Amphiphilic Ti porous transport layer for highly effective PEM unitized regenerative fuel cells

Polymer electrolyte membrane unitized regenerative fuel cells (PEM-URFCs) require bifunctional porous transport layers (PTLs) to play contradictory roles in a single unitized system: hydrophobicity for water drainage in the fuel cell (FC) mode and hydrophilicity for water supplement in the electrolysis cell (EC) mode. Here, we report a high-performance amphiphilic Ti PTL suitable for both FC and EC modes, thanks to alternating hydrophobic and hydrophilic channels. To fabricate the amphiphilic PTL, we used a shadow mask patterning process using ultrathin polydimethylsiloxane (PDMS) brush as a hydrophobic surface modifier, which can change the Ti PTL's surface polarity without decreasing its electrical conductivity. Consequently, performance improved by 4.3 times in FC (@ 0.6 V) and 1.9 times in EC (@ 1.8 V) from amphiphilic PTL. To elucidate reason for performance enhancement, discrete gas emission through the hydrophobic channels in amphiphilic PTL was verified under scanning electrochemical microscopy.

Solutions to the water flooding problem for unitized regenerative fuel cells: status and perspectives

Unitized regenerative fuel cells (URFC) are capable of generating, storing, and releasing energy on demand in a sustainable manner. Water management is of vital importance to achieve maximum performance, durability, and round-trip efficiency in URFCs. However, URFCs suffer from critical issues related to their mode-switching process, water flooding, and membrane dehydration. The essential problem of water management is maintaining a subtle equilibrium between membrane drying and liquid water flooding to prevent membrane dehydration and ensure high URFC performance. This paper provides an overview of the operating principle of URFCs and describes the underlying phenomena related to water management issues. It also summarizes state-of-the-art studies of water management with a focus on recent developments and discusses the technical challenges of water management strategies. In addition, we propose a novel system design to address these critical water management issues. Overall, this review identifies the gaps in the research and development of URFC water management and identifies several essential future developments and research directions for future investigation.