Local reactivity at Pd nanoclusters

ELIZABETH SANTOS; PAOLA QUAINO; LEANDRO PINTO

Saint-Malo

Congreso; 17th Topical Meeting of the International Society of Electrochemistry; 2015

The International Society of Electrochemistry

Nanostructured surfaces can exhibit surprising chemical, mechanical or electronic properties that are distinctly different from those of extended systems. Especially interesting are their electrocatalytic activity, which can be experimentally obtained by local current measurements with the Scanning Electrochemical Potential Microscopy (SECPM) [1]. In a previous work, we have investigated different Pd nanostructures on Au(111) (monomers, rows, embedded clusters and islands) using our own theory of electrocatalysis [2] and found qualitatively good agreement with experimental data for the hydrogen evolution reaction. Electronic parameters obtained from DFT calculations were introduced in our Hamiltonian and the solvent effects were treated according to Marcus - Hush theory. However, the modeling of the solvent needs to be improved. Especially when the proton approaches the electrode, the structure of the solvation shell at the transition state, could be very different if the nanostructure is embedded in the surface very different if the nanostructure is embedded in the surface or not (see Figure). In the case of flat surfaces, the proton should lose a larger number of water molecules in its solvation sheath when it is close to the electrode than in the second case. We have combined our electrocatalysis theory with molecular dynamic in order to obtain quantitative results. We focus on the Volmer step of the hydrogen evolution reaction and calculate the activation barrier. The potential of mean force (pmf) has been calculated by using molecular dynamics and from this we have derived the energy of solvent reorganization as a function of the distance of the reactant from the reaction site.