Surface Acidity Dictates Proton Transport in WO3/ZrO2: Proton-Conductive Behavior and Mechanistic Insight

Development of inorganic proton conductors that are applicable in a wide temperature range is crucial for applications such as fuel cells. Most of the reported proton conductors suffer from limited proton conductivity, especially at low temperature. In addition, the mechanism of proton conduction in the conductors is not fully understood, which limits the rational design of advanced proton conductors. In this work, we report the use of metal oxide solid acid as a promising proton conductor. WO3/ZrO2 (WZ) with different surface acidities is synthesized by controlling the content of WO3 on the surface of ZrO2. It is demonstrated that proton conductivity of WZ samples is closely related with their acidity. WZ with the strongest acidity exhibits the highest proton conduction performance at low temperatures, with a proton conductivity of 3.27 × 10-5 S cm-1 at 14 °C. The excellent performance of the WZ-type proton conductor is clarified with theoretical calculations. The results show that the enhanced water adsorption and the lowered activation barrier for breakage of the O-H bond in surface-adsorbed water are the key to the excellent proton-conductive performance of WZ. The experimental results and mechanistic insights gained in this work suggest that WZ is a promising proton conductor, and tailoring the surface acidity of metal oxides is an effective approach to regulate their proton-conductive performance.