As an alternative solution to the low-temperature proton exchange membrane fuel cells (PEMFCs), alkaline fuel cells (AFCs) have regained attention recently.[1-3] However, the development of AFCs has been severely restricted by sluggish kinetics of the oxygen reduction reaction (ORR), catalyst degradation and carbon support corrosion of commercial Pt/C.[4-6] The deterioration of Pt/C, which is highly correlated with the long-term operation hurdle, is one of the key issues to solve. The deterioration is caused by electrochemical corrosion (oxidation) of the carbon support at the cathode.[7-9] The corrosion is particularly accelerated during start-up and shut-down operations, during which the cathode potential can reach voltage of as high as 1.5 V.[10-13] Under these conditions, the carbon material is oxidized to carbon dioxide and/or carbon monoxide. This also leads to the aggregation and migration of Pt nanoparticles as well as their detachment from the carbon support. Therefore, the design of catalysts that can repair themselves under severe conditions has been identified as a primary challenge for fuel cells.[14, 15] Especially the catalysts for ORR require maintaining high activity at high potential during start-up and shut-down operations. Self-repair electrocatalysts for oxygen evolution reaction have been studied.[16, 17] While the self-repair electrocatalysts for ORR have been rarely reported.

Herein, we present for the first time a tri-metallic PdAuCu nanobranched heterostructure as self-repair catalyst for ORR. In this heterostructured PdAuCu, the AuCu alloy serves as a stable support for Cu oxide/Pd heterogeneous interface (AuCu@CuxO/Pd). By tuning the oxidation state of Cu via high potential treatment (HPT), Cu (Ⅱ) was in-situ formed, which is responsible for repairing the catalyst. As the high potential is inevitably experienced at cathode during start-up and shut-down operations of a fuel cell, we proposed this catalyst as a “self-repair” catalyst in a broad sense. This work provides a novel strategy for fabricating efficient ORR catalysts by smartly utilizing the high potential during start-up and shut-down operations.

The ORR activity and durability of PdAuCu after high potential heat-treatment (PdAuCu-HPT) are shown in Figure 1.

Figure 1.  (A) Mass activities of Pt/C, Pd/C, PdAuCu and PdAuCu-HPT at different cycles. ORR polarization curves of (B) initial Pt/C, initial Pd/C, PdAuCu-2000th-HPT and (C) initial Pd/C and Pd/C-2000th-HPT in O₂-saturated 0.1 M KOH solution at room temperature, with a rotation rate of 1600 rpm and a potential sweep rate of 10 mV s^-1.

 

Acknowledgements

This work is supported by National Natural Science Foundation of China (Nos. 51272167 and 21206101 ).

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