Carbon Supported Bimetallic Platinum-Iron Nanocatalysts: Application

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Carbon Supported Bimetallic Platinum-Iron Nanocatalysts: Application in Direct Borohydride/Hydrogen Peroxide Fuel Cell Lanhua Yi, Bin Yu, Wei Yi, Yuanqing Zhou, Rui Ding, and Xianyou Wang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04438 • Publication Date (Web): 20 May 2018 Downloaded from http://pubs.acs.org on May 20, 2018

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ACS Sustainable Chemistry & Engineering

Carbon Supported Bimetallic Platinum-Iron Nanocatalysts: Application in Direct Borohydride/Hydrogen Peroxide Fuel Cell Lanhua Yi a,*, Bin Yu a, Wei Yi b,*, Yuanqing Zhou a, Rui Ding a, Xianyou Wang a,* a

Key Laboratory of Environmentally Friendly Chemistry and Applications of

Ministry of Education, School of Chemistry, Xiangtan University, Xiangtan 411105, China b

Department of Chemistry, School of Chemistry and Molecular Engineering, East

China Normal University, Shanghai 200241, China ∗ Corresponding author. Tel.: +86 731 58292477; fax: +86 731 58292477. E-mail address: [email protected] (L. Yi), [email protected] (W. Yi), [email protected] (X. Wang).

Abstract: Carbon supported bimetallic platinum-iron nanocatalysts (Pt-Fe/C) with various proportions of atoms, applied to direct borohydride/peroxide fuel cell (DBHFC) anode catalyst, are facilely prepared via a simple and low-cost chemical route in aqueous solution at ambient temperature. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) results show the Pt-Fe alloy structure’s existence as well as the mean crystallite size of around 3 nm for Pt-Fe nanoparticals. Enhanced catalytic activity of Pt-Fe/C to BH4− electrooxidation has been observed in electrochemical test (chronoamperometry (CA), cyclic voltammetry (CV), single fuel cell test, rotating disc electrode (RDE) voltammetry) results as well as Pt67Fe33/C owns the best catalytic performance. High maximum power density of 65 mW cm−2 1

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for DBHFC is acquired by using Pt67Fe33/C as anode at 25 ºC. Furthermore, the electron transfer number (n) related to BH4− oxidation is evaluated, and n of 4.9 can be achieved on Pt67Fe33/C electrode.

Keywords: Direct borohydride/peroxide fuel cells (DBHFC); Borohydride oxidation reaction (BOR); Catalytic activity; Anode catalysts

Introduction Direct borohydride fuel cell (DBFC) presents numerous advantages of fast reaction kinetics, high theoretical voltage and specific energy. Because DBFC uses solid borohydride as fuel, the problems come from hydrogen transportation along with hydrogen storage can be avoided. At the same time, CO poisoning would not occur while no carbon element contained in DBFC’s fuel of borohydride. Thus, DBFC has received considerable attention and widely applied in portable devices.1-9 The DBFC’s electrochemical reaction is: Anode: BH 4 − + 8OH − → BO 2 − + 6 H 2 O+ 8e −

E0anode = -1.24 V (vs. SHE)

(1)

Cathode: O 2 + 2 H 2 O + 4 e − → 4 OH −

E0cathode = +0.4 V (vs. SHE)

(2)

The DBFC’s overall cell reaction is: E0cell = 1.64 V (vs. SHE)

BH 4 − + 2 O2 → BO 2 − + 2 H 2 O

(3)

DBHFC which uses H2O2 in acid electrolyte as oxidant possesses much higher theoretical cell voltage (3.01 V), and the DBHFC’s cathode electrochemical reaction is: E0cathode = +1.77 V (vs. SHE)

H 2O 2 + 2 H + + 2 e− → 2 H 2O

2


(4)

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The DBHFC’s overall cell reaction is: E0cell = 3.01 V (vs. SHE)

BH 4 − + 4 H 2 O 2 → BO 2 − + 6 H 2 O

(5)

Nowadays, anode catalysts’ high price is still an obstruction in DBFC’s development. Various materials have been used for DBFC anode catalysts, including Pt, Au, Pd, Ag, and Os (noble metals)10-22, Co, Ni, and Zn (transition metals)22-25 as well as hydrogen storage alloys26,27, etc. Among these catalysts, Pt is the most widely used in DBFC anode catalysts but its valuableness limits its commercialization application in fuel cell technology. Thus, rationally producing bimetallic or multimetallic catalysts has been an effective way to reduce the cost while simultaneously enhance the performance and increase the utilization efficiency of noble metallic catalysts.28,29 In our previous studies, we found that Pt-M/C (M=Zn, Sn, Co, Cu) bimetallic catalysts showed enhanced catalytic activity to BH4− oxidation.30-33 Moreover, Au-Fe/C also proved to be a superior electrocatalyst to BH4− oxidation.34 In this paper, various atom ratios Pt-Fe/C were synthesized via a simple and green approach, then were studied as DBHFC’s anode catalysts. The Pt-Fe/C catalysts’ electrocatalytic performances to BH4− oxidation were analyzed in detail via CV, CA, and RDE voltammetry as well as the single DBHFC performance tests.

Experimental methods Material synthesis. Pt-Fe/C catalysts’ synthesis is in accordance with our previous works.30-34 In the typical synthesis, 64 mg carbon black (Vulcan XC-72R) was ultrasonically dispersed in 100 mL ultrapure water (Milli-Q, 18 MΩ cm). Then, the carbon black suspension was added into 300 mL ultrapure water which contained the 3



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required amounts of H2PtCl6 (Sigma-Aldrich) solution (0.0193 M) and FeCl3 (Alfa-Aesar) solution (0.1 M), 0.28 mL Polyvinylpyrrolidone (PVP) (Sigma-Aldrich) solution (0.1 M). Kept the solution stirring for 1 h, then adjusted the pH to 10 by NaOH solution (3M) and added 1 mL NaBH4 (Alfa-Aesar) solution (1 M) into the solution. After another 24 h stirring, filtered and washed the resulting catalyst until no Cl− was detected by 0.1 M AgNO3 solution, and finally vacuum dried. The as-prepared catalysts with Pt:Fe atom ratios of 50:50, 67:33, 75:25, 100:0 were marked as Pt50Fe50/C, Pt67Fe33/C, Pt75Fe25/C, Pt/C, respectively. The dosages of H2PtCl6 solution (0.0193 M) and FeCl3 solution (0.1 M) were 3.31 mL and 0.64 mL for Pt50Fe50/C, 3.73 mL and 0.36 mL for Pt67Fe33/C, 3.88 mL and 0.25 mL for Pt75Fe25/C, 6.61 mL and 0.00 mL for Pt/C, respectively. The metal loading for each catalyst is 20 wt %. Material characterization. The as-prepared Pt-Fe/C catalysts’ structure and phase were analyzed by XRD (Bruker D8, Cu Kα radiation), and morphology were observed by TEM (JEOL JEM-3010, 300 kV). Electrochemical

measurements.

The

as-prepared

Pt-Fe/C

catalysts’

electrochemical measurements were performed on ATA-1B RDE (Jiangfen Electroanalytical Instrument Co., Ltd., China) attached to CHI660a electrochemical workstation (Chenhua Co., Ltd., China) with a three-electrode one-compartment electrochemical cell consisting of working electrode (Pt-Fe/C), reference electrode (Ag/AgCl), and counter electrode (3×5 cm2 Ni foam mesh for CA and CV, Pt wire for RDE voltammetry). For electrochemical surface area (ECSA) testing, the electrolyte

4


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was argon-saturated 0.5 M H2SO4 (0.1971 V vs. RHE for Ag/AgCl, KClstd reference electrode), and for CA and CV testing, the electrolyte was 3.0 M NaOH + 0.1 M NaBH4 (1.0541 V vs. RHE for Ag/AgCl, KClstd reference electrode), while for RDE voltammetry testing, the electrolyte was 1.0 M NaOH + 0.01 M NaBH4 (1.0259 V vs. RHE for Ag/AgCl, KClstd reference electrode). For making working electrode, 10 mg Pt-Fe/C powder and 0.25 ml Nafion solution (5 wt.%, DuPont Corp.) were ultrasonically mixed with 0.75 ml ultrapure water for 2 h to acquire homogenous catalyst/Nafion ink. 3 µl (for CA and CV tests) or 2 µl (for RDE voltammetry test) catalyst/Nafion ink was dripped on glassy carbon electrode (GCE), then dried it at ambient temperature. The actual metal load on working electrodes was 0.084 mg cm-2 for CA and CV tests as well as 0.056 mg cm-2 for RDE voltammetry tests. Fuel cell test. Figure 1 shows the single DBHFC’s schematic diagram.30-34 DBHFC’s cell performance testing performed on Neware TS-51800 battery measurement system (Neware Technology Co., Ltd., China) as well as using the steady state potential and applied current for acquiring DBHFC power densities. The single DBHFC consists of anode (Pt-Fe/C), cathode (Pt/C), anolyte (3 M NaOH + 1 M NaBH4), catholyte (0.5 M H2SO4 + 2 M H2O2), and separator (Nafion117 membrane). For preparing DBHFC anode and cathode electrodes, mixing Pt-Fe/C with Nafion solution and isopropyl alcohol to acquire well-distributed catalyst ink, then covered it on stainless steel gauze (1×1 cm2) and dried in vacuum, finally pressed it 1 min at a pressure of 10 MPa to ensure its favourable electric contact. The catalyst load is 4.5 mg cm−2 (amounting to 0.9 mg cm−2 actual metal load) on DBHFC anode

5



and cathode electrodes.

Figure 1. DBHFC’s schematic diagram.

Results and discussion Pt-Fe/C catalysts’ XRD patterns are showed in Figure 2. The diffraction peaks of face centered cubic (fcc) Pt observed at 39°, 46° and 67° (contribution of (111), (200), and (220) reflections) were matched with the JCPDS card No. 04-0802, while the other peak of carbon observed at 25° (contribution of (002) reflections) was matched with the JCPDS card No. 75-1621. For Pt-Fe/C catalysts, the diffraction peaks of Pt (at 39°, 46°, 67°) shift to more positive 2θ values indicates that Pt lattice is contracted and Pt-Fe alloy comes into being. Meanwhile, the intensities of Pt diffraction peaks (at 39°, 46°, 67°) decrease with the decrease of Pt ratio and the increase of Fe ratio in Pt-Fe/C catalysts. The lattice parameters (afcc) are calculated by the Bragg formula (Eq. (6)), and the average crystallite sizes (D, nm) are calculated by the Scherrer’s equation (Eq. (7)):31,32

6


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2λ sin θ

(6)

0.9λ B cos θ

(7)

a fcc =

D=

where θ is Pt (220) peak angle, λ is 1.54056 Å, B is full width at half-maximum in radians (FWHM). The calculated afcc of Pt, Pt75Fe25, Pt67Fe33, Pt50Fe50 nanoparticles are 0.3922, 0.3902, 0.3875, and 0.3865 nm, respectively. The calculated D of Pt, Pt75Fe25, Pt67Fe33, Pt50Fe50 nanoparticles are 3.4, 2.7, 2.5, and 2.6 nm, respectively. The Pt-Fe/C catalysts’ smaller afcc indicates that Fe-doping decreases the crystallite size as well as results in Pt (220) peak higher position shifting. The reason might be that the Fe atomic size (1.24 Å) is smaller than the Pt atomic size (1.39 Å), and Fe-doping induces contraction of Pt crystal structure.

Figure 2. Pt-Fe/C catalysts’ XRD patterns. Figure 3 shows Pt-Fe/C catalysts’ TEM images and Pt67Fe33/C catalyst’s HR-TEM

7



images. As seen from Figure 3, Pt-Fe metal nanoparticles for all as-prepare catalysts are small spherical dark spots dispersing on carbon support uniformly with some aggregates, and more aggregates existing in Pt-Fe/C might be caused by Fe-doping. The average sizes of the particles obtained by TEM are consistent with XRD results, which are about 4 nm for Pt nanoparticles as well as about 3 nm for Pt75Fe25, Pt67Fe33, and Pt50Fe50 nanoparticles. From HR-TEM images of Pt67Fe33/C (Figure 3e and 3f), the lattice spacing of 0.2264 nm and 0.2027 nm correspond to Pt {111} facets and Fe {110} facets, respectively. Moreover, TEM-EDS also reflects the presence of Pt and Fe with a Pt/Fe atomic ratios of 2.02:1, which is in accord with the dosages using in catalyst preparation process (Figure 3g). (b)

8


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(c)

(d)

Figure 3. TEM images of as-prepared (a) Pt/C, (b) Pt75Fe25/C, (c) Pt67Fe33/C, (d) Pt50Fe50/C. (e, f) HR-TEM images and (g) TEM-EDS spectra of Pt67Fe33/C. 9



ECSA can be acquired through the hydrogen desorption (QH) coulombic charge in CVs.35 Pt-Fe/C electrodes’ CVs in argon-saturated 0.5 M H2SO4 at scan rate 50 mV s-1 are showed in Figure 4. For all Pt-Fe/C electrodes, the Pt surface electrochemical characteristics (surface oxide formation/stripping and hydrogen adsorption/desorption) are quite obviously. In addition, the redox peak pair related to Fe species oxidation/reduction appeared between +0.35 and +0.65 V.36 The ECSA (based on Pt) of Pt/C, Pt75Fe25/C, Pt67Fe33/C, Pt50Fe50/C, estimated by the charge of hydrogen desorption and 210 µC cm-2 related to a complete H monolayer, were 132, 237, 312 and 287 cm2 mg-1, respectively. Obviously, benefit from the smaller size, Pt67Fe33/C owns the largest ECSA which can increase opportunities of catalyst coming into contact with reactant, and enhance the electrocatalyst catalytic activity.

Figure 4. Pt-Fe/C electrodes’ CVs in argon-saturated 0.5 M H2SO4. Figure 5 is Pt-Fe/C electrodes’ CVs at scan rate 20 mV s-1 in 3.0 M NaOH + 0.1 M NaBH4. As show in the CVs, three oxidation peaks can characterize the BH4− electrooxidation. In positive going sweeping, the oxidation peak a1 (around -0.8 V) 10


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corresponds to borohydride hydrolysis (Eq. (8)) with the H2 electrooxidation followed (Eq. (9)). The following oxidation peak a2 (around -0.5 V) corresponds to BH3OH− oxidation (Eq. (10)), and the final broad hump oxidation peak a3 corresponds to BH4− oxidation (Eq. (1)). As for reverse potential sweeping, the oxidation peak c1 also corresponds to BH3OH− oxidation (Eq. (10)).17 On the Pt75Fe25/C, Pt67Fe33/C, Pt50Fe50/C electrodes, current densityes of peak a3 corresponding to BH4− oxidation are 21.9, 27.8, 20.9 mA cm-2, respectively, but as to Pt/C electrode, it’s only 18.0 mA cm-2. Obviously, Fe-doping improves the Pt/C catalyst catalytic activity to BH4− electrooxidation despite Pt contents in Pt-Fe/C are less than that in Pt/C, moreover, Pt67Fe33/C owns the most excellent catalytic activity. BH 4 − + H 2 O → BH 3OH − + H 2

(8)

H 2 +2OH − → 2H 2O+2e−

(9)

3 BH3OH − + 3OH − → BO 2 − + H 2 + 2 H 2 O+ 3e− 2

11


(10)


Figure 5. CVs of (a) Pt/C, (b) Pt75Fe25/C, (c) Pt67Fe33/C, (d) Pt50Fe50/C in 3.0 M NaOH + 0.1 M NaBH4. The eletrocatalyst catalytic activities were further measured by CA. Figure 6 shows the Pt-Fe/C electrodes’ CAs from –1.2 V to -0.2 V in 3.0 M NaOH + 0.1 M NaBH4. As seen from Figure 6, in the whole BH4− electrooxidation process, all the Pt-Fe/C electrodes show current decay. After 60 s of CA testing, the highest final current density is on Pt67Fe33/C (25.7 mA cm−2), and then on Pt75Fe25/C (22.5 mA cm−2), Pt50Fe50/C (21.3 mA cm−2), Pt/C (18.2 mA cm−2), which also prove that Fe-doping can improve Pt catalyst eletrocatalytic activity to BH4− oxidation, moreover, Pt67Fe33/C has the best catalytic performance.

12


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Figure 6. Pt-Fe/C electrodes’ CAs in 3 M NaOH + 0.1 M NaBH4. Figure 7 is the Pt-Fe/C electrodes’ RDE voltammetries with various rotation rates at scan rate 20 mV s−1 in 1.0 M NaOH + 0.01 M NaBH4. As shown in Figure 7, the oxidative currents start at about -1.05 V and raise with the rotation rate raise. Pt-Fe/C exhibit similar electrocatalytic properties to Pt/C, and there are two distinguishable potential regions (-0.8 to -0.2 V and 0 to +0.2 V) correspond to two oxidation processes (the direct BH4− oxidation process and the BH4− and BH3OH− blended oxidation process) on all as-prepared catalyst electrodes. For a chosen potential oxidation reaction RDE studies, Levich equation (Eq. (11)) can be used to calculate the involved electron number (n):37 jL = 0.62nFD 2/3Cv −1/6ω 1/2

(11)

However, it should be mass-transport limited for all rates of rotation when Levich equation is used, thus, the Koutecky-Levich (K-L) equation (Eq. (12)) is used to calculate n when a kinetic limitation exists:37 13



1 1 1 1 1 1 1 = + = + = + 2/3 −1/6 1/2 j jk jL jk 0.62nFD Cv ω jk Bω1/2

Page 14 of 27

(12)

where jL stands for the diffusion-convection limiting current density, F stands for Faraday constant, D stands for the electrolyte solution diffusion coefficient, C stands for the electrolyte solution bulk concentration, ν stands for the kinematic solution viscosity, ω stands for the electrode rotation rate, j stands for the measured current density, and jk stands for the kinetic controlled current density. The inset of Figure 7 shows the K-L analyses based on the plot at the potential of -0.5 V. On the basis of the linear relation between ω-1/2 and j-1, jk and B can be acquired from figuring out the intercept and the K-L plot slope. Taken D=3.01×10-5 cm2 s-1 and ν=0.0114 cm2 s-1,38 the calculated n on Pt/C, Pt75Fe25/C, Pt67Fe33/C, Pt50Fe50/C are 4.2, 4.8, 4.9, 4.7, respectively. The n value decides catalyst faradic efficiency, thus, Pt-Fe/C catalysts have similar faradic efficiency to Pt/C because of their similar n value.

14


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Figure 7. RDE voltammogram responses of (a) Pt/C, (b) Pt75Fe25/C, (c) Pt67Fe33/C, (d) Pt50Fe50/C with different rotation rates in 1.0 M NaOH + 0.01 M NaBH4. Inset: K-L plot at -0.5 V. Moreover, electrocatalyst intrinsic electrocatalytic activity can be achieved through the current density based on ECSA. After correction from the borohydride diffusion-convection in solution by the Levich method, Tafel plots (the logarithm of kinetic current densities per ECSA (log(ik)ECSA) vs. potential) are obtained (Figure 8). The current densities (based on ECSA) on Pt/C, Pt75Fe25/C, Pt67Fe33/C, Pt50Fe50/C at the potential of -0.85 V are 2.8, 5.0, 7.7 and 4.2 mA cm-2, respectively. The higher kinetic currents on Pt-Fe/C indicate that Fe-doping can enhance Pt catalyst intrinsic catalytic activity and Pt67Fe33/C has the most excellent intrinsic catalytic activity.

15



Figure 8. Tafel plots at rotation rate of 1600 rpm in 1 M NaOH + 0.01 M NaBH4. The single DBHFC polarization plots and power density curves at 25ºC are shown in Figure 9. The DBHFC open circuit voltages (OCVs) of about 1.7 V (Figure 9a) is below the DBHFC theoretical OCV of 3.01 V (Figure 9a) because of the mixed potential generated from BH4− and hydrogen oxidation at anode as well as H2O2 and O2 reduction at cathode.39 The cell voltages decrease linearly with the current density increase, indicating that the cell performances lie on ohmic resistance, mainly ohmic polarization. DBHFC with Pt67Fe33/C anode maintains the slowest cell voltage decay and the highest cell voltage value during the entire test process. Using Pt/C, Pt75Fe25/C, Pt67Fe33/C, Pt50Fe50/C as anode, the DBHFC maximum power densities at 25 ºC are 35, 51, 65 and 44 mW cm−2, respectively (Figure 9b), suggesting that the synergistic effects of Pt and Fe can improve DBHFC performance and Pt67Fe33/C is still the best anode catalyst for DBHFC.

16


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Figure 9. The single DBHFC (a) cell polarization plots, (b) power density curves. Table 1 tabulated the DBFC performance comparison for various reported anode electrocatalysts.

Obviously,

Pt67Fe33/C

exhibits

parallel or

better

catalytic

performance to BH4- electrooxidation, suggesting Pt67Fe33/C is an excellent anode catalyst in DBFC applications.

17



Page 18 of 27

Table 1. DBFC performance comparison for various reported anode catalysts. Anode

Cathode

electrocatalyst

Membrane

Pt/C -2

Nafion 117

(0.2 mg Pt cm )

Pt1Ni1/C

Pt/C

(5 mg metal cm-2)

(4 mg Pt cm-2)

Pt/C

Pt/C cm-2)

(2 mg Pt

Nafion 117

Nafion 212 cm-2)

Ni@Pt/C

Pt/C

(1 mg metal cm-2)

(0.5 mg Pt cm-2)

Ni@Pt/C

Pt/C cm-2)

Ni1Pt1/C

Nafion 117 cm-2)

Pt/C

(1 mg metal

cm-2)

Pt/C (1 mg Pt

Nafion 117

(0.5 mg Pt

Nafion 117

(0.5 mg Pt

cm-2)

Pt/C cm-2)

Nafion 115

(0.5 mg Pt

Au/C

cm-2)

Pt/C

(0.5 mg Au

cm-2)

Pd/C

(4 mg Pt

Nafion 117 cm-2)

Pt mesh

Nafion 212 2

Cu1Pd1/C

(1 × 1 cm )

Au45Co55/C

Au/C

(4.5 mg metal

cm-2)

Au58Ni42/C (4 mg Pt

Nafion 117

(4.5 mg Pt

cm-2)

Au/C

cm-2)

Os/C

(4 mg Pt

Nafion 117 cm-2)

Pt black

(1 mg Os

cm-2)

(4 mg Pt

Nafion 117 cm-2)

Pt/C

Au/C

(4 mg Pt cm-2)

(4 mg Pt cm-2)

Pt67Sn33/C

Pt/C

(4 mg metal

cm-2)

(4 mg Pt

Nafion 117 cm-2)

Pt67Co33/C

Pt/C (4 mg Pt cm-2)

Pt50Cu50/C

Pt/C

(4 mg metal

cm-2)

(4 mg Pt

Nafion 117

Nafion 117 cm-2)

Pt67Zn33/C

Pt/C

(4 mg metal cm-2)

(4 mg Pt cm-2)

Pt/C

Pt/C

(4 mg Pt

cm-2)

(4 mg Pt

Nafion 117

Nafion 117 cm-2)

Pt67Fe33/C

Pt/C

(4 mg metal cm-2)

(4 mg Pt cm-2)

6 M NaOH +

Nafion 117

O2

cm-2)

T

Ref

(°C)

108.5

79.8

(40)

53

60

(28)

420

60

(41)

133.38

60

(42)

68.64

60

(43)

106.63

60

(44)

140

40

(45)

34

20

(10)

20

(12)

-1

1 M NaBH4

0.1 l min

2 M NaOH +

O2

2 M NaBH4

0.2 l min-1

5 M NaOH +

O2 min-1

1 M NaBH4

7.5 ml

2 M NaOH +

1 M H2O2 +

1 M NaBH4

0.5 M H2SO4

2 M NaOH +

2 M H2O2 +

1 M NaBH4

0.5 M H2SO4

2 M NaOH +

2 M H2O2 +

1 M NaBH4

0.5 M H2SO4

3 M NaOH +

O2

1 M NaBH4

0.1 MPa

6 M NaOH +

1 M H2O2 + 1 M

25% NaBH4

HCl + 3 M NaCl

2 M NaOH +

4.5 M H2O2 +

31.4

0.5 M NaBH4

2M HCl

39.8

3 M NaOH +

2 M H2O2 +

66.5

25

(13)

1 M NaBH4

0.5 M H2SO4

3 M NaOH +

2 M H2O2 +

45.74

20

(14)

1 M NaBH4

0.5 M H2SO4

2 M NaOH +

O2

18

25

(22)

69

60

34.13

25

(46)

91.5

25

(30)

79.7

25

(31)

71.6

25

(32)

79.9

25

(33)

35

25

This

0.5 M NaBH4 Nafion 117

(4 mg metal cm-2)

Power density (mW

-2

(0.42 mg metal cm )

(1 mg metal

Oxidation

electrocatalyst

PtRu/C

(2 mg Pt

Fuel

1.25 l

min-1

3 M NaOH +

2 M H2O2 +

1 M NaBH4

0.5 M H2SO4

3 M NaOH +

2 M H2O2 +

1 M NaBH4

0.5 M H2SO4

3 M NaOH +

2 M H2O2 +

1 M NaBH4

0.5 M H2SO4

3 M NaOH +

2 M H2O2 +

1 M NaBH4

0.5 M H2SO4

3 M NaOH +

2 M H2O2 +

1 M NaBH4

0.5 M H2SO4

3 M NaOH +

2 M H2O2 +

1 M NaBH4

0.5 M H2SO4

3 M NaOH +

2 M H2O2 +

1 M NaBH4

0.5 M H2SO4

18


work 65

25

This work

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Conclusions In summary, Pt-Fe/C nanocatalysts with around 3 nm average particle size were synthesized via NaBH4 reduction method at ambient temperature, and exhibited more excellent catalytic performance than Pt/C to BH4− electrooxidation even though its Pt content is below the Pt/C, which revealed that Fe-doping can enhance Pt catalyst catalytic activity obviously. Moreover, Pt67Fe33/C catalyst owns the best catalytic activity to BH4− electrooxidation. At 25ºC, high DBHFC maximum power density (65 mW cm−2) is achieved by using Pt67Fe33/C as anode. Therefore, owing to the advantages of both lower price and more excellent catalytic performance, Pt67Fe33/C will become quite a potential anode electrocatalyst in DBFC applications.

Acknowledgments We acknowledge support from the Collaborative Innovation Center of New Chemical Technologies for Environmental Benignity and Efficient Resource Utilization, Natural Science Foundation of Hunan Province (2016JJ2128), National Natural Science Foundation of China (21506182, 21203161), Scientific Research Fund of Hunan Provincial Education Department (17B254).

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TOC graphic:

Synopsis: Pt67Fe33/C nanocatalyst with higher performance and lower cost would be a promising anode electrocatalyst for DBFCs.

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Carbon Supported Bimetallic Platinum-Iron Nanocatalysts: Application

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