Composition-Controlled PtCo Alloy Nanocubes with Tuned Electrocatalytic Activity for Oxygen Reduction

Modification of the electronic structure and lattice contraction of Pt alloy nanocatalysts through control over their morphology and composition has been a crucial issue for improving their electrocatalytic oxygen reduction reaction (ORR) activity. In the present work, we synthesized PtCo alloy nanocubes with controlled compositions (PtxCo NCs, x = 2, 3, 5, 7, and 9) by regulating the ratio of surfactants and the amount of Co precursor to elucidate the effect of the composition of nanocatalysts on their ORR activity. PtxCo NCs had a Pt-skin structure after electrochemical treatment. The electrocatalysis experiments revealed a strong correlation between ORR activity and Co composition. Pt3Co NCs exhibited the best ORR performance among the various PtxCo NCs. From density functional theory calculations, a typical volcano-type relationship was established between ORR activity and oxygen binding energy (E-OB) on NC surfaces, which showed that Pt3Co NCs had the optimal E-OB to achieve the maximum ORR activity. X-ray photoelectron spectroscopy and X-ray diffraction measurements demonstrated that the electronic structure and lattice contraction of the PtxCo NCs could be tuned by controlling the composition of NCs, which are highly correlated with the trends of E-OB change.