Noble metal clustering and nanopillar formation in an oxide matrix

Photoelectrochemical electrodes used for solar energy harvesting and hydrogen production by water splitting have two essential functional regions: one for photocarrier generation by light absorption and another for hydrogen generation by electrochemical water reduction at the electrode surface. We show that spontaneous segregation of noble metals (Pt, Ir, Pd, Rh) can be used to grow composite materials consisting of an oxide semiconductor matrix (SrTiO3) and an array of vertically-aligned metal nanopillars that allow these two functional regions to be independently engineered. We discuss the noble metal segregation mechanisms, clustering at the initial growth stage, and the thermodynamic and kinetic aspects of nanopillar formation for several different noble metals. In particular, we focus on the role of surface diffusion of metal and oxide species and noble metal encapsulation in the formation of vertically-aligned nanopillar composite materials. (C) 2019 The Japan Society of Applied Physics