Nickel is a cheaper metallic material compared to palladium membranes for H-2 separation. In this work, metallic Ni hollow fiber membranes were fabricated by a combined phase inversion and atmospheric sintering method. The morphology and membrane thickness of the hollow fibers was tuned by varying the spinning parameters like bore liquid flow rate and air gap distance. H-2 permeation through the Ni hollow fibers with N-2 as the sweep gas was measured under various operating conditions. A rigorous model considering temperature profiles was developed to fit the experimental data. The results show that the hydrogen permeation flux can be well described by using the Sieverts' equation, implying that the membrane bulk diffusion is still the rate-limiting step. The hydrogen separation rate in the Ni hollow fiber module can be improved by 4-8% when switching the co-current flow to the countercurrent flow operation. (c) 2017 American Institute of Chemical Engineers AIChE J, 63: 3026-3034, 2017