The present relates to an internally cooled and humidified electrochemical reactor comprising at least one open-pore cellular plate, which is made of a conductive open-cell material adapted to permit direct circulation of gas and liquid through it in a stratified two-phase flow regime, for humidification and cooling of said reactor through convective evaporation across a continuous Knudsen layer. The reactor can incorporate a vapor permeable membrane, a hydrophilic wall, and fluid recirculating systems. It also relates to methods of uniformly feeding the reactants to the reactor, and efficient product removal.