Design of Bifunctional PtIr/TiN Catalysts and Their Application for PEM-URFCs

Unitized regenerative fuel cells based on proton exchange membrane (PEM-URFCs) enable highly efficient bidirectional conversion between the electricity and the hydrogen energy. However, the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the oxygen electrode, as well as the high cost of noble-metal catalysts and their insufficient stability under strongly acidic and high-potential operating conditions, severely hinders the development of PEM-URFCs. In this work, titanium nitride–supported platinum–iridium alloy bifunctional catalysts (PtIr/TiN) were rationally designed and synthesized. PtIr nanoparticles were uniformly loaded on the TiN support, and the synergistic electronic effects arising from alloying, along with the strong metal–support interaction, were exploited to simultaneously enhance the catalytic activity and the durability. Physical characterizations reveal that the PtIr nanoparticles are tightly anchored by the TiN support, forming a highly dispersed alloy structure. Single-cell tests demonstrate a peak power density of 855 mW cm-2 in the fuel cell mode and a low operating voltage of 1.647 V at 1 A cm-2 in the water electrolysis mode for the best performance catalyst, corresponding to a high round-trip efficiency (RTE) of 36% at the current density of 1 A cm-2. This study not only presents the effectiveness of the PtIr/TiN catalyst in improving the overall performance of PEM-URFCs, but also provides a new design insight into bifunctional oxygen electrode catalysts based on the combined strategies of the support engineering and the alloying