Oxygen reduction activity of carbon-supported Pt-M (M = V, Ni, Cr, Co, and Fe) alloys prepared by nanocapsule method

3D Printing to Enable Self-Breathing Fuel Cells

Fuel cells rely on an effective distribution of the reactant gases and removal of the byproduct, that is, water. In this context, bipolar plates are the critical component for the effective management of these fluids, as these dictate to some extent the overall performance of polymer electrolyte membrane fuel cells (PEMFCs). Better bipolar plates can lead to a significant reduction in size, cost, and weight of fuel cells. Herein, we report on the use of photoresin 3D printing to fabricate alternative bipolar plates for operating self-breathing fuel cell stacks. The resulting stack made of 12 self-breathing PEMFCs achieved a power density of 0.3 W/cm2 under ambient conditions (25°C and 20% relative humidity), which is superior to the performance of previously reported self-breathing cells. The problems associated with hydrogen leaks and water flooding could be resolved by taking advantage of 3D printing to precisely fabricate monoblock shapes. The approach of 3D printing reported in this study demonstrates a new path in fuel cell manufacturing for small and portable applications where an important reduction in size and cost is important.

Catalyst Development for High-Temperature Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC) Applications

A constant increase in global emission standard is causing fuel cell (FC) technology to gain importance. Over the last two decades, a great deal of research has been focused on developing more active catalysts to boost the performance of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFC), as well as their durability. Due to material degradation at high-temperature conditions, catalyst design becomes challenging. Two main approaches are suggested: (i) alloying platinum (Pt) with low-cost transition metals to reduce Pt usage, and (ii) developing novel catalyst support that anchor metal particles more efficiently while inhibiting corrosion phenomena. In this comprehensive review, the most recent platinum group metal (PGM) and platinum group metal free (PGM-free) catalyst development is detailed, as well as the development of alternative carbon (C) supports for HT-PEMFCs.

Progress and prospects of dealloying methods for energy-conversion electrocatalysis

Developing hydrogen production and utilization technologies is a promising way to achieve large-scale applications of renewable energy. For both water electrolysis and fuel cell electrode reactions, electrocatalysts are critical to their energy conversion efficiencies. Among the various strategies for improving the performance of electrocatalysts, dealloying has been developed as a commonly used effective post-processing method. It originated from anti-corrosion science and can form metal materials with porous or "skin" nanostructures by selectively dissolving the active components in alloys. There are generally two types of dealloying methods: electrochemical dealloying and chemical dealloying. Electrochemical dealloying is more controllable, while chemical dealloying is simpler and less expensive. In this review, the fundamentals, histories, and progress of dealloying methods for energy conversion electrocatalysis are systematically summarized. Furthermore, current problems and prospects are proposed.

Nanostructure Engineering and Electronic Modulation of a PtNi Alloy Catalyst for Enhanced Oxygen Reduction Electrocatalysis in Zinc-Air Batteries

PtNi nanoalloys have demonstrated electrocatalysis superior to that of benchmark Pt/C catalysts for the oxygen reduction reaction (ORR), yet the underlying mechanisms remain underexplored. Herein, a PtNi/NC catalyst comprising PtNi nanoparticles (∼5.2 nm in size) dispersed on N-doped carbon frameworks was prepared using a simple pyrolysis strategy. Benefiting from the individual components and a hierarchical structure, the PtNi/NC catalyst exhibited outstanding ORR activity and stability (E_1/2 = 0.82 V vs RHE and 8 mV negative shift after 20000 cycles), outperforming a commercial 20 wt % Pt/C catalyst (E_1/2 = 0.81 V and 32 mV negative shift). A prototype zinc-air battery constructed using PtNi/NC as the air electrode catalyst achieved highly enhanced electrochemical performance, outperforming a battery constructed using Pt/C as the ORR catalyst. Density functional theory calculations revealed that the improved ORR activity of the PtNi nanoalloys originated from charge redistribution with a suitable metal d-band center to promote the formation of the ORR intermediates.

Metal-nanocluster Science and Technology: My Personal History and Outlook

Metal nanoclusters (NCs) are among the leading targets in research of nanoscale materials, and elucidation of their properties (science) and development of control techniques (technology) have been continuously studied for...

CoCrFeNi High-Entropy Alloy as an Enhanced Hydrogen Evolution Catalyst in an Acidic Solution

High-entropy alloys (HEAs) have intriguing material properties, but their potential as catalysts has not been widely explored. Based on a concise theoretical model, we predict that the surface of a quaternary HEA of base metals, CoCrFeNi, should go from being nearly fully oxidized except for pure Ni sites when exposed to O2 to being partially oxidized in an acidic solution under cathodic bias, and that such a partially oxidized surface should be more active for the electrochemical hydrogen evolution reaction (HER) in acidic solutions than all the component metals. These predictions are confirmed by electrochemical and surface science experiments: the Ni in the HEA is found to be most resistant to oxidation, and when deployed in 0.5 M H2SO4, the HEA exhibits an overpotential of only 60 mV relative to Pt for the HER at a current density of 1 mA/cm2.

Pt distribution-controlled Ni–Pt nanocrystals via an alcohol reduction technique for the oxygen reduction reaction

The catalytic performance and durability of Ni–Pt alloy nanoparticles synthesized using an alcohol reduction technique were enhanced by controlling the metallic Pt distribution.

Three-step method with self-sacrificial Co to prepare a uniform 5 nm-scale Pt catalyst for the oxygen reduction reaction

Simple and rapid preparation method for a highly dispersed and small-sized CoPt catalyst.

Atomic-Level Manipulations in Oxides and Alloys for Electrocatalysis of Oxygen Evolution and Reduction

As chemical reactions and charge-transfer simultaneously occur on the catalyst surface during electrocatalysis, numerous studies have been carried out to attain an in-depth understanding on the correlation among the surface structure and composition, the electrical transport, and the overall catalytic activity. Compared with other catalysis reactions, a relatively larger activation barrier for oxygen evolution/reduction reactions (OER/ORR), where multiple electron transfers are involved, is noted. Many works over the past decade thus have been focused on the atomic-scale control of the surface structure and the precise identification of surface composition change in catalyst materials to achieve better conversion efficiency. In particular, recent advances in various analytical tools have enabled noteworthy findings of unexpected catalytic features at atomic resolution, providing significant insights toward reducing the activation barriers and subsequently improving the catalytic performance. In addition to summarizing important surface issues, including lattice defects, related to the OER and ORR in this Review, we present the current status and discuss future perspectives of oxide- and alloy-based catalysts in terms of atomic-scale observation and manipulation.

Synergistic Bimetallic Metallic Organic Framework-Derived Pt-Co Oxygen Reduction Electrocatalysts

The rational design of Pt-based electrocatalysts is of paramount importance for the commercialization of proton exchange membrane fuel cells (PEMFCs). Pt-Co alloys and nitrogen-doped carbons have been shown to be effective in enhancing the kinetics of the oxygen reduction reaction (ORR). Herein, we reported on two kinds of Pt-Co electrocatalysts, PtCo ordered intermetallic and PtCo₂ disordered alloys, supported on bimetallic MOF-derived N-doped carbon. The synergistic interaction between Pt-Co nanoparticles and Co-N-C enhanced the overall ORR activity and maintained the integrity of both structures and their electrochemical properties during long-term stability testing. The optimal activity for both PtCo and PtCo₂ occurred after 20 000 potential cycles. The enhanced performance of PtCo was ascribed to the formation of a two-atomic-layer Pt-rich shell and the lattice strain caused by the core-shell PtCo@Pt structure. The increased activity of PtCo₂ was ascribed to the formation of large, spongy, and small solid nanoparticles during electrochemical dealloying and thus the exposure of more Pt sites on the surface. The strategy described herein advances our understanding of the structure-activity relationship in electrocatalysis and sheds light on the future development of more active and durable ORR electrocatalysts.

New insights into O and OH adsorption on the Pt-Co alloy surface: effects of Pt/Co ratios and structures

In this study, the electronic structure and adsorption properties of O and OH for a series of Pt-Co alloys with different Pt/Co ratios (5 : 1, 2 : 1, 1 : 1, 1 : 2, and 1 : 5) were systematically studied using density functional theory calculations. Our computational results demonstrated that the introduced Co atoms have multiple effects on the surface electronic structure in different atomic layers of the alloy, leading to the discrepancies in the electronic structure between Pt-skin structures and non-Pt-skin structures. Moreover, the influence of the surface electronic structure on the adsorption of O and OH slightly differs. Indeed, the adsorption of O is more remarkably affected by the Pt/Co ratio than the OH adsorption and better follows the d-band center theory. Due to the difference of the alloy structure and the effect of different layer Co atoms, the adsorption of O and OH on the alloy configurations with the same Pt/Co ratio has different outcomes. Our results suggested that the oxygen reduction reaction (ORR) activity is related not only to the Pt/Co ratio of alloy surfaces but also to the specific surface structure. Our research can provide theoretical insights into the development of ORR catalysts.

Direct Synthesis of Intermetallic Platinum-Alloy Nanoparticles Highly Loaded on Carbon Supports for Efficient Electrocatalysis

Compared to nanostructured platinum (Pt) catalysts, ordered Pt-based intermetallic nanoparticles supported on a carbon substrate exhibit much enhanced catalytic performance, especially in fuel cell electrocatalysis. However, direct synthesis of homogeneous intermetallic alloy nanocatalysts on carbonaceous supports with high loading is still challenging. Herein, we report a novel synthetic strategy to directly produce highly dispersed MPt alloy nanoparticles (M = Fe, Co, or Ni) on various carbon supports with high catalyst loading. Importantly, a unique bimetallic compound, composed of [M(bpy)₃]²⁺ cation (bpy = 2,2'-bipyridine) and [PtCl₆]^2- anion, evenly decomposes on carbon surface and forms uniformly sized intermetallic nanoparticles with a nitrogen-doped carbon protection layer. The excellent oxygen reduction reaction (ORR) activity and stability of the representative reduced graphene oxide (rGO)-supported L1₀-FePt catalyst (37 wt %-FePt/rGO), exhibiting 18.8 times higher specific activity than commercial Pt/C catalyst without degradation over 20 000 cycles, well demonstrate the effectiveness of our synthetic approach toward uniformly alloyed nanoparticles with high homogeneity.

Ordered Pt3Co Intermetallic Nanoparticles Derived from Metal-Organic Frameworks for Oxygen Reduction

Highly ordered Pt alloy structures are proven effective to improve their catalytic activity and stability for the oxygen reduction reaction (ORR) for proton exchange membrane fuel cells. Here, we report a new approach to preparing ordered Pt₃Co intermetallic nanoparticles through a facile thermal treatment of Pt nanoparticles supported on Co-doped metal-organic-framework (MOF)-derived carbon. In particular, the atomically dispersed Co sites, which are originally embedded into MOF-derived carbon, diffuse into Pt nanocrystals and form ordered Pt₃Co structures. It is very crucial for the formation of the ordered Pt₃Co to carefully control the doping content of Co into the MOFs and the heating temperatures for Co diffusion. The optimal Pt₃Co nanoparticle catalyst has achieved significantly enhanced activity and stability, exhibiting a half-wave potential up to 0.92 V vs reversible hydrogen electrode (RHE) and only losing 12 mV after 30 000 potential cycling between 0.6 and 1.0 V. The highly ordered intermetallic structure was retained after the accelerated stress tests made evident by atomic-scale elemental mapping. Fuel cell tests further verified the high intrinsic activity of the ordered Pt₃Co catalysts. Unlike the direct use of MOF-derived carbon supports for depositing Pt, we utilized MOF-derived carbon containing atomically dispersed Co sites as Co sources to prepare ordered Pt₃Co intermetallic catalysts. The new synthesis approach provides an effective strategy to develop active and stable Pt alloy catalysts by leveraging the unique properties of MOFs such as 3D structures, high surface areas, and controlled nitrogen and transition metal dopings.

Interfacial Structure of PtNi Surface Alloy on Pt(111) Electrode for Oxygen Reduction Reaction

The interfacial structure and activity for the oxygen reduction reaction (ORR) were investigated on a PtNi surface alloy on a Pt(111) electrode (PtNi/Pt(111)). The PtNi surface alloy was prepared by thermal annealing of Ni²⁺ modified on Pt(111) at 573-803 K. After optimizing the alloying temperature and the amount of added Ni, the ORR current density of PtNi/Pt(111) at 0.9 V (reversible hydrogen electrode) is enhanced 9.5 times compared with that of Pt(111), and the activity is decreased by 24% after 1000 potential cycles. The atomic composition and subsurface structure of PtNi/Pt(111) were determined by in situ infrared reflection-absorption spectroscopy and X-ray diffraction. The surface contains a (111)-oriented Pt-skin and the subsurface of the 2nd-5th layers of the PtNi alloy contains less than 11% Ni atoms. The layer spacings of the surface alloy layers are slightly expanded compared with those of bare Pt(111). Homogeneous alloying with a small amount of Ni in the subsurface layers achieves the high ORR activity and durability.

Pt/Co Alloy Nanoparticles Prepared by Nanocapsule Method Exhibit a High Oxygen Reduction Reaction Activity in the Alkaline Media

Oxygen reduction reaction (ORR) catalysts are one of the main topics for fuel cells and metal/air batteries. We found that the platinum-cobalt alloy nanoparticles prepared by our original nanocapsule method exhibited a high ORR catalytic activity in alkaline solution, compared with that of the existing alloy nanoparticles prepared by different methods. The effect of alloy composition on the ORR activity was investigated to find the optimum composition (approximately 40 atom %). We also found that the enhancement of the catalytic activity in alkaline solution appeared in a very narrow range of Co content compared with that in acidic solution.

Weakened CO adsorption and enhanced structural integrity of a stabilized Pt skin/PtCo hydrogen oxidation catalyst analysed by in situ X-ray absorption spectroscopy

In situ X-ray absorption spectroscopy has afforded a detailed structural and electronic characterization of a newly developed stabilized Pt-skin/PtCo alloy nanoparticle catalyst for CO-tolerant H₂ oxidation.

The stability and catalytic activity of W13@Pt42 core-shell structure

This paper reports a study of the electronic properties, structural stability and catalytic activity of the W₁₃@Pt₄₂ core-shell structure using the First-principles calculations. The degree of corrosion of W₁₃@Pt₄₂ core-shell structure is simulated in acid solutions and through molecular absorption. The absorption energy of OH for this structure is lower than that for Pt₅₅, which inhibits the poison effect of O containing intermediate. Furthermore we present the optimal path of oxygen reduction reaction catalyzed by W₁₃@Pt₄₂. Corresponding to the process of O molecular decomposition, the rate-limiting step of oxygen reduction reaction catalyzed by W₁₃@Pt₄₂ is 0.386 eV, which is lower than that for Pt55 of 0.5 eV. In addition by alloying with W, the core-shell structure reduces the consumption of Pt and enhances the catalytic efficiency, so W₁₃@Pt₄₂ has a promising perspective of industrial application.

Nafion-stabilised bimetallic Pt-Cr nanoparticles as electrocatalysts for proton exchange membrane fuel cells (PEMFCs)

The current study investigated the unique combination of alloying (Pt with Cr) and Nafion stabilisation to reap the benefits of catalyst systems with enhanced catalytic activity and improved durability in PEMFCs.

The current study investigated the unique combination of alloying (Pt with Cr) and Nafion stabilisation to reap the benefits of catalyst systems with enhanced catalytic activity and improved durability in PEMFCs. Pt–Cr alloy nanoparticles stabilised with Nafion were chosen in the current study owing to their higher stability in acidic and oxidising media at high temperatures compared to other Pt-transition metal alloys (e.g. Pt–Ni, Pt–Co). Two different precursor : reducing agent (1 : 10 and 1 : 20) ratios were used in order to prepare two different alloys, denoted as Pt–Cr 10 and Pt–Cr 20. The Pt–Cr 20 alloy system (with composition Pt₈₀Cr₂₀) demonstrated higher electrocatalytic activity for the oxygen reduction reaction compared to commercial Pt/C (TKK) catalysts. Accelerated stress tests and single cell tests revealed that Nafion stabilised alloy catalyst systems displayed significantly enhanced durability (only ∼20% loss of ECSA) compared with Pt/C (50% loss of ECSA) due to improved catalyst–ionomer interaction. Furthermore, the Pt–Cr 20 alloy system demonstrated a current density comparable to that of Pt/C making them promising potential electrocatalysts for proton exchange membrane fuel cells.

Catalytic activity for oxygen reduction reaction on platinum-based core-shell nanoparticles: all-electron density functional theory

Pt nanoparticles (NPs) in a proton exchange membrane fuel cell as a catalyst for an oxygen reduction reaction (ORR) fairly overbind oxygen and/or hydroxyl to their surfaces, causing a large overpotential and thus low catalytic activity. Realizing Pt-based core-shell NPs (CSNPs) is perhaps a workaround for the weak binding of oxygen and/or hydroxyl without a shortage of sufficient oxygen molecule dissociation on the surface. Towards the end, we theoretically examined the catalytic activity of NPs using density functional theory; each NP consists of one of 12 different 3d-5d transition metal cores (groups 8-11) and a Pt shell. The calculation results evidently suggest the enhancement of catalytic activity of CSNPs in particular when 3d transition metal cores are in use. The revealed trends in activity change upon the core metal were discussed with respect to the thermodynamic and electronic structural aspects of the NPs in comparison with the general d-band model. The disparity between the CSNP and the corresponding bilayer catalyst, which is the so-called size effect, was remarkable; therefore, it perhaps opens up the possibility of size-determined catalytic activity. Finally, the overpotential for all CSNPs was evaluated in an attempt to choose promising combinations of CSNP materials.