Porphyrin-like metal-functionalized graphene structures have been investigated as possible catalysts for CO2 and CO reduction to methane or methanol. The late transition metals (Cu, Ag, Au, Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, Os) and some p (B, Al, Ga) and s (Mg) metals comprised the center of the porphyrin ring. A clear difference in catalytic properties compared to extended metal surfaces was observed owing to a different electronic nature of the active site. The preference to bind hydrogen, however, becomes a major obstacle in the reaction path. A possible solution to this problem is to reduce CO instead of CO2. Volcano plots were constructed on the basis of scaling relations of reaction intermediates, and from these plots the reaction steps with the highest overpotentials were deduced. The Rh–porphyrin-like functionalized graphene was identified as the most active catalyst for producing methanol from CO, featuring an overpotential of 0.22 V. Additionally, we have also examined the hydrogen evolution and oxidation reaction, and in their case, too, Rh–porphyrin turned out to be the best catalyst with an overpotential of 0.15 V.

I could never be without Cu: An active site has been designed for the catalysis of CO electroxidation. This was achieved by incorporating submonolayer amounts of Cu (orange spheres) into a single crystal of Pt (gray spheres). The electrochemical reactivity of this surface was highly sensitive to the exact position of Cu (see scheme).

Ein aktives Zentrum für die Katalyse der CO‐Elektrooxidation wurde entworfen. Dies gelang durch Einführung von Cu (orangefarbene Kugeln im Schema) in Mengen von weniger als einer Monoschicht in einen Pt‐Einkristall (graue Kugeln). Die elektrochemische Reaktivität der Oberfläche hing stark von der exakten Position der Cu‐Atome ab.

Positioning of copper atoms in the first two layers of a Pt single crystal changes the reactivity of the surface for CO electro‐oxidation. In their Communication on I. Chorkendorff et al. visualize this effect using a 3D “volcano plot”. It shows the overpotential, or catalytic activity, for CO electro‐oxidation as a function of the binding to CO and OH and that the most active catalyst should not bind too weak or too strong to CO and OH.

Die Position des Kupfers in den zwei obersten Schichten eines Pt‐Einkristalls bestimmt die Reaktivität der Oberfläche für die CO‐Elektrooxidation. In ihrer Zuschrift auf veranschaulichen I. Chorkendorff et al. diesen Effekt durch ein 3D‐Vulkandiagramm. Es zeigt das Überpotential, oder die katalytische Aktivität, für die Elektrooxidation von CO als Funktion der Bindungsstärke von CO und OH. Man erkennt, dass der aktive Katalysator CO und OH nicht zu schwach oder zu stark binden sollte.