Purification of Bio-Hydrogen Using Absorption Techniques and the Effect of CO₂ Impurity on the PEMFC Performance

摘要

Biomass has been extensively studied as one of the promising sources for producing biogas in Malaysia such as bio-methane and bio-hydrogen. The fermentation process using bioreactor was one of the technologies to produce bio-hydrogen, which also contained mainly carbon dioxide (CO_(2)) through biological pathway. For fuel cell application, such as polymer electrolyte membrane fuel cell (PEMFC), high purity hydrogen (H_(2)) up to 99.99% was required to generate the electricity. The presence of CO_(2) in H_(2) in a fuel cell will cause CO_(2) poisoning and affect its performance. Hence, the purification of H_(2) from bio-hydrogen was desired to ensure appropriate concentration of H_(2) was achieved for supplying in a fuel cell. Therefore, this study was focused on the absorption technique for purifying the H_(2) from mixed CO_(2) based on the concentration of sodium hydroxide (NaOH) as an absorber solution and the inlet concentration of CO_(2). Besides, most of the previous studies done on the performance of PEMFC mainly focused on the effect of temperature, pressure, pH and type of catalyst in fuel cell. The study on the effect of H_(2) flow rate on the performance of PEMFC was lacking and the optimum flow rate of pure H_(2) in PEMFC has yet to be identified. Since the cost of pure H_(2) was high, fuel cells that operated at optimum H_(2) flow rate for maximum performance were able to prevent H_(2) wastage and reduce the fuel cell operating cost. Moreover, PEMFC was very sensitive to the presence of impurity such as CO_(2) in which it will decrease the performance and lifespan of the platinum catalyst in fuel cell. In addition, issues such as the mechanism of CO_(2) impurity on the performance of PEMFC and the impact of CO_(2) accumulated in fuel cell on the cell voltage and efficiency of fuel cell were always questionable. Furthermore, many previous researches done only focused on the effect of carbon monoxide (CO) and hydrogen sulfide (H_(2)S) on the performance of PEMFC. Hence, the study was also conducted to investigate the operation of PEMFC using different H_(2) flow rate and the effect of CO_(2) impurity in H_(2) fuel to their performance. The effect of absorption conditions, H_(2) flow rate and CO_(2) impurity were discussed on the basis of the PEMFC performances. The power increased with the increasing H_(2) flow rate up to 200 ml min~(-1) for 14W power generation. Meanwhile, the CO_(2) impurity in H_(2) fuel would reduce the PEMFC performance and the degradation of stack power increased with increasing CO_(2) concentration.