Fabrication of Yttrium-Doped Barium Zirconate for High Performance Protonic Ceramic Membranes

Barium zirconate has emerged as the leading candidate material for fabricating dense ceramic membranes for hydrogen separation. B-sites in the ABO3 perovskite are acceptor-doped with a +3 cation – most commonly yttrium – charge-compensated by the formation of oxygen ion vacancies in the lattice. A minor fraction of B-sites can be filled with cerium to give BaZr0.9-xCexY0.1O3-d, x ≤ 0.2. Upon hydration at elevated temperatures, weakly-bound protons are formed in the lattice. This produces a cubic perovskite ceramic proton conductor useful in diverse applications, such as protonic ceramic fuel cells, electrolysers, and catalytic membrane reactors operating at temperatures between 600 and 800 °C. A necessary requirement for fabricating thin ceramic membranes for proton diffusion is to maximize grain size while eliminating percolating porosity. However, high-density, large-grained barium zirconate is a very difficult material to prepare by traditional powder sintering methods. This chapter describes a new methodology for making protonic ceramic membranes with large grains and virtually no residual porosity. This discovery has the potential to have a profound impact on energy conversion efficiency of the various membrane devices envisioned for the coming hydrogen energy economy

Thermo-electrochemical production of compressed hydrogen from methane with near-zero energy loss

[EN] Conventional production of hydrogen requires large industrial plants to minimize energy losses and capital costs associated with steam reforming, water-gas shift, product separation and compression. Here we present a protonic membrane reformer (PMR) that produces high-purity hydrogen from steam methane reforming in a single-stage process with near-zero energy loss. We use a BaZrO3-based proton-conducting electrolyte deposited as a dense film on a porous Ni composite electrode with dual function as a reforming catalyst. At 800 degrees C, we achieve full methane conversion by removing 99% of the formed hydrogen, which is simultaneously compressed electrochemically up to 50 bar. A thermally balanced operation regime is achieved by coupling several thermo-chemical processes. Modelling of a small-scale (10 kg H-2 day-1) hydrogen plant reveals an overall energy efficiency of >87%. 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Entry and exit of water vapor in bulk ceramic proton conductors

An experimental study of the processes occurring during protonation of bulk ceramic proton conductors, BaCe0.9Y0.1O2.95 (BCY10) and BaCe0.8Y0.2O2.9 (BCY20), is presented here. One of the faces of a disc-shaped diffusion membrane was connected to a mass spectrometer in a vacuum system permitting the identification of the species crossing the ceramic-vacuum interface. Exposing the sample to D2O led to a strong signal of D2O+ after a certain lag time. From these lag times, the tracer diffusivity of hydrogen could be determined as a function of temperature. The permeation of steam consisted of two components: a fast component, essentially given by the diffusivities of deuterons (protons), and a slow component, ascribed to chemical diffusion of deuterons (protons) coupled to oxygen vacancies with the possibility of participation of even more complex defects. Dilatometry measurements of different specimens of BCY10 and BCY20 also revealed quite clearly this two-phase pattern during protonation. Diffusion measurements on protonic ceramic membranes using (H2O)-O-18 permitted the determination of the tracer diffusivity of oxygen. All of the above measurements were interpreted in the light of the chemical diffusion model developed by Kreuer et al. (C) 2004 Elsevier B.V. All rights reserved