Journal of Power Sources 206 (2012) 91–96 Contents lists available at SciVerse ScienceDirect Journal of Power Sources jo ur nal homep age: www.elsevier.com/locate/jpowsour The effect of an ultra-thin zirconia blocking layer on the performance of a 1-m-thick gadolinia-doped ceria electrolyte solid-oxide fuel cell Doo-Hwan Myung a,b , Jongill Hong b , Kyungjoong Yoon a , Byung-Kook Kim a , Hae-Weon Lee a , Jong-Ho Lee a , Ji-Won Son a,∗ a High-Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu, Seoul 130-791, Republic of Korea b Dept. of Materials Science and Engineering, Yonsei University, 262 Seong Sanno, Seodaemun-gu, Seoul 120-749, Republic of Korea a r t i c l e i n f o Article history: Received 19 December 2011 Received in revised form 16 January 2012 Accepted 19 January 2012 Available online 5 February 2012 Keywords: Thin-film electrolyte solid-oxide fuel cell Gadolinia-doped ceria Pulsed laser deposition Yttria-stabilized zirconia Reduction-blocking layer a b s t r a c t Ultra-thin (less than 200 nm) yttria-stabilized zirconia (YSZ) blocking layers are employed at the anode side of a 1-m-thick gadolinia-doped ceria (GDC) thin-film electrolyte by pulsed laser deposition. Their effects on a GDC thin-film electrolyte solid-oxide fuel cell (TF-SOFC) are presented. Without blocking layers, the open cell voltage (OCV) of the GDC TF-SOFC is about 0.6 V. By inserting the blocking layer, the OCV increases to over 1 V. As a result, the maximum power density of the TF-SOFC increases from 377 mW cm -2 to over 1 W cm -2 at 600 ◦ C. The present study demonstrates the possibility of obtaining the critical performance at a low temperature regime using thin-film GDC electrolytes. © 2012 Elsevier B.V. All rights reserved. 1. Introduction When minimizing the problems associated with high tem- perature operation, such as chemical reactions between the cell components and microstructural degradation, one of the key issues in the research of solid-oxide fuel cells (SOFCs) is the reduction of the operating temperature [1–4]. Low temperature operation is of significant technical importance to both conventional large- capacity and portable miniaturized SOFCs. It ensures reliability and cost-effectiveness, providing a pathway to commercialization of the former system [3,5], and facilitates thermal management, resulting in a reduction of size of the latter system [6,7]. In terms of the electrolyte, there are two key approaches to decrease the operating temperature: the first is to employ an alternative elec- trolyte material possessing higher ionic conductivity than that of the conventional electrolyte material, such as yttria-stabilized zir- conia (YSZ) [1,3,5,8–13], and the second is to reduce the physical thickness of the conventional electrolyte to secure an appropriate conductance value of the electrolyte [6,14,15]. For an alternative material, doped ceria, such as gadolinia-doped ceria (GDC) and samaria-doped ceria (SDC), is the most studied material due to its high ionic conductivity at an intermediate ∗ Corresponding author. Tel.: +82 2 958 5530; fax: +82 2 958 5529. E-mail address: jwson@kist.re.kr (J.-W. Son). temperature regime, chemical stability with Co-containing cath- odes, and thermal expansion coefficient (TEC) match with adjacent Ni-cermet anodes [12,16]. Ceria-based electrolytes, however, become mixed conductors in the reducing condition because of the partial reduction of Ce 4+ to Ce 3+ , inducing cell voltage and effi- ciency loss due to internal short circuiting [9,11,16]. In addition, there can be further reduction of open circuit voltage (OCV) with a doped ceria electrolyte layer because the OCV of doped ceria is dependent on factors such as electrode materials and the thickness of the ceria layer as well; this is because the gradient of the defect concentration in the electrolyte is dependent on the operating con- dition [9,17]. It was proposed that, as both ionic and electronic fluxes increase with the decrease in thickness of the ceria elec- trolyte, OCV could drop further as a result of thin ceria electrolytes [9]. Therefore, employing a thick ceria electrolyte layer would be an obvious choice to suppress the additional OCV drop. Nonethe- less, OCV deviation from theoretical predictions was observed even at thicknesses of approximately 30–40 m [9,10,17]. This causes a dilemma in obtaining optimal performance of a SOFC with mono- lithic ceria electrolytes. To reduce ohmic loss, the thickness of the electrolyte should be reduced; however, the leakage current increases as the thickness decreases and, as a result, the SOFC out- put power inevitably decreases [9]. An actively studied approach to using a thin doped ceria-based electrolyte in SOFC reliably is to suppress electronic conduction of doped ceria by blocking its exposure to the reducing atmosphere [18]. A layer of a pure ionic conductor such as YSZ was coated at the 0378-7753/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2012.01.117