Enhanced CO poisoning resistance and hydrogen storage in palladium/metal–organic framework composites

Abstract

The significant role of palladium (Pd) in hydrogen isotope storage, separation and purification has been intensifying the optimization protocols toward such noble metals to achieve better performance. One of the most urgent tasks is exploring efficient strategies to improve the poison resistance of Pd against impurity gas, especially CO, so as to retain its surface activity for hydrogen. Herein, we propose a novel approach to enhance anti-poisoning capability by encapsulating Pd nanoparticles (NPs) into MOF-74 (Ni) with unsaturated Ni²⁺ sites, being referred to as the Pd/MOF-74(Ni) composite structure. Through systematic investigation we confirmed the good dispersion of Pd NPs within MOF-74(Ni), the crystallinity of which was preserved, as revealed by physical and chemical characterization. Based on the hydrogen absorption performance of different Pd NP loadings at various temperature and CO concentrations, three advantages of such a composite protocol were obtained. Firstly, at 293 K, the saturated hydrogen absorption time was improved up to 130 times and 144 times compared to that of sponge Pd and Pd NPs, respectively. Secondly, anti-poisoning performance of as-synthesized samples could be tailored by regulating the loading amount of Pd NPs or adjusting experimental temperatures. Thirdly, the maximum hydrogen absorption capacity of such composite samples was 40% higher than that of sponge Pd, ascribed to the spillover effect. Moreover, the hydrogen absorption curves were in line with the JMAK model for all cases and exhibited excellent cycling performance. We also analyzed the anti-poisoning mechanism by using in situ DRIFTS, which indicated strong interaction between CO and unsaturated Ni²⁺ in MOF-74(Ni) which retained the surface activity of palladium. Such a composite protocol based on MOFs may be meaningful in the fields of fuel cells, membrane separation, etc, to realize anti-poisoning effect.