Petrochemistry and Chemical Engineering

Solar water splitting (conversion of sunlight and H₂O to H₂ fuel and O₂ or sunlight and H₂O plus CO₂ to fuel and O₂) is a potential solution to our growing energy availability and environmental concerns. The huge international effort to produce “solar fuel” (artificial photosynthesis) is commensurate with the funding from governments for this research and its potential importance. Statement of the Problem: While we have solar electricity and this is now economically competitive with conventional electricity, we need fuel for many large-scale uses including ship and air transportation. Thus, there is a global effort to realize solar fuel. Solar fuel generation requires three unit operations, a water oxidation catalyst (WOC), generally viewed as the success-limiting factor, a light absorber-charge separator and a reduction (fuel formation) catalyst. We will describe the use of transition metal oxygen anion clusters (polyoxometalates or POMs), as H₂ generation catalysts and more importantly, WOCs. After our initial papers on POM WOCs, many groups have made these molecular versions of metal oxide WOC films and conducted a range of mechanistic and other experiments. We will describe the new POM WOCs that work in acid and how WOCs can be interfaced with photo electrodes to generate H₂ and O₂. Mechanistic studies of the four-electron-transfer process to split water, the first of their kind, will be presented and the implications of this research discussed.