Characterizations of polybenzimidazole based electrochemical hydrogen pumps with various Pt loadings for H-2/CO2 gas separation

Abstract

Carbon capture and storage (CCS) technologies have been intensively researched and developed to cope with climate change, by reducing atmospheric CO2 concentration. The electrochemical hydrogen pumps with phosphoric acid doped polybenzimidazole (FBI) membrane are evaluated as a process to concentrate CO2 and produce pure H-2 from anode outlet gases (H-2/CO2 mixture) of molten carbonate fuel cells MCFC. The FBI-based hydrogen pump without humidification (160 degrees C) can provide higher hydrogen separation performances than the cells with perfluorosulfonic-acid membranes at a relative humidity of 43% (80 degrees C), suggesting that the pre-treatment steps can be decreased for PBI-based systems. With the H-2/CO2 mixture feed, the current efficiency for the hydrogen separation is very high, but the cell voltage increase, compared to the pure hydrogen operation, mainly due to the larger polarization resistance at electrodes, as confirmed by electrochemical impedance spectroscopy (EIS). The performance evaluation with various Pt loadings indicates that the hydrogen oxidation reaction at anodes is rate determining, and therefore the Pt loading at cathodes can be decreased from 1.1 mg/cm(2) to 0.2 mg/cm(2) without significant performance decay. The EIS analysis also confirms that the polarization resistances are largely dependent on the Pt loading in anodes.