Competitive intermetallics formation in Pd-Zn-Cd system via seeded growth from ultra-thin Pd nanosheets for electrocatalytic ethanol oxidation reaction

Abstract

Pd-based catalysts exhibit higher catalytic activity and durability in many electrochemical reactions. However, the electrochemical performance can be further enhanced by fine-tune of the alloy composition. Although binary alloys have been fully studied, the multicomponent alloys are far beyond understanding, which leaves cocktail effect a compromised explanation for the high-entropy alloy. Herein Pd nanosheet-seeded growth was used to synthesize a Pd-Zn-Cd ternary alloy by accurately controlling the Pd-Zn-Cd molar ratio through adjusting the amount of introduced Cd precursor. Through analysis of the crystal phase structure of PdCdZn_x and PdZn_xCd_1−x, the competitive relationship of Zn and Cd in the alloying process with Pd was unveiled: Pd₁Cd₁ intermetallics (IMC) is thermodynamically favored over Pd₁Zn₁ IMC in the ternary system. However, the increased structure stability of PdCd over PdZn does not bring about increased durability in the catalytic ethanol oxidation reaction. The morphology selection of Pd seeds is also crucial for the study, as Pd cubes, Pd tetrahedrons, and Pd octahedrons do not form PdZn in the same protocol. The successful alloying through the seeded growth depends on the maximum diffusion depth of foreign atoms into the seed.