Nanophase Transition Metal Oxides Show Large Thermodynamically Driven Shifts in Oxidation-Reduction Equilibria

Abstract

Feeling the Pinch Nanoparticles exhibit many different properties compared to their larger counterparts, but how the stability of certain phases relative to others is affected by a change in particle size is often unclear. Using a thermodynamic probe sensitive to nanoparticle surfaces, Navrotsky et al. (p. 199 ) show that surface energy strongly influences the stability of some metal oxides relative to others. For example, nanoparticles of CoO, which are stable at larger sizes, are only stable over a very narrow range of conditions due their high surface energies. Cobalt oxides are catalysts that may one day promote the cost-effective generation of hydrogen from water, but nanoparticles in soils and biological systems—including iron and manganese oxides—also feel the pinch of surface energy on their range of stability.