Dopants fixation of Ruthenium for boosting acidic oxygen evolution stability and activity

Abstract

Designing highly durable and active electrocatalysts applied in polymer electrolyte membrane (PEM) electrolyzer for the oxygen evolution reaction remains a grand challenge due to the high dissolution of catalysts in acidic electrolyte. Hindering formation of oxygen vacancies by tuning the electronic structure of catalysts to improve the durability and activity in acidic electrolyte was theoretically effective but rarely reported. Herein we demonstrated rationally tuning electronic structure of RuO2 with introducing W and Er, which significantly increased oxygen vacancy formation energy. The representative W0.2Er0.1Ru0.7O2-δ required a super-low overpotential of 168 mV (10 mA cm−2) accompanied with a record stability of 500 h in acidic electrolyte. More remarkably, it could operate steadily for 120 h (100 mA cm−2) in PEM device. Density functional theory calculations revealed co-doping of W and Er tuned electronic structure of RuO2 by charge redistribution, which significantly prohibited formation of soluble Rux>4 and lowered adsorption energies for oxygen intermediates.

The Sabatier Principle in Electrocatalysis: Basics, Limitations, and Extensions

“…This value is roughly consistent with the experimental overpotential necessary to reach a current density of 10 mA/cm 2 , a benchmark for the solar-cell community (Suntivich et al, 2011b;Diaz-Morales et al, 2016;Seitz et al, 2016). However, some recent materials have overpotentials below 200 mV to sustain of 10 mA/cm 2 (Kim et al, 2017;Su et al, 2018;Retuerto et al, 2019;Hao et al, 2020), indicating that η TD is not necessarily a quantitatively accurate descriptor of electrocatalytic activity (Exner, 2021a). This discrepancy is most likely because the thermodynamic overpotential and the experimental overpotential have different definitions, and thus have no direct physical correlation: while η TD is a purely thermodynamic indicator of activity based on the free-energy landscape at equilibrium (zero overpotential), the experimental overpotential η must be evaluated at some non-zero current density, and is thus always influenced by the kinetics.…”

Boosting the Stability of RuO2 in the Acidic Oxygen Evolution Reaction by Tuning Oxygen‐Vacancy Formation Energies: A Viable Approach Beyond Noble‐Metal Catalysts?

“…Notably, the authors illustrate that the crystal structure of their synthesized electrode material is kept almost unchanged after the catalysis, except for Ru atoms with an oxidation state smaller than 4 which are oxidized to Ru 4+ . However, over‐oxidation of Ru to oxidation states exceeding 4 is not observed, indicating that increasing the oxygen‐vacancy formation energy is a promising strategy to counteract catalyst degradation under the harsh OER conditions [10] …”

“…In a recent article in Nature Communications, Hao et al apply this strategy to RuO 2 in the OER by co-doping W and Er into the RuO 2 lattice, synthesizing an electrode material with the structural formula W 0.2 Er 0.1 Ru 0.7 O 2-δ by a subsequent hydrothermal and calcination process. [10] Using density functional theory (DFT) calculations, the authors demonstrate that for a W 0.2 Er 0.1 Ru 0.7 O 2-δ (110) model electrocatalyst, the oxygen-vacancy formation energy is significantly enlarged compared to RuO 2 (110), indicating superior stability under OER conditions (cf. Figure 1a).…”

Novel engineering of ruthenium‐based electrocatalysts for acidic water oxidation: A mini review

“…The occurrence of V O could lead to the exposure of Ru atoms on the surface, which would be over‐oxidized to solvable Ru species with high valency >4. In order to increase the formation barrier of V O in RuO 2 higher than that of the redox H 2 O/O 2 , Zhang group firstly demonstrated W and Er co‐doping into RuO 2 could synergistically tune the Ru 4d and O 2p orbitals basing DOS from DFT 39 . Figure 4(A) suggested the O 2p band center ( ε p ) of W 0.2 Er 0.1 Ru 0.7 O 2−δ located at −4.12 eV while that of RuO 2 was −3.31 eV.…”

“…(F,G) The chronopotentiometry curves of W 0.2 Er 0.1 Ru 0.7 O 2−δ nanosheets in 0.5 M H 2 SO 4 and W 0.2 Er 0.1 Ru 0.7 O 2−δ as anodic side in acidic PEM, respectively. (A–G) Reproduced from Reference 39 with permission from Nature Publishing Group…”