The Non-Monotonic Surface Charging Behavior of Platinum: Implications for Electrocatalysis in PEFC
Bibliographic record
Abstract
In electrochemical systems, metal surface charging phenomena dictate the strength of electrostatic interactions between the electrified electrode and ions in solution. Historically, the potential of zero charge (pzc) of the metal has been employed to parameterize the surface charging relation [1][2]. However, for a Pt electrode, classical radiotracer experiments of Frumkin and Petrii revealed a non-monotonic charging behavior upon increasing the metal phase potential, with consecutive transitions from a negative to a positive surface charging region and further to another negative surface charging region [3]. Garcia-Araez et al. later reported a similar ‘negative-positive-negative’ charging relation derived from laser-pulsed experiments [4]. This alternating charging behavior defies the role of the pzc as a sufficient descriptor of electrode charging phenomena. The situation calls for an overhaul of the charging relation that must be derived from first principles. This study presents a refined structural model for electrified interfaces, as shown on the left side of Figure 1. The model accounts explicitly for charging effects caused by the formation of a surface oxide layer and a layer of oriented water molecules. An analytical expression for the charging relation is derived. The charging relation is parameterized using experimental data for a Pt surface as well as DFT calculations. It exhibits the three different charging regions observed in the experiments cited above. To illustrate the impact of the modified charging relation, it is employed to study the oxygen reduction reaction in nanoporous electrodes of polymer electrolyte fuel cells. References [1]. Frumkin, A.; Gorodetzkaya A. Z. Phys. Chem. 1928, 136, 451. [2]. Petrii, O. A. Zero charge potentials of platinum metals and electron work functions (Review). Russ. J. Electrochem. 2013, 49, 401. [3]. Frumkin, A. N.; Petrii, O. A. Potentials of zero total and zero free charge of platinum group metals. Electrochim. Acta. 1975, 20, 347. [4]. Garcia-Araez, N.; Climent, V.; Feliu, J. Potential-dependent water orientation on Pt (111), Pt (100), and Pt (110), as inferred from laser-pulsed experiments. Electrostatic and chemical effects. J. Phys. Chem. C. 2009, 113, 9290. Figure 1
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| 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 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.000 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".