Oxygen reduction electrocatalyst of Pt on Au nanoparticles through spontaneous deposition

Palladium/Platinum/Ruthenium Trimetallic Dendritic Nanozymes Exhibiting Enhanced Peroxidase-like Activity for Signal Amplification of Lateral Flow Immunoassays

Developing ultrasensitive lateral flow immunoassays (LFIAs) has garnered significant attention in the field of point-of-care testing. In this study, a trimetallic dendritic nanozyme (Pd@Pt-Ru) was synthesized through Ru deposition on a Pd@Pt core and utilized to enhancing the sensitivity of LFIAs. Pd@Pt-Ru exhibited a Km value of 5.23 mM for detecting H2O2, which indicates an H2O2 affinity comparable with that of horseradish peroxidase. The Ru surface layer reduces the activation energy barrier, which increases the maximum reaction rate. As a proof of concept, the proposed Pd@Pt-Ru nanozyme was incorporated into LFIAs (A-Pd@Pt-Ru-LFIAs) for detecting human chorionic gonadotropin (hCG). Compared with conventional gold nanoparticle (AuNP)-LFIAs, A-Pd@Pt-Ru-LFIAs demonstrated 250-fold increased sensitivity, thereby enabling a visible detection limit as low as 0.1 IU/L. True positive and negative rates both reached 100%, which renders the proposed Pd@Pt-Ru nanozyme suitable for detecting hCG in clinical samples.

Bionic Fe-N-C catalyst with abundant exposed Fe-Nx sites and enhanced mass transfer properties for efficient oxygen reduction

Transition metal and nitrogen co-doped carbon electrocatalysts are promising candidates to replace the precious metal platinum (Pt) in oxygen reduction reactions (ORR). Unfortunately, the electrochemical performance of existing electrocatalysts is restricted due to limited accessibility of active sites. Inspired by jellyfish tentacles, we design an efficient ORR micro-reactor called Fe-Nx/HC@NWs. It features abundant exposed Fe-Nx active sites dispersed on nitrogen-doped cubic carbon cages, which have a hierarchically porous and hairy structure. The accessible, atomically dispersed Fe-Nx sites and the elaborate substrate architecture synergize to provide the catalyst withremarkable ORR catalytic activity, extraordinary long-term stability, and favorable methanol tolerance in an alkaline electrolyte; overall, its performance is comparable to that of commercial carbon-supported Pt. Our synthesis is facile and controllable, paving a new avenue toward advanced non-precious metal-based electrocatalysts for energy storage and conversion.

Thermally Induced Surface Structure and Morphology Evolution in Bimetallic Pt-Au/HOPG Nanoparticles as Probed Using XPS and STM

Bimetallic nanoparticles expand the possibilities of catalyst design, providing an extra degree of freedom for tailoring the catalyst structure in comparison to purely monometallic systems. The distribution mode of two metal species defines the structure of surface catalytic sites, and current research efforts are focused on the development of methods for their controlled tuning. In light of this, a comprehensive investigation of the factors which influence the changes in the morphology of bimetallic nanoparticles, including the elemental redistribution, are mandatory for each particular bimetallic system. Here we present the combined XPS/STM study of the surface structure and morphology of bimetallic Pt-Au/HOPG nanoparticles prepared by thermal vacuum deposition and show that thermal annealing up to 350 °C induces the alloying process between the two bulk-immiscible metal components. Increasing the treatment temperature enhances the extent of Pt-Au alloying. However, the sintering of nanoparticles starts to occur above 500 °C. The approach implemented in this work includes the theoretical simulation of XPS signal intensities for a more meticulous analysis of the compositional distribution and can be helpful from a methodological perspective for other XPS/STM studies of bimetallic nanoparticles on planar supports.

Observing the Structural Evolution of Quasi-Monolayer Pt Shell on Pd Core in the Electrocatalytic Oxygen-Reduction Reaction

The use of a quasi-monolayer Pt shell (Ptqms) on a Pd core (Pdc) can reach cost and activity targets for the electrocatalytic oxygen-reduction reaction (ORR). The structure of PdcPtqms in the ORR will vary; however, direct observation of this issue is scarce. Here, during cyclic staircase voltammetry (ranging from 0.5 to 1.15 VRHE) in 0.1 M O2-saturated HClO4, the structure of PdcPtqms was monitored by in situ X-ray absorption spectroscopy. The qualitative and quantitative structural information clearly exhibits a complete picture that Ptqms will directly restructure to form Pt clusters and holes, while Pdc almost remains stable. These findings identify the initial structural evolution of PdcPtqms in the ORR, highlighting the importance of protecting Pdc in the development of high-performance PdcPtqms electrocatalysts.

Fe(II)-Assisted one-pot synthesis of ultra-small core-shell Au-Pt nanoparticles as superior catalysts towards the HER and ORR

In this work, uniform ultra-small core-shell Au-Pt nanoparticles (denoted as USCS Au-Pt NPs) with Au-decorated Pt surfaces are successfully prepared by Fe(ii)-assisted one-pot co-reduction of Au(iii) ions and Pt(ii) ions in a citrate solution. The as-prepared USCS Au38.4@Au9.3Pt52.3 NPs have an average diameter of 2.3 ± 0.5 nm. It is found that the morphology, composition and size of Au-Pt NPs are highly dependent on the reaction conditions including the addition sequence of the precursors, and the concentrations of Fe(ii) ions, Au(iii) ions and Pt(ii) ions. In addition, USCS Au38.4@Au9.3Pt52.3-NP/C catalysts (USCS Au38.4@Au9.3Pt52.3 NPs loaded on the Vulcan XC-72R carbon black) exhibit excellent electrocatalytic performance towards the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) in acidic media due to the higher electrochemically active surface area (ECSA) and electronic effect between Pt and Au. For instance, USCS Au38.4@Au9.3Pt52.3-NP/C catalysts exhibited greatly enhanced HER activity in terms of overpotential (16 mV at a current density of -10 mA cm-2) and are better than commercial Pt/C catalysts (31 mV at a current density of -10 mA cm-2) reported in the literature thus far, to the best of our knowledge. Strikingly, their mass activity is about 13.1-fold higher than that of commercial Pt/C catalysts. Moreover, they also show an improved ORR activity, Eonset = 1.015 V and E1/2 = 0.896 V, which are positively shifted by nearly 28 mV and 21 mV than those of commercial Pt/C catalysts (0.987 V and 0.875 V), respectively. In addition, they also showed a higher kinetic current density (12.85 mA cm-2 at 0.85 V) and a better long-term durability. Our synthetic strategy presented here may be extended to the preparation of ultra-small Au-based bimetallic or multi-metallic NPs.

Bimetallic PtAu electrocatalysts for the oxygen reduction reaction: challenges and opportunities

Highly active, durable oxygen reduction reaction (ORR) electrocatalysts have an essential role in promoting the continuous operation of advanced energy technologies such as fuel cells and metal-air batteries. Considering the scarce reserve of Pt and its unsatisfactory overall performance, there is an urgent demand for the development of new generation ORR electrocatalysts that are substantially better than the state-of-the-art supported Pt-based nanocatalysts, such as Pt/C. Among various nanostructures, bimetallic PtAu represents one unique alloy system where highly contradictory performance has been reported. While it is generally accepted that Au may contribute to stabilizing Pt, its role in modulating the intrinsic activity of Pt remains unclear. This perspective will discuss critical structural issues that affect the intrinsic ORR activities of bimetallic PtAu, with an eye on elucidating the origin of seemingly inconsistent experimental results from the literature. As a relatively new class of electrodes, we will also highlight the performance of dealloyed nanoporous gold (NPG) based electrocatalysts, which allow a unique combination of structural properties highly desired for this important reaction. Finally, we will put forward the challenges and opportunities for the incorporation of these advanced electrocatalysts into membrane electrode assemblies (MEA) for actual fuel cells.

Combined Experimental and Theoretical Study of the Structure of AuPt Nanoparticles Prepared by Galvanic Exchange

In this article, experiment and theory are combined to analyze Pb and Cu underpotential deposition (UPD) on ∼1.7 nm Au nanoparticles (NPs) and the AuPt structures that result after galvanic exchange (GE) of the UPD layer for Pt. Experimental Pb (0.49 ML) and Pt (0.50 ML) coverages are close to values predicted by density functional theory-molecular dynamics (DFT-MD, 0.59 ML). DFT-MD reveals that the AuNPs spontaneously reconstruct from cuboctahedral to a (111)-like structure prior to UPD. In the case of Pb, this results in the random electrodeposition of Pb onto the Au surface. This mechanism is a consequence of opposing trends in Pb-Pb and Pb-Au coordination numbers as a function of Pb coverage. Cu UPD is more complex, and agreement between theory and experiment takes into account ligand effects (e.g., SO₄^2- present as the electrolyte) and the electric double layer. Importantly, AuPt structures formed upon Pt GE are found to differ markedly depending on the UPD metal. Specifically, cyclic voltammetry indicates that the Pt coverage is ∼0.20 ML greater for Cu UPD/Pt GE (0.70 ML) than for Pb UPD/Pt GE (0.50 ML). This difference is corroborated by DFT-MD theoretical predictions. Finally, DFT-MD calculations predict the formation of surface alloy and core@shell structures for Pb UPD/Pt GE and Cu UPD/Pt GE, respectively.

In Situ Generated Dual-Template Method for Fe/N/S Co-Doped Hierarchically Porous Honeycomb Carbon for High-Performance Oxygen Reduction

Heteroatoms doping is able to produce catalytic sites in carbon materials for oxygen reduction reaction (ORR); while hierarchically porous structure is necessary for efficient exposure and accessibility of the usually limited catalytic sites in such activated carbon catalysts. This work reports an in situ generated dual-template method to synthesize the Fe/N/S co-doped hierarchically porous carbon (FeNS/HPC), with NaCl crystallites formed during the precursor lyophilization process as the primary template to generate ∼500 nm macropores with ultrathin graphene-like carbon-layer walls, and Fe₃O₄ nanoparticles formed during the high-temperature carbonization process as the secondary template to produce mesopores on the walls of macropores. As well as the coexistence of graphitic-N, pyridinic-N, and thiophene-S which are beneficial to ORR, the as prepared FeNS/HPC possesses a highly graphitized and interconnected hierarchical porous structure, giving a specific surface area as high as 938 m² g^-1. As a consequence, it exhibits excellent four-electron oxygen reduction performance in both alkaline and acid electrolytes. The in situ generation and facile solution removal make the present template method a promising way for scale-up preparation of active porous carbon materials for various applications.

Novel Au Catalysis Strategy for the Synthesis of Au@Pt Core-Shell Nanoelectrocatalyst with Self-Controlled Quasi-Monolayer Pt Skin

Design of catalytically active Pt-based catalysts with minimizing the usage of Pt is a major issue in fuel cells. Herein, for the first time, we have developed a Au catalytic reduction strategy to synthesize a Au@Pt core-shell electrocatalyst with a quasi-monolayer Pt skin spontaneously formed from the gold surface catalysis. In the presence of presynthesized gold nanocrystals (used as the catalyst and Au seeds) and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (used as reductant), under the Au surface catalysis, platinum ions can be reduced and deposited on the gold nanocrystals to form a Pt skin surface with a quasi-monatomic thickness. In the present strategy, Pt ions can be reduced only under the catalysis of gold surface and thus when the surface of Au NPs is covered by a monatomic Pt layer, the reduction reaction of Pt ions will be spontaneously turned off. Therefore, the significant advantage of this synthesis strategy is that the formation of quasi-monolayer Pt skin surface can be self-controlled and is completely free of controlling the dosage of platinum ions and the size distribution of Au cores. The synthesized Au@Pt core@shell structure exhibited enhanced electrocatalytic activities for oxygen reduction reaction and methanol oxidation reaction, which are 6.87 and 10.17 times greater than those of Pt/C catalyst, respectively. The present study provides a new strategy for obtaining high-performance bimetallic/multimetallic electrocatalysts with high utilization of precious metals.

Covalent versus Charge Transfer Modification of Graphene/Carbon-Nanotubes with Vitamin B1: Co/N/S-C Catalyst toward Excellent Oxygen Reduction

High-performance nonprecious cathodic catalysts for oxygen reduction are highly demanded for low-temperature polymer electrolyte membrane fuel cells (PEMFCs). Here, we report a noble-meta- free, nitrogen and sulfur codoped graphene(G)/carbon-nanotube(CNT) material decorated with Co nanoparticles (NPs), which serve as catalytic sites for excellent oxygen reduction reaction (ORR) in basic and acidic media. Out of the cathodic catalysts synthesized by either covalent (cov) or charge transfer (CT) modification of graphen oxide (GO) with thiamine (Th: Vitamin B1), ThG/CNT/Co-cov shows more promising ORR properties than ThG/CNT/Co-CT. Catalyst ThG/CNT/Co-cov exhibits onset/halfwave potentials of 0.95/0.86 V in 0.1 M KOH and 0.92/0.83 V in 0.1 M HClO4, which are comparable to those of commercial catalyst Pt/C (0.95/0.86 V). As compared to Pt/C, our catalyst shows higher current densities of 6.72 mA cm(-2) in basic medium and 7.08 mA cm(-2) in acidic medium at 0.55 V (vs reversible hydrogen electrode (RHE)). It also exhibits better catalytic stability and methanol tolerance. High catalytic efficiency and stability of ThG/CNT/Co-cov show a promising prospect of materialization of PEMFCs for clean energy production.

Elucidation of adsorption processes at the surface of Pt(331) model electrocatalysts in acidic aqueous media

The Pt(331) surface has long been known to be the most active pure metal electrocatalyst for the oxygen reduction reaction (ORR) in acidic media. Its activity is often higher than those known for the Pt-based alloys towards ORR, being comparable with the most active Pt3Ni(111), Pt3Y or Pt5Gd, and being more active than e.g. polycrystalline Pt3Ni. Multiple active sites at this surface offer adsorption energies which are close to the optimal binding energy with respect to the main ORR intermediates; nevertheless, the exact location of these sites is still not clear. Taking into account the unique surface geometry of Pt(331), some adsorbates (including some oxygenated ORR-intermediates) should also contribute to the electronic structure of the neighbouring catalytic centres. However, the experimental elucidation of the specific adsorption of oxygenated species at this surface appears to be a non-trivial task. Such information holds the keys to the understanding of the high activity of this material and would enable the rational design of nanostructured ORR catalysts even without alloying. In this work, the electrified Pt(331)/electrolyte interface has been characterised using cyclic voltammetry (CV) combined with potentiodynamic electrochemical impedance spectroscopy (PDEIS) in 0.1 M HClO4 solutions. The systems were studied in the potential region between 0.05 V and 1.0 V vs. RHE, where the adsorption of *H, *OH and *O species is possible in both O2-free and O2-saturated electrolytes. Our CV and PDEIS results support the hypothesis that in contrast to Pt(111), many Pt(331) surface sites are likely blocked by *O species at the polymer electrolyte membrane fuel cell benchmark potential of 0.9 V (RHE). We propose a model illustrated by simplified adsorbate structures at different electrode potentials, which is, however, able to explain the voltammetric and impedance data, and which is in good agreement with previously reported electrocatalytic measurements.

Hemoglobin-carbon nanotube derived noble-metal-free Fe5C2-based catalyst for highly efficient oxygen reduction reaction

High performance non-precious cathodic catalysts for oxygen reduction reaction (ORR) are vital for the development of energy materials and devices. Here, we report an noble metal free, Fe₅C₂ nanoparticles-studded sp² carbon supported mesoporous material (CNTHb-700) as cathodic catalyst for ORR, which was prepared by pyrolizing the hybrid adduct of single walled carbon nanotubes (CNT) and lyophilized hemoglobin (Hb) at 700 °C. The catalyst shows onset potentials of 0.92 V in 0.1 M HClO₄ and in 0.1 M KOH which are as good as commercial Pt/C catalyst, giving very high current density of 6.34 and 6.69 mA cm⁻² at 0.55 V vs. reversible hydrogen electrode (RHE), respectively. This catalyst has been confirmed to follow 4-electron mechanism for ORR and shows high electrochemical stability in both acidic and basic media. Catalyst CNTHb-700 possesses much higher tolerance towards methanol than the commercial Pt/C catalyst. Highly efficient catalytic properties of CNTHb-700 could lead to fundamental understanding of utilization of biomolecules in ORR and materialization of proton exchange membrane fuel cells for clean energy production.

Carbon monoxide mediated chemical deposition of Pt or Pd quasi-monolayer on Au surfaces with superior electrocatalysis for ethanol oxidation in alkaline media

CO-mediated chemical deposition of a Pt or Pd quasi-monolayer on Au surfaces with superior electrocatalysis for ethanol oxidation in alkaline media.

Target-induced nanocatalyst deactivation facilitated by core@shell nanostructures for signal-amplified headspace-colorimetric assay of dissolved hydrogen sulfide

Colorimetric assay platforms for dissolved hydrogen sulfide (H2S) have been developed for more than 100 years, but most still suffer from relatively low sensitivity. One promising route out of this predicament relies on the design of efficient signal amplification methods. Herein, we rationally designed an unprecedented H2S-induced deactivation of (gold core)@(ultrathin platinum shell) nanocatalysts (Au@TPt-NCs) as a highly efficient signal amplification method for ultrasensitive headspace-colorimetric assay of dissolved H2S. Upon target introduction, Au@TPt-NCs were deactivated to different degrees dependent on H2S levels, and the degrees could be indicated by using a Au@TPt-NCs-triggered catalytic system as a signal amplifier, thus paving a way for H2S sensing. The combination of experimental studies and density functional theory (DFT) studies revealed that the Au@TPt-NCs with only 2-monolayer equivalents of Pt (θPt = 2) were superior for H2S-induced nanocatalyst deactivation owing to their enhanced peroxidase-like catalytic activity and deactivation efficiency stemmed from the unique synergistic structural/electronic effects between Au nanocores and ultrathin Pt nanoshells. Importantly, our analytical results showed that the designed method was indeed highly sensitive for sensing H2S with a wide linear range of 10-100 nM, a slope of 0.013 in the regression equation, and a low detection limit of 7.5 nM. Also the selectivity, reproducibility, and precision were excellent. Furthermore, the method was validated for the analysis of H2S-spiked real samples, and the recovery in all cases was 91.6-106.7%. With the merits of high sensitivity and selectivity, simplification, low cost, and visual readout with the naked eye, the colorimetric method has the potential to be utilized as an effective detection kit for point-of-care testing.