Effect of hydrophobic cations on the oxygen reduction reaction on single‒crystal platinum electrodes

Abstract

Highly active catalysts for the oxygen reduction reaction are essential for the widespread and economically viable use of polymer electrolyte fuel cells. Here we report the oxygen reduction reaction activities of single‒crystal platinum electrodes in acidic solutions containing tetraalkylammonium cations with different alkyl chain lengths. The high hydrophobicity of a tetraalkylammonium cation with a longer alkyl chain enhances the oxygen reduction reaction activity. The activity on Pt(111) in the presence of tetra‒n‒hexylammonium cation is eight times as high as that without this cation, which is comparable to the activities on Pt3Co(111) and Pt3Ni(111) electrodes. Hydrophobic cations and their hydration shells destabilize the adsorbed hydroxide and adsorbed water. The hydrophobic characteristics of non‒specifically adsorbed cations can prevent the adsorption of poisoning species on the platinum electrode and form a highly efficient interface for the oxygen reduction reaction.

Revealing the nature of active sites in electrocatalysis

“…7 In situ experimental and computational studies concur that catalytic activities are dictated by the nature of the active sites, which strongly depends on the materials' composition [13][14][15][16][17][18][19][20][21][22] and surface structure, [23][24][25][26] and the electrolyte composition. [27][28][29][30][31] In this perspective, we analyze several fundamental issues related to the elucidation of the electrocatalysts' active centers and factors that modify their catalytic efficiency. Firstly, aspects related to the electronic structure of the active sites are briey discussed; then the role of surface defects is considered, as it is pertinent to ask if surface defects are the only sites able to catalyze electrochemical reactions.…”

Advances and challenges for experiment and theory for multi-electron multi-proton transfer at electrified solid–liquid interfaces

“…13B shows the potential dependence of the charge density of Pt surface oxidation estimated from cyclic voltammetry studies and the band intensity of Pt-OH. 221 The onset potential of OH adsorption shifts positively and the band intensity of Pt-OH decreases due to the presence of THA + . These results are consistent with the charge density of Pt surface oxidation and suggests that THA + has some effects of destabilizing and decreasing OH ad on the Pt(111) surface.…”

“…In addition to the above cations based on the alkaline metals, recent studies showed that organic cations, i.e., quaternary ammonium cations with long alkyl chains, enhanced the ORR activity of Pt. 220,221 The ORR activity of Pt (111) in HClO 4 containing tetrahexylammonium cation (THA + ) at 0.9 V is eight times higher than that without this organic cation. Fig.…”

“…However, it is important to note that . The complexity of model solid/liquid systems increase from Level 2 (alloying, doping, nanostructuring, or other modifications), Level 3 (addition of interfacial promotors on electrode surfaces and/or in electrolyte), 221,[440][441][442][443][444] to Level 4. [445][446][447][448][449][450][451][452][453] VESTA was used to prepare several structure images in the panel A.…”

Caffeinated Interfaces Enhance Alkaline Hydrogen Electrocatalysis

“…In alkaline HER/HOR, cation effects provide a simple demonstration of this approach 7,24,25 . More nuanced effects can be realized with ionic liquid electrolytes in the carbon dioxide reduction reaction (CO2RR) and oxygen reduction reaction (ORR) [26][27][28] . These and other examples have recognized that the electrolyte, in addition to the electrode, provides opportunities to direct chemical transformations.…”