Importance of Interatomic Spacing in Catalytic Reduction of Oxygen in Phosphoric Acid

Abstract

_~TRQpUCTIONGeneral trends between geometricalelectronic properties and electrocatalyst activity have been the subject of many papers and review articles (1-4). In fact, much of the interest may be traced to the "volcano relationship" between the logarithm of the reaction rate and the free energy of adsorption,/kG~d ~, derived from electrochemical ~rInciples for the hydrogen evolution reaction (5,6). Assuming that/kS d remains constant, many workers hav~ ~bserved the "volcano type" behavior between the logarithm of the reaction rate and various quantities which may be rationalized to be proportional to/kH ~ . This assumption should . s * Electrochemacal Society Active Member.

Increased valence theory and the four electron reduction of O2 to H2O

“…If the O2 molecule interacts with only one metal atom (end-on or side-on adsorption), then (at least initially) H,O, is produced (Au); if the O2 molecule is adsorbed at two metal atoms (bridge adsorption), direct 4e -reduction to H,O becomes possible (Pt). This model is corroborated by recent observations, such as the role of interatomic Pt-Pt spacing [5] and the effect of underpotential deposited layers (UPD) of Pb [6], Tl [7] or Bi [8] on Au. In the first case, by alloying pure Pt with foreign metals, an optimum Pt-Pt distance for bridge adsorption of the O2 was obtained; in the second case, the presence of an adsorbed foreign metal on an Au single crystal surface resulted in the direct reduction of 0, to H,O, contrary to the pure Au electrode, which yields H,O, exclusively.…”

Ordered alloy formation for Pt3Fe/C, PtFe/C and Pt5.75Fe5.75Cuy/CO2-reduction electro-catalysts

“…Various Pt based alloys have been explored for decades with the goal to achieve high orr activities [2][3][4][5][6][7][8][9][10][11]. Other catalyst architectures referred to as core-shell, surface strained and Pt enriched catalysts have also been suggested [6,7,[12][13][14][15][16][17].…”

Catalyst, Membrane, Free Electrolyte Challenges, and Pathways to Resolutions in High Temperature Polymer Electrolyte Membrane Fuel Cells

“…Cell performance was highest for the lowest Pt loaded alloys with a gain of 120 mV at 200 mA/mg Pt at 180 • C. This is not surprising considering the lower values of the Pt-Pt interatomic spacing and lattice parameters observed for those alloys. As discussed by Jalan and Taylor [111] and later corroborated by Kim et al [112] (who utilized their own acid leaching process as well as potential excursion techniques outlined by Gottesfeld and associates [113,114] to roughen the alloy catalyst surface) and Min et al [107], lower interatomic spacing generally trends towards higher specific activity (see Figure 1).…”