(486d) PtCo/Coox Nanocomposites As Bifunctional Electrocatalysts for Oxygen Reduction and Evolution Reactions Synthesized Via Tandem Laser Ablation Synthesis in Solution-Galvanic Replacement Reactions

Intermetallic nanostructures extend the range of bulk metallic properties by virtue of their manifold compositional, structural, phase, and morphological variations. The ability to tune structure-property characteristics of metal/intermetallic nanoparticles (NPs), via controlled synthesis techniques, can enable unique physico-chemical properties that find wide-spread scientific applications in new classes of energetic and catalytic materials. In the field of proton exchange membrane fuel cell (PEMFC), efficient yet, low-cost electrocatalysts are indispensable for electrochemical oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). We present a one-step, one-pot solution-phase experimental route that, for the first time, incorporates laser ablation synthesis in solution in tandem with galvanic replacement reaction (LASiS-GRR) to synthesize nanocomposites (NCs) of PtCo nanaoalloy (NA) embedded in CoO_x matrices, which act as bifunctional electrocatalysts. High resolution TEM reveals PtCo NAs of mean sizes ~8.5-17.7 nm embedded in sponge-shaped CoO_x matrices. 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/CoO_xNCs 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 CoO_x matrices that accelerate both ORR and OER through symbiotic adsorption/desorption of intermediate species. Furthermore, the CoO_x matrix  prevents aggregation and/or dissolution of the embedded NAs in alkaline medium. We report a combined overpotential of 756 mV vs. RHE for the PtCo/CoO_x 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.