An apparatus and method is provided for coating a surface of a substrate with at least one film of porous coordination polymer. A body has an interior space for holding the substrate to be coated, at least one inlet, and at least one outlet in communication with the interior space to permit fluid to flow in a downstream direction from the inlet, across the surface of the substrate in the interior space, and through the outlet. A plurality of flow channels are arranged to flow a plurality of different reagent solutions from respective supply sources to the at least one inlet. The flow channels merge into at least one mixing region, positioned upstream of the interior space, to mix the solutions prior to the mixture contacting the surface of the substrate in the interior space. At least one pressure source and valve system are arranged with the supply sources and the flow channels to select at least one combination of the reagent solutions to be mixed and to force the selected reagent solutions to flow from their respective supply sources, through the flow channels, and into the mixing region at different, independently controllable flow rates to regulate respective concentrations of reagents in the mixture.