Synthesis of Three-dimensional Pt-Ag Aerogels and Their Electrocatalytic Performance Toward Oxygen Reduction Reaction†

doi:10.7503/cjcu20170444

Abstract

Abstract:

The etched-platinum-silver aerogel(e-Pt-Ag gel) electrocatalysts with dendritic morphology were synthesized by chemical reduction and hydrothermal method, in which silver nanoparticles were removed by acid- and alkali-etching. X-ray diffraction(XRD), scanning electronic microscopy(SEM) and transmission electron microscopy(TEM) were employed to characterize the composition, structure and morphology of e-Pt-Ag gel. The activity and stability of the catalysts for oxygen reduction reaction(ORR) were studied by cyclic voltammetry(CV) and linear sweeping voltammetry(LSV) methods. The results show that the e-Pt-Ag gel exhibits excellent ORR performance and favorable durability. In detail, the mass and specific activities of e-Pt-Ag gel at 0.9 V are 166.3 mA/mg_Pt and 0.295 mA/cm², respectively, which are 2.0 and 1.8 times that of the commercial Pt/C catalyst[84.9 mA/mg_Pt and 0.163 mA/cm²]. Furthermore, the mass and space activities of the e-Pt-Ag gel only decay 6.1% and 9.1%, respectively, after 5000 electrochemical cycles, showing higher durability of the e-Pt-Ag gel compared with Pt/C(35%, 52.1%).

Key words: Pt-Ag aerogel, Acid- and alkali-etching, Oxygen reduction reaction, Cycle stability

CLC Number:

O646

TrendMD:

HUANG Jipei,LI Yi,YANG Shenhui,ZHOU Yazhou,CHENG Xiaonong,ZHU Jia,YANG Juan. Synthesis of Three-dimensional Pt-Ag Aerogels and Their Electrocatalytic Performance Toward Oxygen Reduction Reaction^†[J]. Chem. J. Chinese Universities, 2018, 39(5): 1063.

Figures/Tables 12

Fig.1 Preparation mechanism of catalysts Note: (A) Pt2+, Ag+ solution; (B) Pt-Ag precursor; (C) alloyed Pt-Ag gel before etching; (D) acid- and alkali-etching; (E) e-Pt-Ag gel catalyst. Possible structures of Pt-Ag bimetallic nanoparticles before and after etching: a. non-uniformly distributed structure; b. random solid solution; c. core-shell structure ordered intermetallic compound; d—f removing the Ag from surface and forming an unstructured structure.

Fig.2 XRD patterns of Pt-Ag gel by two-step method before etching(a), e-Pt-Ag gel by using acid- and alkali- etching method(b) and commerical Pt/C(c)(A) and the corresponding magnification of (A)(B)

Fig.3 SEM images(A, B, D, E) and corresponding EDS spectra(C, F) of Pt-Ag gel(A—C) and e-Pt-Ag gel(D—F)

Fig.4 TEM images of Pt-Ag gel(A), e-Pt-Ag gel(B, C) and the corresponding electron diffraction pattern of (C)(D)

Fig.5 Representative TEM image(A), corresponding HRTEM image(B), HAADF-STEM image(C), Pt(D), Ag(E) elemental mappings and energy dispersive X-ray(EDX) spectrum of Pt-Ag gel(F)

Fig.6 Representative TEM image(A) and corresponding HRTEM image(B), HAADF-STEM image(C), Pt(D), Ag(E), elemental mappings and EDX spectrum of e-Pt-Ag gel catalyst after etching(F)

Fig.7 Cyclic voltammograms of Pt-Ag gel, e-Pt-Ag gel and commercial Pt/C catalysts in N2-saturated 0.1 mol/L HClO4(A) and TEM image of Pt-Ag gel(B)

Fig.8 ORR curves of the catalysts in O2-saturated 0.1 mol/L HClO4 solution at room temperature(1600 r/min, scan rate: 50 mV/s)

Table 1 Comparison of e-Pt-Ag gel and commercial Pt /C(20%) catalysts(before and after ADT)

Sample	ECSA/(m²·g^-1)		Onset potential/V		Half-wave potential/V
Sample	Initial	Final	Initial	Final	Initial	Final
e-Pt-Ag gel(deactivation)	56.5	52.9	0.906	0.898	0.838	0.828
Pt/C(20%)(deactivation)	54.8	41.1	0.883	0.873	0.823	0.802

Fig.9 Electrocatalytic activity of the e-Pt-Ag gel catalyst and commercial Pt/C catalysts(A, B) and ORR-mass activities(left) and space activities(right) of catalysts measured at 0.9 V(C)

Fig.10 ORR polarization curves of e-Pt-Ag gel catalyst(A) and commercial Pt /C(B) catalysts in O2-saturated 0.1 mol/L HClO4 at room temperature before and after ADT(1600 r/min, scan rate: 10 mV/s)

Fig.11 Tafel curves of e-Pt-Ag gel catalyst(A, D) and commercial Pt/C(B, E) and the value changes on mass activities(C) and space activities(F) of the e-Pt-Ag gel catalyst at 0.85 V before and after ADT

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