Changing the Activity of Electrocatalysts for Oxygen Reduction by Tuning the Surface Electronic Structure

Abstract

The fuel cell is a promising alternative to environmentally unfriendly devices that are currently powered by fossil fuels. In the polymer electrolyte membrane fuel cell (PEMFC), the main fuel is hydrogen, which through its reaction with oxygen produces electricity with water as the only by-product. To make PEMFCs economically viable, there are several problems that should be solved; the main one is to find more effective catalysts than Pt for the oxygen reduction reaction (ORR), 1/2 O 2 + 2 H + + 2 e À = H 2 O. The design of inexpensive, stable, and catalytically active materials for the ORR will require fundamental breakthroughs, and to this end it is important to develop a fundamental understanding of the catalytic process on different materials. Herein, we describe how variations in the electronic structure determine trends in the catalytic activity of the ORR across the periodic table. We show that Pt alloys involving 3d metals are better catalysts than Pt because the electronic structure of the Pt atoms in the surface of these alloys has been modified slightly. With this understanding, we hope that electrocatalysts can begin to be designed on the basis of fundamental insight.

Nanostructured Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction reaction

“…They concluded that late transition metal atoms with low coordination numbers (i.e., having open surfaces, steps, edges, kinks and corners) tend to have higher d-states and therefore interact more strongly with adsorbates than do the atoms on close-packed surfaces with high metal coordination numbers. This theory, which has been experimentally validated by Stamenkovic et al 34 and successfully applied in the search for ORR catalysts more effective than Pt, shows that Pt-alloys involving 3d metals are better catalysts than Pt because the electronic structure of Pt atoms on the surface of Pt-alloys has been slightly modified. Stamenkovic et al developed a series of well-characterized alloys that showed interesting volcano-shaped variations in electrocatalytic activity, and provided a starting point for developing and understanding the factors that control ORR kinetics.…”

“…55 Stability testing of Pt 3 M alloys in a vacuum (M = Ir, Co, Ni and Fe) showed that Pt 3 Ir(111) > Pt 3 Co(111) > Pt 3 Ni(111) > Pt 3 Fe(111). 6 Stamenkovic et al 34 studied polycrystalline alloy films of Pt 3 M catalysts (M = Ni, Co, Fe and Ti) to understand the role of 3d metals in the electrocatalytic ORR activity of Pt-alloys. They found that in these Pt 3 M alloys, the first outlayer was enriched by Pt due to surface segregation.…”

Synergetic Effect of Surface and Subsurface Ni Species at Pt−Ni Bimetallic Catalysts for CO Oxidation

“…12 We also studied O 2 dissociation on Pt(111) and a Pt-skin layer on Pt 3 Ni, and a similar trend (0.71 eV on Pt(111) vs 0.97 eV on the Pt-skin) was found. 51,74 On the other hand, adsorption of CO, H, O, and O 2 on Pt-skin surfaces is weakened by the subsurface TMs, 9,10,32,[51][52][53]60 but the destabilization occurs with a similar magnitude. 44,51 For example, binding energies of CO and O 2 on a Pt-skin with subsurface Ru are -1.25 and -0.26 eV, respectively, compared to -1.82 eV/CO and -0.65 eV/O 2 on Pt(111).…”

Elemental Anisotropic Growth and Atomic-Scale Structure of Shape-Controlled Octahedral Pt–Ni–Co Alloy Nanocatalysts

“…Oxygen reduction electrocatalysts are known to play a crucial role on fuel cells performance, being the fundamental studies on the subject still required to overcome these barriers 3,4 . By alloying Pt with other non-noble metals, it is possible to produce cheaper electrocatalysts with novel properties for the oxygen reduction reaction (ORR) due to lattice compression 5,6 and/or modified electronic properties 7,8 . Thus, several studies have shown that binary Pt-M (M=Cr, Mn, Fe, Co, Ni, Cu, V, Ti) nanocrystals (NCs) greatly enhanced the kinetics of the ORR in comparison with standard Pt catalysts [9][10][11] .…”