Defect Engineering of Palladium–Tin Nanowires Enables Efficient Electrocatalysts for Fuel Cell Reactions

Abstract

The defect engineering of noble metal nanostructures is of vital importance because it can provide an additional yet advanced tier to further boost catalysis, especially for one-dimensional (1D) noble metal nanostructures with a high surface to bulk ratio and more importantly the ability to engineer the defect along the longitudinal direction of the 1D nanostructures. Herein, for the first time, we report that the defect in 1D noble metal nanostructures is a largely unrevealed yet essential factor in achieving highly active and stable electrocatalysts toward fuel cell reactions. The detailed electrocatalytic results show that the Pd–Sn nanowires (NWs) exhibit interesting defect-dependent performance, in which the defect-rich Pd4Sn wavy NWs display the highest activity and durability for both the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations reveal that a large number of surface vacancies/agglomerated voids are the driving forces for forming surface grain boundaries (GBs) within Pd4Sn WNWs. These electronic active GB regions are the key factors in preserving the number of Pd0 sites, which are critical for minimizing the intrinsic site-to-site electron-transfer barriers. Through this defect engineering, the Pd4Sn WNWs ultimately yield highly efficient alkaline ORR and MOR. The present work highlights the importance of defect engineering in boosting the performance of electrocatalysts for potentially practical fuel cells and energy applications.

High Active PdSn Binary Alloyed Catalysts Supported on B and N Codoped Graphene for Formic Acid Electro-Oxidation

“…The electro-catalytic performances towards formic acid electro-oxidation for all the samples were tested by the CV at a scan rate of 50 mV s −1 in 1 M HCOOH with 0.5 M H 2 SO 4 , and the results are illustrated in Figure 4. It is generally accepted that the electrooxidation of formic acid follows a dual-pathway mechanism [8,38]. One is a dehydrogenation path which directly produces CO 2 by reaction (2), and the other is a dehydration path which makes CO 2 by multi-step reactions (3)- (5 dual-pathway mechanism [8,38].…”

“…It is generally accepted that the electrooxidation of formic acid follows a dual-pathway mechanism [8,38]. One is a dehydrogenation path which directly produces CO 2 by reaction (2), and the other is a dehydration path which makes CO 2 by multi-step reactions (3)- (5 dual-pathway mechanism [8,38]. One is a dehydrogenation path which directly produces CO2 by reaction (2), and the other is a dehydration path which makes CO2 by multi-step reactions (3−5).…”

“…Obviously, the current densities for the direct oxidation of all the samples are much higher than those of the indirect one. This suggests that these Pd-based catalysts mainly oxidize formic acid through the direct pathway, and only a small amount of formic acid is oxidized by the indirect pathway, which leads to CO ads accumulated on the surface of catalysts [8,40,41]. Generally, the peak current density in the forward scan is used to measure the electro-activity of the catalysts.…”

“…In order to improve the electrocatalytic activity and reduce the usage of the Pd catalysts, one feasible strategy is to form Pd-based alloys by incorporating non-precious metals. PdCo, PdFe, PdCu, PdNiPdSn and PdBi binary electrocatalysts have shown higher catalytic activities and stabilities for the electro-oxidation of small molecules (e.g., alcohol and formic acid) as well as oxygen reduction reation (ORR), than commercial Pd/C catalysts [5][6][7][8][9][10]. For example, Du et al presented Pd86Sn14 showing much enhanced current densities and durability toward ethanol oxidation reaction among three carbon-supported Pd-Sn catalysts [11], while Adam suggested that Pd 1.5 Sn shows the best electro-catalytic activity [12].…”

Versatile Synthesis of Pd−M (M=Cr, Mo, W) Alloy Nanosheets Flower‐like Superstructures for Efficient Oxygen Reduction Electrocatalysis

“…To address this issue, several strategies, including engineering the microstructures ( e. g ., morphology or defects), tuning surface strain, alloying Pd with cheap and oxyphilic metallic elements, and anchoring on proper support to form well‐coupled nanohybrids, have been taken to tune the surface electronic structure of Pd and optimize its adsorption strength for oxygenated species. Among them, the third strategy has been widely adopted, and some Pd‐based nanoalloys, such as Pd−Mn, Pd−Fe, Pd−Co, Pd−Ni, Pd−Cu, Pd−Pb, Pd−Sn, Pd−Ni−Ag, Pd−Fe−Co, and Pd−Cu−Co, have been explored as candidate catalysts for ORR. Despite that great progress has been achieved, most of reported Pd‐based nanoalloys are focused on 0D, and 1D or twinned nanostructures, and still exhibited insufficient activities (mass activities are often lower than 0.2 A mg −1 ).…”