Influence of Support Characteristics on Coverage of Ionomer and Oxygen Reduction Performance for Pt/C Catalysts

doi:10.15541/jim20250004

Abstract

Abstract:

Carbon support is an important component of Pt/C catalyst commonly used in the membrane electrodes of proton exchange membrane fuel cells, and ionomer is one of the key components that make up the catalytic layer. However, the influence of support characteristics on coverage of ionomer and oxygen reduction performance for Pt/C catalysts is still unknown. Here, six different types of representative commercial carbon supports (VC, KB1, KB2, BP, SJR, and AB) were focused. The microstructure and surface chemical properties of the carbon supports and the Pt/C catalysts prepared with and without addition of ionomer were investigated using various characterization methods. The oxygen reduction reaction (ORR) performance of various Pt/C catalysts was tested to explore the electrocatalytic structure-activity relationship of representative carbon supports for Pt catalysts. As revealed, carbon supports with large specific surface areas and rich pore structures, such as KB1, KB2 and BP, contribute to more uniform distribution of Pt particles. Presence of oxygen-containing functional groups on solid carbon supports with strong hydrophilicity, such as VC and SJR, contributes to dispersion of Pt particles. Meanwhile, carbon supports with abundant mesopores in the range of 2-8 nm (KB1 and KB2) are beneficial for improving location of Pt within pores of carbon particles, while those with high specific surface area and full of micropores (BP) and those with medium or low specific surface area (VC, SJR, and AB) have the most Pt nano-particles distributed on the outer surface of the carbon particles. By combining changes in specific surface area and pore structure of various Pt/C samples before and after addition of ionomer, the coverage of ionomer was calculated, and a distribution model of ionomer on different catalyst particles was proposed. On the solid carbon supported catalysts, a certain amount of ionomer basically covers entire outer surface of carbon particles. For the BP supported catalyst which is dominated by micropores, ionomer can block the micropores, resulting in a significant decrease in specific surface area and pore volume. For the mesoporous carbon supported catalysts, the same amount of ionomer is hard to block all micropores and mesopores, leading to lower coverage. Furthermore, ORR activity of Pt/C catalyst mainly depends on the Pt nano-particle size, and the Pt nano-particles located in the pores inside of the carbon particles can be protected from the poisoning of ionomer. Therefore, Pt catalysts supported on the carbon supports of KB series exhibit excellent performance for the ORR kinetics occurring in liquid-phase.

Key words: support characteristic, Pt/C catalyst, coverage of ionomer, oxygen reduction reaction, proton exchange membrane fuel cell

CLC Number:

TQ426

LI Xueru, MA Zhejie, GUO Yujie, LI Ping. Influence of Support Characteristics on Coverage of Ionomer and Oxygen Reduction Performance for Pt/C Catalysts[J]. Journal of Inorganic Materials, 2025, 40(12): 1395-1404.

Figures/Tables 15

Fig. 1 (a) N2 adsorption-desorption isotherms and (b) pore-size distributions of different carbon supports

Fig. 2 FT-IR spectra of different carbon supports Colorful figure is available on website

Table 1 Contact angles and Zeta potentials of different carbon supports

Sample	VC	KB1	KB2	BP	SJR	AB
Contact angle/(°)	40	47	125	94	34	137
Zeta potential/mV	9.8	21.0	24.7	15.3	-1.1	-

Fig. 3 STEM images with secondary electron (SE) mode for Pt catalysts loaded on different carbon supports (a) 0° and (b) 180° of PK-Pt/VC; (c) 0° and (d) 180° of Pt/VC; (e) 0° and (f) 180° of PK-Pt/KB1; (g) 0° and (h) 180° of Pt/KB2; (i) 0° and (j) 180° of Pt/BP; (k) 0° and (l) 180° of Pt/SJR; (m) 0° and (n) 180° of Pt/AB

Fig. 4 (a) Total specific surface area and (b) total pore volume of different carbon supports and Pt/C catalysts

Fig. 5 Pore size distribution curves of different Pt/C catalysts (a) before and (b) after addition of ionomer Colorful figures are available on website

Fig. 6 Reduction rates of specific surface areas and pore volumes of different Pt/C catalysts after addition of ionomer Numbers in the figure represent coverages of ionomer

Fig. 7 TEM images of catalysts containing ionomer for (a) Pt/VC and (b) Pt/KB2 Yellow arrows: ionomer film covering the outer surface of the catalyst particles

Fig. 8 Schematic diagrams of the coverage states of ionomer on catalysts with different characteristics (a) PK-Pt/KB1, Pt/KB2; (b) Pt/BP; (c) Pt/VC, Pt/SJR and Pt/AB Black dot: Pt particle; Blue area: ionomer; Gray area: C

Fig. 9 (a) CV curves, (b) LSV curves, (c) calculated ECSA and MA of different Pt/C catalysts Colorful figures are available on website

Table S1 Specific surface areas, pore volumes and distributions of different carbon supports

Sample	Specific surface area/(m²·g^-1)	Pore area/(m²·g^-1)			Pore volume/(cm³·g^-1)
Sample	Specific surface area/(m²·g^-1)	<2 nm	2-8 nm	>8 nm	<2 nm	2-8 nm	>8 nm	Total
VC	206.9	125.1	43.5	38.3	0.035	0.039	0.478	0.582
KB1	811.1	372.8	353.1	85.2	0.194	0.308	0.730	1.232
KB2	1361.0	291.3	834.3	235.4	0.167	0.807	1.613	2.587
BP	1313.1	903.6	249.0	160.5	0.444	0.204	1.909	2.577
SJR	121.2	15.1	33.4	72.7	0.009	0.032	0.757	0.798
AB	65.6	5.5	42.1	18.0	0.004	0.039	0.135	0.178

Table S2 Average particle sizes and loading amounts of Pt particles on different carbon supports

Catalyst	PK-Pt/VC	Pt/VC	PK-Pt/KB1	Pt/KB2	Pt/BP	Pt/SJR	Pt/AB
Pt loading/% (in mass)	38.6	32.0	38.3	35.8	35.8	37.0	31.9
Average Pt particle size/nm	3.9	3.0	2.5	2.4	2.5	2.6	2.8

Table S3 Percentages of Pt particles distributed inside and outside of the carbon particles for different carbon supports

Catalyst	PK-Pt/VC	Pt/VC	PK-Pt/KB1	Pt/KB2	Pt/BP	Pt/SJR	Pt/AB
Exterior frequency/%	92	90	34	28	85	100	100
Interior frequency/%	8	10	66	72	15	0	0

Table S4 Testing results of ORR on various Pt/C catalytic electrodes

Catalyst	j_lim/(mA·cm^-2)	j_k/(mA·cm^-2)	E_onset/V	E_1/2/V
PK-Pt/VC	5.9	4.3	1.037	0.88
Pt/VC	5.9	3.5	1.033	0.88
PK-Pt/KB1	6.0	5.6	1.048	0.90
Pt/KB2	6.1	5.9	1.042	0.90
Pt/BP	6.1	4.5	1.039	0.88
Pt/SJR	6.0	4.0	1.046	0.87
Pt/AB	5.5	2.7	1.014	0.84

Fig. S1 HRTEM images and histograms of particle size distributions of different Pt catalysts (a, a1) PK-Pt/VC; (b, b1) Pt/VC; (c, c1) PK-Pt/KB1; (d, d1) Pt/KB2; (e, e1) Pt/BP; (f, f1) Pt/SJR; (g, g1) Pt/AB

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