A novel, simple, convenient, and safe, chemical process generates high purity hydrogen gas on demand from stable, aqueous solutions of sodium borohydride, NaBH,, and ruthenium based (Ru), catalyst. When NaBH, solution contacts Ru catalyst, it spontaneously hydrolyzes to form H, gas and sodium borate, a water-soluble, inert salt. When H, is no longer required, Ru is removed from the solution and H, generation stops. Since this H, generator is safer, has quicker response to H, demand, and is more efficient, than commonly used H, generators, it is ideal for portable applications. INTRODUCTION PEM fuel cells are attractive power sources for providing clean energy for transportation and personal electronics applications where low system weight and portability are important. For powering these systems, H, gas is the environmentally desirable anodic fuel of choice since only water is formed as a discharge product. A major hurdlc is how to gcnerate/store controlled amounts of H, fuel directly without resorting to high temperature reformers with significant heat signatures or bulky, pressurized cylinders. Background of the Borohydride H, Generator Our safe, portable H, generator overcomes these problems by using aqueous, alkaline, sodium borohydride (NaBH,, tetrahydroborate) solutions which are extremely stable. However, as found by Schlesinger et al. ( I ) , in the presence of selected metal (or metal boride) catalysts, this solution hydrolyzes to yield H, gas and water-soluble, sodium metaborate, NaBO,. NaBH, + 2 H,O ----> 4 H, + NaBO, P I catalyst This hydrolysis reaction occurs at different rates depending on the catalyst used and its preparation method. Levy et al. (2) and Kaufman and Sen (3) investigated cobalt and nickel borides as catalysts for practical, controlled generation of H, from NaBH, solutions. We studied ruthenium (Ru) based catalyst supported on ion exchange resin beads. Using Ru is based on the work or Brown and Brown (4). who investigated various metal salts and found that ruthenium and rhodium salts liberated H, most rapidly from borohydride solutions. We chose Ru because of its lower cost. Ru catalysts are not consumed during hydrolysis and are reusable. We have designed our system so that reaction [ I ] is either selfregulating or carefully controllable. To generate H,, NaBH, solution is allowed to flow onto a Ru catalyst, or NaBH, solution is injected onto Ru catalyst. This ensures fast response to H, demand i.e. H, is generated only when NaBH, solution contacts Ru catalyst. When H, is no longer needed, NaBH, solution is removed from Ru catalyst and H, production ceases. With molecular weights of NaBH, (38) and 2 H,O (36), forming 41-1, (8), reaction [ I ] has a I-l,storage efficiency of 8/74 = 10.8%. In addition to H,, the other discharge product, NaBO,, commonly found in laundry detergents, is safe. Unlike phosphates, borates are not environmentally hazardous in water supplies. Table I compares operational and safety features of generating H, via base-stabilized NaBH, solutions and via reactive chemical hydrides. Our generator is considerably saferhore efficient than producing H, via other reactive chemicals. The heat generated by our system (75 kJ/mole H, fomied), is less than what is produced by other hydrides (>I25 kJ/mole H,), and ensures a safe, controllable chemical reaction. The total amount of H, produced by reaction [ I ] depends on NaBH, solution volume and concentration. H, generation rates are primarily a function of Ru catalyst active surface area. H, pressure/flow rates can be accurately controlled and made self-regulating by numerous feedback