NOVELTY - The power generating system comprises a fuel cell stack (26) to react hydrogen and oxygen to produce electricity, a source to provide oxygen to the fuel cell stack, and a source to provide hydrogen to the fuel cell stack. The hydrogen source is partially submerged in water, and incorporates a non-hydride metal alloy that reacts with water to produce hydrogen from the water. The reaction is catalyzed by a naturally occurring salt in the water. The metal alloy is contained in a reactor volume that allows unassisted entry of surrounding water.    USE - The power generating system is useful for operating below a surface of a body of sea water for personal flotation, watercraft, platforms dinghies, diving apparatus, emergency situations, lifeboats, buoys, battery charging, auxiliary lighting, powering sensors, communications and signaling, propulsion, powering tools, winches, other mechanical functions, submerged operations and heating and cooling.    ADVANTAGE - The power generating system can be simply, reliably and safely operated, is provided at low cost, has a dormant shelf life of two or more years without sealing or substantial loss of energy storage, and can provide power on demand without active controls using the high energy conversion efficiency of fuel cells without use hydride compounds.    DETAILED DESCRIPTION - The power generating system comprises a fuel cell stack (26) to react hydrogen and oxygen to produce electricity, a source to provide oxygen to the fuel cell stack, and a source to provide hydrogen to the fuel cell stack. The hydrogen source is partially submerged in water, and incorporates a non-hydride metal alloy that reacts with water to produce hydrogen from the water. The reaction is catalyzed by a naturally occurring salt in the water. The metal alloy is contained in a reactor volume that allows unassisted entry of surrounding water such that hydrogen gas produced in the reactor volume supplies the fuel cell stack at a hydrostatic pressure representing a depth of water contacting the metal alloy. A hydrogen volume defines a reactor water level and an amount of alloy surface wetted by water to control a rate of hydrogen generation to meet a rate of hydrogen consumption by the fuel cell stack in response to an electrical load demand. The oxygen source provides oxygen to the fuel cell stack below the surface, and comprises air flow from above the water surface, a portion of submerged air suitable for human breathing and/or dissolved oxygen recovered from the surrounding water. The fuel cell stack operates below the water surface, and dissociates hydrogen from the hydrogen source at an anode side of the fuel cell stack into protons and electrons to produce an electric current. The fuel cell stack recombines the hydrogen with dissociated oxygen from the oxygen source on a cathode side by reaction in a presence of an electrolyte to produce water and heat. The fuel cell stack is cooled by heat conduction paths from high temperature regions of the fuel cell stack to the water surrounding a portion of the system. The metal alloy is storable in air for more than two years with less than 1% degradation of hydrogen generation capability, and comprises removably replaceable castings. The castings are configured to provide a sufficient reaction surface area to provide hydrogen to meet a fuel cell stack hydrogen demand without more than 5% loss of hydrogen to the surrounding water. The hydrogen volume provides sufficient space above the metal alloy to prevent water entrainment and gas/water bubbles transport to the fuel cell stack and below the metal alloy to inhibit a loss of hydrogen to the surrounding water. The catalyzing salt is dispersed in the metal alloy in an amount of greater than 3 wt.%. The system is configured such that the total buoyancy of the system varies by less than 40% during a complete reaction of the metal alloy. A portion of the produced hydrogen or separate-air forced from the reactor volume by immersion in the water, is stored in a flotation volume to increase buoyancy in the water. The oxygen source includes lung exhaust from a self contained underwater breathing apparatus (SCUBA). The oxygen source is configured to provide air to the fuel cell stack by free convection induced by heat from the fuel cell stack, from lung exhaust from a person breathing and/or from a portion of air also available for breathing by persons submerged below the water surface. The oxygen source is further configured to provide oxygen to the fuel cell stack using a hydrophobic microporous hollow fiber membrane or a gas-liquid contactor, which allows gas but not liquid to pass through, to recover dissolved oxygen from the surrounding water while utilizing an internal process vacuum induced by oxygen consumption of the fuel cell stack. The oxygen source is configured to move air to the fuel cell stack using a unit for cooling the fuel cell stack supplemental to a cooling provided by the surrounding water. The fuel cell stack includes hydrogen gas channel inlet, oxygen and/or air gas channel inlets and fuel cells that include a proton-conducting polymer electrolyte membrane between the anode side and the cathode side, with hydrogen and oxygen reactions at catalyst surfaces and with heat transfer provided near the gas channel inlets. The fuel cell stack outputs a potable water product. The hydrogen and oxygen are provided to the fuel cell stack in the absence of active pressure or flow controls, valves and/or regulators. The system further includes: a filter, float valve and/or relief valve configured to prevent water droplets from entering the fuel cell stack; a floating buoy structure; and a connection line configured to transport gas and/or liquid to and/or from the system. The system is connected to a submerged application platform or user. The heat from the fuel cell stack and/or from the metal alloy is transferred to the surrounding water and is utilized for warming a person in the water for attracting fish in cold water, for inducing mechanical motion and/or for warming to increase oxygen migration through the hydrophobic microporous hollow fiber membrane. The catalyzing salt in the water is a naturally occurring sea salt. The fuel cell stack comprises a planar fuel cell configuration having planar cells arranged side-by-side parallel to adjacent cells. An INDEPENDENT CLAIM is included for a power generating method for operating below a surface of a body of sea water using a system.    DESCRIPTION OF DRAWING(S) - The diagram shows a perspective, cut-away view of an electrical power generation system in a water environment.    Metal alloy fuel (14)    Reactor volume (16)    Threaded rod (20)    Fuel cell stack (26)    Membrane. (38)