Saturday, 25 February 2017

The potential of yttrium-doped barium zirconate electrolyte for high-performance fuel cells

Source: "Demonstrating the potential of yttrium-doped barium zirconate electrolyte for high-performance fuel cells", Nature Communications 8, Article number: 14553 (2017), doi:10.1038/ncomms14553; Published online: 23 February 2017

Authors

School of Mechanical Engineering, Korea University, Anam-ro 145, Seongbuk-gu, Seoul 02841, Republic of Korea
Kiho Bae, Dong Young Jang, Hyung Jong Choi, Donghwan Kim & Joon Hyung Shim

High-Temperature Energy Materials Research Center, Korea Institute of Science and Technology (KIST), 5, Hwarang-ro 14-gil, Seongbuk-gu, Seoul 02792, Republic of Korea
Kiho Bae, Donghwan Kim, Jongsup Hong, Byung-Kook Kim, Jong-Ho Lee & Ji-Won Son

Nanomaterials Science and Engineering, Korea University of Science and Technology (UST), KIST Campus, Seoul 02792, Republic of Korea
Jong-Ho Lee & Ji-Won Son

Abstract

In reducing the high operating temperatures (≥800 °C) of solid-oxide fuel cells, use of protonic ceramics as an alternative electrolyte material is attractive due to their high conductivity and low activation energy in a low-temperature regime (≤600 °C). Among many protonic ceramics, yttrium-doped barium zirconate has attracted attention due to its excellent chemical stability, which is the main issue in protonic-ceramic fuel cells. However, poor sinterability of yttrium-doped barium zirconate discourages its fabrication as a thin-film electrolyte and integration on porous anode supports, both of which are essential to achieve high performance. Here we fabricate a protonic-ceramic fuel cell using a thin-film-deposited yttrium-doped barium zirconate electrolyte with no impeding grain boundaries owing to the columnar structure tightly integrated with nanogranular cathode and nanoporous anode supports, which to the best of our knowledge exhibits a record high-power output of up to an order of magnitude higher than those of other reported barium zirconate-based fuel cells.

Discussion

To fabricate highly efficient and physically/chemically stable PCFCs (Protonic-Ceramic Fuel Cells), an anode-supported fuel cell configuration based on BZY thin films is demonstrated in the current study. The multi-scale anode structure with reducing grain and pore sizes is confirmed to provide flat surface favourable to thin-film deposition as well as improve physical integration. On the anodes, a grain-boundary-free columnar BZY (Barium Zirconate) electrolyte with significantly reduced thickness was successfully fabricated by PLD (Pulsed Laser Deposition). This thin BZY electrolyte is believed to substantially reduce the ohmic resistance compared with those of BZY-PCFCs quoted in literature, which is the main reason for the cell performance enhancement. The nano-porous electrodes clearly shown by TEM (Transmission Electron Microscopy) images were also sufficient to implement low-polarization resistance, providing increasing reaction sites on the both side of the electrolyte. As results, significantly improved power outputs were obtained from the fuel cell configuration with the maximum power density of 740 mW cm−2 at 600 °C that has not achieved from the other BZY-based PCFCs so far. This performance improvement using BZY provides an opportunity for practical use of PCFCs potentially solving the conflicting challenges between high performance and chemical stability that have been faced in PCFCs until now.


Image: Figure 5: TEM (Transmission Electron Microscopy) characterization on the optimized PCFC.

From: Demonstrating the potential of yttrium-doped barium zirconate electrolyte for high-performance fuel cells

(a) A schematic diagram of single column in the thin BZY electrolyte and the neighbouring electrode grains in the fuel cell configuration with possible charge transport path. (b) Bright-field image of dense BZY electrolyte in the middle and nano-porous electrodes. The top and bottom layers are LSC cathode and Ni–BZY nano-AFL, respectively. Scale bar, 0.2 μm. (c) Higher magnification of bright-field image at the interfaces between the electrolyte and the electrodes, clearly showing the grain structure of each elements. Scale bars, 0.1 μm. (d) Dark-field image of the area shown in b. The highlighted single column demonstrates it contains a single grain. Scale bar, 0.2 μm. (e) A SAED pattern deduced from the marked area in b, which matches with cubic perovskite BZY. Scale bar, 2 nm−1. (f) HR-TEM image of the marked area in b showing the lattice images. Scale bar, 1 nm.

Read more at: http://www.nature.com/articles/ncomms14553