Effect of Hydrophobic Cations on the Inhibitors for the Oxygen Reduction Reaction on Anions and Ionomers Adsorbed on Single-Crystal Pt Electrodes.

Weakening of the poisoning by the specifically adsorbed anions assists in developing next-generation electrocatalysts for use in low-temperature fuel cells. In this study, we evaluated how hydrophobic cations with different alkyl chain lengths affect the oxygen reduction reaction (ORR) activities on the single-crystal Pt surfaces in contact with sulfuric acid solution and Nafion ionomers. Interfacial tetraalkylammonium cations with longer alkyl chains activated the ORR on the Pt(111) surface. In a solution containing tetrahexylammonium cations (THA+), the ORR activities on Pt(111) in sulfuric acid solution and on Nafion-modified Pt(111) in perchloric acid solution were four and eight times higher than those in the solutions without THA+, respectively. Infrared spectroscopy revealed the reduction of the amount of (bi)sulfate anions and the sulfonate group of Nafion adsorbed on Pt(111) due to the presence of THA+. The hydrophobic cations weaken the noncovalent interactions between specifically adsorbed species and promote the ORR.