The influence of rare earth gadolinium (Gd3+) ion doping on optical and photoelectrochemical properties of TiO2 is studied. The hierarchical clump-type TiO2 nanostructure was fabricated using poly-vinyl acetate as soft-template. The optical absorbance quantity of TiO2 was strikingly promoted at bandgap energy region (380 nm) by Gd3+ doping, as well as it extend a wide absorbance in visible wavelength region (400 - 800 nm) elucidating the sub-bandgap formation. As a result, Gd3+:TiO2 exhibits high photocurrent density than undoped TiO2 in photoelectrocatalytic experiments. Another plausible reason for enhancing the photocurrent density at Gd3+:TiO2 was analyzed through electrochemical impedance spectroscopy. The underlying mechanism of surface states controlled charge transfer at TiO2/electrolyte interfaces affected the photoelectrocatalytic hydrogen fuel generation, and compete with Gd3+ ion doping through bottlenecking of photoelectrons trapping at surface states. The improved charge separation (e(-)/h(+)) at Gd3+:TiO2 result effective photoelectron collection and thus yield 180 % higher hydrogen gas (similar to 2.34 mL.h(-1).cm(-2)) generation compare to pristine TiO2 (1.28 mL.h(-1).cm(-2)) under UV light irradiation. The improved optical and charge transfer characteristics of hierarchical TiO2 by Gd3+ ions can be implemented to wide range of other metal oxide based photocatalytic fuel generation. (C) The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.