The
development of highly efficient and durable bifunctional oxygen
catalysts for high-performance unitized regenerative fuel cells (URFCs)
is crucial for their practical application. Herein, the nanophase-separated
ultrafine PtCoW alloy and the Ir nanocrystals covalently coupled with
carbon were prepared by using a strawberry-like Ir/C hybrid as a structure-oriented
template. The resultant Pt-based ternary alloy and the IrO2-covered metallic Ir feature a well-defined nanophase-separated structure
with double active sites for oxygen reduction reaction (ORR) and oxygen
evolution reaction (OER). In acidic environments, the bifunctional
catalysts exhibit a total overpotential difference of 585 mV, showing
much higher activity and stability compared with commercial Pt/C and
IrO2. The outstanding bifunctional performance can be attributed
to the strong particle-to-particle interaction between PtCoW and the
neighboring Ir in their composite. Density functional theory calculations
further confirm that the formed IrO2(100)∥Ir(111)
epitaxial structure can lower the binding energy of reaction intermediates,
thus improving OER kinetics. Moreover, the downshifted d-band center
of Pt and the compressive strain in PtCoW alloy should be responsible
for the remarkably enhanced ORR activity. Therefore, this work may
contribute to URFC systems used as safe and efficient energy storage
and conversion devices for space flights, vehicles, and stations.
For these above Pt-based alloys, there are reported results showing that the center of the d-band of the alloyed platinum is affected by the unsaturated d-orbital electrons of the alloyed transition metals, which contributes to the adsorption of oxygen-containing groups on the platinum surface, thereby boosting the ORR kinetics. [9] Based on the ORR mechanisms on the Pt alloys, Markovic and coworkers [10] proposed a well-known volcanic relationship between the center of the d-band of alloyed Pt atoms and the catalytic activities of Pt 3 M (M = Fe, Co, Ni, Cu, etc.). Among the Pt 3 M alloys, Pt 3 Co shows the best ORR activity and stability but has not yet meet the requirements for commercial application of proton exchange membrane fuel cell vehicle. [11] To resolve this issue, introducing a third alloy element into binary alloys of Pt is a route idea to further enhance the electrocatalytic performance for ORR. By this way, Duan and co-workers and Huang and co-workers [8,9] fabricated Pt 3 NiMo ternary alloy through solvothermal reduction with N,N-dimethylformamide as a sol
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