University of California, Merced

Mixed-valent Mn oxides show promise as water oxidation catalysts, potentially providing renewable and sustainable clean energy. Yet, there is little fundamental understanding of the thermodynamic and mechanistic factors controlling transformation (and reactivity) at the nanoscale. Recently, room temperature transformation of nanoparticle Mn₂O₃ produced Mn₃O₄. Perturbation of strongly-associated surface (SAS) water thermodynamically drove mineral phase transformation via surface energy differences of two nanoscale Mn oxides that share redox phase equilibrium. However, not all particles transformed. Two hypotheses were developed and then probed with XAS to determine if the mechanism of transformation involved surface island formation or if it were entirely size-mediated with the tiniest particles most susceptible to complete transformation.