Adsorbed cobalt porphyrins act like metal surfaces in electrocatalysis
Bibliographic record
Abstract
Abstract Carbon electrodes chemically modified with molecular active sites are potent catalysts for key energy conversion reactions. Generally, it is assumed that these molecularly modified electrodes operate by the same redox mediation mechanisms observed for soluble molecules, in which electron transfer and substrate activation occur in separate elementary steps. Here, we uncover that, depending on the solvent, carbon-bound cobalt porphyrin can carry out electrolysis by the non-mediated mechanisms of metal surfaces in which electron transfer and substrate activation are concerted. We chemically modify glassy carbon electrodes with cobalt tetraphenylporphyrin units that are anchored by flexible aliphatic linkages to form CH-CoTPP. In acetonitrile, CH-CoTPP displays a clear outer-sphere Co(II/I) process which catalyzes the H2 evolution reaction by a step-wise, redox-mediated reaction sequence. In contrast, clear surface redox waves are not observed for CH-CoTPP in aqueous media and H2 evolution proceeds via a non-mediated, concerted proton-electron transfer reaction sequence over a wide pH range. The data suggest that, in aqueous electrolyte, the CoTPP fragments reside inside the electrochemical double layer and are electrostatically coupled to the surface. This coupling allows CH-CoTPP to carry out catalysis without being pinned to the redox potential of the molecular fragment. These studies highlight that the simple adsorption of molecules can lead to reaction mechanisms typically reserved for metal surfaces, ex-posing new principles for the design of molecularly-modified electrodes.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 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".