Chemical approaches to artificial photosynthesis

TLDR

The early 1970s Fujishima–Honda experiment demonstrated TiO₂ photoelectrochemical water splitting, and the 1973 OPEC oil embargo spurred a surge in research into artificial photosynthesis to produce solar fuels. The study targets water splitting into H₂ and O₂ and light‑driven CO₂ reduction to hydrocarbons, with methane shown as a representative product. Band‑gap excitation of anatase TiO₂ in a Pt‑counter‑electrode photoelectrochemical cell with applied bias successfully split water into hydrogen and oxygen.

Abstract

In the early 1970s, the works by Fujishima and Honda (1) and Honda et al. (2) reported on the results of a now famous experiment. They showed that band gap excitation of anatase TiO2 in a photoelectrochemical cell with a Pt counter electrode and an applied bias resulted in water splitting into hydrogen and oxygen. The timing of the result was impeccable. In 1973, the Organization of the Petroleum Exporting Countries (OPEC) declared an embargo on oil imports to the West, resulting in gasoline shortages and long lines at gas pumps. Suddenly, there was a pressing need for energy independence and new ways of providing for the energy-hungry economies of Western Europe, Japan, and the United States. The international research community responded. There was a short lived explosion of interest in converting sunlight into high-energy molecules by what we now call artificial photosynthesis to make solar fuels. Target reactions were water splitting into hydrogen and oxygen (1) and light-driven reduction of CO2 by water to give CO, other oxygenates, or hydrocarbons. Methane is shown as the product in equation 2, but the ultimate target is liquid hydrocarbons to power our existing energy infrastructure (1 and 2):