An easily sintered, chemically stable indium and tin co-doped barium hafnate electrolyte for hydrogen separation

Abstract

As a novel type of proton conductor, BaHfO3-based proton conductor has a promising application potential, but its poor sinterability and low conductivity limit its application as hydrogen separation membrane materials. In this paper, In and Sn co-doping BaHfO3 strategy was adopted to further optimize its sinterability and electrical conductivity. BaHf0.9−xInxSn0.1O3−δ (x = 0.05–0.25) proton conductors were prepared by high temperature solid state method. The results of X-ray diffraction show that In3+ and Sn4+ have been successfully doped into the lattice to form a cubic perovskite structure. BaHf0.7In0.2Sn0.1O3−δ (BHSI) was facilely sintered and reached a relative density above 96.25% at 1600 °C. The scanning electron microscope observation shows that the introduction of In3+ and Sn4+ can effectively improve the sinterability and increase the grain size of the sample. High relative density and big grain size allow reducing the volume fraction of grain boundaries and increasing the electrical conductivity of BHSI. The total conductivity of BHSI in wet air reaches 5.69 × 10−3 S cm−1 at 700 °C. In addition, BHSI also shows excellent chemical stability in pure H2 and CO2, 200 ppm H2S and water steam, and boiling water. The obtained BHSI membranes were evaluated for hydrogen separation under a mode-pure protonic conductor with external short circuit. The hydrogen separation performance of BHSI membrane was tested systematically. Gas humidification on the feed side and sweep side can obviously increase the hydrogen permeation fluxes. BHSI membrane still maintains a stable hydrogen permeation performance, even 3% CO2 and 100 ppm H2S was introduced into the feed gas, respectively.