Comparative study to understand the intrinsic properties of Pt and Pd catalysts for methanol and ethanol oxidation in alkaline media

Fe-Pd nanoflakes decorated on leached graphite disks for both methanol and formic acid electrooxidation with excellent electrocatalytic performance

This paper introduces a unique and simple method for fabricating of inexpensive electrocatalysts for use in direct methanol fuel cells. The leached Fe1-Pd1 NFs/graphite (leached Fe1-Pd1/graphite) disk electrode was successfully obtained via uniform dispersion of Zn powder into the matrix of commercial graphite powder (98%), pressing under optimized pressure followed by the treatment in H2SO4 solution containing Fe+2 and Pd+2 cations, leading to the partial leaching out of Zn from graphite matrix, as well as partial electroless substitution of Fe-Pd nanoflakes with Zn metal. Based on the morphology studies, binary Fe-Pd nanoflakes with a large surface area uniformly dispersed on the leached graphite disk. The leached Fe-Pd/G disk showed the exceptional electrocatalytic activity toward methanol and formic acid oxidation without electrocatalyst poisoning being observed, in contrast to the leached Pd/graphite and leached Fe/graphite disks. This is due to the high surface area, and synergistic effect of Pd and Fe. The findings of this work may be used for the mass manufacture of graphite-based disks for commercial fuel cell applications using available graphite powders. The linear range of washed Fe1-Pd1/G electrocatalyst for measuring methanol was about 0.1-1.3 M, and its detection limit was calculated at about 0.03 M. Furthermore, the linear range of the nanocatalyst for measuring formic acid was about 0.02-0.1 M, and its detection limit was calculated at about 0.006 M.

Black phosphorous/palladium functionalized carbon aerogel nanocomposite for highly efficient ethanol electrooxidation

Direct ethanol fuel cells have great potential for practical power applications due to their easy operation, high energy density, and low toxicity. However, the slow and incomplete ethanol electrooxidation (EEO) reaction is a major drawback that hinders the development of this type of fuel cell. Here, we report a facile approach for the preparation of highly active, low cost and stable electrocatalysts based on palladium (Pd) nanoparticles and black phosphorus/palladium (BP/Pd) nanohybrids supported on a carbon aerogel (CA). The nanocomposites show remarkable catalytic performance and stability as anode electrocatalysts for EEO in an alkaline medium. A mass peak current density of 8376 mA mg_Pd ^-1 is attained for EEO on the BP/Pd/CA catalyst, which is 11.4 times higher than that of the commercial Pd/C catalyst. To gain deep insight into the structure-property relationship associated with superior electroactivity, the catalysts are well characterized in terms of morphology, surface chemistry, and catalytic activity. It is found that the BP-doped CA support provides high catalyst dispersibility, protection against leaching, and modification of the electronic and catalytic properties of Pd, while the catalyst modifies CA into a more open and conductive structure. This synergistic interaction between the support and the catalyst improves the transport of active species and electrons at the electrode/electrolyte interface, leading to rapid EEO reaction kinetics.

Effect of Anode Material on Electrochemical Oxidation of Low Molecular Weight Alcohols-A Review

The growing climate crisis inspires one of the greatest challenges of the 21st century-developing novel power sources. One of the concepts that offer clean, non-fossil electricity production is fuel cells, especially when the role of fuel is played by simple organic molecules, such as low molecular weight alcohols. The greatest drawback of this technology is the lack of electrocatalytic materials that would enhance reaction kinetics and good stability under process conditions. Currently, electrodes for direct alcohol fuel cells (DAFCs) are mainly based on platinum, which not only provides a poor reaction rate but also readily deactivates because of poisoning by reaction products. Because of these disadvantages, many researchers have focused on developing novel electrode materials with electrocatalytic properties towards the oxidation of simple alcohols, such as methanol, ethanol, ethylene glycol or propanol. This paper presents the development of electrode materials and addresses future challenges that still need to be overcome before direct alcohol fuel cells can be commercialized.

Self-driven microstructural evolution of Au@Pd core-shell nanoparticles for greatly enhanced catalytic performance during methanol electrooxidation

The lack of direct insight into the microstructural evolution of catalytic materials under electrochemical polarization has inhibited the development of heterogeneous catalysts. By investigating a typical Au@Pd core-shell nanostructure, the present study discloses the microstructural evolution of heterogeneous catalytic materials during the methanol electrooxidation reaction (MOR). The electrocatalytic activity of the as-prepared Au@Pd_core-shell nanoparticles continuously increased during the first 100 successive voltammetry cycles of the MOR. Microstructural characterization studies revealed that during the MOR, an Au/Pd mixed bimetallic shell was formed by the self-driven microstructural evolution of the Au@Pd_core-shell nanoparticles. Both the experimental and calculation results indicated that the Au/Pd mixed bimetallic shell reduced the binding strength of OH^- and CO on the catalyst surface. The exposed Au atoms in the shell region also produced large-scale reactive ˙OH radicals that facilitated the oxidative removal of the adsorbed carbonaceous species from the adjacent Pd active sites.

Effect of Pd on the Electrocatalytic Activity of Pt towards Oxidation of Ethanol in Alkaline Solutions

The understanding of electrocatalytic activity and poisoning resistance properties of Pt and Pd nanoparticles, recognized as the best electrocatalysts for the ethanol oxidation reaction, is an essential step for the commercialization of direct ethanol fuel cells (DEFCs). In this paper, mono and bimetallic Pt and Pd nanoparticles with different atomic ratios have been synthesized to study their electrocatalytic properties for an ethanol oxidation reaction in alkaline solutions. The different nanoparticles were physiochemically characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The electrochemical characterization was performed by cyclic voltammetry and chronoamperometry measurements. The electrochemical measurements indicate that Pt nanoparticles have much higher electrocatalytic activity for ethanol oxidation than Pd nanoparticles. The studies with bimetallic PtPd nanoparticles showed a significant impact of their composition on the ethanol oxidation. Thus, the highest electrocatalytic activity and poisoning resistance properties were obtained for Pt3Pd2 nanoparticles. Moreover, this study demonstrates that the poisoning of the catalyst surface through ethanol oxidation is related to the prevalence of the acetaldehyde–acetate route and the polymerization of acetaldehyde through aldol condensation in the alkaline media.

Convenient Synthesis of 3D Fluffy PtPd Nanocorals Loaded on 2D h-BN Supports as Highly Efficient and Stable Electrocatalysts for Alcohol Oxidation Reaction

Fuel cells hold great promise for clean and sustainable energy, whereas their widespread commercialization strongly depends on the development of highly efficient and stable electrocatalysts. Herein, three-dimensional fluffy PtPd nanocorals (NCs) loaded on two-dimensional (2D) hexagonal boron nitride (h-BN) supports were successfully achieved by a simple one-step strategy based on ultraviolet (UV) laser-excited photochemical reaction. As for alcohol oxidation reaction, the h-BN/PtPd NCs with unique nanoporous surface provide more enhanced electrocatalytic performances than many previous nanocatalysts, owing to abundant active sites and plentiful charge-transfer channels formed on high electrode-electrolyte contact area. Especially, the mass activity of h-BN/PtPd NCs is about 962.8 mA mg_PtPd ^-1 in methanol oxidation reaction in alkaline solution, which can be maintained at ∼274.9 mA mg_PtPd ^-1 (28.6% of the initial one) even after a 5 × 10⁴ s durability test. The present work not only offers an advanced electrocatalyst for long-term fuel cells but also provides a versatile route for construction of complex metallic nanocomposites on 2D supports, holding great potential for diverse energy-related applications.

Stable and Efficient Nitrogen-Containing Carbon-Based Electrocatalysts for Reactions in Energy-Conversion Systems

High activity and stability are crucial for the practical use of electrocatalysts in fuel cells, metal-air batteries, and water electrolysis, including the oxygen reduction reaction, hydrogen evolution reaction, oxygen evolution reaction, and oxidation reactions of formic acid and alcohols. Electrocatalysts based on nitrogen-containing carbon (N-C) materials show promise in catalyzing these reactions; however, there is no systematic review of strategies for the engineering of active and stable N-C-based electrocatalysts. Herein, a comprehensive comparison of recently reported N-C-based electrocatalysts regarding both electrocatalytic activity and long-term stability is presented. In the first part of this review, the relationships between the electrocatalytic reactions and selection of the element to modify the N-C-based materials are discussed. Afterwards, synthesis methods for N-C-based electrocatalysts are summarized, and strategies for the synthesis of highly stable N-C-based electrocatalysts are presented. Multiple tables containing data on crucial parameters for both electrocatalytic activity and stability are displayed in this review. Finally, constructing M-N_x moieties is proposed as the most promising engineering strategy for stable N-C-based electrocatalysts.

Promoting Effect of Ni(OH)2 on Palladium Nanocrystals Leads to Greatly Improved Operation Durability for Electrocatalytic Ethanol Oxidation in Alkaline Solution

Most electrocatalysts for the ethanol oxidation reaction suffer from extremely limited operational durability and poor selectivity toward the CC bond cleavage. In spite of tremendous efforts over the past several decades, little progress has been made in this regard. This study reports the remarkable promoting effect of Ni(OH)₂ on Pd nanocrystals for electrocatalytic ethanol oxidation reaction in alkaline solution. A hybrid electrocatalyst consisting of intimately mixed nanosized Pd particles, defective Ni(OH)₂ nanoflakes, and a graphene support is prepared via a two-step solution method. The optimal product exhibits a high mass-specific peak current of >1500 mA mg^-1_Pd , and excellent operational durability forms both cycling and chronoamperometric measurements in alkaline solution. Most impressively, this hybrid catalyst retains a mass-specific current of 440 mA mg^-1 even after 20 000 s of chronoamperometric testing, and its original activity can be regenerated via simple cyclic voltammetry cycles in clean KOH. This great catalyst durability is understood based on both CO stripping and in situ attenuated total reflection infrared experiments suggesting that the presence of Ni(OH)₂ alleviates the poisoning of Pd nanocrystals by carbonaceous intermediates. The incorporation of Ni(OH)₂ also markedly shifts the reaction selectivity from the originally predominant C2 pathway toward the more desirable C1 pathway, even at room temperature.

Ternary Pt9RhFex Nanoscale Alloys as Highly Efficient Catalysts with Enhanced Activity and Excellent CO-Poisoning Tolerance for Ethanol Oxidation

To address the problems of high cost and poor stability of anode catalysts in direct ethanol fuel cells (DEFCs), ternary nanoparticles Pt₉RhFe_x (x = 1, 3, 5, 7, and 9) supported on carbon powders (XC-72R) have been synthesized via a facile method involving reduction by sodium borohydride followed by thermal annealing in N₂ at ambient pressure. The catalysts are physically characterized by X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy, and their catalytic performance for the ethanol oxidation reaction (EOR) is evaluated by cyclic and linear scan voltammetry, CO-stripping voltammograms, and chronopotentiometry. All the Pt₉RhFe_x/C catalysts of different atomic ratios produce high EOR catalytic activity. The catalyst of atomic ratio composition 9:1:3 (Pt/Rh/Fe) has the highest activity and excellent CO-poisoning tolerance. Moreover, the enhanced EOR catalytic activity on Pt₉RhFe₃/C when compared to Pt₉Rh/C, Pt₃Fe/C, and Pt/C clearly demonstrates the presence of Fe improves catalytic performance. Notably, the onset potential for CO oxidation on Pt₉RhFe₃/C (0.271 V) is ∼55, 75, and 191 mV more negative than on Pt₉Rh/C (0.326 V), Pt₃Fe/C (0.346 V), and Pt/C (0.462 V), respectively, which implies the presence of Fe atoms dramatically improves CO-poisoning tolerance. Meanwhile, compared to the commercial PtRu/C catalyst, the peak potential on Pt₉RhFe₃/C for CO oxidation was just slightly changed after several thousand cycles, which shows high stability against the potential cycling. The possible mechanism by which Fe and Rh atoms facilitate the observed enhanced performance is also considered herein, and we conclude Pt₉RhFe₃/C offers a promising anode catalyst for direct ethanol fuel cells.

Cobalt Oxide and Cobalt-Graphitic Carbon Core-Shell Based Catalysts with Remarkably High Oxygen Reduction Reaction Activity

The vital role of ethylenediaminetetraacetic acid on the structure and the oxygen reduction reaction activity of the non-precious-metal-based pyrolyzed catalyst is reported and elaborated. The resultant catalyst can overtake the performance of commercial Pt/C catalyst in an alkaline medium.