A summary of the recent advances in homogeneous light-driven catalytic oxidation reactions is provided either using sacrificial agents or with complete functional cells. In this work, a photoelectrosynthesis model cell (PESC) for H2 generation together with methyl phenyl sulfide (MeSPh) oxidation to the corresponding sulfoxide (MeS(O)Ph) with H2O and using sunlight has been prepared and characterized. We have built a two compartment PESC connected through a Nafion proton exchange membrane. The cathode consists of a platinum mesh in a pH 7.0 buffered solution. The photoanode consist on a FTO/TiO2-P-bpy-RuII,2+ (where P-bpy-RuII,2+ is [RuII(P-bpy)(bpy)2]2+ and P-bpy is 2,2′-bipyridine-4,4′-bis(phosphonic acid)) electrode immersed in the same pH 7.0 solution. The anodic compartment also contains the catalyst {[RuII(trpy)(H2O)]2(μ-pyr-dc)}(OAc) (trpy is 2,2′:6′,2″-terpyridine and pyr-dc3− is the pyrazolato-3,5-dicarboxylato trianion) abbreviated as [H2O-RuIIRuII-OH2]+ (2,2+) in homogenous solution. The illumination under sun simulated 1.5 AMG (100 mW cm−2) together with an external input of −0.43 V vs. SSCE led to the formation of hydrogen gas and the oxidation of the sulfide to sulfoxide. Last but not least, all the significant reactions involved have been characterized both from a thermodynamic and also from a kinetics viewpoint to analyze the system losses.