PtCo/CoOx nanocomposites: Bifunctional electrocatalysts for oxygen reduction and evolution reactions synthesized via tandem laser ablation synthesis in solution-galvanic replacement reactions

摘要

Efficient yet, low-cost electrocatalysts are indispensable for electrochemical oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). Here we present laser ablation synthesis in solution in tandem with galvanic replacement reaction (LASiS-GRR), for the first time, as a facile route to synthesize nanocomposites (NCs) of PtCo nanaoalloy (NA) embedded in CoOx matrices as bifunctional electrocatalysts. High resolution TEM reveals PtCo NA of mean sizes similar to 8.5-17.7 nm embedded in sponge-shaped CoOx matrices, while electron diffraction and X-ray diffraction data along with energy dispersive X-ray spectrometry (EDX) confirm the NC compositions and crystalline structures. Detailed electrochemistry data indicates outstanding ORR and OER activities for the PtCo/CoOx NCs while exhibiting better stability than the respective standard nanocatalysts. Such activities are ascribed to the shrunken lattice constants of alloyed PtCo that promote oxygen adsorption and the synergic "spillover" effect from high surface area CoOx matrices that accelerate both ORR and OER through symbiotic adsorption/desorption of intermediate species, while preventing aggregation and/or dissolution in alkaline medium. We report a combined overpotential of 756 mV vs. RHE for the PtCo/CoOx NC with 33.3% (molar) Pt content which is the best value ever reported for catalysts supported by carbon black. The enhanced bifunctional catalytic activities of the NCs are attributed to their unique heteronanostructures tailored by our one-pot, "green" synthesis route of LASiS-GRR. (C) 2015 Elsevier B.V. All rights reserved.