CaO-Promoted Graphene-Supported Palladium Nanocrystals as a Universal Electrocatalyst for Direct Liquid Fuel Cells

One-pot Synthesis of PdCuAg and CeO2 Nanowires Hybrid with Abundant Heterojunction Interface for Ethylene Glycol Electrooxidation

Introducing CeO2 into Pd-based nanocatalysts for electrocatalytic reactions is a good way to solve the intermediate toxicity problem and improve the catalytic performance. Here we reported a simple strategy to synthesize the PdCuAg and CeO2 nanowires hybrid via a one-pot synthesis process under strong nanoconfined effect of specific surfactant as templates. Owing to the structural (ultrathin nanowires, abundant heterojunction/interfaces between metal and metal oxide) and compositional (Pd, Cu, Ag, CeO2) advantages, the hybrid showed significantly enhanced catalytic activity (6.06 A mgPd -1) and stability, accelerated reaction rate, and reduced activation energy toward electrocatalytic ethylene glycol oxidation reaction.

An Unprecedented CeO2/C Non-Noble Metal Electrocatalyst for Direct Ascorbic Acid Fuel Cells

Direct ascorbic acid fuel cells (DAAFCs) employ biocompatible ascorbic acid (AA) as fuel, allowing convenient storage, transportation, and fueling as well as avoiding fuel crossover. The AA oxidation reaction (AAOR) largely governs the performance of DAAFCs. However, AAOR electrocatalysts currently have low activity, and state-of-the-art ones are limited to carbon black. Herein, we report the synthesis of an unprecedented AAOR electrocatalyst comprising 3.9 ± 1.1 nm CeO2 nanoparticles evenly distributed on carbon black simply by the wet chemical precipitation of Ce(OH)3 and a subsequent heat treatment. The resultant CeO2/C shows a remarkable AAOR activity with a peak current density of 13.1 mA cm-2, which is 1.7 times of that of carbon black (7.67 mA cm-2). According to X-ray photoelectron spectroscopy (XPS), the surface Ce3+ of CeO2 appears to contribute to the AAOR activity. Furthermore, our density functional theory (DFT) calculation reveals that that the proton of the hydroxyl group of AA can easily migrate to the bridging O sites of CeO2, resulting in a faster AAOR with respect to the pristine carbon, -COOH, and -C=O sites of carbon. After an i-t test, CeO2/C loses 17.8% of its initial current density, which is much superior to that of carbon black. CeO2 can capture the electrons generated by the AAOR to protect the -COOH and -C=O sites from being reduced. Finally, DAAFCs fabricated with CeO2/C exhibit a remarkable power density of 41.3 mW cm-2, which is the highest among proton-exchange-membrane-based DAAFCs in the literature.

Pronounced effect of yttrium oxide on the activity of Pd/rGO electrocatalyst for formic acid oxidation reaction

A highly efficient and stable electrocatalyst comprised of yttrium oxide (Y₂O₃) and palladium nanoparticles has been synthesized via a sodium borohydride reduction approach. The molar ratio of Pd and Y was varied to fabricate various electrocatalysts and the oxidation reaction of formic acid was checked. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD) are used to characterize the synthesized catalysts. Among the synthesized catalysts (Pd_yY_x/rGO), the optimized catalyst i.e., Pd₆Y₄/rGO exhibits the highest current density (106 mA cm^-2) and lowest onset potential compared to Pd/rGO (28.1 mA cm^-2) and benchmark Pd/C (21.7 mA cm^-2). The addition of Y₂O₃ to the rGO surface results in electrochemically active sites due to the improved geometric structure and bifunctional components. The electrochemically active surface area 119.4 m² g^-1 is calculated for Pd₆Y₄/rGO, which is ∼1.108, ∼1.24, ∼1.47 and 1.55 times larger than Pd₄Y₆/rGO, Pd₂Y₈/rGO, Pd/C and Pd/rGO, respectively. The redesigned Pd structures on Y₂O₃-promoted rGO give exceptional stability and enhanced resistance to CO poisoning. The outstanding electrocatalytic performance of the Pd₆Y₄/rGO electrocatalyst is ascribed to uniform dispersion of small size palladium nanoparticles which is possibly due to the presence of yttrium oxide.

Nickel -supported PdM (M = Au and Ag) nanodendrites as formate oxidation (electro)catalytic anodes for direct fuel cells and hydrogen generation at room temperature

The study provides a proof of concept for the first time that unique palladium-gold (PdAu) and palladium-silver (PdAg) nanodendrites are bifunctional catalytic active sites for formate oxidation reactions (FORs) and formate dehydrogenation reactions (FDRs). The unique nanodendritic structure was developed via a simple galvanic displacement reaction for the direct growth of PdAu and PdAg nanodendrites on a nickel foam (PdAu/NiNF and PdAg/NiNF). These PdAu/NiNF and PdAg/NiNF electrodes exhibited 2.32 and 1.59 times higher specific activity than that of the commercial Pd/C electrode and promising stability toward FORs. Moreover, the PdAu/NiNF and PdAg/NiNF nanodendrites were also highly active and selective catalysts for hydrogen generation from a formate solution with turnover frequency (TOF) values of 311 h^-1 and 287 h^-1 respectively. Impressively, a passive air-breathing formate fuel cell with PdAu/NiNF used as an anode can yield an open-circuit voltage of 1.12 V and a peak power density of 21.7 mW cm^-2, which outperforms most others reported in the literature. PdAu and PdAg nanodendritic catalysts supported on a nickel foam demonstrate an open structure and uniform catalyst distribution and offer a promising nanoalloy for air-breathing formate fuel cells and on-site chemical hydrogen production systems.

PdPbAg alloy NPs immobilized on reduced graphene oxide/In2O3 composites as highly active electrocatalysts for direct ethylene glycol fuel cells

rGO-modified indium oxide (In2O3) anchored PdPbAg nanoalloy composites (PdPbAg@rGO/In2O3) were prepared by a facile hydrothermal, annealing and reduction method. Electrochemical tests showed that the as-prepared trimetallic catalyst exhibited excellent electrocatalytic activity and high resistance to CO poisoning compared with commercial Pd/C, mono-Pd and different bimetallic catalysts. Specifically, PdPbAg@rGO/In2O3 has the highest forward peak current density of 213.89 mA cm-2, which is 7.89 times that of Pd/C (27.07 mA cm-2). After 3600 s chronoamperometry (CA) test, the retained current density of PdPbAg@rGO/In2O3 reaches 78.15% of the initial value. Its excellent electrocatalytic oxidation performance is attributed to the support with large specific surface area and the strong synergistic effect of PdPbAg nanoalloys, which provide a large number of interfaces and achievable reactive sites. In addition, the introduction of rGO into the In2O3 matrix contributes to its excellent electron transfer and large specific surface area, which is beneficial to improving the catalytic ability of the catalyst. The study of this novel composite material provides a conceptual and applicable route for the development of advanced high electrochemical performance Pd-based electrocatalysts for direct ethylene glycol fuel cells.

Rich grain boundaries endow networked PdSn nanowires with superior catalytic properties for alcohol oxidation

Networked nanowire (NNW)-structured catalysts have attracted extensive attention due to their large surface area and structural stability, which mean that they have excellent catalytic activity and stability and can be used as anode reaction catalysts for use in direct alcohol fuel cells (DAFCs). Herein, a series of networked PdSn nanowires synthesized via a modified polyol strategy are used as efficient DAFCs anode reaction catalysts. The introduction of Sn plays an important role in the improvement of catalytic behavior, in which the existence of Sn promotes the oxidation of intermediates by providing abundant oxyphilic species. Moreover, the generated PdSn NNWs-3 with optimal content show rich grain boundaries and an even NNW structure, which provides more active sites to further improve catalytic performance, so it exhibits excellent activity toward alcohol oxidation. The mass activities of PdSn NNWs-3 toward the ethanol oxidation reaction (EOR) and the methanol oxidation reaction (MOR) are 8105.0 and 3099.5 mA mg_Pd^-1, which are 6.9 and 10.7 times higher than those of Pd/C, respectively. Compared with Pd/C, the PdSn NNWs also display enhanced stability towards the EOR and MOR. This work demonstrates that NNW nanocatalysts indeed exhibit excellent catalytic performance for alcohol oxidation reactions.

Low temperature scalable synthetic approach enabling high bifunctional electrocatalytic performance of NiCo2S4 and CuCo2S4 thiospinels

Ternary metal sulfides are currently in the spotlight as promising electroactive materials for high-performance energy storage and/or conversion technologies. Extensive research on metal sulfides has indicated that, amongst other factors, the electrochemical properties of the materials are strongly influenced by the synthetic protocol employed. Herein, we report the electrochemical performance of uncapped NiCo₂S₄ and CuCo₂S₄ ternary systems prepared via solventless thermolysis of the respective metal ethyl xanthate precursors at 200 and 300 °C. The structural, morphological and compositional properties of the synthesized nanoparticles were examined by powder X-ray diffraction (p-XRD), transmission electron microscopy (TEM), high-resolution TEM, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) techniques. Electrochemical studies indicate that NiCo₂S₄ nanoparticles synthesized at 300 °C exhibit superior energy storage characteristics with a high specific capacitance of ca. 2650 F g⁻¹ at 1 mV s⁻¹, as compared to CuCo₂S₄ nanoparticles, which showcased a specific capacitance of ca. 1700 F g⁻¹ at the same scan rate. At a current density of 0.5 A g⁻¹, NiCo₂S₄ and CuCo₂S₄ nanoparticles displayed specific capacitances of 1201 and 475 F g⁻¹, respectively. In contrast, CuCo₂S₄ nanoparticles presented a higher electrocatalytic activity with low overpotentials of 269 mV for oxygen evolution reaction (OER), and 224 mV for the hydrogen evolution reaction (HER), at 10 mA cm⁻². The stability of the catalysts was examined for 2000 cycles in which a negligible change in both OER and HER activities was observed.

A scalable solventless approach is employed to prepare NiCo₂S₄ and CuCo₂S₄ with bare surface for enhanced supercapacitance and water splitting. The particles exhibit good energy storage and electrocatalytic activity as well as stability.

Metal-organic interface engineering for coupling palladium nanocrystals over functionalized graphene as an advanced electrocatalyst of methanol and ethanol oxidation

Adjusting the surface structures and electronic structures of metal nanocrystals (NCs) by the metal-organic interface interaction is an emerging strategy to enhance their electrocatalytic behavior. In this work, the d-phenylalanine-functionalized graphene (DPHE-GS) anchoring Pd NCs (denoted as Pd/DPHE-GS) was fabricated via the diazo-reaction followed by a simple chemical reduction. Owing to the metal-organic interface interaction between Pd NCs and DPHE, the size, distribution and electronic structures of Pd NCs on the surface of DPHE-GS can be adjusted. Therefore, the Pd/DPHE-GS shows the highest electrocatalytic activity and the most robust long-term durability and stability towards methanol and ethanol oxidation reaction (MOR and EOR) compared to the commercial Pd/C and other counterparts. This work presents an effective interface engineering strategy to enhance electrocatalytic property.

In situ electrochemical activation as a generic strategy for promoting the electrocatalytic hydrogen evolution reaction and alcohol electro-oxidation in alkaline medium

In situ electrochemical activation as a new pre-treatment method is extremely effective for enhanced electrocatalytic performances for different applications. With the help of this method, in situ surface modification of electrocatalyst is achieved without using pre-made seeds or complex synthesis procedure. Herein, with the purpose of finding an in situ and simple electrochemical activation protocol, the green synthesis of Au/Pd nanoparticles (AuPd) by means of polyoxometalate (POM) is reported. Structural analysis of the AuPd nanohybrid unveil the Au-core/Pd-shell structure which surrounded by POM. We propose a novel cathodic electrochemical activation in phosphate buffer solution which can greatly boost the electrocatalytic activity of the as-prepared AuPd and Pd electrocatalyst not only for hydrogen evolution reaction (HER) as a model of electro-reduction, but also for methanol and ethanol electro-oxidation reaction (MOR & EOR). For the HER in 1 M NaOH solution, after the electrochemical activation, the needed potential to drive a geometrical current density of 10 mA cm-2 significantly decreases from - 400 mV vs. the reversible hydrogen electrode (RHE) to -290 mV vs. RHE. For the EOR and MOR, electrochemically activated AuPd realized 3.4- and 2.9- fold increase in mass current density (mA mgPd -1) with respect to the pristine AuPd electrocatalyst, respectively.

Re-dispersion of Pd-based bimetallic catalysts by hydrothermal treatment for CO oxidation

The Pd/CeO₂ catalyst, which is highly active catalyst in automobile emission control especially for CO oxidation, often suffers from severe sintering under harsh condition, specifically hydrothermal treatment. Here, we report re-dispersion of Pd-based bimetallic (Pd–Fe, Pd–Ni, and Pd–Co) catalysts deposited on ceria by hydrothermal treatment at 750 °C using 10% H₂O. The re-dispersion was confirmed by various characterization techniques of transmission electron microscopy, CO chemisorption, CO-diffuse reflectance infrared Fourier transform, CO-temperature programmed desorption, and X-ray absorption spectroscopy. The dispersion of Pd increased significantly after hydrothermal treatment, resulting in improved CO oxidation activity. The presence of secondary transition metals enhanced the CO oxidation activity further, especially hydrothermally treated Pd–Fe bimetallic catalyst showed the highest activity for CO oxidation.

PdM (M: Fe, Co, Ni) catalysts deposited on ceria were hydrothermally treated, resulting in re-dispersion of the metal species. They showed enhanced activity for CO oxidation.

Retention of anions in cobalt hydroxide with Ni substitution to emphasize the role of anions and cations for high current density in oxygen evolution reactions

Herein, we report the fabrication of remarkably fine nickel-substituted α-Co(OH)2 sheets using an ingenious co-precipitation method at a lower pH value. An α-CoNiOOH sheet retains the parent α-Co(OH)2 structure consisting of both tetrahedral (Td) and octahedral (Oh) sites with the retention of interlayer chloride ions, which is in contrast to the previous reports. The as-synthesized α-CoNiOOH sheet exhibits excellent oxygen evolution reactions (OERs) and produces a current of 10 mA cm-2 at an overpotential of merely 190 mV in an alkaline environment. Moreover, the α-CoNiOOH sheet attains an exceptionally high current density of 100 mA cm-2 at a low overpotential of only 270 mV. Additionally, this electrocatalyst possesses a 33 mV dec-1 Tafel slope with higher values of TOF (11 s-1) and double-layer capacitance (7.76 mF cm-2). This enhancement is attributed partially to the substitution of Ni during the conversion of α-Co(OH)2 to α-CoNiOOH and partially to the exceptionally thin sheets allowing potential octahedral sites for improved oxygen evolution reactions.

Toxicity and mechanism of mesoporous silica nanoparticles in eyes

The study on the safety of nanomaterials in eyes is still in its early stages. In this study, we put our focus on the effect of one important nanoparticle feature - large surface area - to assess eye safety. To this end, mesoporous silica nanoparticles (MSiNPs) were for the first time employed as a model to evaluate their toxicity in eyes. The porosity of the MSiNPs endows them with a large surface area and the ability to attach to surrounding chemical or biological molecules, further enhancing their surface reactivity and toxic effects. Therefore, to better mimic MSiNP exposure in real environments, we also introduced other hazardous substances such as silver ions (Ag+) to the system and then investigated their synergistic nanotoxicity. Our results showed that the exposure to MSiNPs-Ag+ and even Ag+ at a safe dose, resulted in more significant toxicity than the MSiNPs alone, as evidenced from cell viability, apoptosis, reactive oxygen species (ROS) production, and DNA damage experiments. RNA-Sequencing analysis revealed that the mRNA surveillance signalling pathway plays a unique role in regulating MSiNPs-Ag+-induced cytotoxicity. Besides this, severe corneal damage and dry eye were observed in rat models upon exposure to MSiNPs-Ag+ compared to MSiNPs. Most importantly, we also proposed a protein corona-based therapy to treat MSiNP-induced corneal disease, where the corneal damage could be rescued by fetal bovine serum (FBS) treatment.