWs-FI) by simultaneous carbon-coated TiO2 and functional interfacial doping of Mo. The support has the special one-dimensional structure with more pyridine type N anchor positioning and the Mo functionalized interface compared to the unfunctionalized NC@TNWs support. NC@MTNWs-FI shows the Mo/N synergistic electron donating effect to its supported PtRu NPs, which in turn changes its catalytic activity. Electrochemical tests have shown that it significantly improves the catalytic performance for methanol electrooxidation in terms of activity and durability relative to PtRu/NC @ TNW and

commercial PtRu/C catalysts. This work provides a new strategy for the synthesis of modified carriers for Pt-based catalysts. Credit author statement Yun-Long Zhang: Conceptualization, Investigation, Writing Original Draft, Jia-Long Li: Methodology, Validation, Writing Original Draft, Lei Zhao: Project administration, Writing - Review & Editing, Xu-Lei Sui: Supervision, Qing-Yan Zhou: Writing - Review & Editing, Xiao-Fei Gong: Resources, Jia-Jun Cai: Methodology, Jia-

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Fig. 6. TEM images (a, c) and PtRu NPs size distribution (b, d) of PtRu/C@MTNCs-FI before and after APCT; TEM images (e, g) and PtRu NPs size distribution (f, h) of PtRu/NC@TNWs

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Zhan Li: Formal analysis, Da-Ming Gu: Visualization, Zhen-Bo Wang: Funding acquisition. Declaration of competing interest The authors declare no competing financial interest. Acknowledgments We acknowledge the National Natural Science Foundation of China (Grant No. 21273058, 21673064, 51802059 and 21503059), China postdoctoral science foundation (Grant No. 2018M631938, 2018T110307 and 2017M621284), Heilongjiang Postdoctoral Fund (LBH-Z17074) and Fundamental Research Funds for the Central Universities (Grant No. HIT. NSRIF. 2019040 and 2019041). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.electacta.2019.135410. References [1] L.-M. Zhang, X.-L. Sui, L. Zhao, G.-S. Huang, D.-M. Gu, Z.-B. Wang, Carbon (2017) 121. S0008622317305900. [2] X. Zhao, M. Yin, L. Ma, L. Liang, C. Liu, J. Liao, T. Lu, W. Xing, Energy Environ. Sci. 4 (2011) 2736e2753. [3] S.C. Thomas, X. Ren, S. Gottesfeld, P. Zelenay, Electrochim. Acta 47 (2002) 3741e3748. [4] S. Basri, S.K. Kamarudin, W.R.W. Daud, Z. Yaakub, Int. J. Hydrogen Energy 35 (2010) 7957e7970. [5] Y. Du, Y.-B. Shen, Y.-L. Zhan, F.-D. Ning, L.-M. Yan, X.-C. Zhou, Chinese Chemical Letters, 2017. [6] Z. Wen, J. Liu, J. Li, Adv. Mater. 20 (2010) 743e747. [7] Y. Mu, H. Liang, J. Hu, L. Jiang, L. Wan, J. Phys. Chem. B 109 (2005) 22212e22216. [8] C. Yu, K. Yang, Y. Xie, Q. Fan, J.C. Yu, Q. Shu, C. Wang, Nanoscale 5 (2013) 2142e2151. [9] Y. Chen, J. Wang, H. Liu, R. Li, X. Sun, S. Ye, S. Knights, Electrochem. Commun. 11 (2009) 2071e2076. ~ ez, Mater. Res. Express 1 (2014), [10] F. Paraguay-Delgado, M. Malac, G. Alonso-Nun 045026. [11] Y. Yu, O.Y. Gutierrez, G.L. Haller, R. Colby, B. Kabius, V.V. Jar, A. Jentys, J.A. Lercher, J. Catal. 304 (2013) 135e148. [12] E. Herrero, J.M. Feliu, A. Aldaz, J. Electroanal. Chem. 368 (1994) 101e108. [13] F. Luo, Q. Zhang, K. Qu, L. Guo, H. Hu, Z. Yang, W. Cai, H. Cheng, ChemCatChem 11 (2018). [14] J. Prabhuram, T.S. Zhao, Z.K. Tang, R. Chen, Z.X. Liang, J. Phys. Chem. B 110 (2006) 5245e5252. [15] A.V. Tripkovi c, K.D. Popovi c, B.N. Grgur, B. Blizanac, N.M. Markovi c, Electrochim. Acta 47 (2002) 3707e3714.

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