Stabilizing Highly Active Ru Sites by Suppressing Lattice Oxygen Participation in Acidic Water Oxidation

Abstract

In hydrogen production, the anodic oxygen evolution reaction (OER) limits the energy conversion efficiency and also impacts stability in proton-exchange membrane water electrolyzers. Widely used Ir-based catalysts suffer from insufficient activity, while more active Ru-based catalysts tend to dissolve under OER conditions. This has been associated with the participation of lattice oxygen (lattice oxygen oxidation mechanism (LOM)), which may lead to the collapse of the crystal structure and accelerate the leaching of active Ru species, leading to low operating stability. Here we develop Sr–Ru–Ir ternary oxide electrocatalysts that achieve high OER activity and stability in acidic electrolyte. The catalysts achieve an overpotential of 190 mV at 10 mA cm–2 and the overpotential remains below 225 mV following 1,500 h of operation. X-ray absorption spectroscopy and 18O isotope-labeled online mass spectroscopy studies reveal that the participation of lattice oxygen during OER was suppressed by interactions in the Ru–O–Ir local structure, offering a picture of how stability was improved. The electronic structure of active Ru sites was modulated by Sr and Ir, optimizing the binding energetics of OER oxo-intermediates.

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†).…”

Insight into Structural Evolution, Active Sites, and Stability of Heterogeneous Electrocatalysts

“…Note that LOER is al attice oxygen oxidation process involving direct O-O coupling and the formation of ahighly active oxyhydroxide surface layer, which is critical for the structural evolution triggered by electrode imbalance.I n addition to the activity,the regulation of surface evolution is demonstrated as an efficient approach to improve the durability of electrocatalysts. [15] DFT calculations on rutile Ru-based oxides indicated that doping of Sr and Ir could expand the Ru lattice and increase the disorder of catalysts, facilitating both the OER activity and stability of as-formed active species (Figure 1d,e). As expected, the optimized Sr 1.7 Ru 5 Ir 1 O 13.7 exhibited an extremely low overpotential at 10 mA cm À2 [h 10 = 190 mV vs.r eversible hydrogen electrode (RHE, all the following mentioned potentials are against RHE)] in acidic media.…”

Regulation of Electrocatalytic Activity by Local Microstructure: Focusing on the Catalytic Active Zone

“…Zhang and Wen prevented the collapse of the crystal structure of Ru-based catalysts by inhibiting the participation of lattice oxygen in the reaction, aiming to improve the stability of Ru-based catalysts. [14] The electronic structure of active Ru sites was modulated by Sr and Ir double modulation strategy, and the ratio of Sr to Ir was optimized according to DFT calculation to achieve the optimal activity and stability (Figure 7a). The prepared SrRuIr oxide catalyst showed an overpotential of only 223 mV at 10 mA cm À 2 for 1,500 h (Figure 7b and c).…”

“…The obtained SrRuIr oxide OER catalyst realized 1 A cm À 2 at ~1.5 V consistently over 150 h in PEM electrolyzer and exhibited an overpotential of only 223 mV after 1,500 h at 10 mA cm À 2 in three electrodes system. [14] This excellent performance was achieved due to the strong interaction among RuÀ OÀ Ir local structures, which stabilizing the Ru atom and preventing the dissolution of the catalyst. In addition, compared with IrO 2 catalyst, the SrRuIr oxide catalyst avoided the use of a large number of expensive Ir metals and reduced the cost of the catalyst, and this catalyst is expected to achieve further practical applications.…”

“…The wavelet transform of EXAFS (WT-EXAFS) spectra of f) Ru K-edge and g) Ir L 3 -edge of SrRuIr. Reproduced with permission from Ref [14]…”