Ultrafine FePd Nanoalloys Decorated Multiwalled Cabon Nanotubes toward Enhanced Ethanol Oxidation Reaction

Electrocatalytic ethanol oxidation reaction: recent progress, challenges, and future prospects

Direct ethanol fuel cells (DEFCs) have been widely considered as a feasible power conversion technology for portable and mobile applications. The economic feasibility of DEFCs relies on two conditions: a notable reduction in the expensive nature of precious metal electrocatalysts and a simultaneous remarkable improvement in the anode's long-term performance. Despite the considerable progress achieved in recent decades in Pt nanoengineering to reduce its loading in catalyst ink with enhanced mass activity, attempts to tackle these problems have yet to be successful. During the ethanol oxidation reaction (EOR) at the anode surface, Pt electrocatalysts lose their electrocatalytic activity rapidly due to poisoning by surface-adsorbed reaction intermediates like CO. This phenomenon leads to a significant loss in electrocatalytic performance within a relatively short time. This review provides an overview of the mechanistic approaches during the EOR of noble metal-based anode materials. Additionally, we emphasized the significance of many essential factors that govern the EOR activity of the electrode surface. Furthermore, we provided a comprehensive examination of the challenges and potential advancements in electrocatalytic EOR.

Pd-Sb Rhombohedra with an Unconventional Rhombohedral Phase as a Trifunctional Electrocatalyst

Crystal phase engineering is an important strategy for designing noble-metal-based catalysts with optimized activity and stability. From the thermodynamic point of view, it remains a great challenge to synthesize unconventional phases of noble metals. Here, a new class of Pd-based nanostructure with unconventional rhombohedral Pd₂₀ Sb₇ phase is successfully synthesized. Benefiting from the high proportion of the unique exposed Pd₂₀ Sb₇ (003) surface, Pd₂₀ Sb₇ rhombohedra display much enhanced ethanol oxidation reaction (EOR) and oxygen reduction reaction performance compared with commercial Pd/C. Moreover, Pd₂₀ Sb₇ rhombohedra are also demonstrated as an effective air cathode in non-aqueous Li-air batteries with an overpotential of only 0.24 V. Density functional theory calculations reveal that the unique exposed facets of Pd₂₀ Sb₇ rhombohedra can not only reduce the excessive adsorption of CH₃ CO* to CH₃ COOH on Pd for promoting EOR process, but also weaken CO binding and CO poisoning. This work provides a new class of unconventional intermetallic nanomaterials with enhanced electrocatalytic activity.

Electronic and lattice strain dual tailoring for boosting Pd electrocatalysis in oxygen reduction reaction

Deliberately optimizing the d-band position of an active component via electronic and lattice strain tuning is an effective way to boost its catalytic performance. We herein demonstrate this concept by constructing core-shell Au@NiPd nanoparticles with NiPd alloy shells of only three atomic layers through combining an Au catalysis with the galvanic replacement reaction. The Au core with larger electronegativity modulates the Pd electronic configuration, while the Ni atoms alloyed in the ultrathin shells neutralize the lattice stretching in Pd shells exerted by Au cores, equipping the active Pd metal with a favorable d-band position for electrochemical oxygen reduction reaction in an alkaline medium, for which core-shell Au@NiPd nanoparticles with a Ni/Pd atomic ratio of 3/7 exhibit a half-wave potential of 0.92 V, specific activity of 3.7 mA cm^-2, and mass activity of 0.65 A mg^-1 at 0.9 V, much better than most of the recently reported Pd-even Pt-based electrocatalysts.

Ordered PdCu-Based Core-Shell Concave Nanocubes Enclosed by High-Index Facets for Ethanol Electrooxidation

Crystal phase engineering is a powerful strategy for regulating the performance of electrocatalysts toward many electrocatalytic reactions. Herein we demonstrate that Au@Pd₁Cu concave nanocubes (CNCs) with an ordered body-centered cubic (bcc) PdCu alloy shell enclosed by many high active high-index facets can be adopted as highly active yet stable electrocatalysts for the ethanol oxidation reaction (EOR). These CNCs are more efficient than other nanocrystals with a disordered face-centered cubic (fcc) PdCu alloy surface and display high mass and specific activities of 10.59 A mg_pd^-1 and 33.24 mA cm^-2, which are 11.7 times and 4.1 times higher than those of commercial Pd black, respectively. Our core-shell CNCs also exhibit robust durability with the weakest decay in activity after 250 potential-scanning cycles, as well as outstanding antipoisoning ability. Alloying with Cu and the ordered bcc phase surface can provide abundant OH_ads species to oxidize carbonaceous poison to avoid catalyst poisoning, and the exposed high-index facets on the surface can act as highly catalytic sites.

Oxygen-rich PdSnCu nanocrystals with particle connection features as enhanced catalysts for ethanol oxidation reaction

Most electrocatalysts show a high mass and special activity during the ethanol oxidation reaction, but those still suffer from limited stability, finite renewable capability and poor anti-poisoning durability. Furthermore, the reliable structure and appropriate composition of catalysts are fairly associated with the electrocatalysis performance. Herein, we report the development of trimetallic Pd₆₁Sn₃₄Cu₅nanocrystals (NCs) whose rough surfaces are rich in step atoms and coupled with abundant of SnO_xand CuO, which may effectively boost reaction activity and rapidly remove carbonaceous intermediate, respectively. Under the tuning on the composition, the defect rich Pd₆₁Sn₃₄Cu₅NCs exhibit elevated electrocatalysis activity and durability for ethanol oxidation reaction with an optimized mass activity (1.26 AmgPd-1) and specific activity (10.6 mA cm^-2), which is about 2.21 and 2.58 times greater than that of the commercial Pd/C catalyst (0.57 AmgPd-1and 4.1 mA cm^-2).

A comprehensive and critical review of the recent progress in electrocatalysts for the ethanol oxidation reaction

The human craving for energy is continually mounting and becoming progressively difficult to gratify. At present, the world's massive energy demands are chiefly encountered by nonrenewable and benign fossil fuels. However, the development of dynamic energy cradles for a gradually thriving world to lessen fossil fuel reserve depletion and environmental concerns is currently a persistent issue for society. The discovery of copious nonconventional resources to fill the gap between energy requirements and supply is the extreme obligation of the modern era. A new emergent, clean, and robust alternative to fossil fuels is the fuel cell. Among the different types of fuel cells, the direct ethanol fuel cell (DEFCs) is an outstanding option for light-duty vehicles and portable devices. A critical tactic for obtaining sustainable energy sources is the production of highly proficient, economical and green catalysts for energy storage and conversion devices. To date, a broad range of research is available for using Pt and modified Pt-based electrocatalysts to augment the C2H5OH oxidation process. Pt-based nanocubes, nanorods, nanoflowers, and the hybrids of Pt with metal oxides such as Fe2O3, TiO2, SnO2, MnO, Cu2O, and ZnO, and with conducting polymers are extensively utilized in both acidic and basic media. Moreover, Pd-based materials, transition metal-based materials, as well as transition metal-based materials are also points of interest for researchers nowadays. This review article delivers a broad vision of the current progress of the EOR process concerning noble metals and transition metals-based materials.

Iron-Palladium magnetic nanoparticles for decolorizing rhodamine B and scavenging reactive oxygen species

HYPOTHESIS

Here, FePd magnetic nanoparticles (MNPs) are developed as artificial enzymes with high biocompatibility and reusability.

EXPERIMENT

The nanoparticles (NPs) are synthesized in an aqueous solvent by one-pot synthesis utilizing glutathione (GSH) and cysteine (Cys) as surfactants.

FINDINGS

The prepared hydrophilic FePd NPs are redispersible in water. Further, they exhibit catalytic activity for the degradation of rhodamine B (RhB), as well as for the inhibition of reactive oxygen species (ROS) production induced by H₂O₂, which are two- and seven-fold enhancements of their catalytic performances, respectively, compared with that of horseradish peroxidase. The computational simulation and electrochemical analysis indicate that the enhancement of the catalytic effect is due to the protection of the MNP surface by GSH and Cys. In vitro experiments reveal that FePd MNPs behave like a peroxidase and decrease the ROS in mammalian cells. The cytotoxicity assessment of FePd MNPs via exposures to different cell lines for over seven days indicates that they can maintain the cell viability of >90% for up to 20 μgmL^-1 concentration. FePd MNPs with high saturation magnetization and biocompatibility can be utilized as recyclable peroxidase-mimicking nanozymes and biosensors in a variety of catalytic and biological applications.

In Situ-Formed PdFe Nanoalloy and Carbon Defects in Cathode for Synergic Reduction-Oxidation of Chlorinated Pollutants in Electro-Fenton Process

Complete dechlorination and mineralization of chlorophenols via the reduction-oxidation-mediated electro-Fenton process with a composite bulk cathode is first proposed. The in situ formation of a PdFe nanoalloy and carbon defects as key active sites is mutually induced during the formation of a carbon aerogel-based electrode. Specifically, the PdFe nanoalloy promotes the generation of [H]_ads as reduction sites and improves the electron transfer via an electrical circuit, while the carbon defects selectively favor the 2e^- oxygen reduction pathway. Notably, this work implies a novel electrocatalytic model for the formation of ·OH via (2 + 1)e^- oxygen reduction by a consecutive reaction with carbon defects and a PdFe nanoalloy. Complete total organic carbon removal and dechlorination of 3-chlorophenol were performed after 6 h. The kinetic rate constant for removing haloacetamides (HAMs) in drinking water was 0.21-0.41 h^-1, and the degradation efficiency was self-enhanced after electrolysis for 2 h because of the increased concentration of [H⁺]. The specific energy consumption was ∼0.55 W·h·g^-1 at 100% removal of some HAMs, corresponding to a power consumption of 0.6-1.1 kW·h for complete dehalogenation per ton of drinking water in waterworks. Moreover, the PdFe alloy/CA exhibited extreme mechanical and electrochemical stability with limited iron (∼0.07 ppm) and palladium (0.02 ppm) leaching during the actual application.

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.

Black Phosphorus-Graphene Heterostructure-Supported Pd Nanoparticles with Superior Activity and Stability for Ethanol Electro-oxidation

Rational design supporting material for palladium (Pd)-based catalyst can maximize its electrocatalytic performance for ethanol oxidation reaction (EOR) catalyst in alkaline condition. Utilizing the unique two-dimensional structures and outstanding physicochemical property of graphene and black phosphorus (BP), herein, we proposed and designed a black phosphorus-graphene heterostructure for supporting Pd nanoparticles. Through merely ball-milling of activated graphene (AG) and black phosphorus (BP), the AG-BP hybrid with a linkage of P-C bonding is used as supports of Pd. The obtained Pd/AG-BP hybrid exhibits ultrahigh electrochemical activity toward EOR. Remarkably, it can achieve a high mass peak current density of ∼6004.53 and ∼712.03 mA mg_Pd^-1 before and after the durability tests of 20 000s on EOR, which are ∼7.19 and 80 times higher than those of commercial Pd/C. The experimental analysis and density-functional-theory calculation show that Pd becomes more positive with electrons transfer from Pd to AG-BP supports and is liable to absorb the OH radicals for removing CO_ads intermediate to release active sites on EOR, together with the excellent ability to generate additional OH militants after combining with the AG-BP heterostructure.

The electrooxidation of formic acid catalyzed by Pd–Ga nanoalloys

Pd–Ga nanoalloys exhibit enhanced catalytic activity and stability towards the HCOOH oxidation reaction.

Carbon- and Binder-Free Core-Shell Nanowire Arrays for Efficient Ethanol Electro-Oxidation in Alkaline Medium

To achieve high electrochemical surface area (ECSA) and avoid carbon support and binder in the anode catalyst of direct ethanol fuel cell, herein, we design freestanding core-shell nickel@palladium-nickel nanowire arrays (Ni@Pd-Ni NAs) without carbon support and binder for high-efficiency ethanol electro-oxidation. Bare Ni nanowire arrays (Ni NAs) are first prepared using the facile template-assistant electrodeposition method. Subsequently, the Ni@Pd-Ni NAs are formed using one-step solution-based alloying reaction. The optimized Ni@Pd-Ni NA electrode with a high ECSA of 64.4 m² g^-1_Pd exhibits excellent electrochemical performance (peak current density: 622 A g^-1_Pd) and cycling stability for ethanol electro-oxidation. The facilely obtained yet high-efficiency core-shell Ni@Pd-Ni NA electrode is a promising electrocatalyst, which can be utilized for oxygen reduction reaction, urea, hydrazine hydrate, and hydrogen peroxide electro-oxidation, not limited to the ethanol electro-oxidation.

Palladium islands on iron oxide nanoparticles for hydrodesulfurization catalysis

Deposition of thin Pd islands on iron oxide nanoparticles results in a 4-fold activity enhancement in HDS and suppresses cracking.

Highly Efficient Dual Active Palladium Nanonetwork Electrocatalyst for Ethanol Oxidation and Hydrogen Evolution

Tunable palladium nanonetwork (PdNN) has been developed for catalyzing ethanol oxidation reaction (EOR) and hydrogen evolution reaction (HER) in alkaline electrolyte. 3D PdNN is regarded as a dual active electrocatalyst for both EOR and HER for energy conversion application. The PdNN has been synthesized by the simple chemical route with the assistance of zinc precursor and a surfactant (i.e., cetyltrimethylammonium bromide, CTAB). The thickness of the network can be tuned by simply adjusting the concentration of CTAB. Both EOR and HER have been performed in an alkaline electrolyte, and characterized by different voltammetric methods. The 3D PdNN has shown 2.2-fold higher electrochemical surface area than the commercially available Pt/C including other tested catalysts with minimal Pd loading. As a result, it provides a higher density of EOR and HER active sites and facilitated the electron transport. For example, it shows 2.6-fold higher mass activity with significantly lower CO₂ production for EOR and the similar overpotential (110 mV @ 10 mA cm^-2) for HER compared to Pt/C with better reaction kinetics for both reactions. Thus, the PdNN is proved as an efficient electrocatalyst with better electrocatalytic activity and stability than state-of-the-art Pt/C for both EOR and HER because of the crystalline, monodispersed, and support-free porous nanonetwork.

One-Pot Hydrothermal Synthesis of Carbon Dots with Efficient Up- and Down-Converted Photoluminescence for the Sensitive Detection of Morin in a Dual-Readout Assay

Blue luminescent carbon dots (CDs) with a high photoluminescence (PL) quantum yield (48.3 ± 5.3%) were prepared by the one-pot hydrothermal reaction of citric acid with poly(ethylenimine) (PEI). The CDs display bright PL, narrow emission spectra, pH-dependent PL intensity, high photostability, and up-converted luminescence. The CDs exhibit a quenching of both down- and up-conversion PL in the presence of morin and thus serve as useful probes for morin detection. Both down- and up-conversion measurements allow the quantification of concentrations from 0 to 300 μmol/L with a detection limit of 0.6 μmol/L, and this dual-mode detection increases the reliability of the measurement. The proposed method of determination is simple, sensitive, and cost-effective, with potential applications in clinical and biochemical assays.

Structural Regulation of PdCu2 Nanoparticles and Their Electrocatalytic Performance for Ethanol Oxidation

Two types of PdCu₂ nanoparticles were prepared through one-pot synthesis and a two-step reducing process, named as PdCu₂-1 and PdCu₂-2, respectively. The morphology and structure of as-prepared samples were investigated by transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma-optical emission spectrometry. Results showed that more Pd atoms were buried in the inside of PdCu₂-1, whereas more available Pd sites were distributed on the surface of PdCu₂-2. The electrochemical measurements indicated that both PdCu₂-1 and PdCu₂-2 nanoparticles showed a higher electrocatalytic activity than that for pure Pd nanoparticles. In particular, PdCu₂-2 predictably exhibited a better stability and durability as well as a lower onset potential and a higher catalytic current density than that of PdCu₂-1 toward ethanol oxidation in alkaline media. On the basis of these studies, the formation mechanisms of both the PdCu₂ catalysts and the relationship between their structure and properties were discussed in this paper.

Microbial synthesis of highly dispersed PdAu alloy for enhanced electrocatalysis

Biosynthesis based on the reducing capacity of electrochemically active bacteria is frequently used in the reduction of metal ions into nanoparticles as an eco-friendly way to recycle metal resources. However, those bionanoparticles cannot be used directly as electrocatalysts because of the poor conductivity of cell substrates. This problem was solved by a hydrothermal reaction, which also contributes to the heteroatom doping and alloying between Pd and Au. With the protection of graphene, the aggregation of nanoparticles was successfully avoided, and the porous structure was maintained, resulting in better electrocatalytic activity and durability than commercial Pd/C under both alkaline (CH₃CH₂OH, 6.15-fold of mass activity) and acidic (HCOOH, 6.58-fold of mass activity) conditions. The strategy developed in this work opens up a horizon into designing electrocatalysts through fully utilizing the abundant resources in nature.

Metal Bromide Controlled Interfacial Aromatization Reaction for Shape-Selective Synthesis of Palladium Nanostructures with Efficient Catalytic Performances

Herein, the effect of diverse metal bromides for the shape evolution of palladium nanostructures (Pd NS) has been demonstrated. Aromaticity-driven reduction of bromopalladate(II) is optimized to reproducibly obtain different Pd NS at the water/organic layer interface. In this soft interfacial strategy, a redox potential driven reaction has been performed, forming the thermodynamically more stable (>10(4) -fold) PdBr4 (2-) precursor from PdCl4 (2-) by adding extra metal bromides. In the process, the reductant, Hantzsch dihydropyridine ester (DHPE), is aromatized. Interestingly, alkali metal bromides devoid of coordination propensity exclusively evolve Pd nanowires (Pd NWs), whereas in the case of transition metal bromides the metal ions engage the 'N' donor of DHPE at the interface, making the redox reaction sluggish. Hence, controlled Pd nanoparticles growth is observed, which evolves Pd broccolis (Pd NBRs) and Pd nanorods (Pd NRs) at the interface in the presence of NiBr2 and CuBr2 , respectively, in the aqueous solution. Thus, the effect of diverse metal bromides in the reaction mixture for tailor-made growth of the various Pd NS is reported. Among the as-synthesized materials, the Pd NWs stand to be superior catalysts and their efficiency is almost 6 and 2.5 times higher than commercial 20 % Pd/C in the electrooxidation of ethanol and Cr(VI) reduction reaction by formic acid, respectively.

Effects of Fe2+ ion doping on LiMnPO4 nanomaterial for lithium ion batteries

Carbon-coating and Fe-doping of LiMnPO₄ resulted in superior cycling and rate performance as LIB cathode materials.

Facile one-pot preparation of Pd–Au/PEDOT/graphene nanocomposites and their high electrochemical sensing performance for caffeic acid detection

Bimetallic Pd–Au/PEDOT/rGO nanocomposites were facilely prepared by a one-pot method for the electrochemical detection of CA.

Analysis of the effect of biofouling distribution on electricity output in microbial fuel cells

Biofouling inside the catalyst layer decreased reaction sites and oxygen diffusion which mainly impaired cathode activity.