Molecular Control of Heterogeneous Electrocatalysis through Graphite Conjugation
Bibliographic record
Abstract
Conspectus The efficient interconversion of electrical and chemical energy requires catalysts capable of accelerating multielectron reactions at or near electrified interfaces. These reactions can be performed at metallic surface sites on heterogeneous electrocatalysts or through redox mediation at molecular electrocatalysts. The relative ease of synthesis and characterization for homogeneous catalysts has allowed for molecular-level control over the active site and permitted systematic tuning of activity and selectivity. Similar control is difficult to achieve with heterogeneous electrocatalysts, because they typically exhibit a distribution of active site geometries and local electronic structures, which are challenging to modify with molecular precision. However, metallic heterogeneous electrocatalysts benefit from a continuum of electronic states that distribute the redox burden of multielectron transformations, enabling more efficient catalysis. We envisioned that we could combine the attractive properties of molecular and heterogeneous catalysts by integrating tunable molecular active sites into the delocalized band states of a conductive solid. The Surendranath group has developed a class of electrocatalysts in which molecules are strongly electronically coupled to graphitic electrodes through a conductive, aromatic pyrazine linkage such that they behave like metallic surface active sites. In this Account, we discuss the dual role of these graphite-conjugated catalysts (GCCs) as a platform with which to answer molecular-level questions of metallic active sites and as a tool with which to fundamentally alter the mechanism and enhance the performance of molecular active sites. We begin by describing the electrochemical and spectroscopic studies that demonstrated that GCC sites behave like metallic active sites rather than simply as redox mediators attached to electrode surfaces. We then discuss how electrochemical studies of a series of graphite-conjugated acids enabled the construction of a molecular model for the thermochemistry of proton-coupled electron transfer reactions at GCC sites based on the p K a of the molecular analogue of the conjugated site and the potential of zero free charge of the electrode. In the final section, we discuss the effects of graphite conjugation on the mechanism and rate of oxygen reduction, hydrogen evolution, and carbon dioxide reduction catalysis across four different GCC platforms involving N-heterocycle, organometallic, and metalloporphyrin active sites. We discuss how molecular-level tuning at graphite-conjugated active sites directly correlates to changes in catalytic activity for the oxygen reduction reaction. We demonstrate that graphite-conjugated porphyrins show enhanced catalytic oxygen reduction activity over amide-linked porphyrins. Lastly, we describe how catalysis at graphite-conjugated sites proceeds through mechanisms involving concerted electron transfer and substrate activation, in stark contrast to the mechanisms observed for molecular analogues. Overall, we showcase how GCCs provide a rich platform for controlling heterogeneous catalysis at the molecular level.
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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".