A Microfluidic Electrochemical Cell with Integrated Palladium Hydride Reference Electrode
Bibliographic record
Abstract
Microfluidic devices have potential to be a great addition to the aqueous electrochemistry toolbox, for instance as an analog to the rotating ring-disk electrode, with an enhanced control of mass transport due to laminar flow. The photolithography process makes fabrication of various cell designs relatively fast, and it is possible to make electrodes of many different materials, including electrocatalyst particles. While the restricted volume of a microchannel provides excellent mass transport control, it introduces a very high solution resistance. This will create a significant shift in solution potential in the channel even at moderate currents, and makes the measurement of electrode potentials in the microchannel a challenge. In order to accurately measure potentials of electrodes in a microfluidic cell it is essential to characterize and minimize the effects of this potential distribution. Using a traditional reference electrode, and placing it in an outlet chamber essentially maximizes the uncompensated solution resistance, due to the necessity of having the counter electrode downstream of the working electrode. To solve the problems with the potential distribution, we fabricated a microfluidic electrochemical cell with an integrated palladium hydride reference electrode in a side channel upstream of the working electrode. A schematic of a cell is shown in Figure 1a. The cell design is relatively simple, and does not require salt bridges or ion conducting membranes in the cell to provide electrical contact to the reference electrode. This configuration results in low uncompensated resistance for single electrode experiments, and minimizes it for multiple electrode experiments. The placement of the reference electrode in a stagnant side channel eliminates influence of the species in the main channel on the reference electrode potential. Using PdH as the reference electrode makes the use of a wide range of acid and buffered electrolytes possible, and the presence of unfavorable ions such as chlorine can be eliminated. The reference electrode was charged in situ from a thin-film palladium electrode, and was able to hold a stable potential for up to eight hours of experiments. The relationship between the potential shift at one electrode, the cell geometry, and current through electrodes located upstream was probed using the half-wave potential of Ru(bpy)3 3+ oxidation and oxygen evolution as model reactions. Figure 1b shows how the potential for oxidation of Ru(bpy)3 3+ shifts at the SE at different anodic currents through the WE. This is the best case scenario for a cell with 100 µm wide electrodes and a 100 µm gap between the electrodes. If we allow for potential shifts up to 5 mV at the SE, the maximum current at the WE becomes 4 µA, using a 0.1 M Na2SO4 supporting electrolyte. 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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".