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Nickel-based selenides are believed to be promising non-precious metal electrocatalysts, and have been widely used for both oxygen evolution reactions (OER) and hydrogen evolution reactions (HER). Here, we control the aging time to prepare Ni_xSe_y with different fractal structures as a bifunctional catalyst. An obtained sample with an aging time of 80 min shows outstanding electrocatalytic performance for hydrogen evolution reactions (HER) with an overpotential of 225 mV (η@10 mA/cm²) and for oxygen evolution reactions (OER) with an overpotential of 309 mV (η@50 mA/cm²). Moreover, to further improve catalytic activity, we doped Fe in Ni_xSe_y to obtain the ternary nickel-based selenide, Fe_0.2Ni_0.8Se (FNSs). The HER activity of FNS increased two-fold at 10 mA/cm², and the overpotential of OER decreased to 255 mV at 50 mA/cm². The synthetic strategy and research results of this work have a certain reference value for other low-cost and high-efficiency transition metal catalysts for electrocatalytic water splitting.