Article Cite This: ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX
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Proton Conduction and Fuel Cell Using the CuFe-Oxide Mineral Composite Based on CuFeO2 Structure Yan Wu,*,† Jing Zhang,† Lingyao Li,† Jie Wei,‡ Jianfeng Li,‡ Xiang Yang,† Chunjie Yan,*,† Chenggang Zhou,*,† and Bin Zhu*,† †
Engineering Research Center of Nano-Geo Materials of Ministry of Education, Faculty of Materials Science and Chemistry, China University of Geosciences, 388 Lumo Road, Wuhan 430074, China ‡ Ministry of Education Key Laboratory of Spectrochemical Analysis and Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China S Supporting Information *
ABSTRACT: High ionic conductivity has attracted considerable attention for use in energy applications, such as solid oxide fuel cells (SOFCs). Novel proton conductivity was discovered in a delafossite-based CuFe-oxide composite from a natural mineral. Low-temperature (400−550 °C) SOFCs (LTSOFCs) using the natural CuFe-oxide composite as an electrolyte were demonstrated. Power densities of 775 mW cm−2 were achieved at 550 °C for the CuFeO2 electrolyte, 423 mW cm−2 for the CuFe-oxide from the natural mineral, and 672 mW cm−2 by further introducing proton-dominating conduction into the CuFe-oxide natural material. We found that the CuFeO2 delafossite structure played a key role in high ionic conductivity. Theoretical calculations indicated that enhanced proton transport through the Cu−O layer was associated with a low activation energy (0.23−0.26 eV) and rapid transport kinetics, which were consistent with the experimental results. Both theoretical and experimental results demonstrated that the CuFeO2 delafossite material possessed advantages for high ionic conductors and LTSOFCs. Fundamental studies and a deeper scientific understanding from this work provide a new theoretical approach to design novel material families and functions based on natural mineral materials for ionic conductors and advanced applications, resulting in a new generation of LTSOFCs. KEYWORDS: natural CuFe-oxide mineral, CuFeO2, natural CuFe-oxide-based composite, proton conduction, low-temperature solid oxide fuel cells
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cm−1). This goal has not yet been achieved. Over recent decades, extensive studies have been conducted on new materials with the objective of achieving LTSOFCs.9−12 Proton-conducting perovskite oxide electrolytes and ceria− carbonate composite materials have been explored for use in LTSOFCs. These materials have a wide range of catalytic activities and conductivities compared to conventional oxideion-conducting YSZ electrolytes. These materials also exhibit various novel functionalities and provide substantial opportunities for use in LT devices. High proton or oxide-ion conductivity is essential to ensure high performance in a LTSOFC.5,13,14 Recently, materials with proton-conducting phases have demonstrated high performance in LTSOFCs.15,16 A material capable of proton transport can exhibit greatly enhanced ionic conductivity, thus leading to enhanced SOFC performance.17−19 One approach to promoting SOFC commercialization is to use low-cost materials with high ionic conductivity. Some
INTRODUCTION Solid ionic-conducting oxides have been used in a wide array of applications ranging from batteries to fuel cells and sensors.1 These materials form the key components of electrochemical or energy conversion devices with huge market potential. A typical example of such a material is yttrium-stabilized zirconia (YSZ), which has been successfully used as an oxide-ion (O2−)conducting electrolyte for solid oxide fuel cells (SOFCs). However, the oxide-ion conductivity in commercially available YSZ is poor at temperatures below 700 °C.2−4 Proton conduction in oxides has attracted extensive attention in recent years.5,6 Proton conductors generally exhibit more favorable transport kinetics than the oxide-ion transport kinetics in oxideion conductors; proton conductors thus offer intriguing potential for high-performance, lower-temperature SOFC operation. Despite these advantages, the high grain-boundary resistance and fabrication challenges have thus far constrained the applications of proton conductors.7,8 The challenge for low-temperature (LT; ≤600 °C) SOFCs is to develop a technically useful solid material capable of both oxide-ion and proton conduction at a sufficiently LT (
