Highly Active and Durable Ultrasmall Pd Nanocatalyst Encapsulated in Ultrathin Silica Layers by Selective Deposition for Formic Acid Oxidation

PdMo Bimetallene Coupled with MXene Nanosheets as Efficient Bifunctional Electrocatalysts for Formic Acid and Methanol Oxidation Reactions

In this study, we demonstrate a facile soft chemistry strategy for the in situ growth of two-dimensional (2D) ultrathin PdMo bimetallene tightly coupled with Ti3C2Tx MXene nanosheets (PdMo/Ti3C2Tx) using a robust stereoassembly process. The 2D PdMo bimetallene offers numerous unsaturated Pd atoms and simultaneously induces combined bimetallic alloy and strain effects, while the Ti3C2Tx matrix effectively optimizes the electronic structure of PdMo bimetallene via a face-to-face interface interaction and guarantees exceptional electrical conductivity. As a consequence, the newly designed PdMo/Ti3C2Tx nanoarchitecture expresses remarkable electrocatalytic properties for the formic acid and methanol electro-oxidation, in terms of large electrochemically active surface areas, ultrahigh catalytic activity, strong antipoisoning ability, and dependable long-term stability, all of which are better than those of conventional Pd nanoparticle catalysts supported by Ti3C2Tx and carbon matrices.

Boosting the Electrocatalytic Formic Acid Oxidation Activity via P-PdAuAg Quaternary Alloying

Direct formic acid fuel cells (DFAFCs) are considered promising sustainable power sources due to their high energy density, nonflammability, and low fuel crossover. However, serious CO poisoning and activity attenuation of the anodic formic acid oxidation reaction (FAOR) greatly restrict the output and durability of DFAFCs. Inspired by the specific relationship between the composition, type, and property of alloys, in this work, we synthesize a series of hybrid substitutional/interstitial quaternary alloys P-PdAuAg by means of a novel polyphosphide route to address these issues. Due to the simultaneous interstitial P-doping and metal (Au, Ag, Pd) co-reduction, the P-PdAuAg quaternary alloy obtained is only 3 nm in diameter with abundant defects. It not only achieves a new high mass activity of 8.08 A mg_Pd^-1 (6.78 A mg_catalyst^-1) but also maintains high stability in the high potential range and harsh reaction conditions. Both the activity and anti-poisoning ability are far exceeding those of the currently reported FAOR catalysts. Detailed density functional theory (DFT) calculations reveal that the superb electrochemical performances originate from the shift of the d-band center of Pd as a result of the synergistic electronic/ligand effects between Pd, Au, Ag, and P. The introduction of interstitial P inhibits the occurrence of an indirect reaction pathway on Pd, while Au and Ag suppress the adsorption of CO and optimize the sequential dehydrogenation steps, leading to boosted reaction kinetics and CO tolerance. This work pioneered a facile way for the synthesis of Pd-based substitutional/interstitial hybrid alloys, providing a promising means of further improving the performance of alloying catalysts.

Metal-Micelle Cooperativity: Phosphine Ligand-Free Ultrasmall Palladium(II) Nanoparticles for Oxidative Mizoroki-Heck-type Couplings in Water at Room Temperature

The amphiphile PS-750-M generates stable, phosphine ligand-free, and catalytically active ultrasmall Pd(II) nanoparticles (NPs) from Pd(OAc)₂, preventing their precipitation, polymerization, and oxidation state changes. PS-750-M directly interacts with Pd(II) NP surfaces, as confirmed by high-resolution mass spectrometry and IR spectroscopy, resulting in their high stability. The Pd cations in NPs are most likely held together by hydroxides and acetate ions. The NPs were characterized by HRTEM, revealing their morphology and particle size distribution, and by HRMS and IR, providing evidence for NP-amphiphile interaction. The NP catalytic activity was examined in the context of oxidative Mizoroki-Heck-type couplings in water at room temperature. Hot filtration, hot extraction, and three-phase tests indicate heterogeneous catalysis occurring at the micellar interface rather than homogeneous catalysis occurring in the solution. NMR studies indicate that the catalytic activity stems from metal cation-π interactions of the styrene along with transmetalation by the arylboronic acid, followed by insertion and β-H elimination to furnish the coupled product along with the reoxidation of Pd by benzoquinone to complete the catalytic cycle. This method is very mild and sustainable, both in terms of NP synthesis and subsequent catalysis, and shows broad substrate scope while circumventing the need for organic solvents for this important class of couplings.

Fluorescent Test Paper via the In Situ Growth of COFs for Rapid and Convenient Detection of Pd(II) Ions

With the extensive use of palladium derivatives in the industry, their environmental pollution has become more and more serious. Herein, allyl functionalized hydrazone 2D COFs (XB-COFs) were found for selective fluorescent detection of Pd²⁺ (detection concentration of 0.29 μM) in water. The stable structure of the hydrazone bond and the complexation ability of allyl to Pd²⁺ cause XB-COF to have a good fluorescence sensing effect in both acid and alkaline solutions, and its adsorption capacity for Pd²⁺ is up to 120 mg g^-1. During the interaction between XB-COF and Pd²⁺, a part of Pd²⁺ can be reduced to Pd nanoparticles with a diameter of about 10 nm. A fluorescent test paper was prepared by the in situ growth of XB-COF onto a filter paper, which can realize visualization detection of Pd²⁺ in 10 s with the naked eye or under a 365 nm UV lamp. This is the first time a fluorescent test paper based on in the situ growth of COFs has been applied for the detection of heavy metal ions, which provides a new platform for the application of COF materials in the medical health field, food safety, and environmental protection.

Esterification of glycerol with acetic acid using a sulfonated polyphenylene sulfide non-woven fabric as a catalyst

In this work, the esterification of glycerol with acetic acid (HOAc) was investigated under sulfonated polyphenylene sulfide non-woven fabric (SPSF) as a solid catalyst. The effects of the amount of catalyst, reaction temperature, molar ratio of glycerol to HOAc and the reaction time on the esterification were studied in detail. It was found that SPSF has good catalytic activity and stability. Under the reaction conditions of the molar ratio of glycerol/HOAc of 1:6 (glycerol 0.1 mol), the reaction temperature of 110 °C, the amount of catalyst of 3 g, and the reaction time of 2 h, the glycerol conversion and the selectivity to diacetin (DAG) reached upto 96 and 56.1%, respectively. Reusability test of SPSF showed that no significant declination in the glycerol conversion and the selectivity was observed after five reaction cycles. The experimental results proved the esterification of glycerol with HOAc by SPSF a promising and green process.

Potential and pH Dependence of the Buried Interface of Membrane-Coated Electrocatalysts

Semipermeable silica membranes are attractive as protective coatings for metal electrocatalysts such as platinum, but their impact on the catalytic properties has not been fully understood. Here, we develop a first-principles formalism to investigate how silica membranes interact with the surface of platinum metal electrocatalysts to develop a better understanding of the membrane-metal interplay. By generalizing the concept of Pourbaix diagrams to electrochemical solid-solid interfaces, we establish which bonds are formed between the SiO₂ membrane and Pt(111) surface in aqueous electrolytes for different pH values and potential biases. We find that the membrane termination changes as a function of the pH and potential, which affects the adhesion strength and the energy requirements for partial membrane detachment, controlling the Pt surface area that is accessible for reactant species. The charge transfer between the Pt surface and SiO₂ membrane is also pH- and potential-dependent and results in changes of the Pt surface d-band states, which are known to correlate with catalytic activity. Our analysis reveals the complex response of a buried interface to the electrochemical environment and identifies trends that are expected to apply also to other membrane-coated electrocatalysts.

Cyclic voltammetry electrodeposition of well-dispersed Pd nanoparticles on carbon paper as a flow-through anode for microfluidic direct formate fuel cells

The preparation of low-loading and high-performance Pd-based electrodes is required for direct formate fuel cells. In this study, cyclic voltammetry electrodeposition is used to electrodeposit Pd nanoparticles on carbon paper (Pd/CP) and achieve excellent activity and promising stability toward the formate oxidation reaction (FOR). The prepared electrode shows a thin layer of hemispherical and well-dispersed Pd nanoparticles on the fibers of the carbon paper. The open structure and uniform catalyst distribution make the Pd/CP electrode show 2.56-fold higher active area and stability in the FOR as compared with those of commercial Pd/C catalysts. An air-breathing microfluidic direct formate fuel cell (μDFFC) with a Pd/CP electrode used as a flow-through anode is constructed to further assess electrode performance. The Pd/CP electrode with low Pd loading, 0.105 mg cm-2, delivers a peak power density and limiting current density of 46.6 mW cm-2 (443.8 mW mg-1Pd) and 288.4 mA cm-2, respectively. The performance of the μDFFC is superior to those of most others reported in the literature, further boosting the commercialization of this direct formate fuel cell to power next-generation portable electronics.

Synthesis of a Rationally Designed Multi-Component Photocatalyst Pt:SiO2:TiO2(P25) with Improved Activity for Dye Degradation by Atomic Layer Deposition

Photocatalysts for water purification typically lack efficiency for practical applications. Here we present a multi-component (Pt:SiO₂:TiO₂(P25)) material that was designed using knowledge of reaction mechanisms of mono-modified catalysts (SiO₂:TiO₂, and Pt:TiO₂) combined with the potential of atomic layer deposition (ALD). The deposition of ultrathin SiO₂ layers on TiO₂ nanoparticles, applying ALD in a fluidized bed reactor, demonstrated in earlier studies their beneficial effects for the photocatalytic degradation of organic pollutants due to more acidic surface Si–OH groups which benefit the generation of hydroxyl radicals. Furthermore, our investigation on the role of Pt on TiO₂(P25), as an improved photocatalyst, demonstrated that suppression of charge recombination by oxygen adsorbed on the Pt particles, reacting with the separated electrons to superoxide radicals, acts as an important factor for the catalytic improvement. Combining both materials into the resulting Pt:SiO₂:TiO₂(P25) nanopowder exceeded the dye degradation performance of both the individual SiO₂:TiO₂(P25) (1.5 fold) and Pt:TiO₂(P25) (4-fold) catalysts by 6-fold as compared to TiO₂(P25). This approach thus shows that by understanding the individual materials’ behavior and using ALD as an appropriate deposition technique enabling control on the nano-scale, new materials can be designed and developed, further improving the photocatalytic activity. Our research demonstrates that ALD is an attractive technology to synthesize multicomponent catalysts in a precise and scalable way.

Enhancement of the performance of Pd nanoclusters confined within ultrathin silica layers for formic acid oxidation

The optimized design of highly active and stable anode electrocatalysts is essential for high performance direct formic acid fuel cells (DFAFCs). Herein, a facile and cost-effective strategy was proposed to fabricate a robust ultrasmall Pd nanocluster confined within ultrathin protective silica layers anchored on nitrogen doped reduced GO (NrGO) through generating amine functionalized graphene oxide with 3-aminopropyl triethoxysilane (APTES), followed by tuning the thickness of protective silica layers by precisely controlling the amount of tetraethylorthosilicate (TEOS). Amine functionalized graphene oxide generated by using APTES favors the formation of ultrasmall Pd nanoclusters due to the coordination of amine to PdCl24- while the confinement effect of ultrathin protective silica layers stabilizes ultrasmall Pd nanoclusters and impedes the agglomeration and sintering of ultrasmall Pd nanoclusters during electrocatalysis. As a result, the ultrasmall Pd nanoclusters (∼1.4 nm) confined in silica layers on NrGO (Pd/NrGO@SiO2) demonstrate a very high forward peak current density for formic acid oxidation (FAO) of 2.37 A mg-1, outperforming the Pd/C catalyst (0.30 A mg-1) and the Pd/rGO catalyst obtained by a conventional method (0.42 A mg-1). More importantly, our confined Pd catalysts show the highest stability of only 5% inconspicuous degradation of the initial mass activity after 1000 cycles, compared with Pd/C (almost 100% loss), Pd/rGO (61.5% loss) and Pd/NrGO (73.2% loss). These strategies in this work provide a new prospect for the design of excellent noble catalysts to overcome the challenges in the practical application of DFAFCs.