To explore the electrochemical characteristic of 2H-and 3R-type superlattice structure isomerides which are consisted of [REMgNi4] and [RENi5] subunits, we prepare A(2)B(7)-type Pr-Mg-Ni-based alloys composed of different amounts of 2H and 3R phases and mainly study the effects on properties including the charging/discharging and absorption/desorption process. The volume change of [PrMgNi4] and [PrNi5] subunits before and after hydrogenation/dehydrogenation is calculated. The results show that the expansion and shrinkage rates of the two subunits in 2H- and 3R-type phases are close, which may be the leading cause that the alloy exhibits single platform in P-C-T curve. While electrochemical measurement shows that the cycling stability of the alloy electrodes improves with the increase of 2H-type phase and the high rate dischargeability at 1500 mA g(-1) shows opposite trend. It is found that the exchange current density gradually increases from 499.8 to 653.8 mA g(-1) and the hydrogen diffusion coefficient of the alloys increases from 7.6 x 10(-9) to 8.8 x 10(-9) cm(2) s(-1) when the 3R phase abundance increases from 38.5 wt% to 59.3 wt%, indicating that the 3R-type phase is beneficial to the charge transfer rate and hydrogen diffusion of the alloy. (C) 2019 The Electrochemical Society.