Salinity gradient (SG) energy is a large untapped energy source available worldwide. Here we applied MoS2 with tunable interlayer spacing to a concentration flow cell for efficient SG energy recovery. By expanding the interlayer from 0.63 nm to 0.96 nm, the ion diffusion resistance was significantly reduced and the pseudocapacitance was largely promoted. These enhanced electrochemical properties resulted in a superior performance of the concentration flow cell on SG energy extraction. The cell with interlayer-expanded MoS2 electrodes produced 11 times of the average power density compared with the cell with original MoS2 electrodes when using model seawater and river water solutions. The interlayer-expanded MoS2 was also among the most durable materials for SG energy harvesting as it allowed the cell to run over 120 cycles and work efficiently at varying salinity concentrations. When provided with brine water (300 g L−1 NaCl) and fresh water (1 g L−1 NaCl), the cell yielded a peak power density of 16 W m−2, an average power density of 1.4 W m−2, and an energy density of 181 J m−2. All these evidences support that the interlayer-expanded MoS2 is a prospective material for SG energy recovery in concentration flow cells.