High temperature electrochemical hydrogen membrane separation using a PGM-based catalyst

Abstract

Hydrogen, as energy carrier, is expected to play an indispensable role in the future energy prospects. Subsequently, significant advancements in research and development of hydrogen-based technologies, in the areas of low cost hydrogen production, separation/purification, hydrogen storage (e.g. compression, liquid, chemical compounds etc.), hydrogen distribution and hydrogen transportation, are required. Among several technologies under consideration for hydrogen infrastructure, the use of an electrochemical hydrogen separator is very probable, since both hydrogen purification/separation and hydrogen compression (for storage purposes) are integrated and addressed. Some advances have already been made in this field, including the development of high-temperature membranes, doped with phosphoric acid, to overcome the limitations associated with conventional low-temperature membranes. However, limited studies had been performed on these membranes and their operations under various conditions and feed compositions are largely unexplored. The first part of the work reported, addresses the aforementioned issue through experimental investigation of the performance of a high-temperature TPS-based membrane under various feed compositions (containing CH₄, CO₂ and NH₃, balance hydrogen) over a temperature range of 100-160°C. The performance parameters used included polarisation curves, electrochemical impedance spectroscopy, hydrogen purity, hydrogen separation selectivity, hydrogen flux/permeability, and general efficiencies (current, voltage and power). Results showed that a high purity hydrogen (>99.9%) was achieved, from a low purity feed (20% H₂) with the H₂/CH₄ mixtures. Also, hydrogen purities of 98-99.5 % were achieved with 10% CO₂ in the feed and 96-99.5% with 50% CO₂ in the feed stream. Moreover, electrochemical hydrogen separation was rendered inappropriate for separating hydrogen–rich streams containing NH₃. The second part of the work focussed on the poisoning effect of CO on Pt. An integrated approach of high-temperature operation and Pt-Ru as bimetallic catalyst was implemented and tested with a 2% CO (balance hydrogen) inlet. The performance of Pt-Ru/C and Pt/C was compared under the same operating conditions. The electrochemical active surface area was then determined to evaluate the CO poisoning of the two catalysts. In generaral, Pt-Ru showed better CO tolerance over the entire temperature range (80-160°C). Also, temperature played a crucial role in the mitigation of CO poisoning in the case of Pt-Ru.