Hierarchical Palladium-Copper-Silver Porous Nanoflowers as Efficient Electrocatalysts for CO2 Reduction to C2+ Products

Abstract

In recent years, Cu-based multi-metallic nanocrystals with controlled elemental distributions have been extensively studied for potential applications as electrocatalysts for CO₂ reduction reaction (CO₂RR). Modifying Cu electrocatalysts with secondary or additional metals offers a viable approach to manipulate the overall d-band structure which would cause the shift in the d-band center. Such manipulation can affect the surface affinity of Cu towards key intermediates and thus the following catalytic pathway. Apart from endeavors to adjust the electronic structure, morphological engineering provides effective avenues to enhance the electrocatalytic performance of CO₂RR. In contrast to quasi-spherical particles with irregular shapes, a 3D-assembled porous structure utilizing 2D nanosheets as building blocks offers advantages such as maximizing surface atom exposure and creating numerous diffusion channels and reactive sites for intermediates formed during catalysis. Yet, it is technique challenging to construct such type of nanoarchitecture via a rationally-design synthetic routes and traditional stepwise self-assembling strategy is time-consuming and lack of versatile control over the structural parameters of resulting products. Therefore, it holds significant value to develop a synthesis method capable of yielding high-purity formations of unique nanostructures. These structures should possess accurately controlled elemental compositions and electronic configurations, and establish a potential correlation between structural benefits and enhanced electrochemical performance in CO₂RR. Herein, we report the controlled synthesis of palladium-copper-silver (Pd-Cu-Ag) nanocrystals with rationally-designed two-dimensional (2D)-three-dimensional (3D) hybrid architectures and validated with the promising use for electrochemical CO₂ reduction (CO₂RR). The synthetic procedure includes the conversion of Au@Cu_xO nanospheres into CuAg hierarchical nanoflowers (HNFs), as directed by the capping agent octadecyltrimethyl ammonium chloride. Interestingly, the nanosheets are formed in situ as the building block. Following galvanic replacement reaction between CuAg HNFs and Na₂PdCl₄ removes Ag and Cu, introduces zero-valent Pd, and creates abundant pores on the nanosheets. These CuAg-based products are tested as CO₂RR electrocatalysts, in which the Pd_0.7Cu_40.0Ag_59.7 PHNFs displayed the optimized performance in terms of C₂₊ products selectivity (69.5%) and C₂₊ partial current density (−349.1 mA·cm⁻²). As revealed by density functional theory (DFT) simulations, PdAgCu surface has distinct electronic property, which lower the reaction barrier for C-C coupling, protruding the exceptional advantage of the Pd doping towards CuAg electrocatalysts for CO₂ reduction. The present study offers a straightforward approach to fabricate hierarchical multi-metallic nanostructures with the porous nanosheet as building block, and validates its structural advantage in electrocatalysis, shedding light on the rational design of efficient CO₂RR catalyst.

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