NiO is the answer
The use of hydrogen reduction of oxide creates abundant lattice defects in NiO or any other oxide when exposed to hot hydrogen over an extended timeframe. Hydrogen based NiO reduction will create large numbers of O vacancies in the surface of the NiO crystal. The presence of O vacancies leads to an increase in the adsorption energy of H2 and substantially lowers the energy barrier associated with the cleavage of the H-H bond. At the same time, adsorbed hydrogen can induce the migration of O vacancies from the bulk to the surface of the oxide. These large numbers of O vacancies provide the nuclear active sites where large numbers of hydrogen atoms are drawn and packed in. The oxygen within the bulk of the NiO particle will strongly attract H into the particle. This hydrogen reduction process of NiO will produce a nickel metal foam like structure on the surface of the NiO particle heavily packed with H. See the following http://www.google.com/url?sa=t&source=web&cd=11&ved=0CB0QFjAAOAo&url=https%3A%2F%2Fpubweb.bnl.gov%2Fpeople%2Ffrenkel%2FNIO%2Fjacs.pdf&ei=sgyrTauKHOn20gHnhcH5CA&usg=AFQjCNFQpN-Hy2kt7yqpK3zilbCxaDGbRA&sig2=IM5WSgAI5S3nc-6x3952CA Abstract: Reduction of an oxide in hydrogen is a method frequently employed in the preparation of active catalysts and electronic devices. Synchrotron-based time-resolved X-ray diffraction (XRD), X-ray absorption fine structure (NEXAFS/EXAFS), photoemission, and first-principles density-functional (DF) slab calculations were used to study the reaction of H2 with nickel oxide. In experiments with a NiO(100) crystal and NiO powders, oxide reduction is observed at atmospheric pressures and elevated temperatures (250-350 °C), but only after an induction period. The results of in situ time-resolved XRD and NEXAFS/EXAFS show a direct NiO to Ni transformation without accumulation of any intermediate phase. During the induction period, surface defect sites are created that provide a high efficiency for the dissociation of H2. A perfect NiO(100) surface, the most common face of nickel oxide, exhibits a negligible reactivity toward H2. The presence of O vacancies leads to an increase in the adsorption energy of H2 and substantially lowers the energy barrier associated with the cleavage of the H-H bond. At the same time, adsorbed hydrogen can induce the migration of O vacancies from the bulk to the surface of the oxide. A correlation is observed between the concentration of vacancies in the NiO lattice and the rate of oxide reduction. These results illustrate the complex role played by O vacancies in the mechanism for reduction of an oxide. The kinetic models frequently used to explain the existence of an induction time during the reduction process can be important, but a more relevant aspect is the initial production of active sites for the rapid dissociation of H2.
