<sup>1</sup>H–<sup>1</sup>H Double Quantum NMR Investigation of Proton Dynamics in Solid Acids
Bibliographic record
Abstract
Currently, the most popular proton exchange membrane (PEM) for fuel cell applications is Nafion. However, Nafion does not retain its high conductivity at high temperatures due to its dependence on water for proton transport. Because operational temperatures higher than the evaporation point of water are desirable, a family of solid acids was investigated. Cations known to transport protons were paired with anions to make acidic salts. Solid acids discussed here include imidazole paired with trifluoromethanesulfuric acid as well as imidazole, benzimidazole and adenine paired with methanesulfonic acid. Solid-state NMR was utilized to show the relative mobility of protons through double-quantum filter (DQF) experiments. The POST-C7 homonuclear dipolar-recoupling scheme was paired with DUMBO homonuclear decoupling to produce 1 H double-quantum coherence buildup curves for the hydrogen-bonded protons of interest. Experimental buildup curves, which reflect both local structure as well as dynamics, are compared to theoretical curves of the static system. The SPINEVOLUTION-simulated curves utilized up to eight pairs of homonuclear dipolar couplings within a sphere of 7 Å diameter centered on the proton of interest. Steep buildup of the DQ curve and maxima at short recoupling times in the buildup curves indicate strong dipole–dipole coupling and are interpreted to indicate limited dynamics of the H-bonded protons. In contrast, shallower buildup curves and maxima at longer recoupling times imply that H-bonded protons (in an otherwise similar structure) are associated with local mobility, which reduces their local dipolar coupling and may facilitate proton transport. Bulk proton conductivities measured via electrochemical impedance spectroscopy were compared to DQF measurements to understand proton conduction within these materials.
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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 | 0.000 |
| 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 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".