Characterization of doping atoms (Ta, Nb) in advanced PEM fuel cell supports and catalysts as well as of the surface-solvent interaction of laser-generated Pt nanoparticles : A XAFS study
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Bibliographic record
Abstract
PEM fuel cells are an interesting energy source for mobile applications. Efforts to improve their weaknesses cost, performance, and durability include improving the catalysts’ supports. Encouraging approaches are C-TiO<sub>2</sub> hybrid and core-shell supports whereas titanium dioxide is commonly doped to increase its electric conductivity.<br /> In this thesis I studied the impact of Ta-/Nb- co-doping on a TiO<sub>2</sub> nano-support, C-TiO<sub>2</sub> hybrid/core-shell supports made by adding two kinds of carbon black and a Pt-TiO<sub>2</sub> catalyst-support unit. XANES results show that both dopants replaced Ti atoms and are statistically distributed in their respective TiO<sub>2</sub> host structure (which is either predominantly rutile or anatase). There is also evidence of interaction between these dopants and both the carbon supports as well as Pt catalyst, most likely via bridging oxygen atoms. EXAFS analysis reveals that Nb incorporation did distort the TiO<sub>2</sub> host structure of at least one sample to a greater extent compared to Ta incorporation. The core-shell support displays the highest degree of disorder and smallest particle size, which is most likely correlated.<br /> Reduction/oxidation experiments show that Pt atoms in PtPd nano-catalysts supported on C-TiO<sub>2</sub> hybrid nano-supports have a low affinity for oxidation and are easily reduced.<br /> Pulsed laser ablation in liquid (PLAL) has proven its usefulness as a nanoparticle (NP) synthesis method alternative to traditional chemical reduction methods.<br /> Additive-free Pt NPs were synthesized by PLAL and their interaction characterized in situ with H<sub>2</sub>O, a sodium phosphate buffer and sodium citrate as well as a TiO<sub>2</sub> support. XANES results indicate that the respective NP-solvent interaction varies in strength. The ions added ex situ diffuse through the particles’ electric double layer and interact electrostatically with the Stern plane. Consequently, these ions weaken the interaction of the functional OH-groups which are bound to the partially oxidized platinum surfaces and cause their partial reduction. Comparing XANES/EXAFS spectra of laser-generated with wet-chemically synthesized Pt NPs indicate different types of Pt-O bonds: a Pt(IV)O<sub>2</sub>-type in case of wet-chemical and a Pt(II)O-type in case of laser-generated NPs. A comparison of unsupported laser-generated platinum NPs in H<sub>2</sub>O with TiO<sub>2</sub>-supported ones shows no whiteline intensity differences and also an identical number of Pt-O bonds in both cases. This suggests that in the deposition process at least part of the double layer coating stays intact and that the ligand-free particle properties are preserved.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it