Key Takeaways & Executive Findings
- •• 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. • UV/ozone patterning offers a low-cost and scalable method to create amphiphilic patterns on hydrophobic silanized Ti PTLs, enabling precise alignment with the bipolar plate flow field. • The serpentine-patterned Ti PTL effectively enhances oxygen removal in water electrolyzer mode and mitigates water flooding in fuel cell mode, ensuring uninterrupted water and gas flow.
Abstract
While unitized regenerative fuel cells (URFCs) are promising for renewable energy storage, their efficient operation requires simultaneous water management and gas transport, which is challenging from the standpoint of water management. Herein, a novel approach is introduced for examining the alignment hydrophilic pattern of a Ti porous transport layer (PTL) with the flow field of a bipolar plate (BP). UV/ozone patterning and is employed to impart amphiphilic characteristics to the hydrophobic silanized Ti PTL, enabling low-cost and scalable fabrication. The hydrophilic pattern and its alignment with the BP are comprehensively analyzed using electrochemical methods and computational simulations. Notably, the serpentine-patterned (SP) Ti PTL, wherein the hydrophilic channel is directly aligned with the serpentine flow field of the BP, effectively enhances oxygen removal in the water electrolyzer (WE) mode and mitigates water flooding in the fuel cell (FC) mode, ensuring uninterrupted water and gas flow. Further, URFCs with SP configuration exhibit remarkable performance in the WE and FC modes, achieving a significantly improved round-trip efficiency of 25.7% at 2 A cm−2.
1. Introduction
Unitized regenerative fuel cells (URFCs) have emerged as a promising solution for auxiliary energy storage in applications utilizing renewable energy sources [1–6]. URFCs are especially attractive for long-term energy storage because they offer a high theoretical specific energy density without self-discharge [7, 8].
As illustrated in Fig. 1, URFC refers to a single cell with the capability to function in two distinct operation modes, namely the water electrolyzer (WE) and fuel cell (FC) modes. Therefore, the efficient operation of URFCs necessitates simultaneous transport of both hydrophilic water and hydrophobic gas through the cell. However, this inherent contradiction in the round-trip operation poses significant challenges, particularly in the water management in the oxygen electrode, which is crucial for achieving a high round-trip efficiency (RTE) [9].
The porous transport layer (PTL), also referred to as the gas diffusion layer (GDL), plays a crucial role [10] in facilitating water transport from the bipolar plate (BP) to the catalyst layer (CL) in the WE mode and vice versa in the FC mode while ensuring uninterrupted gas transport. To achieve this, carbon-based GDLs, which are conventionally employed in FCs, are used in URFCs [11, 12]. Nevertheless, the hydrophobicity and poor corrosion resistance of the carbon-based GDL remains a fundamental concern that requires further investigation [13].
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Sung Min Lee, Keun Hwan Oh, Hwan Yeop Jeong, Duk Man Yu, Tae-Ho Kim (2025). Regulating Water Transport Paths on Porous Transport Layer by Hydrophilic Patterning for Highly Efficient Unitized Regenerative Fuel Cells. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01684-6
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Frequently Asked Questions
What is the main contribution of this paper?
The paper introduces a novel approach to regulate water transport paths in porous transport layers (PTLs) by hydrophilic patterning, significantly enhancing the round-trip efficiency of unitized regenerative fuel cells (URFCs).
How does the hydrophilic patterning improve URFC performance?
The hydrophilic patterning, especially the serpentine configuration aligned with the bipolar plate flow field, enhances oxygen removal in water electrolyzer mode and mitigates water flooding in fuel cell mode, ensuring uninterrupted water and gas flow.
What is the achieved round-trip efficiency?
The URFCs with the serpentine-patterned Ti PTL achieve a round-trip efficiency of 25.7% at a current density of 2 A cm−2.
What fabrication method is used for the hydrophilic patterning?
UV/ozone patterning is employed to impart amphiphilic characteristics to the hydrophobic silanized Ti PTL, enabling low-cost and scalable fabrication.
What is the significance of aligning the hydrophilic pattern with the bipolar plate flow field?
Alignment ensures that the hydrophilic channels directly correspond to the flow field, optimizing water and gas transport, which is critical for high performance in both fuel cell and water electrolyzer modes.
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