In Situ Monitoring of Nanoparticle Formation during Iridium‐Catalysed Oxygen Evolution by Real‐Time Small Angle X‐Ray Scattering

Abstract

Real‐time Small Angle X‐Ray Scattering (SAXS) has been used to investigate the homogeneity of a series of molecular iridium complexes during water oxidation catalysis in aqueous NaIO4 solution through a continuous flow cell. The results obtained for the unstable [Cp*Ir(OH2)3]2+ precursor forming amorphous IrOx nanoparticles (NPs) in‐situ validate and complement previous Dynamic Light Scattering (DLS) studies by providing enhanced sensitivity for small particle sizes and increased temporal resolution under realistic reaction conditions. Correlating particle formation profiles with O2 evolution traces allowed homogeneous catalysis to be clearly distinguished from heterogeneous catalysis. A series of seven pyridine−alkoxide Cp*Ir complexes are shown to be fully homogeneous by SAXS, validating previous studies and confirming their catalysis to be molecular in nature throughout the reaction.

Potential‐ and Buffer‐Dependent Catalyst Decomposition during Nickel‐Based Water Oxidation Catalysis

“…Detection of in situ ‐generated nanoparticles can be very challenging. Hence, publications on molecular WOCs generally include multiple experiments to prove that the catalyst activity stems from a molecular species [44,52–54] . In the context of our ongoing research to explore novel first‐row metal‐based WOCs, [55] we were interested in developing novel nickel‐based catalysts.…”

“…Hence, publications on molecular WOCs generally include multiple experiments to prove that the catalyst activity stems from a molecular species. [44,[52][53][54] In the context of our ongoing research to explore novel first-row metalbased WOCs, [55] we were interested in developing novel nickelbased catalysts. We aimed at applying previously developed design rules to optimize the catalyst, [56] but found that active NiO x layers are formed under certain conditions.…”