Reaction Mechanism for Oxygen Reduction on Platinum: Existence of a Fast Initial Chemical Step and a Soluble Species Different from H₂O₂

Abstract

The oxygen reduction reaction (ORR) on platinum in perchloric acid is studied under transient conditions at stationary and non-stationary electrodes. Only under these conditions, the presence of a fast initial chemical step in the mechanism, giving rise to a soluble, short-lived intermediate proposed to be the HO 2 * radical, is revealed, by comparing experimental and calculated curves by numerical simulations of simple reaction schemes. The formation of this species and the existence of a zero-current cycle involving it would be the main reasons for the lack of reduction currents at potentials higher than the ORR reaction onset. Additionally, regardless of the exact subsequent steps after the initial chemical reaction, if HO 2 * is generated it would disproportionate to hydrogen peroxide, which implies that both species would be always produced during the ORR on Pt. The presence of HO 2 * and H 2 O 2 would profoundly affect the durability of Pt-based catalysts and should be taken into account in the design of materials for fuel cell cathodes.

Recent Advances in Bio‐Templated Metallic Nanomaterial Synthesis and Electrocatalytic Applications

“…As a promising technology to solve the energy crisis, proton exchange membrane fuel cells (PEMFCs) transform chemical energy into electricity through electrochemical reactions at the cathode and anode [173,174] . However, due to the sluggish kinetics of the ORR at the cathode, fuel cells face a critical barrier to realize large scale commercialization [175,176] . In principle, ORR can occur under both acidic and alkaline conditions.…”

Structure effects on electrocatalysts. Oxygen reduction on Te-modified Pt(111) surfaces: Site-blocking vs electronic effects

“…This fact holds true even at low Te-coverages θ Te ≈ 0.05 or after holding the potential by several minutes at 0.9 < E < 1.15 V, a procedure that has been reported to increase the magnitude of the ORR peak at 0.85 V on both Pt(111) and (poly)Pt stationary electrodes. 50,56 Thus, it would be possible that, instead of a simple site-blocking effect, a part of ORR reduction currents comes from a catalysis of the ORR by the redox cycle of Te adatoms on the surface, as suggested to occur in the case of Tl adlayers on Au(111) electrodes. 35,36 In this case, the decrease in the ORR activity at high potentials at increasing θ Te , as evidenced in Figs.…”

“…The term −βn ′ F/ RT was considered to be 59 mV, i.e., the predicted theoretical value by employing an integer number (2) to give a Tafel slope close to the experimental value (66 mV); (ii) a negligible coverage of ORR reactive intermediates, as is usually reported for the ORR on Pt surfaces. 8,42,56,57 (iii) Also, x and r ads are independent of θ Te , although they depend on the O 2 -flux.…”

Electrocatalytic Behavior of PtCu Clusters Produced by Nanoparticle Beam Deposition

“…Platinum represents the material of choice for many electrocatalytic reactions, including the oxygen reduction reaction (ORR), 1 methanol oxidation reaction (MOR), 2 and the hydrogen evolution reaction (HER), 3 which lie at the core of energy conversion devices such as fuel cells and electrolyzers. However, the high cost and supply risks associated with Pt have been an obstacle to the widespread adoption of such green technologies and so substantial efforts have focused on developing catalysts with reduced Pt-content.…”