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

Pd "Kills Two Birds with One Stone" for the Synthesis of Catalyst: Dual Active Sites of Pd Triggers the Kinetics of O2 Electrocatalysis

Noble metal-based catalyst, despite their exorbitant cost, are the only successful catalyst for bifunctional oxygen electrocatalysis owing to their capability to drive forward the reaction rate kinetically. Therefore, it is desirable to diminish the noble metal loading without any compromise in the catalyst performance. In this study, the aim to achieve two goals with one action via a single-step route to have ultra-low loading of Pd in the catalyst. The Pd is used as a catalyst for C─C bond formation followed by complexation reactions or vice versa, in conventional Suzuki-Miyaura cross-coupling (SMCC) reaction, which yields a Pd-based porous organic polymer. Interestingly, it is found that dispersed Pd nanocluster (PdNC ) is present together with Pd single atom doped into nanocarbon (Pd-NC) matrix in the catalyst (PdNC /Pd-NC800 ) that obtained after pyrolysis of the porous polymer. The catalyst exhibits remarkable bifunctional activity and durability towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Further, it is studied that the in situ attenuated total reflection infrared (ATR-IR) spectroscopy at different electrochemical potentials during ORR and OER to observe the reaction intermediates. The homemade zinc-air battery with the catalyst displayed great performance, establishing the significance of PdNC /Pd-NC800 as a bifunctional oxygen electrocatalyst.

Sulfur and phosphorus co-doping optimized electronic structure and modulated intermediate affinity on PdSP metallene for ethanol-assisted energy-saving H2 production

Coupling cathodic hydrogen evolution reaction (HER) and anodic electrochemical oxidation of organic small molecules in a co-electrolysis system could simultaneously realize high-value chemical generation and energy-saving hydrogen production, which, however, require high-performance electrocatalysts. In this work, we developed a one-step solvothermal method to synthesize S, P-co-doped Pd metallene (PdSP metallene) and employed it as a bifunctional electrocatalyst for both the HER and ethanol oxidation reaction (EOR). The co-doping of S and P atoms into Pd metallene could introduce multiple active sites and increase the electrochemically-active surface area. Moreover, the electronic interactions between Pd, S, and P atoms could regulate the electronic structure of the active sites and modulate the intermediate affinity on the resultant PdSP metallene, thus boosting the electrocatalytic HER and EOR performance. In the HER-EOR co-electrolysis system with bifunctional PdSP metallene electrocatalysts, only a 0.88 V of electrolysis voltage was required to fulfill 10 mA cm^-2 current density, much lower than that of pure water electrolysis (1.41 V) using the same electrocatalysts.

Toward Overcoming the Challenges in the Comparison of Different Pd Nanocatalysts: Case Study of the Ethanol Oxidation Reaction

Precious metal nanoparticles, in particular palladium nanomaterials, show excellent catalytic properties and are key in the development of energy systems. For instance, ethanol fuel cells are promising devices for sustainable energy conversion, where Pd-based catalysts are key catalysts for the related ethanol oxidation reaction (EOR). Pd is a limited resource; thus, a remaining challenge is the development of efficient and stable Pd-based catalysts. This calls for a deeper understanding of the Pd properties at the nanoscale. This knowledge can be gained in comparative studies of different Pd nanomaterials. However, such studies remain challenging to perform and interpret due to the lack of cross-studies using the same Pd nanomaterials as a reference. Here, as-prepared sub 3 nm diameter surfactant-free Pd nanoparticles supported on carbon are obtained by a simple approach. The as-prepared catalysts with Pd loading 10 and 30 wt % show higher activity and stability compared to commercially available counterparts for the EOR. Upon electrochemical testing, a significant size increase and loss of electrochemical active surface are observed for the as-prepared catalysts, whereas the commercial samples show an increase in the electrochemically active surface area and moderate size increase. This study shines light on the challenging comparison of different catalysts across the literature. Further advancement in Pd (electro)catalyst design will gain from including self-prepared catalysts. The simple synthesis detailed easily leads to suitable nanoparticles to be used as a reference for more systematic comparative studies of Pd catalysts across the literature.

Fabrication of Composite Material with Pd Nanoparticles and Graphene on Nickel Foam for Its Excellent Electrocatalytic Performance

Incorporation of precious metallic nanoparticles onto a carbon support material is used to obtain an electrocatalyst for ethanol oxidation. A composite material of spherical palladium nanoparticles (Pd NPs), reduced graphene oxide (rGO), and polydopamine (PDA) on three-dimensional nickel foam (NF) substrate (Pd/rGO/PDA@NF) has been synthesized for ethanol electrocatalysis. The Pd nanoparticles were obtained via reduction of precursor K2PdCl4 using ascorbic acid at 60 °C for 80 min. The rGO with large specific surface area was used in catalysts to provide large amounts of active sites for Pd NPs. Meanwhile, Pd NPs as an effective ingredient in catalyst exhibited excellent electrochemical activity of ethanol oxidation. Local surface plasmon resonance was carried out to determine the optimal concentration of precursor K2PdCl4 aqueous solution, and the absorbance peak of Pd NPs was found at about 340–370 nm by UV-visible spectroscopy. An enhanced property of the composite material Pd/rGO/PDA@NF was demonstrated to catalyze the ethanol oxidation reaction in alkaline electrolyte solution. A higher ratio of forward scan peak current intensity (If) to reverse scan peak current intensity (Ib) was 1.59, which demonstrated the significant anti-poison effect to carbonaceous intermediates of the Pd/rGO/PDA@NF. The value of If can maintain 90.6% after 400 cycles, indicating the higher cycling stability and better electrocatalytic performance toward ethanol oxidation.

Effect of Metal Substrate on Electrocatalytic Property of Palladium Nanowire Array for High Performance Ethanol Electro-Oxidation

In this research, a high performance, ionomer-free electrocatalyst based on vertically aligned palladium (Pd) nanowire array was developed as an anode electrode toward ethanol oxidation reaction (EOR) in an alkaline environment. Using a one-step electrodeposition method, the Pd nanowires with controlled length were obtained by varying the electrodeposition current density and the synthesis time. Scanning electron microcopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD) were employed to characterize the morphology, chemical composition, and crystal structure of the Pd nanowires. The length effects of the nanowires, in the range of 0.8-4.5 μm, and various metal substrates, such as Ag, Cu, Ni, and Ti, were investigated for their electrochemical activities. The results demonstrated that Ag was the most active substrate to facilitate the ethanol oxidation reaction of the Pd nanowire array (NWA) electrocatalyst, which could be related to its good electrical conductivity. The stability test of the Pd NWA/Ag over time for EOR was also carried out, and the catalytic activity was recovered after the electrode was replaced with a new ethanol solution. Electrochemical impedance spectroscopy (EIS) measurements were performed to provide insights in the electron transfer resistance between the electrode and analyte. Gas chromatography and UV-vis spectroscopy were employed to measure the concentration of chemical species, which helped elucidate the overall reaction mechanism on the electrode surfaces.

Atomic layer deposition of palladium nanoparticles on a functional electrospun poly-cyclodextrin nanoweb as a flexible and reusable heterogeneous nanocatalyst for the reduction of nitroaromatic compounds

We here show a rational approach for the fabrication of a flexible, insoluble catalytic electrospun nanoweb of cross-linked cyclodextrin (CD) for the reduction of nitroaromatics. CD nanofibers were produced by electrospinning an aqueous HP-β-CD solution containing a multifunctional cross-linker (i.e., 1,2,3,4-butanetetracarboxylic acid, BTCA) and were subsequently cross-linked by heat treatment, which led to an insoluble electrospun poly-CD nanoweb. The poly-CD nanoweb was decorated with Pd nanoparticles (Pd-NPs) by atomic layer deposition (ALD) technique over 20 cycles to give rise to a catalytic electrospun nanoweb (i.e., Pd@poly-CD). The formation of the Pd-NPs on the poly-CD nanofiber surface was clearly evidenced by TEM and STEM imaging, which displayed the homogeneously distributed Pd-NPs with a mean size of 4.34 nm. ICP-MS analysis revealed that the Pd content on the Pd@poly-CD nanoweb was 0.039 mg per mg of nanoweb. The catalytic performance of the Pd@poly-CD nanoweb was tested for the reduction of a nitroaromatic compound (i.e., 4-nitrophenol (4-NP)), and high catalytic performance of the Pd@poly-CD nanoweb was observed with a corresponding TOF value of 0.0316 min-1. XPS was used to explore the oxidation state of Pd atoms before and after the catalytic reduction of 4-NP, and no significant change was observed after catalytic reactions. In brief, the Pd@poly-CD nanoweb having handy, flexible, structural stability and reusability can be effectively used in environmental applications as a heterogeneous nanocatalyst for the reduction of toxic nitroaromatics.

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.

Facile and green synthesis of palladium nanoparticles loaded into cyclodextrin nanofibers and their catalytic application in nitroarene hydrogenation

Facile and green synthesis of Pd nanoparticles using cyclodextrin and their electrospinning into polymer-free nanofibers were reported.

Size effect studies in catalysis: a simple surfactant-free synthesis of sub 3 nm Pd nanocatalysts supported on carbon

Supported Pd nanoparticles are prepared under ambient conditions via a surfactant-free synthesis. Pd(NO₃)₂ is reduced in the presence of a carbon support in alkaline methanol to obtain sub 3 nm nanoparticles. The preparation method is relevant to the study of size effects in catalytic reactions like ethanol electro-oxidation.

A simple surfactant-free synthesis of sub 3 nm carbon-supported Pd nanocatalysts is introduced to study size effects in catalysis.