The reduction of the layered perovskites Ln 2 Ti 2 O 7 (LnTO, with lanthanide Ln= La, Pr, Nd) was studied with the aim to shift the UV photocalytic activity for water splitting in the visible range by Ti 3+ donor doping. For all phases, after reduction by CaH , the absorbance is extended beyond the UV-vis region, giving rise to a gap-like edge in the mid-infrared at ~0.4eV with a dark coloration of the samples. When the precursor with Ln= La was reduced under high temperature H 2 flow, we found a progressive nanotexturation down to 300 nm, which is responsible for a degree of Ti 3+ segregation at the surface. Magnetic measurements, thermal analysis and powder neutron diffraction (PND) reveal that the sample reduced by both routes have a similar amount of anion vacancy with δ = 0.27 (in La 2 Ti 2 O 7-δ). It represents a limited topotactic reduction stage, prior to the reconstructive reduction into La 5 Ti +3.8 5 O 17 observed in more sever reducing conditions. For the sample reduced by CaH 2 , a minor amount of hydride appears to be incorporated (~0.02 H per FU), with a Ti 3+-Hbonding observed by HYSCORE electron paramagnetic resonance (EPR) and density functional theory (DFT) calculations. Preliminary electrocatalysis tests show a promising anodic activity for water splitting hydrogen evolution with a voltage onset as low as 0.6V vs. RHE.
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