Activation of Osmium by the Surface Effects of Hydrogenated TiO₂ Nanotube Arrays for Enhanced Hydrogen Evolution Reaction Performance

Efficientcathodes for the hydrogen evolution reaction (HER) inacidic water electrolysis rely on the use of expensive platinum groupmetals (PGMs). However, to achieve economically viable operation,both the content of PGMs must be reduced and their intrinsically strongH adsorption mitigated. Herein, we show that the surface effects ofhydrogenated TiO2 nanotube (TNT) arrays can make osmium,a so far less-explored PGM, a highly active HER electrocatalyst. Thesedefect-rich TiO2 nanostructures provide an interactivescaffold for the galvanic deposition of Os particles with modulatedadsorption properties. Through systematic investigations, we identifythe synthesis conditions (OsCl3 concentration/temperature/reactiontime) that yield a progressive improvement in Os deposition rate andmass loading, thereby decreasing the HER overpotential. At the sametime, the Os particles deposited by this procedure remain mainly sub-nanometricand entirely cover the inner tube walls. An optimally balanced Os@TNTcomposite prepared at 3 mM/55 & DEG;C/30 min exhibits a record lowoverpotential (& eta;) of 61 mV at a current density of 100 mA cm(-2), a high mass activity of 20.8 A mg(Os) (-1) at 80 mV, and a stable performance in an acidic medium.Density functional theory calculations indicate the existence of stronginteractions between the hydrogenated TiO2 surface andsmall Os clusters, which may weaken the Os-H* binding strengthand thus boost the intrinsic HER activity of Os centers. The resultspresented in this study offer new directions for the fabrication ofcost-effective PGM-based catalysts and a better understanding of thesynergistic electronic interactions at the PGM|TiO2 interface.