Approaching the Volcano Top: Iridium/Silicon Nanocomposites as Efficient Electrocatalysts for the Hydrogen Evolution Reaction.

Electrolysis of water to generate hydrogen is an important issue for the industrial production of green and sustainable energy. The best electrocatalyst currently available for the hydrogen evolution reaction (HER) is platinum. We herein show that iridium can be manipulated to achieve a record high HER activity surpassing platinum in every aspect: a lower overpotential at any given current density, a higher current density, and mass activity for all bias potentials applied and a catalyst cost reduction of 50% for the same hydrogen generation rate. The superior HER activity was achieved by a binary Ir/Si nanowire catalyst design in which (as density functional theory calculations show) two distinct strategies act in synergy: (i) decreasing the size of the iridium nanoparticles to ∼2.2 nm and (ii) dividing the H2-generation process to three steps occurring on two different catalysts: H adsorption on iridium, H diffusion to silicon, and H2 desorption from silicon.