A great technological challenge facing our global future is the development of renewable energy. Rising standards of living in a growing world population will cause global energy consumption to increase dramatically over the next half-century. Energy consumption is predicted to increase at least two-fold, from our current burn rate of 12.8 TW to 28 – 35 TW by 2050. A short-term response to this challenge is the use of methane and other petroleum-based fuels as hydrogen sources. However, external factors of economy, environment, and security dictate that this energy need be met by renewable and sustainable sources with water emerging prominently as the primary carbon-neutral hydrogen source and light as an energy input. This area of research in our group is summarized by a simple equation:

The above equation is aimed at driving the energetically unfavorable, water-splitting reaction to produce fuel – hydrogen and oxygen. The photon may be captured directly by a transition metal catalyst or indirectly by a transition metal catalyst at the surface of a photovoltaic (PV) cell. The transition metal complex can the use the solar converted energy (from the PV or directly) to act on water and rearrange its bonds to produce hydrogen and oxygen – a solar fuel. In this way, solar photons are converted into high-energy chemical bonds, the energy of which can be released in a fuel cell. The construction of such a cycle, however, reveals daunting challenges because it relies on chemical transformations that are not understood at the most basic levels. Unexplored basic science issues are immediately confronted when the water splitting problem is posed in the simplest chemistry framework,

The overall transformation is challenging because: (1) It is a multielectron process, (2) proton transfer must accompany electron transfer (i.e., PCET) – both electron and proton inventories need to be managed, and (3) strong bonds need to be activated to close a catalytic cycle.

This photochemical water splitting problem shares basic chemical commonalities with the activation of other small molecules of energy consequence, including CO₂, N₂ and CH₄, H₂ and O₂. All involve bond-making and –breaking processes that require multielectron transfers often coupled to proton transfer events. Our research efforts have addressed the foregoing italicized research themes by expanding the reactivity of metal complexes in ground and electronic excited states beyond conventional one-electron transfer. We have created molecules that react in multielectron steps from their electronic excited states. We have been examining the coupling of electrons and protons in catalytic small molecule reactions (see PCET section for more information). We are inventing a myriad of new ways to photoactivate stable metal-ligand bonds, especially those involving oxygen. Against this backdrop of knowledge, hydrogen- and oxygen-producing catalysts have been developed and are continually being improved.