Electrolyser including a reactor (2) comprising a housing (4), fluidic channels (6a, 6b, 6c) within the housing, and electrodes (16a, 16c) comprising an anode (16a) and a cathode (16c). The fluidic channels include an inter-electrode channel (6b) arranged between the anode (16a) and cathode (16c) and connected to an anode channel inlet (8a) for injection of an electrolyte into the inter-electrode channel (6b), a cathode channel (6c) separated from the inter-electrode channel (6b) by a porous cathode side wall (14c) comprising a plurality of canals (20), and an anode channel (6a) separated from the inter-electrode channel (6b) by a porous anode side wall (14a) comprising a plurality of canals (20). Each canal has a tapered shape such that an inlet surface area (Si) of the canal is greater than an outlet surface area (So) of the canal, the inlet surface area being on a side of the porous walls bounding the inter-electrode channel (6b).