A dense pyrophosphate proton-conducting membrane for hydrogen separation at intermediate temperatures

The hydrogen permeation membranes that work at intermediate temperatures have received significant attention in recent years because they can efficiently couple hydrogen production and applications. Among them, the pyrophosphate-type membranes with high protonic conductivity at intermediate temperatures are ideal candidates. However, the low relative density of pyrophosphate materials is a huge challenge for practical applications, and few pyrophosphate-type membranes were reported for hydrogen separation. In this work, by adding ZnO sintering aid and doping the low-valence Mg²⁺ ions into the Sn-site of the SnP₂O₇, dense membranes are obtained for hydrogen permeation. The relative density and conductivity of the developed Sn_0.9Mg_0.1P₂O₇–ZnO (SM_0.1P–ZnO) membranes are up to 94.6 % and 0.08 mS cm⁻¹ (at 400 °C), respectively. The maximum hydrogen permeation flux of the SM_0.1P–ZnO membrane is 4.03 mol h⁻¹ m⁻² when humidified Ar is supplied on the sweeping side and 80 % H₂–20 % He is supplied on the feed side. In addition, the SM_0.1P–ZnO membrane exhibits good stability during 300 h of operation at 400 °C, which is promising for practical hydrogen separation at intermediate temperatures.