Molten copper hexaoxodivanadate: an efficient catalyst for SO3 decomposition in solar thermochemical water splitting cycles

Abstract

Molten copper hexaoxodivanadate (CuV₂O₆) was identified as an active catalyst for SO₃ decomposition, which is an oxygen generation step in solar thermochemical water splitting cycles, at moderate temperatures (ca. 600 °C). The SO₃ decomposition over CuV₂O₆ was significantly accelerated when the reaction temperature approached the melting point (ca. 630 °C) compared with solid phases of Cu₂V₂O₇ as well as other compounds in the CuO–V₂O₅ system with higher melting points (≥780 °C). A possible intermediate CuSO₄ species formed by SO₃ adsorption onto the Cu oxide site may decompose promptly to evolve SO₂ and O₂ on contact with the molten catalyst phase. Furthermore, the molten catalyst contained a large fraction of monovalent Cu formed by spontaneous desorption of oxygen. A possible reaction mechanism consisting of the fast dissolution of CuSO₄ and Cu²⁺/Cu⁺ redox cycles in the melt is proposed.