Facile Method To Study Catalytic Oxygen Evolution Using a Dissolved Oxygen Optical Probe: An Undergraduate Chemistry Laboratory To Appreciate Artificial Photosynthesis.

Artificial photosynthesis (AP) is a synthetic chemical process that replicates natural photosynthesis to mass produce hydrogen as a clean fuel from sunlight-driven water splitting (2H2O → O2 + H2). In both natural and artificial photosynthesis, an oxygen-evolving catalyst (OEC) is needed to catalyze oxygen production from water (2H2O → O2 + 4H+ + 4e-). Herein, we present a simple undergraduate laboratory experiment for monitoring the catalytic oxygen-evolution reaction using a dissolved oxygen optical probe, a luminescent probe that can continuously measure the concentration of dissolved oxygen in aqueous solutions. The laboratory experiment consists of two parts. First, students identify and evaluate the necessary criteria for an active molecular O2-evolving catalyst. Second, students use a kinetic protocol based on the method of initial rates to derive an empirical rate law expression and calculate the turnover frequency and rate constant for a benchmark OEC, [RuII(tpy)(bpy)(H2O)]2+ (tpy is 2,2':6',2"-terpyridine; bpy is 2,2'-bipyridine). The use of simple transition metal complexes allows students to easily grasp how the choice of transition metals and the coordinated organic ligands can greatly impact the overall catalytic performance. Students collect time-dependent dissolved oxygen plots, and analyze and interpret oxygen-evolution data using modern equipment. This laboratory protocol is simple, and allows students to relate many fundamental topics such as thermodynamics, kinetics, redox and coordination chemistry, and catalysis to advances in current chemical research to help broaden their understanding of artificial photosynthesis. [ABSTRACT FROM AUTHOR]