Magnetic composites exhibit distinct flux properties due to gradient interfaces. Such composites can be used, for example, to improve fuel cells and batteries and to effect transport and separation of different chemical species, such as transition metal species (lanthanides and actinides). A variety of devices can be made utilizing the composites, including a separator, an electrode for channeling flux of magnetic species, an electrode for effecting electrolysis of magnetic species, a system for channeling electrolyte species, a system for separating particles with different magnetic susceptibilities, as well as improved fuel cells, batteries, and oxygen concentrators. Various magnetic composites can be used, for example, to make a separator for distinguishing between two chemical species, to form a flux switch to regulate the flow of a chemical species, to control chemical species transport and distribution, to produce rechargeable batteries having longer secondary cycle life and improved output power, and to enable the production of ambient pressure fuel cells having enhanced performance and reduced weight.