New Pyrochlore-like Oxyfluorides Na_2-2xSn_xM₂O₅F₂ (M = Nb⁵⁺ or Ta⁵⁺ and 1 ≤ x ≤ 0) as Potential Candidates for Overall Water Splitting Photocatalysis

Edouard Boivin (1) , Sébastien Saitzek (2) , François Fauth (3) , Marielle Huvé (4) , Pascal Roussel (4) , Houria Kabbour (4)

1 UCCS - Unité de Catalyse et Chimie du Solide - UMR 8181
2 UCCS Équipe Couches Minces & Nanomatériaux
3 ALBA Synchrotron, Cerdanyola del Vallés, Barcelona
4 UCCS Équipe Matériaux inorganiques, structures, systèmes et propriétés

Lone pair containing oxyfluorides have recently emerged as efficient and stable photocatalysts for overall water splitting (OWS). In this work we have obtained several new potential OWS photocatalysts with pyrochlore structure (i.e., Na_2–2xSn_xM₂O₅F₂ with M = Nb⁵⁺ or Ta⁵⁺ and 1 ≤ x ≤ 0) through kinetically controlled ion-exchange reaction from Na₂M₂O₅F₂. Rietveld refinement of the structures as well as DFT indicate the Sn²⁺ lone pair stereochemical activity. The partial density of states reveals contributions at the top of the valence band that are mainly composed of a Sn _5s–Sn _5p hybridization through the (O,F) _2p orbitals. This leads to a significant narrowing of the band gap and an improvement of the photoconduction response by a factor ca. 50 with respect to the x = 0 compound, Na₂Nb₂O₅F₂. The Mott–Schottky measurements show that all materials possess band edge positions encompassing the thermodynamic redox potential of H⁺/H₂ and O₂/H₂O. However, the valence band of SnNb₂O₅F₂ may not be oxidative enough to overcome the overpotential associated with the O^2– oxidation and hence could be unsuitable for OWS photocatalysis in contrast with Na_1.5Sn_0.25Nb₂O₅F₂.

Domaines: Catalyse; Chimie; Matériaux

Edouard Boivin, Sébastien Saitzek, François Fauth, Marielle Huvé, Pascal Roussel, et al.. New Pyrochlore-like Oxyfluorides Na_2-2xSn_xM₂O₅F₂ (M = Nb⁵⁺ or Ta⁵⁺ and 1 ≤ x ≤ 0) as Potential Candidates for Overall Water Splitting Photocatalysis. Chemistry of Materials, 2023, ⟨10.1021/acs.chemmater.2c02801⟩. ⟨hal-03989924⟩