Preparation and performance of composite proton conducting membranes for H2S solid oxide fuel cells

Three various proton conducting membranes for H2S solid oxide fuel cells, such as Li2SO4 + Al2O3, Li2SO4 + Na2SO4 + Al2O3 and Li2SO4 + Li2WO4 + Al2O3, were fabricated by the conventional route (designated micro-composite sample) and a new technique (nano-composite sample prepared by gel-solution method), respectively. The morphology and microstructure of the fabricated membranes were characterized by scanning electron microscope (SEM). The compactivity and tightness of nano membranes are better than those of micro membranes. Ion conductivity (electric conduction) of the fabricated membranes increases at first with temperature, and then maintains almost constant at its maximum value. In the H2S stream environment, the H2S electrochemical oxidation and chemical stability of three cells, each of which has one of the mentioned various proton conducting membranes separately, were observed respectively. It was found that the conductivity and electrochemical performance of Li2SO4 + Li2WO4 + Al2O3 and Li2SO4 + Na2SO4 + Al2O3 composite electrolytes are better than those of Li2SO4 + Al2O3 electrolyte. The suitable operating temperature of fuel cell with Li2SO4 + Li2WO4 + Al2O3 composite electrolyte is the highest, which is above 700°C, while the composite Li2SO4 + Al2O3 membrane cells have lower operating temperature between 650°C and 700°C. Performance and chemical stability of nano composite membrane fuel cells are better than those of micro composite membrane fuel cells. The electrochemical performance of fuel cell having the configuration of H2S, (MoS2 + NiS + Ag + electrolyte + starch)/electrolyte/(NiO + Ag + electrolyte + starch), air was investigated at 680-750°C and 101.13 kPa, and it was found that the fuel cell using nano composite Li2SO4 + Li2WO4+ Al2O3 as electrolyte can produce a maximum power density up to 130 mW &middot cm-2 with the corresponding current density of 175 mA &middot cm-2 at 750°C.