The Preparation Of High Temperature Proton Conductor By Sol-gel Method And Its Application In Electrochemical Synthesis Of Ammonia

A lot of researches have been done since the high temperature proton conductor (HTPC) was reported in 1980's, such as: conduction mechanism, structure, related electrical characterization, application research, etc. The potential application value of HTPC in gas sensors, SOFCs(solid oxide fuel cells) and gas separators is attributed to its high proton conduction ranges at high temperature under atmosphere containing hydrogen. Due to its working temperature varying between the temperatures at which industrial hydrogenation- and dehydrogenation-reactor work, its potential application is prospective in industrial field. While, the synthesis of ammonia using HTPC under atmosphere reported by George Marnellos and Michael Stoukides makes its perspective of application more practical and even more charming.In this paper, we adopted nano-tech to prepare HTPC-prepared by high temperature solid state reaction reported in literatures and tried to reduce the sintering temperature, shorten the sintering time, and improve its hardness and mechanical strength, at the same time, improve its sintering density as well as its proton conduction. There are three kinds of HTPC were synthesized-SCY(SrCe0.95Y0.05O3-δ), BCNd(BaCe0.9Nd0.1O3- δ ), BCN18(Ba3Ca1.18Nb1.82O9-δ ). Parameters such as working temperatures, different gas ambiences and gas humidity were changed to characterize the electrical properties of HTPC sinters prepared. This paper contains three sections:( 1 ) Nano powders were prepared by citrate method (SCY, BCNd, BCN18), and the grain size ranged from 30 to 60nm. Sintering temperature is reduced as well as the sintering time. The sinters obtained by nano-tech is more dense. The sintering shrinkage of nano powders increases with the temperature. Compared to traditional method treated specimens, shrinkage of isostatically treated specimens is larger. Ceramics made from nano-powders have excellent hardness and mechanical strength and can need the requirement when applied.( 2 ) The electrochemical properties of sinters at intermediate temperature(400-600℃): The conduction of ceramics obtained increases with temperature in different gases. The conductivity and temperature was according with Arrhenius relation:Under air atmosphere, it suggests the conduction specimen is electronic holeand oxygen ions. Under a containing-hydrogen atmosphere, the conductivity is increases apparently, proton conduction is a dominant process. When it is expose to humidity atmosphere, its conductivity is higher than that of dry air. The electrical conduction increasing with the sintering density suggests that nano-tech preparation is superior to conventional ones.( 3 ) The sintered HTPC was applied to the synthesis of ammonia under atmospheric pressure. Ammonia was aynthesized from nitrogen and hydrogen at atmospheric pressure in a solid state proton-conducting cell reactor. Several important factors of ammonia synthesis were investigated and the optimal synthetic temperature was found. The rate of production is rNH3 = 2.84×10-9mol/(s.cm2) using SCY as solid state electrolyte, and rNH3 = 8.9 × 10-8 mol/(s.cm2) for BCNd as solid state electrolyte. Because of the heterogeneous limitation of conventional solid-state method, the new wet chemical synthesis method was applied. This method can effectively improve its protonic conductivity, therefor, ammonia production enhance 2-3 magnitude. At thesame time, due to the conductivity of BaCeO3-base HTPC is higher than that of SrCeO3-base, it can obtain higher ammonia production.