Mastering the production of solar fuels by artificial photosynthesis will be a considerable feat. In other words, use light to either split water into hydrogen and oxygen or reduce CO2 to methanol or hydrocarbons: 2H2O + 4hv → O2 + 2H2; 2H2O + CO2 + 8hv → 2O2 + CH4. The modular approach uses light absorption, electron transfer in excited states, directed long range electron transfer and proton transfer, both driven by free energy gradients, combined with proton coupled electron transfer (PCET) and single electron activation of multielectron catalysis. Until recently, a lack of molecular catalysts, especially for water oxidation, has limited progress in this area. Analysis of the water oxidation mechanism for the "blue" Ru dimer cis,cis-[(bpy)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+ (bpy is 2,2'-bipyridine) has opened a new, general approach to single site catalysts both in solution and on electrode surfaces.
The Meyer Group has developed a class of molecules with a general reactivity toward water oxidation whose properties can be "tuned" systematically by synthetic variations based on mechanistic insight. These molecules catalyze water oxidation driven either electrochemically or by Ce(IV). Researchers in the Meyer Group are working to incorporate these catalysts into a functioning photoelectrochemical cell to produce solar fuels.
As published in JACS, notable progress has been made recently in the Meyer Group in identifying single-site catalysts for water oxidation including detailed elucidation of mechanism. For applications in electrocatalysis or photoelectrocatalysis, transferring solution reactivity to conducting or semiconductor solution interfaces is important to accelerate rates and minimize catalyst in a device configuration.
Electrocatalytic water oxidation occurs through the use of the phosphonate-derivatized single-site catalyst which functions on conducting and semiconductor oxide surfaces, retains the solution mechanism on the surface, and provides a basis for sustained, electrocatalytic water oxidation over a range of pH values.