Due to this greater stability, we focus on FeSA-N5-C. This section investigates adsorption properties of reactant and product molecules on these three catalysts, including four molecules of O2, HCHO, CO2, and H2O. To obtain the most stable adsorption geometries of gas molecules on catalyst, the adsorption configuration was first optimized as shown in Figure . It can be seen that on the surface of FeSA-N3-C, all four molecules form bonds with the catalyst.