Channel Diameter Effect of Porous Carbon Microparticles on PEMFC Performance for Highly Active Ultra-Low Pt Catalysts
Bibliographic record
Abstract
Proton exchange membrane fuel cells (PEMFCs) have received much attention as environmentally benign automotive power sources. PEMFCs can offer a large amount of electricity required for autonomous vehicles that battery-powered systems may not be able to provide. However, because PEMFC electrodes are based on expensive and scarce Pt catalysts, Pt minimization is necessary to expand the PEMFC market. To reduce Pt usage, various attempts have been made to increase the intrinsic activity of Pt catalysts, particularly at the cathode where the oxygen reduction reaction (ORR) occurs. Despite decades of progress, high ORR activity was typically reported in half-cell setups and frequently failed to show corresponding performance in single-cell. Catalysts with low Pt content perform poorly in the high-current density region because the thick catalyst layer limits mass transport. [1] In addition, low Pt loading catalysts typically suffer more in long-term operation. [2] As a result, it is critical to develop PEMFC catalysts with low Pt content that can facilitate mass transport while also exhibiting high durability. Herein, we report highly active and durable PtFe@C catalysts with ultra-low amounts of Pt (1 wt%) on channeled mesoporous carbon (CMC) particles. These CMC particles are designed to have continuous channels with open porosity and a large surface area, facilitating the mass transport behavior and maximizing cell performance. Block-copolymer particles (BCPs) with different molecular weights were used to fabricate CMC particles with pore diameters ranging from 13 to 63 nm. Two steps of pre-crosslinking and hyper-crosslinking were conducted prior to the carbonization step to preserve the porous internal structure of the BCP-based carbon support during high-temperature treatment. After depositing Pt onto the support by facile incipient wetness impregnation method followed by reduction, thin layers of carbon shell were observed to encapsulate the PtFe alloy nanoparticles. The channel diameter effect on the mass transport was studied in both half-cell and single-cell. Interestingly, from the cell performance obtained with varying channel diameters and different oxygen concentrations, we concluded that both reactant (proton and oxygen) supply and product (water) removal were greatly enhanced with larger channel size. With the largest channel diameter of 63 nm, initial mass activity in the single-cell was obtained to be 3.5 A mg Pt -1 , which is the highest value reported to date to the best of our knowledge. Cell performance under H 2 -air flow, which is the industrially relevant condition, surpassed the commercial 20 wt% Pt/C with only 1/20 of the Pt loading. The origin of enhanced cell performance upon enlarging the channel diameter was investigated by separating kinetic, ohmic (electronic and ionic charge transport), and mass transport overpotentials. Both the proton and oxygen transport resistance were confirmed to be reduced with larger channel size. Moreover, carbon shell protected Fe from getting leached out in an acidic environment, resulting in preserved catalyst structure and high durability. The outstanding performance of 51 kW/g Pt in H 2 /air condition after 30,000 cycles of accelerated degradation tests (ADTs) was observed. This work will open a new paradigm to develop PEMFC catalysts with much higher activity and durability while simultaneously minimizing Pt use. References [1] A. Kongkanand, M. F. Mathias, J . Phys. Chem. Lett. 2016 , 7 , 1127-1137. [2] R. Borup , A. Weber, Fuel Cell Performance and Durability Consortium, US DOE 2019 Annual Merit Review Proceedings, https://www.hydrogen.energy.gov/pdfs/review19/fc135_borup_2019_o.pdf (accessed: September 2021).
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 teacher head, 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".