Proton transport controlled at surface layer of CeO2 by gradient-doping with a built-in-field effect

Abstract

Ceramic fuel cells hold an important position for the sustainable energy future using renewable energy sources with high efficiency. The design and synthesis of active materials, interface engineering and having capability of low operating temperature is considered as an important factor to further increase the power output and stability of ceramic fuel cell devices. A novel methodology has vital importance to develop new functionalities of existing materials by introducing new different effects. The built-in electric field (BIEF) is one of the most recently used approaches to improve charge transfer and ionic conductivity of solid oxide materials. Herein, we demonstrate gradient doping strategy in CeO2–δ structure to produce BIEF effect and to modulate the proton transport effectively at the surface layer rather than bulk structure. The inclusions of La and Sr metal ions at the surface and Co-metal ions into bulk-layer of CeO2 form the gradiently doped structure. The gradient doping into CeO2 highly improves the proton transport properties through the surface layer by modifying the energy levels. Moreover, unbalanced charge distribution due to gradient doping produces built-in electric-field to provide extra driving force for protons transport through surface layer. The acquired gradiently doped fluorite structure exhibits remarkable proton conductivity of >0.2 S/cm, as a result ceramic fuel cell shows power output of >1000 mW/cm2 while operating at 500 °C. This unique work highlights the critical role of gradiently doped electrolyte in electrochemical conversion energy devices and offers new understanding and practices for sustainable energy future.