The formation of H-2 in the radiolysis of liquid water containing nanometer sized ZrO2 particles was found to be dependent on the crystalline structure of the particle. Zirconia particles of a few tens of nanometer diameter may be formed with the tetragonal crystalline structure at room -temperature rather than the more stable monoclinic form for bulk zirconia. Radiolysis of liquid water containing tetragonal ZrO2 particles exhibits a significant increase in the decomposition of water to H-2 compared to the monoclinic form. Annealing the tetragonal particles to the monoclinic structure results in the loss of excess H-2 production above that found with water alone. The results show that surface morphology is extremely important in the decomposition of liquids at solid interfaces, which may have many consequences ranging from nuclear waste storage to the H, economy.