Photocatalytic approaches using two sets of semiconductor particles and a pair of redox shuttle mediators are considered as a safe and economic solution for solar water splitting. Here, we report on accurate experimental characterization techniques for photocatalytic half reactions investigating the gas as well as the liquid products. The method is exemplified utilizing photocatalytic titania particles in an iron-based aqueous electrolyte for effective oxygen evolution and mediator reduction reactions under illumination. Several product characterization methods, including an optical oxygen sensor, pressure sensor, gas chromatography, and UV-Vis spectroscopy are used and compared for accurate, high-resolution gas-products and mediator conversion measurements. Advantages of each technique are discussed. A high Faraday efficiency of 97.5%±2% is calculated and the reaction rate limits are investigated.