Wen Xing

High Temperature Proton Conductivity of ZrP2O7

Undoped ZrP 2 O 7 and 2 mol % Sc-, Y-, and La-doped ZrP 2 O 7 have been synthesized by an aqueous phosphoric acid route and characterized by X-ray diffraction and scanning electron microscopy. The samples were fabricated by conventional and spark plasma sintering (SPS), and the electrical conductivity was examined from 500 to 1000°C as a function of p(O 2 ) and p(H2 0 ) or p(D 2 O) by impedance spectroscopy. The conductivity of the materials in H 2 O was higher than in D 2 O and dry atmospheres, indicating that proton conductivity is dominant, supported also by transport number measurements. The conductivity was independent of p(O 2 ) at all temperatures, showing that the conductivity is predominantly ionic (protonic) under oxidizing as well as more reducing conditions. The p(H 2 O) and temperature dependencies of the conductivity were modeled assuming that protons are charge-compensated by oxygen interstitials. The attempted acceptor doping does not influence the conductivity significantly. Less dense samples exhibit a conductivity contribution at low temperatures assigned to internal surfaces; this is avoided in the SPS samples. .

Dual phase high-temperature membranes for CO2 separation – performance assessment in post- and pre-combustion processes

Dual phase membranes are highly CO2-selective membranes with an operating temperature above 400 °C. The focus of this work is to quantify the potential of dual phase membranes in pre- and post-combustion CO2 capture processes. The process evaluations show that the dual phase membranes integrated with an NGCC power plant for CO2 capture are not competitive with the MEA process for post-combustion capture. However, dual phase membrane concepts outperform the reference Selexol technology for pre-combustion CO2 capture in an IGCC process. The two processes evaluated in this work, post-combustion NGCC and pre-combustion IGCC, represent extremes in CO2 partial pressure fed to the separation unit. Based on the evaluations it is expected that dual phase membranes could be competitive for post-combustion capture from a pulverized coal fired power plant (PCC) and pre-combustion capture from an Integrated Reforming Cycle (IRCC).