Iridium single-atom catalyst on nitrogen-doped carbon for formic acid oxidation synthesized using a general host–guest strategy

Single-atom catalysts not only maximize metal atom efficiency, they also display properties that are considerably different to their more conventional nanoparticle equivalents, making them a promising family of materials to investigate. Herein we developed a general host–guest strategy to fabricate various metal single-atom catalysts on nitrogen-doped carbon (M₁/CN, M = Pt, Ir, Pd, Ru, Mo, Ga, Cu, Ni, Mn). The iridium variant Ir₁/CN electrocatalyses the formic acid oxidation reaction with a mass activity of 12.9 AmgIr−1 whereas an Ir/C nanoparticle catalyst is almost inert (~4.8 × 10⁻³ AmgIr−1). The activity of Ir₁/CN is also 16 and 19 times greater than those of Pd/C and Pt/C, respectively. Furthermore, Ir₁/CN displays high tolerance to CO poisoning. First-principle density functional theory reveals that the properties of Ir₁/CN stem from the spatial isolation of iridium sites and from the modified electronic structure of iridium with respect to a conventional nanoparticle catalyst. [Figure not available: see fulltext.].