Jaerim Kim, Hyeonjung Jung, Zhaoping Shi, Yong Wang, Jiantao Li, Eunji Shim, Hongmin An, Shuang Yang, Kyuwook Ihm, Sungsik Lee, Yoon Jun Son, Ke Xie, Michal Bajdich, Edward H. Sargent. “Stabilizing lattice oxygen in RuO₂ with high-valent 5d Re dopants for durable acidic water electrolysis.” ChemRxiv (). https://doi.org/10.26434/chemrxiv.15007618/v1

5d transition-metal-doped RuO₂ catalyst series and RuO₂ reference
O K-edge XAS Decreased t₂g peak intensity for the 5d transition-metal-doped RuO₂ catalysts compared with bare RuO₂
Main, p. 8; SI, p. 17
Re-RuO₂ catalyst and RuO₂ reference
HAADF-STEM (JEOL ARM200CF), Re-RuO₂ Nanoparticle morphology with around 10 nm diameter; atomically dispersed Re dopants in the RuO₂ lattice
EDS, Re-RuO₂ Uniform dispersion of Re dopants in the RuO₂ matrix; atomic composition: Re 10.16 at%, Ru 89.84 at%
High-resolution TEM (JEOL ARM200CF), lattice spacing Re-RuO₂: 0.35 nm, RuO₂ (110); RuO₂: 0.33 nm, RuO₂ (110)
Powder XRD (Cu Kα, λ = 1.5418 Å) Re-RuO₂ corresponded to the rutile structure without impurity phases; annotated reflections: (110), (101), (200), (211), (220), (002), (112), (310), (301), (202); the diffraction peaks, including (110), shifted toward lower 2θ relative to RuO₂; RuO₂ PDF#43-1027
Raman spectroscopy (532 nm) RuO₂: E₁g 523 cm⁻¹, A₁g 642 cm⁻¹, B₂g 710 cm⁻¹; Re-RuO₂: broadened and red-shifted vibrational modes
O K-edge XAS, excitations ~532 and ~535 eV, assigned to O 1s transitions to unoccupied O 2p–Ru 4d hybridized states of split t₂g and e_g; ~545 eV, assigned to O 1s transitions to Ru 5sp hybridized orbitals
O K-edge XAS, t₂g peak intensity Accompanying text: Re-RuO₂ 1.85, RuO₂ 2.10; plot annotation: Re-RuO₂ 1.87, RuO₂ 2.10
O K-edge XAS, I_t₂g/I_e_g and 10 Dq Re-RuO₂ showed smaller I_t₂g/I_e_g and 10 Dq values than RuO₂; 10 Dq plot annotations: Re-RuO₂ 2.82 eV, RuO₂ 2.97 eV; assigned Ru oxidation state n<4
XPS (Al Kα, 1486.6 eV), Ru 3p Re-RuO₂ peak shifted from 462.5 eV to 462.1 eV relative to RuO₂
XPS (Al Kα, 1486.6 eV), O 1s Lattice oxygen 529.3 eV, oxygen vacancy 531.2 eV, adsorbed water 533 eV; Re-RuO₂ lattice oxygen shifted to ~529.0 eV
XPS (Al Kα, 1486.6 eV), Re 4f, Re-RuO₂ Incorporated Re species in mixed-valence states
Re L-edge XANES, ReO₂ and Re₂O₇ references Estimated Re oxidation state in Re-RuO₂: accompanying text +5.54; plot annotation 5.536
Main, pp. 10–12; SI, pp. 3, 19–24, 27
Re-RuO₂ catalyst and RuO₂ reference under electrochemical conditions
DEMS (H₂¹⁸O-containing 0.5 M H₂SO₄, 1 mV s⁻¹) Re-RuO₂ showed a decreased ratio of ³⁴O₂ signal to ³⁶O₂ signal relative to RuO₂
Ru K-edge XANES (0.5 M H₂SO₄), applied-potential series Re-RuO₂ showed negligible change in oxidation states; RuO₂ showed increased white-line intensity and an edge shift toward higher energy with increasing potential. RuO₂ showed a rapid rise in Ru valence state with a white-line edge shift above 1.4 V; Re-RuO₂ maintained a nearly unchanged white-line edge position until 1.6 V, followed by a gentle shift at 1.8 V
Re L-edge XANES, Re-RuO₂, applied-potential series White-line intensity first increased from OCP to 1.2 V and then decreased above 1.4 V
CV (0–1.5 V vs. RHE), RuO₂ Redox peaks around 0.6 V, Ru³⁺/Ru⁴⁺; 1.2 V, Ru⁴⁺/Ru⁶⁺; and 1.4 V, Ru⁶⁺/Ru⁸⁺
CV (0–1.5 V vs. RHE), Re-RuO₂ Dominant Ru³⁺/Ru⁴⁺ peak compared with Ru⁴⁺/Ru⁶⁺ and Ru⁶⁺/Ru⁸⁺, indicating Ru oxidation state between 3+ and 4+; distinctly decreased Ru⁴⁺/Ru⁶⁺ peak area; disappearance of the Ru⁶⁺/Ru⁸⁺ peak