Electrocatalysis

Our current use of fossil fuels is unsustainable. Electrochemistry could provide future generations with a cleaner and greener alternative. Electricity from intermittent renewables, including solar or wind power, could be converted into synthetic fuels such as hydrogen, methanol or even ammonia. Alternatively, energy from the sun could be harvested directly and converted into a fuel in a single device using photoelectrochemical cells. The electricity could then be released using fuel cells. The widespread uptake of these devices is contingent on the development of improved catalysts to drive the reactions at their electrodes. The electrode acts as a heterogeneous catalyst, and is known as an electrocatalyst. New electrocatalysts are need that are active (i.e. efficient), selective, stable, inexpensive and abundant enough to be produced on a large scale. 

Our research encompasses the following reactions, important for the production of synthetic fuels:

  • Oxygen evolution
  • Hydrogen evolution
  • CO2 reduction to organic fuels
  • N2 reduction to NH3

The reactions which we investigate in relation to fuel cells include:

  • Oxygen reduction to H2O or H2O2
  • Hydrogen oxidation
  • Methanol oxidation

Our experiments are conducted on transition metals, alloys, oxides and sulfides, in all forms, from nanoparticles to single crystals. We are particularly interested in the rational discovery of new electrocatalyst materials, on the basis of insight from model experiments and theoretical calculations.  We enjoy close internal collaborations with the surface scientists and photoelectrochemists at SURFCAT, as well as the theoretical electrochemists from the Centre for Atomic Scale Materials Design (CAMD).

  Cyclic voltammogram of the electrooxidation of a CO adlayer to CO2 on different single crystal alloy surfaces

Figure showing the cyclic voltammogram of the electrooxidation of a CO adlayer to CO2 on different single crystal alloy surfaces. The electrocatalytic activity increases in the following order: Pt(111) > Cu/Pt(111) near-surface alloy (NSA) > Cu/Pt(111) surface alloy. It turns out that the activity for CO electroxidation of these surfaces is highly sensitive to the exact position of Cu in the first two atomic layers. For further details, see reference 1, below. 

 

 

 

 

 

 

 

The stability of a Cu monolayer on Au(111) under reaction conditions (change of potential) investigated in situ using electrochemical scanning tunneling microscope

 

The stability of a Cu monolayer on Au(111) under reaction conditions (change of potential) has been investigated in situ using electrochemical scanning tunneling microscope.  Image (a) shows the closed Cu monolayer after electrodeposition on Au(111).  Despite the high strain, the monolayer is closed and defect-free. Image size 14 nm, U =-115 mV. Image (b) shows a (2x2) phase visible when going to lower potential. Image size 12 nm. At even more negative potentials potential (below U = -500mV), the Cu film breaks up and reveals the underlying substrate (c). Image size 106 nm.  The experiments demonstrate that the film may not be stable under conditions where a very cathodic bias needs to be applied, e.g. CO2 reduction to hydrocarbons. For further details and a comparison to Cu(111) and Au(111), see reference 2, below.

 

Surface specific activity of platinum for oxygen electroreduction

 

Figure showing how the surface specific activity of platinum for oxygen electroreduction increases with particle size, in correlation to the fraction of terrace sites at the particle surface (as determined from the temperature programmed desorption of CO.  For further details, see reference 3, below.

 

Cyclic voltammogram in O2-saturated 0.1 M HClO4 of Pt5Gd in comparison to Pt

 

Left: cyclic voltammogram in O2-saturated 0.1 M HClO4 of Pt5Gd in comparison to Pt; the data demonstrate that Pt5Gd is both highly active (i.e. efficient) at electroreducing oxygen, and that its performance is very stable.  Right: non-destructive depth profile of Pt5Gd, produced using angle resolved X-ray photoelectron spectroscopy, along with a schematic illustration of its atomic structure. For further details, see reference 4, below.

  

Selected publications - Electrocatalysis

  1. Bandarenka, A. S., Varela, A. S., Karamad, M. R., Calle-Vallejo, F., Bech, L., Perez-Alonso, F. J., Rossmeisl, J., Stephens, I. E. L. & Chorkendorff, I. The design of an active site towards optimal electrocatalysis: Overlayers, surface alloys and near-surface alloys of Cu/Pt(111). Angewandte Chemie International Edition 51, 11845-11848 (2012).
     
  2. Schlaup, C. & Horch, S. In-situ STM study of phosphate adsorption on Cu(111), Au(111) and Cu/Au(111) electrodes. Surf. Sci. 608, 44-54 (2013).
     
  3. Perez-Alonso, F. J., McCarthy, D., Nierhoff, A., Hernandez-Fernandez, P., Strebel, C., Stephens, I. E. L., Nielsen, J. H. & Chorkendorff, I. The effect of size on the oxygen electroreduction activity of mass-selected platinum nanoparticles. Angewandte Chemie International Edition 51, 4641-4643 (2012).
     
  4. Escudero-Escribano, M., Verdaguer-Casadevall, A., Malacrida, P., Grønbjerg, U., Knudsen, B. P., Jepsen, A. K., Rossmeisl, J., Stephens, I. E. L. & Chorkendorff, I. Pt5Gd as a highly active and stable catalyst for oxygen electroreduction. J. Am. Chem. Soc. 134, 16476-16479 (2012).
     
  5. Stephens, I. E. L., Bondarenko, A. S., Grønbjerg, U., Rossmeisl, J. & Chorkendorff, I. Understanding the oxygen reduction reaction on platinum and its alloys. Energy Environ. Sci. 5, 6744-6762 (2012).
     
  6. Stephens, I. E. L. & Chorkendorff, I. Minimizing the Use of Platinum in Hydrogen-Evolving Electrodes. Angew. Chem.-Int. Edit. 50, 1476-1477 (2011).
     
  7. Stephens, I. E. L., Bondarenko, A. S., Pérez-Alonso, F. J., Calle-Vallejo, F., Bech, L., Johansson, T. P., Jepsen, A. K., Frydendal, R., Knudsen, B. P., Rossmeisl, J. & Chorkendorff, I. Tuning the Activity of Pt(111) for Oxygen Electroreduction by Subsurface Alloying. J. Am. Chem. Soc. 133, 5485-5491 (2011).
     
  8. Greeley, J., Stephens, I. E. L., Bondarenko, A. S., Johansson, T. P., Hansen, H. A., Jaramillo, T. F., Rossmeisl, J., Chorkendorff, I. & Nørskov, J. K. Alloys of platinum and early transition metals as oxygen reduction electrocatalysts. Nature Chemistry 1, 552-556 (2009).
     
  9. Jaramillo, T. F., Jorgensen, K. P., Bonde, J., Nielsen, J. H., Horch, S. & Chorkendorff, I. Identification of active edge sites for electrochemical H2evolution from MoS2 nanocatalysts. Science 317, 100-102 (2007).
     
  10. Greeley, J., Jaramillo, T. F., Bonde, J., Chorkendorff, I. B. & Nørskov, J. K. Computational high-throughput screening of electrocatalytic materials for hydrogen evolution. Nature Materials 5, 909-913 (2006).

Contact

Ib Chorkendorff
Professor
DTU Physics
+45 45 25 31 70

Contact

Sebastian Horch
Associate Professor
DTU Physics
+45 45 25 32 32

Contact

Jakob Kibsgaard
Assistant Professor
DTU Physics
+45 45 25 32 90