Thickness dependence of proton conductivity of anodic ZrO2-WO3-SiO2 nanofilms

► Efficient proton-conducting two-layered ZrO2-WO3-SiO2 nanofilms were formed by anodizing. ► The proton conductivity was highly enhanced by reducing the film thickness. ► The thin outer layer of ZrO2 contributed to the thickness dependence of the proton conductivity.