Extraction of hydrogen from hydrogen blended natural gas by protonic ceramic hydrogen pumps

Abstract

Compared with conventional hydrogen delivery techniques, blending hydrogen into natural gas grids appears as the most promising approach to realize long-distance, large-scale, and low-energy consumption hydrogen transportation. Protonic ceramic hydrogen pump (PCHP) demonstrates inherent advantages for hydrogen extraction from hydrogen blended natural gas (HBNG) with low hydrogen content to acquire pure hydrogen for diverse consumers at the downstream of natural gas grids. Here, several PCHPs were devised for hydrogen purification and alternative anode materials were developed to optimize the separation performance. By comparing the protonic conductivity, BaCe0.7Zr0.1Y0.16Zn0.04O3-δ (BCZYZ71) was identified as the electrolyte for PCHPs which was prepared through tape casting-lamination process. With conventional Ni cermet electrode, the symmetric cell of Ni-BCZYZ71|BCZYZ71|Ni-BCZYZ71 displays a decent capability for hydrogen extraction out of HBNG, at 600 ℃ and 1.5 V, the hydrogen separation rate (JH2) reaches 1.28 mL min-1 cm-2 at current density of 203.00 mA cm-2 with anode supplied with HBNG (25%H2-75%CH4). A composite electrode consisting of electronic conductor (SrFe0.9Cu0.1O3-δ) and protonic conductor (BCZYZ71) was devised as an alternative anode. The anode of SrFe0.9Cu0.1O3-δ-BCZYZ71 delivers a moderate performance while it exhibits a favorable durability for hydrogen separation. The anodic performance of SrFe0.9Cu0.1O3-δ-BCZYZ71 is improved significantly by Pd layer modification with JH2 reaching 1.59 mL min-1 cm-2 at 1.86 V and 243.60 mA cm-2 under 600 ℃. A triple conductor of BaCe0.5Fe0.5O3-δ was employed as anode for PCHP firstly whose anodic performance is improved substantially by Pd layer modification and Ni impregnation. For all the developed PCHPs, high operating temperature and high hydrogen partial pressure of HBNG will yield favorable pumping performance due to the reduction in ohmic and polarization resistances. The works in this thesis represent novel approach to extract hydrogen out of HBNG and shed light on the development of alternative anode material for PCHP.