Studies of the Oxygen Reduction Reaction of Pt Single Crystals Alloys in Alkaline Media

Abstract

Understanding the factors controlling trends in activity for electrocatalytic oxygen reduction is of fundamental interest; as this reaction is paramount for future energy conversion schemes.1 Recently, numerous reports have suggested significant divergences between catalytic performances of noble metal surfaces for this reaction in acidic and basic electrolyte.2 Prior work3 by us have elucidated the Sabatier volcano for the oxygen reduction reaction in 0.1 M HClO4 using the Cu/Pt(111) near-surface alloy system. In the present work the surface binding of *OH reaction intermediates were weakened by ligand effects introduced by varying subsurface Cu coverage in Pt(111). Thus, we related the observed oxygen electroreduction activities to the shifts in OH adsorption potentials, derived from the base cyclic voltammograms, in both acidic3 and alkaline media. Remarkably, similar trend persists between *OH binding shifts and Cu/Pt(111) oxygen reduction activities relative to pure Pt(111); this being independent of the electrolyte going from acid to alkaline. Notably, Cu/Pt(111) near-surface alloy surfaces in 0.1 M NaOH or KOH, while exhibiting similar trend in relative activity independent of electrolyte, exhibits a substantial ~2- and <4.5-fold improvement in activity compared to when in 0.1 M HClO4, respectively. This suggests a fundamental effect of changing the cation present in the electrolyte. Moreover, by optimizing the Cu subsurface content a substantial activity enhancement is observed, which in 0.1 M KOH results in exceptionally high specific activities on the order of 101±8 mA/cm2 at 0.9 V vs. the reversible hydrogen electrode. Hence, our results confirm that *OH binding energies governs the activity in both acid and alkaline media i.e. a Sabatier volcano relationship persist in alkaline media. Furthermore, our results open up discussions of relevant aspects describing the cation interplay with the catalyst surface. A. Kongkanand and M. F. Mathias, J. Phys. Chem. Lett., 7, 1127–1137 (2016).J. Staszak-Jirkovský et al., ACS Catal., 5, 6600–6607 (2015).I. E. L. Stephens et al., J. Am. Chem. Soc., 133, 5485–5491 (2011).