Oxygen reduction on nanocrystalline ruthenia – local structure effects

Abstract

Nanocrystalline ruthenium dioxide and doped ruthenia of the composition Ru1−xMxO2 (M = Co, Ni, Zn) with 0 ≤ x ≤ 0.2 were prepared by the spray-freezing freeze-drying technique.

Towards identifying the active sites on RuO2(110) in catalyzing oxygen evolution

“…S6, ESI †), which explicitly shows that the bridge Ru site is filled prior to the CUS site, in accordance with previous surface science [26][27][28]30 and DFT results. 36,45 Further evidence for this surface structure fitted from CTR measurements at 0.5 V RHE ( Fig. 2D and Fig.…”

“…Previous CTR measurements of RuO 2 (110) in base 38 have reported the filling of the CUS Ru sites at B0.8 V RHE , while the bridge site is unfilled. 38 However, such findings are contradictory to surface science [26][27][28]30 and DFT studies, 36,45 Fig. S1, ESI †).…”

“…DFT calculations show that Ru CUS sites on RuO 2 (110) are filled with -OH at B0.6 V RHE while hydroxylated bridge Ru sites become deprotonated at B1.0 V RHE . 45 On the other hand, experimentally, RuO 2 (110) exhibits redox reactions at B1.0 and B1.3 V RHE in base 5,46,47 and B0.7, B1.1 and B1.4 V RHE in acid prior to the OER, 48 which can be attributed to successive deprotonation/oxidation of adsorbates bound to Ru sites. [17][18][19] In addition, adsorption of -OH and -O at the Ir CUS site based on the DFT results occurs at B0.9 and B1.3 V RHE , which correlates well with the first redox transition at 0.9 V RHE , but differs significantly from the second redox transition at 1.5 V RHE .…”

Rationality in the new oxygen evolution catalyst development

“…[17] The Ir-Ir bonding distance was, however, replaced by a ratio of the crystallographic unit cell parameters c/a. Although this approach has a certain potential for the catalysts with rutile structure [15,68] it's general applicability is questionable since the trends in c/a parameter reflect rather the clustering of the dopant [14,[68][69][70] in the rutile structure than the actual change of the binding energetics of the active sites.…”

“…1). Figure. 1 Schematic drawing of the dependence of a O-O bridge in the metal-metal distance of a rutile type catalyst as a function of the c/a parameter, adapted from [69]. The metal-metal distance is a parameter that can easily be measured using XRD or, to better account for distortions within the material, using XAS (x-ray absorption spectroscopy).…”