Article Highlight | 11-Dec-2025

Regulating water transport paths on porous transport layer by hydrophilic patterning for highly efficient unitized regenerative fuel cells

Shanghai Jiao Tong University Journal Center

Regulating Water Transport Paths on Porous Transport Layer by Hydrophilic Patterning for Highly Efficient Unitized Regenerative Fuel Cells

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  • Novel amphiphilic patterned titanium porous transport layers (PTLs) significantly enhance the round-trip efficiency of unitized regenerative fuel cells (URFCs), achieving an impressive round-trip efficiency of 25.7% at a current density of 2 A cm-2.
  • The serpentine configuration of the patterned PTL excels in both fuel cell (FC) and water electrolyzer modes, resulting in a sevenfold increase in current density in FC mode compared to URFCs using hydrophilic pristine Ti PTLs.
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Credit: Sung Min Lee, Keun Hwan Oh, Hwan Yeop Jeong, Duk Man Yu*, Tae-Ho Kim*.

Unitized regenerative fuel cells (URFCs) promise compact, long-duration storage for renewables, yet their round-trip efficiency (RTE) is throttled by a single-component dilemma: the porous transport layer (PTL) must feed water in electrolyzer mode and expel it in fuel-cell mode. Now, a Korea Research Institute of Chemical Technology (KRICT) team led by Prof. Duk Man Yu and Prof. Tae-Ho Kim shows that UV-ozone-patterned amphiphilic Ti PTLs solve this conflict, lifting RTE to a record 25.7 % at 2 A cm-2—a 7× current-density jump in fuel-cell mode versus hydrophilic pristine Ti.

Why This Design Matters

  • Water-Path Engineering: 1 mm-wide hydrophilic serpentine channels are perfectly aligned with the bipolar-plate flow field, delivering water straight to the catalyst layer in WE mode while draining product water away in FC mode.
  • Gas-Path Protection: Hydrophobic inter-channel regions keep O₂ paths open, eliminating flooding that crashed the pristine Ti PTL at only 0.28 A cm-2.
  • Scalable Lithography-Free Patterning: 2 h UV/ozone exposure through a quartz-chrome mask after FDDTS silanization yields roll-to-roll-compatible 220 µm-deep wettability patterns (27° vs 126° contact angle).
  • Catalyst-Light: 1.3 mg cm-2 total loading (0.7 mg Ir + 0.3 mg Pt) operates on air feed—no pure O2 required.

Performance & Durability

  • WE mode: 5.82 A cm-2 @ 1.94 V, mass-transfer resistance 3.25 mΩ cm2 (identical to fully hydrophilic Ti).
  • FC mode: 0.87 W cm-2 peak power, 2 A cm-2 @ 0.43 V.
  • 280 h continuous cycling (80 °C, ambient pressure):
    – WE degradation +96 µV h-1 (slight improvement via Ir-ECSA recovery)
    – FC degradation –211 µV h-1 (27 % Pt-ECSA loss, no membrane or PTL damage).
  • Radical test (90 °C, 30 % RH OCV 100 h): fluorine gradient across channels unchanged, validating pattern stability.

Mechanism & Simulation

GeoDict 3-D two-phase flow confirms:

  • Through-plane water velocity in hydrophilic channels (18.7 µm s-1) is 5× that of hydrophobic regions, suppressing saturation under 7 kPa capillary pressure.
  • In-plane O2 diffusivity remains high because gases bypass liquid-filled hydrophilic lines through adjacent hydrophobic pores, cutting mass-transport loss to 18 mΩ cm2 (vs 370 mΩ cm2 for un-patterned).

Challenges & Outlook

Catalyst dissolution during WE→FC mode switching still dominates long-term fade; the group is now exploring pulse-shaped potential protocols and Pt-Ir gradient electrodes to lock platinum oxides. Meanwhile, the serpentine-patterned Ti PTL is being scaled to 100 cm2 single-cell stacks with a target RTE >30 % at 3 A cm-2.

This work delivers a low-cost, corrosion-tolerant water-management platform that uncouples URFC performance trade-offs and brings reversible fuel cells closer to practical renewable-energy storage.

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