Rhombohedral Pd-Sb Nanoplates with Pd-Terminated Surface: An Efficient Bifunctional Fuel-Cell Catalyst

Developing high-performance electrocatalysts for the ethanol oxidation reaction (EOR) and the oxygen reduction reaction (ORR) is essential for the commercialization of direct ethanol fuel cells, but it is still formidably challenging. In this work, a novel Pd-Sb hexagonal nanoplate for boosting both cathodic and anodic fuel cell reactions is prepared. Detailed characterizations reveal that the nanoplates have ordered rhombohedral phase of Pd₈ Sb₃ (denoted as Pd₈ Sb₃ HPs). The Pd₈ Sb₃ HPs exhibit much enhanced activity toward the oxidation of various alcohols. Particularly, Pd₈ Sb₃ HPs/C displays superior specific and mass activities of 29.3 mA cm^-2 and 4.5 A mg_Pd ^-1 toward the EOR, which are 7.0 and 11.3 times higher than those of commercial Pd/C, and 9.8 and 3.8 times higher than those of commercial Pt/C, respectively, representing one of the best EOR catalysts reported to date. In situ electrochemical attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) measurements reveal that Pd₈ Sb₃ HPs/C can effectively promote the C₂ pathway of the EOR. As revealed by density functional theory calculations, the high EOR activity of the Pd₈ Sb₃ HPs can be ascribed to the reduced energy barrier of ethanol dehydrogenation. Additionally, Pd₈ Sb₃ HPs/C also shows superior performance in the ORR. This work advances the controllable synthesis of the Pd-Sb nanostructure, giving huge impetus for the design of high-efficiency electrocatalysts for energy conversion and beyond.

Engineering gold-platinum core-shell nanoparticles by self-limitation in solution

Core-shell particles with thin noble metal shells represent an attractive material class with potential for various applications ranging from catalysis to biomedical and pharmaceutical applications to optical crystals. The synthesis of well-defined core-shell architectures remains, however, highly challenging. Here, we demonstrate that atomically-thin and homogeneous platinum shells can be grown via a colloidal synthesis method on a variety of gold nanostructures ranging from spherical nanoparticles to nanorods and nanocubes. The synthesis is based on the exchange of low binding citrate ligands on gold, the reduction of platinum and the subsequent kinetically hindered growth by carbon monoxide as strong binding ligand. The prerequisites for homogeneous growth are low core-binding ligands with moderate fast ligand exchange in solution, a mild reducing agent to mitigate homonucleation and a strong affinity of a second ligand system that can bind to the shell's surface. The simplicity of the described synthetic route can potentially be adapted to various other material libraries to obtain atomically smooth core-shell systems.

Insights into reaction mechanisms of ethanol electrooxidation at the Pt/Au(111) interfaces using density functional theory

Understanding ethanol electrooxidation reaction kinetics is fundamental to the development of direct ethanol fuel cells.

Codeposition of Platinum and Gold on Nickel Wire Electrodes via Galvanic Replacement Reactions for Electrocatalytic Oxidation of Alcohols

Codeposition of Pt and Au on Ni wire was performed using a simple treatment of immersing Ni wire in aqueous solutions containing both K2PtCl4 and HAuCl4. For evaluating the electrochemical properties of the thus-prepared electrodes, cyclic voltammograms (CVs) of 1.0 M ethanol in 1.0 M NaOH aqueous solutions were recorded. Compared with Pt- or Au-deposited Ni wire electrodes prepared by treating Ni wire in aqueous solutions of a single component, e.g., 1.0 mM K2PtCl4 or 1.0 mM HAuCl4, a noteworthy increase in the electrocatalytic current was observed for the oxidation of ethanol with a PtAu-codeposited Ni (PtAu/Ni) wire electrode even when it was prepared in an aqueous solution containing both 0.10 mM K2PtCl4 and 0.10 mM HAuCl4. In addition, the shape and the peak potentials of CVs recorded using PtAu/Ni wire electrodes were found to be different from those recorded with the Pt- or Au-deposited Ni wire electrodes. Because the CV responses typical of the PtAu/Ni wire electrodes were observed even when a PtAu/Ni wire electrode was prepared in an aqueous solution containing both 0.010 mM K2PtCl4 and 1.0 mM HAuCl4, it is considered that a small amount of Pt was effectively modified or incorporated and affected the electrochemical properties significantly. The CV results for ethanol oxidation were compared with those for the electrocatalytic oxidations of methanol, 1-propanol, and 2-propanol. Besides, the CV results recorded with the present PtAu/Ni wire electrodes are discussed in comparison with some previous results obtained using other PtAu nanoelectrocatalysts.

Au Nanoparticles Modified with Pt, Ru and SnO2 as Electrocatalysts for Ethanol Oxidation Reaction in Acids

The anodic reaction in direct ethanol fuel cells (DEFCs), ethanol oxidation reaction (EOR) faces challenges, such as incomplete electrooxidation of ethanol and high cost of the most efficient electrocatalyst, Pt in acidic media at low temperature. In this study, core-shell electrocatalysts with an Au core and Pt-based shell (Au@Pt) are developed. The Au core size and Pt shell thickness play an important role in the EOR activity. The Au size of 2.8 nm and one layer of Pt provide the most optimized performance, having 6 times higher peak current density in contrast to commercial Pt/C. SnO₂ as a support also enhances the EOR activity of Au@Pt by 1.73 times. Further modifying the Pt shell with Ru atoms achieve the highest EOR current density that is 15 and 2.5 times of Pt/C and Au@Pt. Our results suggest the importance of surface modification in rational design of advanced electrocatalysts.

Nanocatalysts for Electrocatalytic Oxidation of Ethanol

The use of ethanol as a fuel in direct alcohol fuel cells depends not only on its ease of production from renewable sources, but also on overcoming the challenges of storage and transportation. In an ethanol-based fuel cell, highly active electrocatalysts are required to break the C-C bond in ethanol for its complete oxidation at lower overpotentials, with the aim of increasing the cell performance, ethanol conversion rates, and fuel efficiency. In recent decades, the development of wet-chemistry methods has stimulated research into catalyst design, reactivity tailoring, and mechanistic investigations, and thus, created great opportunities to achieve efficient oxidation of ethanol. In this Minireview, the nanomaterials tested as electrocatalysts for the ethanol oxidation reaction in acid or alkaline environments are summarized. The focus is mainly on nanomaterials synthesized by using wet-chemistry methods, with particular attention on the relationship between the chemical and physical characteristics of the catalysts, for example, catalyst composition, morphology, structure, degree of alloying, presence of oxides or supports, and their activity for ethanol electro-oxidation. As potential alternatives to noble metals, non-noble-metal catalysts for ethanol oxidation are also briefly reviewed. Insights into further enhancing the catalytic performance through the design of efficient electrocatalysts are also provided.

Pt-Richcore/Sn-Richsubsurface/Ptskin Nanocubes As Highly Active and Stable Electrocatalysts for the Ethanol Oxidation Reaction

Direct ethanol fuel cells are one of the most promising electrochemical energy conversion devices for portable, mobile and stationary power applications. However, more efficient and stable and less expensive electrocatalysts are still required. Interestingly, the electrochemical performance of the electrocatalysts toward the ethanol oxidation reaction can be remarkably enhanced by exploiting the benefits of structural and compositional sensitivity and control. Here, we describe the synthesis, characterization, and electrochemical behavior of cubic Pt-Sn nanoparticles. The electrochemical activity of the cubic Pt-Sn nanoparticles was found to be about three times higher than that obtained with unshaped Pt-Sn nanoparticles and six times higher than that of Pt nanocubes. In addition, stability tests indicated the electrocatalyst preserves its morphology and remains well-dispersed on the carbon support after 5000 potential cycles, while a cubic (pure) Pt catalyst exhibited severe agglomeration of the nanoparticles after a similar stability testing protocol. A detailed analysis of the elemental distribution in the nanoparticles by STEM-EELS indicated that Sn dissolves from the outer part of the shell after potential cycling, forming a ∼0.5 nm Pt skin. This particular atomic composition profile having a Pt-rich core, a Sn-rich subsurface layer, and a Pt-skin surface structure is responsible for the high activity and stability.

Electrocatalytic oxidation of ethanol at Pd, Pt, Pd/Pt and Pt/Pd nano particles supported on poly 1,8-diaminonaphthalene film in alkaline medium

An ethanol oxidation reaction (EOR) in alkaline medium was carried out at palladium (Pd) or platinum (Pt) nanoparticles/poly 1,8-diaminonaphthalene (p1,8-DAN) composite catalyst electrodes. Pd and Pt were incorporated onto a p1,8-DAN/GC electrode by a cyclic voltammetry (CV) strategy. The obtained Pd/p1,8-DAN/GC, Pt/p1,8-DAN/GC, Pt/Pd/p1,8-DAN/GC and Pd/Pt/p1,8-DAN/GC modified electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and cyclic voltammetry (CV) techniques. Electrode surface areas (ESAs) of the obtained catalysts were calculated by carbon monoxide (CO) adsorption using differential electrochemical mass spectroscopy (DEMS). The electrocatalytic oxidation of ethanol (EtOH) at the catalyst electrodes was considered in 0.5 M NaOH solutions by CV and chronoamperometric techniques. The catalyst electrodes significantly enhanced the catalytic efficiency for EOR compared to a bare glassy carbon (GC) electrode. Bimetallic catalyst electrodes demonstrate improved catalytic activity, superior durability and higher tolerance to (CO) poison generated in the development of EOR compared with Pd/p1,8-DAN and Pt/p1,8-DAN catalysts, giving priority to Pt/Pd/p1,8-DAN/GC electrodes. Viability parameters, such as NaOH and EtOH concentrations, scan rate and upper potential limits, were examined and analyzed. This study suggests that the prepared catalysts have pronounced potential applications in direct EOR in fuel cells.

An ethanol oxidation reaction (EOR) in alkaline medium was carried out at palladium (Pd) or platinum (Pt) nanoparticles/poly 1,8-diaminonaphthalene (p1,8-DAN) composite catalyst electrodes.

Rational one-step synthesis of porous PtPdRu nanodendrites for ethanol oxidation reaction with a superior tolerance for CO-poisoning

Precise fabrication of porous ternary Pt-based nanodendrites is very important for electrochemical energy conversion owing to high surface area and great molecular accessibility of these nanodendrites. Herein, PtPdRu porous nanodendrites (PNDs) were prepared via a facile one-step ultrasonic irradiation approach at room temperature. Intriguingly, the ultrasonic irradiation drove the formation of PtPdRu PNDs with spatially interconnected porous structures, whereas magnetic stirring produced PtPdRu nanoflowers (NFs) with less porosity. The formation mechanism was ascribed to the acoustic cavitation effect and fast-reduction kinetics under sonication. The as-made PtPdRu PNDs displayed a superior catalytic performance towards ethanol oxidation reaction with a high tolerance for CO-poisoning as compared to PtPdRu NFs, PtPd NDs, and commercial Pt/C catalyst.

Pd supported on carbon containing nickel, nitrogen and sulfur for ethanol electrooxidation

Carbon material containing nickel, nitrogen and sulfur (Ni-NSC) has been synthesized using metal-organic frameworks (MOFs) as precursor by annealing treatment with a size from 200 to 300 nm. Pd nanoparticles supported on the Ni-NSC (Pd/Ni-NSC) are used as electrocatalysts for ethanol oxidation in alkaline media. Due to the synergistic effect between Pd and Ni, S, N, free OH radicals can form on the surface of Ni, N and S atoms at lower potentials, which react with CH₃CO intermediate species on the Pd surface to produce CH₃COO⁻ and release the active sites. On the other hand, the stronger binding force between Pd and co-doped N and S is responsible for enhancing dispersion and preventing agglomeration of the Pd nanoparticles. The Pd(20 wt%)/Ni-NSC shows better electrochemical performance of ethanol oxidation than the traditional commercial Pd(20 wt%)/C catalyst. Onset potential on the Pd(20 wt%)/Ni-NSC electrode is 36 mV more negative compared with that on the commercial Pd(20 wt%)/C electrode. The Pd(20 wt%)/Ni-NSC in this paper demonstrates to have excellent electrocatalytic properties and is considered as a promising catalyst in alkaline direct ethanol fuel cells.