Because the direct electrochemical reduction ofCO2 is difficult (overvoltage, low selectivity...), it seems more interesting to do it in two stages. In the first stage, we can electrolyze water into oxygen and hydrogen, a technology that has been mastered and does not have the same selectivity problems, even if it still requires further optimization in terms of activity, yield and cost. In a second phase, hydrogen can be used as a source of (chemical) energy and protons for the hydrogenation ofCO2 to formic acid, methanol or methane. This reaction also requires catalysts.
This lecture presents the history of this field, describing the different catalysts used and the constant improvements made. The story perhaps begins at the beginning of the 20thcentury with Sabatier's heterogeneous catalysts (Nobel Prize 1912). For homogeneous catalysts, it began with Noyori's ruthenium complexes in 1994. In the late 2000s, excellent Iridium-based catalysts were proposed. Finally, from the 2010s onwards, the issue of metal scarcity, which makes it necessary to move away from noble metals, leads to new catalysts based on cobalt and iron.
Finally, this lecture discusses the possibility of implementing a virtuous cycle, in whichCO2 is hydrogenated to formic acid - which thus constitutes a stable and liquid, and therefore easily transportable, form of hydrogen. This is obviously valid if the cycle can be closed with the reverse reaction of dehydrogenation of formic acid, the latter then being a source of hydrogen. To implement this cycle, catalysts are needed, the first examples of which have only recently appeared.
