O2 Reduction at Se Modified Surfaces: Characterization by SPM and DEMS

Abstract

Metal chalcogenides have been extensively studied as catalysts for oxygen reduction reactions, due to their tolerance for small organic molecules especially in relation to fuel cell applications. We have recently reported that also adsorption of Se on polycristalline Ru leads to an increased activity as compared to Ru.[1]. A theoretical study also showed that intermediate surface contents of Ru or Rh by Se or S lead to an increased activity.[2] However, fundamental studies on well-defined rhodium (Rh) single-crystal surfaces modified with chalcogenides (Se) are very rare. Here, irreversible adsorption of Se on Rh(111) was examined by voltammetric technique. Surface structure characterization of Se modified Rh(111) substrate was achieved using cyclic voltammetry and in situ STM and AFM. STM images also show a roughening starting at step edges for Se adsorption at certain potentials, similar to the roughening transition observed on Au(111) surface for S and Se adsorption [3][4] or As on Pt(111)[5], suggesting the formation of an. Se–Rh intermetallic compound. Results on the effect on oxygen reduction activity will be presented. It was observed that chalcogenides usually stripped off under fuel cell operating conditions [6] and also electrochemical hydrogen selenide formation at lower potentials [7].Here, we used differential electrochemical mass spectrometery (DEMS) for an additional quantitative characterisation of Se adlayers via reductive desorption on model fcc metal surfaces like [Rh(111), Pt(111) and Au(111)] References [1] N. Bogolowski, T. Nagel, B. Lanova, S. Ernst, H. Baltruschat, K. Nagabhushana and H. Boennemann, J. Appl. Electrochem., 37 (2007) 1485 [2] Tritsaris, G. A.; Nørskov, J. K.; Rossmeisl, J.; Electrochim. Acta 56 (2011) 9783.[3] C. Wei, N. Myung, K. Rajeshwar, J. Electroanal. Chem. 375 (1994) 109.[4] T.A. Sorenson, K. Varazo, D.W. Suggs and J.L. Stickney, Surf. Sci., 470 (2001) 197.[5] X.Y. Xiao and H. Baltruschat, Langmuir, 19 (2003) 7436.[6] D. C. Papageorgopoulos, F. Liu and O. Conrad, Electrochimica Acta 52 (2007) 4982.[7] M. O. Solaliendres, A. Manzoli, G. R. Salazar-Banda, K. I. B. Eguiluz, S. T. Tanimoto and S. A. S. Machado, J. Solid State Electrochem. 12 (2008) 679.