An abrupt interface electroreduction catalyst includes a porous gas diffusion layer and a catalyst layer providing a sharp reaction interface. The electroreduction catalyst can be used for converting CO2 into a target product such as ethylene. The porous gas diffusion layer can be hydrophobic and configured for contacting gas-phase CO2 while the catalyst layer is disposed on and covers a reaction interface side of the porous gas diffusion layer. The catalyst layer has another side contacting an electrolyte and can be hydrophilic, composed a metal such as Cu and is sufficiently thin to prevent diffusion limitations of the reactant in the electrolyte and enhance selectivity for the target product. The electroreduction catalyst can be made by vapor deposition methods and can be used for electrochemical production of ethylene in reaction system.