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A simple preparation of very high methanol tolerant cathode electrocatalyst for direct methanol fuel cell based on polymer-coated carbon nanotube/platinum.

Yang Z, Nakashima N - Sci Rep (2015)

Bottom Line: Here, we describe a simple and novel methodology to fabricate a practically applicable electrocatalyst with a high methanol tolerance based on poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole]-wrapped multi-walled carbon nanotubes, on which Pt nanoparticles have been deposited, then coated with poly(vinylphosphonic acid) (PVPA).The polymer coated electrocatalyst showed an ~3.3 times higher oxygen reduction reaction activity compared to that of the commercial CB/Pt and methanol tolerance in the presence of methanol to the electrolyte due to a 50% decreased methanol adsorption on the Pt after coating with the PVPA.Meanwhile, the peroxide generation of the PVPA coated electrocatalyst was as low as 0.8% with 2 M methanol added to the electrolyte, which was much lower than those of the non-PVPA-coated electrocatalyst (7.5%) and conventional CB/Pt (20.5%).

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Motooka Nishi-ku, Fukuoka 819-0395, Japan.

ABSTRACT
The development of a durable and methanol tolerant electrocatalyst with a high oxygen reduction reaction activity is highly important for the cathode side of direct methanol fuel cells. Here, we describe a simple and novel methodology to fabricate a practically applicable electrocatalyst with a high methanol tolerance based on poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole]-wrapped multi-walled carbon nanotubes, on which Pt nanoparticles have been deposited, then coated with poly(vinylphosphonic acid) (PVPA). The polymer coated electrocatalyst showed an ~3.3 times higher oxygen reduction reaction activity compared to that of the commercial CB/Pt and methanol tolerance in the presence of methanol to the electrolyte due to a 50% decreased methanol adsorption on the Pt after coating with the PVPA. Meanwhile, the peroxide generation of the PVPA coated electrocatalyst was as low as 0.8% with 2 M methanol added to the electrolyte, which was much lower than those of the non-PVPA-coated electrocatalyst (7.5%) and conventional CB/Pt (20.5%). Such a high methanol tolerance is very important for the design of a direct methanol fuel cell cathode electrocatalyst with a high performance.

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Electrochemical measurements of the conventional CB/Pt, MWNT/PyPBI/Pt and MWNT/PyPBI/Pt/PVA.ORR polarization curves for the CB/Pt (a), MWNT/PyPBI/Pt (b) and MWNT/PyPBI/Pt/PVPA (c) in O2-saturated 0.1 M HClO4 and varying concentrations of methanol at 25 °C, rotation rate of 1600 rpm, and sweep rate of 10 mV/s. In all figures, methanol concentrations are: 0 M (red), 0.5 M (black), 1 M (blue) and 2 M (green). (d) Methanol oxidation reaction (MOR) curves were recorded in 0.1 M HClO4 and 1 M methanol at a scan rate of 50 mV/s for the CB/Pt (black line), MWNT/PyPBI/Pt (blue line), and MWNT/PyPBI/Pt/PVPA (red line) before durability test.
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f2: Electrochemical measurements of the conventional CB/Pt, MWNT/PyPBI/Pt and MWNT/PyPBI/Pt/PVA.ORR polarization curves for the CB/Pt (a), MWNT/PyPBI/Pt (b) and MWNT/PyPBI/Pt/PVPA (c) in O2-saturated 0.1 M HClO4 and varying concentrations of methanol at 25 °C, rotation rate of 1600 rpm, and sweep rate of 10 mV/s. In all figures, methanol concentrations are: 0 M (red), 0.5 M (black), 1 M (blue) and 2 M (green). (d) Methanol oxidation reaction (MOR) curves were recorded in 0.1 M HClO4 and 1 M methanol at a scan rate of 50 mV/s for the CB/Pt (black line), MWNT/PyPBI/Pt (blue line), and MWNT/PyPBI/Pt/PVPA (red line) before durability test.

Mentions: The ORR is the cathodic reaction in an actual fuel cell32. During the fuel cell operation in the DMFCs, the methanol crossover is the most serious drawback since it lowers the voltage of the cells, leading to degradation of the FC performance. As shown in Fig. 2, the ORR was measured in the presence of a given concentration of methanol (for rotating disc current densities, see Supplementary Information, Fig. S4, 5 and 6). In the absence of methanol, the mass activities of the CB/Pt, MWNT/PyPBI/Pt and MWNT/PyPBI/Pt/PVPA calculated using the Levich-Koutecky equation, 1/i = 1/ik+1/id(where i is the experimentally measured current, and id is the diffusion-limited current.), were 48.8, 187.0 and 157.7 mA/mgPt at 0.85 V vs. RHE, respectively33343536 The PVPA-coated electrocatalyst showed a slight decrease in the ORR activity by 15.6% compared to that of the MWNT/PyPBI/Pt due to the polymer-coating of the Pt-NPs. The specific activity was calculated by dividing the mass activity by the electrochemical surface area (ECSA). The ECSAs of the MWNT/PyPBI/Pt and MWNT/PyPBI/Pt/PVPA were 44.7 and 42.3 m2/gPt, respectively, (see Supplementary Information, Fig. S7)3738, and the Pt utilization efficiency of the MWNT/PyPBI/Pt was almost the same as described in our previous report39. The specific activities were 0.42 and 0.37 mA/cm2Pt for the MWNT/PyPBI/Pt and MWNT/PyPBI/Pt/PVPA, respectively. These obtained values were much higher than that of the commercial CB/Pt (specific activity: 0.08 mA/cm2Pt, ECSA: 60.6 m2/gPt) similar to previous reports4041. Meanwhile, the diffusion-limited current density of the PVPA-coated electrocatalyst (−5.2 mA/cm2, see red line in Fig. 2c) was almost identical to that of the MWNT/PyPBI/Pt (−5.3 mA/cm2, see red line in Fig. 2b), suggesting that the PVPA coating showed a negligible effect on the O2 accessibility42. For the MWNT/PyPBI/Pt, we observed small methanol oxidation peak at 0.9 V vs. RHE in the presence of methanol in the electrolyte (see Fig. 2b). On the contrary, almost no such peak was recognized for the MWNT/PyPBI/Pt/PVPA, indicating the suppression of the methanol oxidation due to effect of methanol absorption caused by the polymer coating3143.


A simple preparation of very high methanol tolerant cathode electrocatalyst for direct methanol fuel cell based on polymer-coated carbon nanotube/platinum.

Yang Z, Nakashima N - Sci Rep (2015)

Electrochemical measurements of the conventional CB/Pt, MWNT/PyPBI/Pt and MWNT/PyPBI/Pt/PVA.ORR polarization curves for the CB/Pt (a), MWNT/PyPBI/Pt (b) and MWNT/PyPBI/Pt/PVPA (c) in O2-saturated 0.1 M HClO4 and varying concentrations of methanol at 25 °C, rotation rate of 1600 rpm, and sweep rate of 10 mV/s. In all figures, methanol concentrations are: 0 M (red), 0.5 M (black), 1 M (blue) and 2 M (green). (d) Methanol oxidation reaction (MOR) curves were recorded in 0.1 M HClO4 and 1 M methanol at a scan rate of 50 mV/s for the CB/Pt (black line), MWNT/PyPBI/Pt (blue line), and MWNT/PyPBI/Pt/PVPA (red line) before durability test.
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f2: Electrochemical measurements of the conventional CB/Pt, MWNT/PyPBI/Pt and MWNT/PyPBI/Pt/PVA.ORR polarization curves for the CB/Pt (a), MWNT/PyPBI/Pt (b) and MWNT/PyPBI/Pt/PVPA (c) in O2-saturated 0.1 M HClO4 and varying concentrations of methanol at 25 °C, rotation rate of 1600 rpm, and sweep rate of 10 mV/s. In all figures, methanol concentrations are: 0 M (red), 0.5 M (black), 1 M (blue) and 2 M (green). (d) Methanol oxidation reaction (MOR) curves were recorded in 0.1 M HClO4 and 1 M methanol at a scan rate of 50 mV/s for the CB/Pt (black line), MWNT/PyPBI/Pt (blue line), and MWNT/PyPBI/Pt/PVPA (red line) before durability test.
Mentions: The ORR is the cathodic reaction in an actual fuel cell32. During the fuel cell operation in the DMFCs, the methanol crossover is the most serious drawback since it lowers the voltage of the cells, leading to degradation of the FC performance. As shown in Fig. 2, the ORR was measured in the presence of a given concentration of methanol (for rotating disc current densities, see Supplementary Information, Fig. S4, 5 and 6). In the absence of methanol, the mass activities of the CB/Pt, MWNT/PyPBI/Pt and MWNT/PyPBI/Pt/PVPA calculated using the Levich-Koutecky equation, 1/i = 1/ik+1/id(where i is the experimentally measured current, and id is the diffusion-limited current.), were 48.8, 187.0 and 157.7 mA/mgPt at 0.85 V vs. RHE, respectively33343536 The PVPA-coated electrocatalyst showed a slight decrease in the ORR activity by 15.6% compared to that of the MWNT/PyPBI/Pt due to the polymer-coating of the Pt-NPs. The specific activity was calculated by dividing the mass activity by the electrochemical surface area (ECSA). The ECSAs of the MWNT/PyPBI/Pt and MWNT/PyPBI/Pt/PVPA were 44.7 and 42.3 m2/gPt, respectively, (see Supplementary Information, Fig. S7)3738, and the Pt utilization efficiency of the MWNT/PyPBI/Pt was almost the same as described in our previous report39. The specific activities were 0.42 and 0.37 mA/cm2Pt for the MWNT/PyPBI/Pt and MWNT/PyPBI/Pt/PVPA, respectively. These obtained values were much higher than that of the commercial CB/Pt (specific activity: 0.08 mA/cm2Pt, ECSA: 60.6 m2/gPt) similar to previous reports4041. Meanwhile, the diffusion-limited current density of the PVPA-coated electrocatalyst (−5.2 mA/cm2, see red line in Fig. 2c) was almost identical to that of the MWNT/PyPBI/Pt (−5.3 mA/cm2, see red line in Fig. 2b), suggesting that the PVPA coating showed a negligible effect on the O2 accessibility42. For the MWNT/PyPBI/Pt, we observed small methanol oxidation peak at 0.9 V vs. RHE in the presence of methanol in the electrolyte (see Fig. 2b). On the contrary, almost no such peak was recognized for the MWNT/PyPBI/Pt/PVPA, indicating the suppression of the methanol oxidation due to effect of methanol absorption caused by the polymer coating3143.

Bottom Line: Here, we describe a simple and novel methodology to fabricate a practically applicable electrocatalyst with a high methanol tolerance based on poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole]-wrapped multi-walled carbon nanotubes, on which Pt nanoparticles have been deposited, then coated with poly(vinylphosphonic acid) (PVPA).The polymer coated electrocatalyst showed an ~3.3 times higher oxygen reduction reaction activity compared to that of the commercial CB/Pt and methanol tolerance in the presence of methanol to the electrolyte due to a 50% decreased methanol adsorption on the Pt after coating with the PVPA.Meanwhile, the peroxide generation of the PVPA coated electrocatalyst was as low as 0.8% with 2 M methanol added to the electrolyte, which was much lower than those of the non-PVPA-coated electrocatalyst (7.5%) and conventional CB/Pt (20.5%).

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Motooka Nishi-ku, Fukuoka 819-0395, Japan.

ABSTRACT
The development of a durable and methanol tolerant electrocatalyst with a high oxygen reduction reaction activity is highly important for the cathode side of direct methanol fuel cells. Here, we describe a simple and novel methodology to fabricate a practically applicable electrocatalyst with a high methanol tolerance based on poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole]-wrapped multi-walled carbon nanotubes, on which Pt nanoparticles have been deposited, then coated with poly(vinylphosphonic acid) (PVPA). The polymer coated electrocatalyst showed an ~3.3 times higher oxygen reduction reaction activity compared to that of the commercial CB/Pt and methanol tolerance in the presence of methanol to the electrolyte due to a 50% decreased methanol adsorption on the Pt after coating with the PVPA. Meanwhile, the peroxide generation of the PVPA coated electrocatalyst was as low as 0.8% with 2 M methanol added to the electrolyte, which was much lower than those of the non-PVPA-coated electrocatalyst (7.5%) and conventional CB/Pt (20.5%). Such a high methanol tolerance is very important for the design of a direct methanol fuel cell cathode electrocatalyst with a high performance.

No MeSH data available.


Related in: MedlinePlus