@article{32380,
  author = {Yagya N Regmi and Xiong Peng and Julie C Fornaciari and Max Wei and Deborah J Myers and Adam Z Weber and Nemanja Danilovic},
  title = {A low temperature unitized regenerative fuel cell realizing 60\% round trip efficiency and 10 000 cycles of durability for energy storage applications},
  abstract = {<p>Unitized regenerative fuel cells (URFC) convert electrical energy to and from chemical bonds in hydrogen. URFCs have the potential to provide economical means for efficient long-term, seasonal, energy storage and on-demand conversion back to electrical energy. We first optimize the catalyst layer for discrete electrolyzer and fuel cell and then configure the URFC. The goal is to identify a cost competitive configuration for URFCs, and demonstrate it in terms of upper limit of round trip efficiencies (RTEs). Two possible configurations of URFCs are compared via experiments and techno-economic analysis (TEA), which emphasize the advantages of the unconventional constant-electrode (CE) URFC over the traditional constant-gas (CG) configuration. We also study the stability via accelerated stress tests (ASTs) and demonstrate steady state operation in a daily cycle for day to night energy shifting. From the investigations, the optimum composition of the URFC anode catalyst layer is 90 at\% Ir-black balanced by Pt-black for both CE and CG configurations. At 80 {\textdegree}C and 1 A cm-2, the optimized CE URFC achieves 57\% and 60\% RTE with air and O2 as the reductant gases, respectively. We then evaluated the differences in durability using an AST over 10k charge{\textendash}discharge cycles; the results reveal that the wider potential window at the anode in CE (0.05{\textendash}1.55 V) has minimal effect on catalyst layer stability compared to CG (0.55{\textendash}1.55 V). Furthermore, there was no degradation up to the range of 2k{\textendash}5k cycles; beyond that the fuel cell (discharge) performance degraded while the electrolyzer (charge) performance was still stable. The observations here indicate substantial potential to employ URFCs as efficient and cost-effective bidirectional energy-conversion devices within energy storage and utilization systems after appropriate technological and operational optimizations.</p>},
  year = {2020},
  booktitle = {Energy \& Environmental Science},
  journal = {Energy \& Environmental Science},
  series = {Energy \& Environmental Science},
  month = {02/2020},
  issn = {1754-5692},
  doi = {10.1039/C9EE03626A},
  language = {eng},
}