Lanthanum Manganite-based Air Electrode Catalysts and Their Application to Lithium-air Batteries: Effects of Carbon Support Oxidation

Abstract

Acid-treated Ketjen Black (a-KB) carbon supports were prepared to investigate how oxidation of the carbon surface influences La 0.6 Sr 0.4 MnO 3 (LSM) nanoparticle distribution, and conjugation to the carbon support. 30 wt.% LSMloaded a-KB (LSM/a-KB) materials were prepared as air-electrode catalysts for rechargeable lithium-air batteries (LABs). a-KB exhibited a significant degree of O-containing (C-O, COO) surface functional groups, which resulted in the formation of smaller LSM nanoparticles and enhanced homogeneity over the carbon support when compared with the pristine KB support. Consequently, C-O-Mn bonds were formed, which increased the Mn oxidation state, and concomitantly enhanced conjugation resulting in improved catalytic activity. Additionally, the overpotential was reduced during charging (Li 2 O 2 decomposition). Furthermore, LSM/a-KB enhanced the cyclability of the LAB test cell. Scanning electron microscopy observations revealed that LSM/a-KB efficiently decomposed the Li 2 O 2 deposition layer, even after the 15th charge cycle when compared with LSM/KB. The LSM/a-KB air-electrode exhibited a more homogeneous and smaller-sized (and/or amorphous) Li 2 O 2 deposition after discharging. Therefore, the oxidation of the carbon surface, resulting in enhanced LSM nanoparticle distribution on, and conjugation to, the a-KB surface, influences the homogeneity of the Li 2 O 2 deposition onto the support during the discharge process leading to its facile decomposition during the following charge process.

Morphology of Thin-Film Nafion on Carbon as an Analogue of Fuel Cell Catalyst Layers

“…59 Notably, however, Ketjen EC-600JD has demonstrated relatively similar surface chemistries to our samples, C:O1:O2 ≈ 1:0.19:0.18. 60 This suggests that our samples' surface chemistries are relevant to PEMFC CCLs, though they are not fully representative of all common CBs used in PEMFCs.…”

“…Literature indicates that CB, like graphite, is comprised of sp 2 -hybridized carbon particles. 63 59 and Saito et al, 60 respectively. These two CBs are common in PEMFC CCLs, and their range of graphiticity (1.07 to 1.46 eV) is similar to the range covered by our samples (0.73−1.44 eV).…”

“…rGO-A and rGO-V are less graphitic, according to their broadened C 1s peak. XPS data for Vulcan XC-72 and Ketjen EC-600JD in Table are taken from Pantea et al and Saito et al, respectively. These two CBs are common in PEMFC CCLs, and their range of graphiticity (1.07 to 1.46 eV) is similar to the range covered by our samples (0.73–1.44 eV).…”

“… a Roughness, graphiticity, surface chemistry, and hydrophilicity help characterize similarities between samples and the CB (see Section ). Roughness values are taken from the interfacial widths in the best-fit dry SLD profiles. b Hydrophilicity is thickness dependent and is moderate for the two-sheet graphene film here. c Hydrophilicity is reported broadly for CBs and is not specific to Vulcan XC-72 or Ketjen EC-600JD. d XPS information (i.e., C 1s fwhm and C:O1:O2) for Vulcan XC-72 is from Pantea et al e XPS information (i.e., C 1s fwhm and C:O1:O2) for Ketjen EC-600JD is from Saito et al …”