Hierarchically skeletal multi-layered Pt-Ni nanocrystals for highly efficient oxygen reduction and methanol oxidation reactions

Lattice-Strained Bimetallic Nanocatalysts: Fundamentals of Synthesis and Structure

Bimetallic nanostructured catalysts have shown great promise in the areas of energy, environment and magnetics. Tunable composition and electronic configurations due to lattice strain at bimetal interfaces have motivated researchers worldwide to explore them industrial applications. However, to date, the fundamentals of the synthesis of lattice-mismatched bimetallic nanocrystals are still largely uninvestigated for most supported catalyst materials. Therefore, in this work, we have conducted a detailed review of the synthesis and structural characterization of bimetallic nanocatalysts, particularly for renewable energies. In particular, the synthesis of Pt, Au and Pd bimetallic particles in a liquid phase has been critically discussed. The outcome of this review is to provide industrial insights of the rational design of cost-effective nanocatalysts for sustainable conversion technologies.

Highly Dispersed Ultrasmall High-Entropy Alloys Nanoparticles as Efficient Electrocatalysts for Oxygen Reduction in Acidic Media

High-entropy alloys nanoparticles (HEAs NPs) have gained considerable attention due to their extensive compositional tunability and intriguing catalytic properties. However, the synthesis of highly dispersed ultrasmall HEAs NPs remains a formidable challenge due to their inherent thermodynamic instability. In this study, highly dispersed ultrasmall (ca. 2 nm) PtCuGaFeCo HEAs NPs are synthesized using a one-pot solution-based method at 160 °C and atmospheric pressure. The PtCuGaFeCo NPs exhibit good catalytic activity for the oxygen reduction reaction (ORR). The half-wave potential relative to the reversible hydrogen electrode (RHE) reaches 0.88 V, and the mass activity and specific activity are approximately six times and four times higher than that of the commercial Pt/C catalyst. Based on X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) analyses, the surface strain and optimized coordination environments of PtCuGaFeCo have led to high ORR activities in acidic media. Moreover, the ultrasmall size also plays an important role in enhancing catalytic performance. The work presents a facile and viable synthesis strategy for preparing the ultrasmall HEAs NPs, offering great potential in energy and electrocatalysis applications through entropy engineering.

PtNi alloy nanoparticles grown in situ on nitrogen doped carbon for the efficient oxygen reduction reaction

Currently, Pt based materials are still the most efficient oxygen reduction reaction (ORR) catalysts. However, their poor stability obstructs the commercial viability of fuel cells. To lower the reaction potential barrier and enhance the stability, we constructed alloy PtNi nanoparticles (NPs) with a Pt-rich surface supported on nitrogen-doped carbon (NC) via a simple one-step solvothermal method using easily accessible reagents. The synthesized PtNi/NC exhibits enhanced mass activity (MA), specific activity (SA), and positive onset potential compared with commercial Pt/C catalysts. Meanwhile, the half-wave potential shifted negatively to only 18 mV after 5000 cycles for PtNi/NC, indicating excellent stability. The enhanced ORR performance can be ascribed to the introduction of Ni into Pt optimizing the adsorption energy of Pt towards oxygen by adjusting the d band center of the Pt atom and stronger interaction between the metal NPs and support. Our work provides a potential synthesis strategy for developing a Pt-based catalyst with a low Pt loading and high ORR performance.

Conductivity-enhanced porous N/P co-doped metal-free carbon significantly enhances oxygen reduction kinetics for aqueous/flexible zinc-air batteries

Heteroatom-doped metal-free carbon catalysts for oxygen reduction reactions have gained significant attention because of their unusual activity and economic cost. Here, a novel N/P co-doped porous carbon catalyst (NPPC) with a high surface area for oxygen reduction reaction (ORR) is constructed by a facile high-temperature calcination method employing ZIF-8 as the precursor and red phosphorus as the phosphorus source. In particular, ZIF-8 is firstly calcined to obtain N-doped carbon (NC) followed by further calcination with red phosphorus to obtain NPPC. Ultraviolet photoelectron spectroscopy (UPS) analysis shows that the ultra-low amount of P doping could significantly decrease the work function from 4.32 to 3.86 eV. The resultant catalyst exhibits a promising electrocatalytic activity with a half-wave potential (E_1/2) of 0.87 V and a limiting current density (J_L) of 5.15 mA cm^-2. Besides, it also shows improved catalytic efficiency and excellent durability with a negligible decay of J_L after 2000 CV cycles. Moreover, aqueous and solid-state flexible zinc-air batteries (ZAB) using the catalyst show a promising application potential. This work provides new insight into developing P/N-doped metal-free carbon ORR catalysts.

A high-performance Pt-based catalyst for the methanol oxidation reaction: effect of electrodeposition mode and cocatalyst on electrocatalytic activity

The influence of supporting material, cocatalyst, and electrodeposition mode on MOR activity.

Low-temperature N-anchored ordered Pt3Co intermetallic nanoparticles as electrocatalysts for methanol oxidation reaction

To enhance nanocatalyst performance and durability for the methanol oxidation reaction (MOR) in a direct methanol fuel cell, small-sized (2.1 nm) and structurally ordered Pt₃Co intermetallic nanoparticles are uniformly anchored onto nitrogen-doped carbon nanotubes (N-CNTs) via a low-temperature N-anchoring method, and the N-doping abilities of different N-containing reagents are compared. After investigating the microstructure of Pt₃Co/N-CNTs and evaluating their catalytic activity for the MOR, the results show that N-doping facilitates the uniform loading of Pt₃Co NPs and plays a crucial role in improving the electrocatalytic activity of Pt₃Co NPs supported on CNTs. Pt₃Co/N-CNT-M with melamine as the N dopant exhibits the highest MOR activity and stability among all N-CNT-supported Pt₃Co NPs and Pt/N-CNT-M. Density functional theory calculations suggest that the doping of N enhances the binding energy of CNTs to Pt₃Co NPs, and the MOR mechanism shows that the introduction of Co is the reason for the enhancement of MOR reaction kinetics. The excellent electrochemical performance of Pt₃Co/N-CNT-M is mainly attributed to the synergistic effect of N and Pt₃Co intermetallic nanoparticles. The combination of ordered alloy nanoparticles and high-performance carrier N-CNT-M described herein exhibits great potential for fuel cells and may provide an unequivocal direction for the optimization of catalyst performance.

Materials Research Directions Toward a Green Hydrogen Economy: A Review

A constellation of technologies has been researched with an eye toward enabling a hydrogen economy. Within the research fields of hydrogen production, storage, and utilization in fuel cells, various classes of materials have been developed that target higher efficiencies and utility. This Review examines recent progress in these research fields from the years 2011-2021, exploring the most commonly occurring concepts and the materials directions important to each field. Particular attention has been given to catalyst materials that enable the green production of hydrogen from water, chemical and physical storage systems, and materials used in technical capacities within fuel cells. The quantification of publication and materials trends provides a picture of the current state of development within each node of the hydrogen economy.

Simply prepared electrocatalyst of CoFe alloy and nitrogen-doped carbon with multi-dimensional structure and high performance for rechargeable zinc-air battery

Simple and green preparation of highly-performed electrocatalysts for reaction both at cathode (oxygen reduction reaction (ORR)) and anode (oxygen evolution reaction (OER)) is crucial for boosting the application of meta-air battery. CoFe alloy and nitrogen doped carbon (CoFe-NC) material was prepared by a one-step carbonization procedure to construct a highly efficient electrocatalysis in this work. CoFe-NC displays a three-dimensional (3D) flower-like morphology composed of ordered stacked 2D nanosheets, which is entangled by 1D carbon nanotubes (CNTs). Its structure and electrocatalytic performance are compared with that of nitrogen doped carbon materials obtained from 2D zeolitic-imidazolate frameworks (ZIF) with no metal or single metal, as well as 3D ZIF with bimetal. Benefiting from the multi-dimensional structure of bimetal nanoparticles, 1D CNTs, 2D nanosheets, and 3D flowers, as well as the abundant active sites of Co/Fe-N_xand pyridine nitrogen, CoFe-NC displays a high half-wave potential of 0.896 V for ORR and low overpotential of 370 mV at 10 mA cm^-2for OER. Furthermore, compared with the primary and rechargeable Zn-air batteries fabricated with commercial Pt/C-RuO₂catalysts, the CoFe-NC catalysts assembled Zn-air batteries show a higher specific capacity (812.2 mAh g^-1), open circuit potential (1.59 V), power density (183.4 mW cm^-2), and stability. Hence, a facile and environmental-friendly strategy is provided for rational design and synthesis of bifunctional electrocatalysts for zinc-air batteries.

Natural polysaccharides based self-assembled nanoparticles for biomedical applications - A review

In recent years, nanoparticles (NPs) derived from the self-assembly of natural polysaccharides have shown great potential in the biomedical field. Here, we described several self-assembly modes of natural polysaccharides in detail, summarized the natural polysaccharides mostly used for self-assembly, and provided insights into the current applications and achievements of these self-assembled NPs. As one of the most widespread substances in nature, most natural polysaccharides exhibit advantages of biodegradability, low immunogenicity, low toxicity, and degradable properties. Therefore, they have been fully explored, and the application of chitosan, hyaluronic acid, alginate, starch, and their derivatives has been extensively studied, especially in the fields of biomedical. Polysaccharides based NPs were proved to improve the solubility of insoluble drugs, enhance tissue target ability and realize the controlled and sustained release of drugs. When modified by hydrophobic groups, the amphiphilic polysaccharides can self-assemble into NPs. Other driven forces of self-assembly include electrostatic interaction and hydrogen bonds. Up to the present, polysaccharides-based nanoparticles have been widely applied for tumor treatment, antibacterial application, gene therapy, photodynamic therapy and transporting insulin.

Surface unsaturated WOx activating PtNi alloy nanowires for oxygen reduction reaction

PtNi alloy nanoparticles display promising catalytic activity for oxygen reduction reaction (ORR), while the Ostwald ripening of particles and the dissolution/migration of surface atoms greatly affect its stability thus restricting the application. Herein, the WO_x-surface modified PtNi alloy nanowires (WO_x-PtNi NWs) exhibiting enhanced ORR catalytic property is reported, which has high aspect ratio with the diameter of only 2 ∼ 3 nm. It is found that the WO_x-PtNi NWs shows a volcano relationship between the ORR activity and the content of WO_x. The WO_x-(0.25)-PtNi NWs has the best performance among all the synthesized catalysts. Its mass activity (0.85 A mg^-1_Pt) is reduced by only 23.89% after 30k cycles durability test, which is much more stable than that of PtNi NWs (0.33 A mg^-1_Pt, 45.94%) and Pt/C (0.14 A mg^-1_Pt, 57.79%). Hence this work achieves an effective regulation of the ORR activity for PtNi alloy NWs by the synergistic effect of WO_x on Pt.

Green Microwave-Assisted Synthesis of CoFeRu-Based Electrocatalyst for the Oxygen Reduction Reaction

A simple and rapid synthesis of a CoFeRu-based electrocatalyst by a microwave-assisted method (using water as the microwave absorbing solvent) is reported in this work. Agglomerates with different sizes and shapes are observed by scanning electron microscopy technique. The energy dispersive X-ray spectroscopy shows a low atomic percentage of Co and similar atomic percentage of Fe and Ru. However, the X-ray diffraction exhibits only the presence of metallic Ru and Fe₂O₃ (hematite) phases. The oxygen reduction without and with 2 mol L⁻¹ methanol is studied using the rotating disk electrode technique. The electrochemical kinetic parameters obtained are compared to a similar electrocatalyst reported in the literature, which was synthesized using a mixture of an organic solvent with DI water as the microwave absorbing solvent. An improvement on the activity of the electrocatalyst synthesized is observed, where high Tafel slopes are not observed. The electrocatalyst also showed tolerance to the presence of methanol during the oxygen reduction reaction.

Morphology and Structure Controls of Single-Atom Fe–N–C Catalysts Synthesized Using FePc Powders as the Precursor

Understanding the origin of the high electrocatalytic activity of Fe–N–C electrocatalysts for oxygen reduction reaction is critical but still challenging for developing efficient sustainable nonprecious metal catalysts used in fuel cells. Although there are plenty of papers concerning the morphology on the surface Fe–N–C catalysts, there is very little work discussing how temperature and pressure control the growth of nanoparticles. In our lab, a unique organic vapor deposition technology was developed to investigate the effect of the temperature and pressure on catalysts. The results indicated that synthesized catalysts exhibited three kinds of morphology—nanorods, nanofibers, and nanogranules—corresponding to different synthesis processes. The growth of the crystal is the root cause of the difference in the surface morphology of the catalyst, which can reasonably explain the effect of the temperature and pressure. The oxygen reduction reaction current densities of the different catalysts at potential 0.88 V increased in the following order: FePc (1.04 mA/cm2) < Pt/C catalyst (1.54 mA/cm2) ≈ Fe–N–C-f catalyst (1.64 mA/cm2) < Fe–N–C-g catalyst (2.12 mA/cm2) < Fe–N–C-r catalyst (2.35 mA/cm2). By changing the morphology of the catalyst surface, this study proved that the higher performance of the catalysts can be obtained.