Fig. 3: Charge transfer between LSCF and PrO_x.

a Operando Pr M_4,5-edge XAS spectra of a single-phase PrO_x (80 nm) and an LSCF (100 nm) modified with 5 nm PrO_x thin film electrode measured under different applied biases at 700 °C and with an atmospheric oxygen pressure of 1 mbar. b Fraction of Pr³⁺ in LSCF modified with PrO_x and single-phase PrO_x electrodes calculated using the linear combination of reference spectra of Pr³⁺ and Pr^4+29. c The hole concentration in LSCF and the first 5 nm from the LSCF/PrO_x interface in PrO_x modified LSCF at various oxygen chemical potentials is calculated under the assumption that charge transfer impacts only the first 5 nm from the interface and is uniformly distributed within this region. The gray dashed line represents the change in the hole concentration after modification which is calculated from (b). d Current density versus electron hole concentration. The hole concentration of LSCF was calculated based on the defect chemistry model of LSCF bulk (as shown in Fig. S14a in SI), while the hole concentration of LSCF modified with PrO_x was calculated by equation (4).