1D alloy ultrafine Pt-Fe nanowires as efficient electrocatalysts for alcohol electrooxidation in alkaline media

Recent progress on the synthesis of metal alloy nanowires as electrocatalysts

Benefiting from both one-dimensional (1D) morphology and alloy composition, metal alloy nanowires have been exploited as advanced electrocatalysts in various electrochemical processes. In this review, the synthesis approaches for metal alloy nanowires are classified into two categories: direct syntheses and syntheses based on preformed 1D nanostructures. Ligand systems that are of critical importance to the formation of alloy nanowires are summarized and reviewed, together with the strategies imposed to achieve the co-reduction of different metals. Meanwhile, different scenarios that form alloy nanowires from pre-synthesized 1D nanostructures are compared and contrasted. In addition, the characterization and electrocatalytic applications of metal alloy nanowires are briefly discussed.

PtM/Mx By (M=Ni, Co, Fe) Heterostructured Nanobundles as Advanced Electrocatalyst for Hydrogen Evolution Reaction

Optimizing the electronic and synergistic effect of hybrid electrocatalysts based on Pt and Pt-based nanocatalysts is of tremendous importance towards a superior hydrogen evolution performance under both acidic and alkaline conditions. However, developing an ideal Pt-based hydrogen evolution reaction (HER) electrocatalyst with moderated electronic structure as well as strong synergistic effect is still a challenge. Herein, we fabricated boron (B)-doped PtNi nanobundles by a two-step method using NaBH₄ as the boron source to obtain PtNi/Ni₄ B₃ heterostructures with well-defined nanointerfaces between PtNi and Ni₄ B₃ , achieving an enhanced catalytic HER performance. Especially, the PtNi/Ni₄ B₃ nanobundles (PtNi/Ni₄ B₃ NBs) can deliver a current density of 10 mA cm^-2 at the overpotential of 14.6 and 26.5 mV under alkaline and acidic media, respectively, as well as outstanding electrochemical stability over 40 h at the current density of 10 mA cm^-2 . Remarkably, this approach is also universal for the syntheses of PtCo/Co₃ B and PtFe/Fe₄₉ B with outstanding electrocatalytic HER performance.

Recent Achievements in Noble Metal Catalysts with Unique Nanostructures for Liquid Fuel Cells

In recent years, research efforts have been focused on the design and fabrication of highly efficient catalysts for liquid fuel cells, because the use of these cells is an important approach for alleviating environmental pollution and energy crises. However, the limitations of the catalytic performance of industrial Pt/C have strongly hindered the development of these fuel cells. The catalyst morphology has a strong impact on its performance; nanostructured catalysts are preferred as they offer large specific surface area and more exposed active centers. In view of this, many catalysts with unique structures have been synthesized in recent years, all of which show excellent catalytic performance characteristics. Despite these achievements, few efforts have been made to survey this field comprehensively. Herein, the recent advances in catalysts for liquid fuel cells are summarized, with a focus on noble metal catalysts with unique morphologies such as nanowires, nanosheets, and assembly structures. Their formation mechanisms are discussed critically. The relationship between the unique morphologies and excellent performance of these catalysts is also explored. This work may provide guidelines for the further development of liquid fuel cells.

From bimetallic PdCu nanowires to ternary PdCu-SnO2 nanowires: Interface control for efficient ethanol electrooxidation

At present, although a large number of palladium-based nanowire electrocatalysts have been prepared, there are few reports on nanowires containing rich metal oxides. Herein, porous PdCu alloy nanowires and PdCu-SnO₂ nanowires were prepared by using a galvanic displacement synthesis method. Due to their one-dimensional structure, rough surfaces with non-homogeneous edges, electronic effect, and the advanced PdCu/SnO₂ interface of the as-synthesized PdCu-SnO₂ nanowire catalysts, they exhibited a mass activity of 7770.0 mA mg^-1 towards ethanol oxidation, which was 7.6-fold higher than that of Pd/C catalysts (1025.0 mA mg^-1). In addition, they behaved strong durability upon chronoamperometry and continuous cyclic voltammetry tests. The electrochemical measurements demonstrated that SnO₂ was introduced into the PdCu/SnO₂ interface, which promoted the oxidation of ethanol at a lower potential and accelerated the oxidation of Pd-CO_ads via SnO₂-OH_ads to regenerate the active sites. This research highlights the significance of introducing metal oxides into the nanostructure interface, and the performance of Pd-containing catalysts towards ethanol oxidation reaction was greatly improved.

High-density surface protuberances endow ternary PtFeSn nanowires with high catalytic performance for efficient alcohol electro-oxidation

Developing cost-effective catalysts with superb activity and stability to alcohol electro-oxidation is a decisive factor towards the progress of direct alcohol fuel cells (DAFCs). Rationally utilizing the architectural and surface microstructural sensitivity of nanocatalysts can significantly increase their electrocatalytic properties. Here, we report an appropriate route that allows the fabrication of ultrafine PtFeSn nanowires (NWs) with tunable compositions. Interestingly, the addition of Sn reconstructed the surface microstructures, making ultrafine 1D NWs rich in a large number of surface protuberances, which may facilitate the oxidation of ethanol and methanol. Impressively, further catalytic studies demonstrate that all the PtFeSn NWs exhibit excellent catalytic capabilities for ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR), and display composition-related electrocatalytic activity with Pt1Fe0.20Sn0.46 NWs, possessing the highest activity for EOR and MOR. In addition, the trimetallic PtFeSn NWs exhibit significant meliorative durability relative to PtFe NWs and commercial Pt/C. The superb electrocatalytic performance is ascribed to its one-dimensional (1D) structure, atomic-level fine diameter, synergistic effect among Pt, Fe, and Sn components and abundant protuberances on the surface. Thus, this study highlights the significance of accurate structure- and surface-controlled Pt-based NWs for electrocatalysis and provides a universal approach for designing multi-component catalysts.

Bimetallic Pd96Fe4 nanodendrites embedded in graphitic carbon nanosheets as highly efficient anode electrocatalysts

A facile route to anchor a nanoalloy catalyst on graphitic carbon nanosheets (GCNs) has been developed for preparing high-performance electrode materials for application in direct alcohol fuel cells (DAFCs). Uniformly dispersed bimetallic Pd-Fe nanoparticles (NPs) with tunable composition have been immobilized on GCNs derived from mesocarbon microbeads (MCMBs) by a one-pot radiolytic reduction method. The Pd-Fe/GCN hybrid shows promising electrocatalytic activity for the methanol, ethanol, ethylene glycol, tri-ethylene glycol and glycerol oxidation reactions in alkaline medium. The as-prepared flower-shape Pd₉₆Fe₄/GCN nanohybrids have high mass activity for the ethanol oxidation reaction (EOR), which is ∼36 times (11 A per mg Pd) higher than that of their monometallic counterparts. Moreover, the onset oxidation potential for the EOR on the Pd₉₆Fe₄/GCN nanohybrids negatively shifts ca. 780 mV compared to that on commercial Pd/C electrocatalysts, suggesting fast kinetics and superior electrocatalytic activity. Additionally, chronoamperometry measurements display good long-term cycling stability of the Pd₉₆Fe₄/GCN nanohybrids for the EOR and also demonstrate only ∼7% loss in forward current density after 1000 cycles. The superior catalytic activity and stability may have originated from the modified electronic structure of the Pd-Fe nanoalloys and excellent physicochemical properties of the graphitic nanosheets. The present synthetic route using GCNs as the supporting material will contribute to further design of multimetallic nanoarchitectures with controlled composition and desired functions for fuel cell applications.

Ultrathin PtNi nanozyme based self-powered photoelectrochemical aptasensor for ultrasensitive chloramphenicol detection

Nanozymes have gained increasing attention in the field of biosensing. Rationally designed nanozymes with excellent catalytic activity are accessible to substitute natural enzymes. Herein, a novel self-powered photoelectrochemical (PEC) aptasensor was constructed for ultrasensitive detection of chloramphenicol (CAP) based on ultrathin PtNi nanowires (NWs) as nanozyme and benzene-ring doped g-C₃N₄ (BR-CN) as the photoactive material. The prepared 1-nm-thick PtNi nanozyme acted as a peroxidase, possessing higher catalytic activity than natural horseradish peroxidase (HRP) and other Pt-based mimic enzymes. Through the biotin-streptavidin specific interaction, streptavidin modified PtNi nanozyme was introduced into the dual-stranded DNA (dsDNA) formed by complementary DNA and biotinylated CAP aptamer. The PtNi nanozyme catalyzed 4-chloro-1-naphthol (4-CN) oxidation to generate insoluble precipitation on the electrode surface, resulting in an obvious photocurrent reduction. In the presence of CAP, the CAP aptamer was released from the electrode due to strong affinity with CAP, causing the decrease of catalytic precipitation and consequently the generation of a high photocurrent signal. On the basis of PtNi nanozyme signal amplification, the developed self-powered PEC aptasensor showed a wide linear range of 0.1 pM-100 nM with an ultralow detection limit of 26 fM for the determination of CAP. This work provides a feasible strategy for the design of high-activity nanozyme and self-powered PEC biosensor to achieve the ultrasensitive detection of target analyte.

Tunable engineering hollow carbon nanomaterial served as an excellent catalyst for oxygen reduction reaction and hydrogen evolution reaction

Fe and N functionalized hollow carbon spheres (Fe/N-HCS) with hierarchically porous structure are constructed. Remarkably, it is discovered that the pyrolysis temperature effects the chemical composition intensively. At 800 °C, only graphitic-N and oxidized-N are formed for all as-prepared samples. The surface area and pores can be precisely tuned, the surface area of all Fe/N-HCS samples is more than 500  m² g^-1 benefiting from the porous hollow structure. Thus, the optimized Fe/N-HCS exhibits excellent oxygen reduction reaction performance in term of onset potential (1.00 V vs. RHE), half-wave potential (0.87 V vs. RHE), good stability as well as methanol tolerance for oxygen reduction reaction, even surpassing the Pt in alkaline condition and more competitive in acidic condition; Furthermore, the optimized Fe/N-HCS displays better hydrogen evolution reaction activity in acidic condition with onset overpotential of 40 mV and overpotential to deliver 10 mA cm^-2 at 170 mV, indicating better active. It is found that Fe/N-HCS improve the hydrogen evolution reaction activity after electrodeposition trace quantity of Pt, which shows 170 mV of overpotential to deliver 100 mA cm^-2. X-ray photoelectron spectroscopy result indicates the loading of Pt is roughly 0.11 at%, thus, the improved performance is basically due to the synergistic effect between Pt and Fe/N-HCS.