TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Fuel Cell: In the redox fuel cell, at least a portion of the wall defining the catholyte channel is open to expose the interior of the catholyte channel to at least a portion of the active surface of the porous member. The porous member comprises one or more of sintered glass, metal powders, porous membranes, meshes and drilled or punctured sheets. The average pore size in the active surface of the porous member is 5-100 microns, preferably 20-50 microns. The active surface is formed of or coated with a hydrophilic material. The porous member, except for the active surface, is formed of a hydrophobic material, where the porous member is an elongate member, and where the porous member is a cylindrical and/or tubular. The porous member comprises a substrate having holes through it, each hole comprising a gas inlet and a gas outlet, where the width of the gas outlet is greater than the width of the gas inlet. The cross-sectional shape of each hole is one selected from circular, triangular, square, rectangular, pentagonal, hexagonal, heptagonal, octagonal, nonagonal and decagonal. The width of the gas outlet is an order of magnitude greater than the width of the gas inlet. The hole tapers regularly or irregularly from the gas inlet towards the gas outlet. The hole density on the substrate ranges from 400-10000 holes/cm2. The substrate has a square pitch and the hole density on the substrate ranges from 1000-2500 holes/cm2. The thickness of the substrate ranges from 20-1000 microns, preferably 50-100 microns. The gas inlet width ranges from 0.1-0.2 gas outlet width, where the average gas inlet width ranges from 2-10 microns. The average gas outlet width ranges from 5-100 microns, preferably 20-50 microns. The substrate has an active surface towards the gas outlets of the holes, where at least a portion of the active surface is formed of or coated with a hydrophilic material. The gas outlet comprises a lip projecting away from the active surface. The fuel cell comprises stainless steel foil and/or polyimide film. The cross-sectional shape of each hole is circular, and the widths of the gas inlet and gas outlet are the diameters of the gas inlet and gas outlet. The angle of taper from the gas inlet towards the gas outlet is relative to the longitudinal axis of each hole and ranges from 6-26 degrees , preferably 10-15 degrees . Each hole is a frustoconical shape. The catholyte channel is provided as a tube adjacent to the exterior surface of the porous member, where the catholyte channel is formed within the porous member, and where the catholyte channel is provided with rotation means, where the rotation means comprise an offset liquid inlet into the catholyte channel, or a diversion member. The catholyte channel increases in cross section area in the direction of catholyte flow. The regeneration zone additionally comprises an expansion chamber in fluid communication with the catholyte channel; and a separation chamber in fluid communication with the channel, where the separation chamber comprises a cyclone separator. The porous member is generally planar. The regeneration zone comprises: a chamber in which the regeneration reaction takes place; a first inlet port for receiving into the chamber reduced redox mediator couple from the cathode region of the cell; a first outlet port for supplying oxidized redox mediator couple to the cathode region of the cell; and/or a second inlet port for receiving a supply of oxidant; and a second outlet port for venting gas, water vapor and/or heat from the chamber. The fuel cell further comprises at least one demister provided in or upstream of the second outlet port of the regeneration zone; a condenser provided in or upstream of the second outlet port of the regeneration zone for condensing water vapor and, optionally, returning the condensed vapor to the regeneration zone. The catholyte solution further comprises a redox catalyst for assisting electron transfer between the oxidant and the at least partially reduced redox mediator couple. The redox mediator couple and/or the redox catalyst when present comprises: a polyoxometallate compound; a polyoxometallate compound with a divalent counterion; an N-donor compound; a multi-dentate N-donor ligand comprising at least one heterocyclic substituent selected from pyrrole, imidazole, 1,2,3-triazole, 1,2,4-triazole, pyrazole, pyridazine, pyrimidine, pyrazine, indole, tetrazole, quinoline, isoquinoline and from alkyl, alkenyl, aryl, cycloalkyl, alkaryl, alkenaryl, aralkyl, aralkenyl groups substituted with one or more of the heterocyclic groups; a multidentate macrocyclic N-donor ligand; a modified ferrocene species; a modified ferrocene species comprising a bridging unit between the cyclopentadienyl rings; and/or a ligated transition metal complex. Preferred Process: In operating the redox fuel cell, the flow rate of catholyte solution through the catholyte channel is at least 0.2 m/second, or 0.5-1.5 m/second.