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Polymer electrolyte membrane fuel cells require elaborate water management to operate effectively. Bipolar membrane fuel cells (BPMFCs) have the potential for self-humidification, but BPMFC developed to date have not demonstrated this feature and have operated at very modest power densities. By improving the pattern and fabrication process of bipolar membranes, we have realized and demonstrated BPM fuel cells that operate under completely self-humidifying conditions and that achieve a two order of magnitude gain in power density (265 mW cm^-2). A water transport model and in situ experimental characterization are used to elucidate the unique interfacial water generation and distribution behavior inside the BPM.