Structural and Electronic Transformations of Pt/C, Pd@Pt(1 ML)/C and Pd@Pt(2 ML)/C Cathode Catalysts in Polymer Electrolyte Fuel Cells during Potential-step Operating Processes Characterized by In-situ Time-resolved XAFS

Inhibitive effect of Pt on Pd-hydride formation of Pd@Pt core-shell electrocatalysts: An in situ EXAFS and XRD study

“…It is well established that Pt is a better HER catalyst than Pd and the onset potential for the HER is at more positive potentials for the Pt/C reference catalyst as seen in Fig. 4b, in agreement with Trasatti's original measurements [46] and the DFT calculations of Norskov et al [47] A study of the kinetics of H abs /hydride formation at the Pd@Pt catalyst electrodes using in situ time resolved EXAFS or XRD, such as those recently reported by Iwasawa's group for oxide formation at Pd@Pt catalysts [48] would be required to provide further comparison to this aspect of the thin film study by Bartlett and Marwan [45].…”

Simultaneous Operando Time-Resolved XAFS–XRD Measurements of a Pt/C Cathode Catalyst in Polymer Electrolyte Fuel Cell under Transient Potential Operations

“…The Pt metallic nanoparticles with 2.6 ± 0.9 nm dimension are regarded to constitute approximately 5 Pt layers, assuming sphere structures with the fcc arrangement . At 1.4 V RHE , the CN­(Pt–Pt) and CN­(Pt–O) were determined to be 5.3 ± 1.0 and 2.2 ± 0.5, respectively (Table S1), which are well reproduced by the values 5.7 (eq S2) and 2.4 (eq S3), respectively simulated by assuming the formation of a surface tetragonal Pt 2+ O phase layer. , The potential dependent surface structures at 0.4 and 1.4 V RHE are illustrated in Figure S2a,b, respectively.…”

“…The averaged change amounts of the fast and slow parts in the time profiles of the Pt charging, Pt–O bond formation, Pt–Pt bond dissociation and Pt metallic-phase size under the transient potential operation 0.4 V RHE → 1.4 V RHE were 47% and 53%, respectively as shown in Figure (inset). It suggests that the fast transformations proceed up to the nearly saturated oxygen coverage at the Pt surface, where CN­(Pt–O) for surface Pt–O bonds at saturation is regarded to be 2.0, similar to the previous reports . The Pt surface at 1.4 V RHE is fully covered by the tetragonal PtO layer with CN­(Pt–O) = 4 (Figure S2).…”

“…The MEA (3.0 × 3.3 cm, 0.6 mg-Pt/Ru cm −2 ; Pt, 2.6 ± 0.9 nm) used in this study was provided by Eiwa Co. Ltd., Japan. QXANES and QEXAFS spectra were analyzed in the similar way to the previous reports, 11,14,15 using the Larch code (v0.9.20a) containing the IFEFFIT Package (Athena and Artemis) (SI). The extracted k 3weighted Pt L III -edge EXAFS oscillations were Fourier transformed into R-space over k = 30−130 nm −1 , and the curve fittings were performed in the R-space (0.12−0.31 nm).…”

“…Time-resolved quick X-ray absorption fine structure (QXAFS) enables in situ element-selective investigation on the dynamic transformations of the local structures and oxidation states of Pt nanoparticles in Pt/C cathode catalysts under the PEFC operating conditions, − whereas time-resolved XRD enables in situ measurements of dynamic transformations of the long-period ordered crystalline structures of Pt electrocatalysts. − We have designed a combined system for simultaneous time-resolved measurements of QXAFS and XRD of MEA cathode catalysts. Here we report the first example of simultaneous operando time-resolved QXAFS–XRD measurements at each acquisition time of 20 ms to evidence the dynamic structural and electronic behavior of an MEA Pt/C cathode catalyst under the transient voltage cyclic operations 0.4 V → 1.4 V → 0.4 V (vs RHE).…”