Clarifying the zeolitic imidazolate framework effect on superior electrochemical properties of hydrogen storage alloys

Zeolitic imidazolate framework ZIF-8 polyhedral crystal is coated uniformly on the surface of hydrogen storage alloys (HSAs) using a simple method of wet-chemical. On the one hand, the adsorption of H2 on ZIF-8 verified by density functional theory simulations is in favor of the suppression of side reaction of H2 evolution, enlisting the improved discharge capacity. On the other hand, the adsorbed H2 on ZIF-8 is able to be desorbed to H atom further adsorbed on HSAs, increasing the H concentration on electrode/electrolyte interface, which is beneficial to the enhanced electrochemical reaction rate and H diffusion rate. As a consequence, compared with the bare HSAs electrode, the HSAs/ZIF-8 hybrid electrode exhibits excellent electrochemical performances for enhanced maximum discharge specific capacity (302.6 vs. 328.2 mAh g–1) and superior high-rate dischargeability (capacity retention increases from 13.5 to 30.2% at a discharge current density of 3000 mA g–1). Furthermore, another ZIF-based system of HSAs/ZIF-67 electrode shows similar electrochemical properties to the HSAs/ZIF-8 electrode; besides, the extended system of HSAs/ZIF-8-graphene hybrid electrode also exhibits enhanced rate capabililty.