The methods include steps for making a fuel cell layer, making a compact chemical reactor with high aspect ratio cavities from components with low aspect ratio cavities, and forming of a high aspect ratio compact chemical reactor using low aspect ratio layers. The methods entail forming at least two process layers; forming a perimeter barrier on at least one side of one of the process layers creating an intermediate assembly with at least one low aspect ratio cavity; repeating the initial steps to create additional intermediate assemblies with at least one low aspect ratio cavity; joining intermediate assemblies to create a compact chemical reactor with high aspect ratio cavities; and joining the compact chemical reactor with high aspect ratio cavities to two reactant plenums to facilitate a transport process between reactant plenums and process layers.