The absorption of hydrogen into commercially pure alpha titanium (Grade-2) has been studied on oxide-free (pH <= 3) surfaces at 25 degrees C under both potentiostatic and galvanostatic conditions. The rate of hydrogen absorption was found to be extremely rapid on oxide-free surfaces and the formation of surface hydrides catalyzed the proton reduction process. Complete hydride coverage of the surface very significantly suppressed the rate of hydrogen absorption, which is consistent with the known decrease in diffusivity of hydrogen in the hydride phase. SIMS imaging showed that absorption occurred preferentially at iron-containing intermetallic particles located along grain boundaries, leading to the coexistence of cathodically active hydrided sites and anodically active alpha titanium sites. (c) 2006 Elsevier Ltd. All rights reserved.