Room Temperature Synthesis of [Pd(cyclam)] 5 {H 3 Nb 6 O 19 } 2  ⋅ 26H 2 O: a Suitable Precursor for the in‐situ Generation of a Highly Active Catalyst for Light‐Driven Hydrogen Evolution

• Published in: European journal of inorganic chemistry 2021-11, Vol.2021 (43), p.4482-4488
• Main Authors: Müscher‐Polzin, Philipp, Poschmann, Michael, Näther, Christian, Bensch, Wolfgang
• Format: Article
• Language: English
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.202100616

The first Pd 2+ containing polyoxoniobate [Pd(cyclam)] 5 {H 3 Nb 6 O 19 } 2  ⋅ 26H 2 O ( I ) was prepared at room temperature. In the structure, two hexaniobate clusters are surrounded by a bi‐capped cube formed by Pd 2+ centered complexes. This motif is arranged in a layer‐like fashion with crystal water molecules located between cations and anions. Temperature resolved in‐situ X‐ray diffraction experiments demonstrate that successive removal of the crystal water molecules leads to formation of several crystalline intermediate phases. Water sorption investigations show that thermally removed H 2 O can be successfully reintegrated proceeding via two distinct steps. The catalytic performance for the light‐driven hydrogen evolution reaction (HER) was investigated in a sacrificial system and fluorescein Na + salt as sensitizer yielding a high value of 90 μmol/h H 2 . Surprisingly, a composite Pd@Na 7 [HNb 6 O 19 ] ⋅ 15H 2 O is in‐situ formed during the catalytic reaction by cation exchange with simultaneous reduction of Pd 2+ nanoparticles decorating the hexaniobate support. The recovered catalyst was even more active producing 157 μmol/h H 2 with an apparent quantum efficiency of 1.85 %. Photocatalytic experiments performed with ex‐situ generated Pd nanoparticles deposited on Na 7 [HNb 6 O 19 ] ⋅ 15H 2 O show much lower activities indicating a synergistic effect of the in‐situ generated Pd@Na 7 [HNb 6 O 19 ] ⋅ 15H 2 O catalyst.