Rare-earth-regulated Ru-O interaction within the pyrochlore ruthenate for electrocatalytic oxygen evolution in acidic media

Abstract

Ruthenium-based catalyst is one of the most active catalysts for oxygen evolution reaction (OER) in acid media. However, the strong bonding between the Ru sites and oxygen intermediates leads to high overpotential to trigger the OER process. Hence, pyrochlore rare-earth ruthenate (RE 2-Ru 2 O 7) structures with a series of rare-earth elements (Nd, Sm, Gd, Er, and Yb) were constructed to tune the electronic structure of the Ru sites. Surface structure analysis indicated that the increase of the radius of the rare-earth cations resulted in higher content of defective oxygen (the percentage of the defective oxygen increased from 29.5% to 49.7%) in the RE 2 Ru 2 O 7 structure due to the weakened hybridization of the Ru-O bond. This reduced the valence states of the Ru sites and enlarged the gap between the 4d band center and the Fermi level (E F) of Ru, resulting in the weakened adsorption of oxygen intermediates and the improved OER performance in acid media. Among the as-prepared ruthenium pyrochlores, Nd 2 Ru 2 O 7 displayed the lowest OER onset overpotential (210 mV) and Tafel slope (58.48 mV dec −1), as well as 30 times higher intrinsic activity and much higher durability than the state-of-art RuO 2 catalyst.

An indium-induced-synthesis In0.17Ru0.83O2 nanoribbon as highly active electrocatalyst for oxygen evolution in acidic media at high current densities above 400 mA cm−2

“…S11†). What is even more remarkable is that among the most recent ruthenium-based acidic OER electrocatalysts reported in 2021 (Table 1), 44–49 In 0.17 Ru 0.83 O 2 -350 has the highest mass activity (1094.90 A g Ru −1 @ η = 300 mV) and the lowest Tafel slope of 32.62 mV dec −1 (Fig. 3b, S12 and Table S5†).…”

Mitigation of RuO6 octahedron distortion by enhanced A-site electronegativity in pyrochlore for acidic water oxidation

“…2c), the peaks with the binding energies from low to high are lattice oxygen (O L ), surface oxygen species (O sur ), oxygen vacancies (O V ) and adventitious species (O adv ). 29,38 Due to the lattice oxygen mechanism (LOM), the existence of more defective oxygen could accelerate the generation of O 2 through the capture of a lattice oxygen atom by the intermediate oxygen species, leading to the rapid dissolution of Ru atoms. In order to avoid this situation, much work has been done to prevent the generation of oxygen vacancies.…”

“…Herein, we rationally manipulate the substitution of the Asite atoms in Y 2 Ru 2 O 7 (YRO) by Ho 3+ , which has an identical ionic radius to Y 3+ but higher electronegativity (Y: 1.291 vs. Ho: 1.377, coordination number: CN ¼ 8; Table S1 †). 37,38 XRD pattern studies together with Rietveld renement were carried out to study the lattice structures of HRO and YRO, especially the bond angle and bond length for the RuO 6 octahedral distortion. Then, we combined the characterization and DFT theoretical calculations to understand how the A-site electronegativity affected the structure of the RuO 6 octahedron and further, the catalytic activity and stability.…”

Electrocatalytic acidic oxygen evolution reaction: From nanocrystals to single atoms

“…It exhibits 30 times more intrinsic activity compared to benchmark RuO 2 . [ 78 ] A novel class of iridium electrocatalyst named as 12L‐perovskites (Ba 4 MIr 3 O 12 ; M = Pr, Bi, Nb) was developed for electrocatalytic water oxidation in acidic media. 12L‐perovskites were comprised of a unique subunit of trinuclear face shared IrO 6 octahedral strings presented in Figure 3D.…”