Electrocatalytic Water Splitting (H₂O → H₂+½ O₂)

Artificial photosynthesis (AP) using solar energy to convert H₂O into H₂ (a fuel) and O₂ is a most promising approach to a carbon-neutral cycle and scalable energy storage. Electrocatalysis provides an attractive candidate route to AP, which could extend to all intermittent renewable energy resources. A major challenge in renewable energy technology is water splitting, which uses solar radiation to photoelectrochemically convert water molecules into H₂ (a fuel) and O₂. Here both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) present challenges for the catalysts. The detailed reaction mechanisms had not yet been established for either one. We did the first mechanisms under electrochemical conditions and including free energy reaction barriers for the transition states for both systems. Here we separately consider the two electrochemical half-reactions, HER and OER, which require drastically different catalysts for optimal performance.