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Ionic liquid modification for carbon-supported platinum (Pt/C) electrocatalysts to enhance their oxygen reduction reaction (ORR) activity has been well recognized. However, the research has only been reported on the low-Pt-loading Pt/C electrocatalysts, e.g., 20 wt%, while in practical applications, usually high-Pt-loading Pt/C electrocatalysts of 45–60 wt% are used. In this work, ionic liquid modification is systematically investigated for a Pt/C electrocatalyst with 60 wt% Pt loading for its ORR activity in the cathode in proton exchange membrane fuel cells (PEMFCs). Various adsorption amounts are studied on the catalyst surface. Different modification behavior is found. Mechanism exploration shows that the adsorption of ionic liquid mainly happens on the Pt electrocatalyst surface and in the micropores of the carbon support. The highest fuel cell power performance is achieved at an ionic liquid loading of 7 wt%, which is much higher than the 3 wt% reported for the low-Pt-loading Pt/C. [ABSTRACT FROM AUTHOR]

[Display omitted] Intermetallic compounds are emerging as promising oxygen reduction reaction (ORR) catalysts for fuel cells due to their typically higher activity and durability compared to disordered alloys. However, the preparation of intermetallic catalysts often requires high-temperature annealing, which unfortunately leads to adverse sintering of the metal nanoparticles. Herein, we develop a scalable site-selective sulfur anchoring strategy that effectively suppresses alloy sintering, ensuring the formation of efficient intermetallic electrocatalysts with small sizes and high ordering degrees. The alloy-support interactions are precisely modulated by selectively modifying the alloy-support interfaces with oxidized sulfur species, thus simultaneously blocking both the nanoparticle migration and Oswald ripening pathways for sintering. Using this strategy, sub-5 nm PtCo intermetallic electrocatalysts enclosed by two atomic layers of Pt shells have been successfully prepared even at a metal loading higher than 30 wt%. The intermetallic catalysts exhibit excellent ORR performances in both rotating disk electrode and membrane electrode assembly conditions with a mass activity of 1.28 A mg Pt −1 at 0.9 V (vs. RHE) and a power density of 1.0 W cm−2 at a current density of 1.5 A cm−2. The improved performances result from the enhanced Pt-Co electronic interactions and compressive surface strain generated by the highly ordering structure, while the atomic Pt shells prevent the dissolution of Co under highly acidic conditions. This work provides new insights to inhibit the sintering of nanoalloys and would promote the scalable synthesis and applications of platinum-based intermetallic catalysts. [ABSTRACT FROM AUTHOR]

Studying the ORR activity of platinum-based electrocatalysts is an urgent task in the development of materials for proton-exchange membrane fuel cells. The catalytic ink composition and the formation technique of a thin layer at the RDE play a significant role in studying ORR activity. The use of a polymer ionomer in the catalytic ink provides viscosity as well as proton conductivity. Nafion is widely used as an ionomer for research both at the RDE and in the MEA. The search for ionomers is a priority task in the development of the MEA components to replace Nafion. The study also considers the possibility of using the LF4-SK polymer as an alternative ionomer. The comparative results on the composition and techniques of applying the catalytic layer using LF4-SK and Nafion ionomers are presented, and the influence of the catalytic ink composition on the electrochemical characteristics of commercial platinum–carbon catalysts and a highly efficient platinum catalyst based on an N-doped carbon support is assessed. [ABSTRACT FROM AUTHOR]

The use of platinum-free (Pt) cathode electrocatalysts for oxygen reduction reactions (ORRs) has been significantly studied over the past decade, improving slow reaction mechanisms. For many significant energy conversion and storage technologies, including fuel cells and metal–air batteries, the ORR is a crucial process. These have motivated the development of highly active and long-lasting platinum-free electrocatalysts, which cost less than proton exchange membrane fuel cells (PEMFCs). Researchers have identified a novel, non-precious carbon-based electrocatalyst material as the most effective substitute for platinum (Pt) electrocatalysts. Rich sources, outstanding electrical conductivity, adaptable molecular structures, and environmental compatibility are just a few of its benefits. Additionally, the increased surface area and the simplicity of regulating its structure can significantly improve the electrocatalyst's reactive sites and mass transport. Other benefits include the use of heteroatoms and single or multiple metal atoms, which are capable of acting as extremely effective ORR electrocatalysts. The rapid innovations in non-precious carbon-based nanomaterials in the ORR electrocatalyst field are the main topics of this review. As a result, this review provides an overview of the basic ORR reaction and the mechanism of the active sites in non-precious carbon-based electrocatalysts. Further analysis of the development, performance, and evaluation of these systems is provided in more detail. Furthermore, the significance of doping is highlighted and discussed, which shows how researchers can enhance the properties of electrocatalysts. Finally, this review discusses the existing challenges and expectations for the development of highly efficient and inexpensive electrocatalysts that are linked to crucial technologies in this expanding field. [ABSTRACT FROM AUTHOR]

With the increasing demand for green and efficient energy storage devices， advanced technologies for clean energy conversion have attracted close attention from researchers. Fuel cells with environmental friendliness and high energy conversion efficiency are promising alternatives to traditional energy sources. However， Pt catalysts with high commercialization degrees in the industrial catalysis field have some problems， such as high cost， poor stability and weak anti-toxicity ability， which limits the further development of fuel cells. The development of non-Pt oxygen reduction reaction （ORR） catalysts with abundant reserves， low cost and excellent performance is an effective way to improve the efficiency of fuel cells. In this paper， based on the research results at home and abroad in recent years， various types of non-Pt system ORR catalysts， including non-precious metal and non-metal catalysts， are systematically introduced. The advantages， disadvantages and modification strategies of various catalysts are summarized， and challenges and prospects for the development of ORR electrocatalysts are put forward. [ABSTRACT FROM AUTHOR]

The design of Pt-based electrocatalysts with high efficiency towards acid oxygen reduction reactions is the priority to promote the development and application of proton exchange membrane fuel cells. Considering that the Pt atoms on the surfaces of the electrocatalysts face the problems of interference of non-active species (such as OHad, OOHad, CO, etc.), high resistance of mass transfer at the liquid–solid interfaces, and easy corrosion when working in harsh acid. Researchers have modified the surfaces' local environment of the electrocatalysts by introducing surface modifiers such as silicon or carbon layers, amine molecules, and ionic liquids on the surfaces of electrocatalysts, which show significant performance improvement. In this review, we summarized the research progress of surface modified Pt-based electrocatalysts, focusing on the surface modification strategies and their mechanisms. In addition, the development prospects of surface modification strategies of Pt-based electrocatalysts and the limitations of current research are pointed out. [ABSTRACT FROM AUTHOR]

The high cost and poor reliability of cathodic electrocatalysts for the oxygen reduction reaction (ORR), which requires significant amounts of expensive and scarce platinum, obstructs the broad applications of proton exchange membrane fuel cells (PEMFCs). The principles of ORR and the reasons for the poor stability of Pt-based catalysts are reviewed. Moreover, this paper discusses and categorizes the strategies for enhancing the stability of Pt-based catalysts in fuel cells. More importantly, it highlights the recent progress of Pt-based stability toward ORR, including surface-doping, intermetallic structures, 1D/2D structures, rational design of support, etc. Finally, for atomic-level in-depth information on ORR catalysts in fuel cells, potential perspectives are suggested, such as large-scale preparation, advanced interpretation techniques, and advanced simulation. This review aims to provide valuable insights into the fundamental science and technical engineering for practical Pt-based ORR electrocatalysts in fuel cells. [ABSTRACT FROM AUTHOR]

Sluggish oxygen reduction reaction (ORR) of electrodes is one of the main challenges in fuel cell systems. This study explored the kinetics of the ORR reaction mechanism, which enables us to understand clearly the electrochemical activity of the electrode. In this research, electrocatalysts were synthesized from platinum (Pt) catalyst with multi-walled carbon nanotubes (MWCNTs) coated by three polymers (polybenzimidazole (PBI), sulfonated tetrafluoroethylene (Nafion), and polytetrafluoroethylene (PTFE)) as the supporting materials by the polyol method while hexachloroplatinic acid (H2PtCl6) was used as a catalyst precursor. The oxygen reduction current of the synthesized electrocatalysts increased that endorsed by linear sweep voltammetry (LSV) curves while increasing the rotation rates of the disk electrode. Additionally, MWCNT-PBI-Pt was attributed to the maximum oxygen reduction current densities at −1.45 mA/cm2 while the minimum oxygen reduction current densities of MWCNT-Pt were obtained at −0.96 mAcm2. However, the ring current densities increased steadily from potential 0.6 V to 0.0 V due to their encounter with the hydrogen peroxide species generated by the oxygen reduction reactions. The kinetic limiting current densities (JK) increased gradually with the applied potential from 1.0 V to 0.0 V. It recommends that the ORR consists of a single step that refers to the first-order reaction. In addition, modified MWCNT-supported Pt electrocatalysts exhibited high electrochemically active surface areas (ECSA) at 24.31 m2/g of MWCNT-PBI-Pt, 22.48 m2/g of MWCNT-Nafion-Pt, and 20.85 m2/g of MWCNT-PTFE-Pt, compared to pristine MWCNT-Pt (17.66 m2/g). Therefore, it can be concluded that the additional ionomer phase conducting the ionic species to oxygen reduction in the catalyst layer could be favorable for the ORR reaction. [ABSTRACT FROM AUTHOR]

Hydrogen has the potential to be one of the solutions that can address environmental pollution and greenhouse emissions from traditional fossil fuels. However, high costs hinder its large-scale commercialization, particularly for enabling devices such as proton exchange membrane fuel cells (PEMFCs). The precious metal Pt is indispensable in boosting the oxygen reduction reaction (ORR) in cathode electrocatalysts from the most crucial component, i.e., the membrane electrode assembly (MEA). MEAs account for a considerable amount of the entire cost of PEMFCs. To address these bottlenecks, researchers either increase Pt utilization efficiency or produce MEAs with enhanced performance but less Pt. Only a few reviews that explain the approaches are available. This review summarizes advances in designing nanocatalysts and optimizing the catalyst layer structure to achieve low-Pt loading MEAs. Different strategies and their corresponding effectiveness, e.g., performance in half-cells or MEA, are summarized and compared. Finally, future directions are discussed and proposed, aiming at affordable, highly active, and durable PEMFCs. [ABSTRACT FROM AUTHOR]

This work explores a novel and sustainable synthesis strategy for developing platinum-group metal (PGM)-free catalysts with high electrocatalytic activity, emphasizing the significance of hierarchically porous structures to improve electrocatalytic performance. We present an easily scalable method that utilizes magnesium salt as the precursor of sacrificial template to synthesize mesoporous carbon-based catalysts. The catalysts are doped with nitrogen and iron, while manganese is added to increase the stability of the catalyst under highly corrosive acidic conditions. The electrochemical oxygen reduction reaction (ORR) is investigated in acidic media using the rotating disk electrode technique. The electrocatalytic activity of the prepared catalysts is evaluated in proton exchange membrane fuel cell (PEMFC), where a significant increase in performance is achieved with the hierarchically porous carbon catalyst. The results demonstrate the potential of these catalysts as efficient and durable alternatives to PGM-based cathode catalysts in PEMFCs. [Display omitted] • Mesoporous catalysts are prepared from alkylresorcinols using an Mg-based template. • High ORR activity of Fe- and FeMn-doped M-N-C catalysts in RDE test in acidic media. • FeMn-doped electrocatalyst exhibits increased stability in AST and low H 2 O 2 yield. • Excellent PEMFC results were obtained using PGM-free materials as cathode catalysts. [ABSTRACT FROM AUTHOR]

The durability of low temperature proton exchange membrane fuel cell (PEMFC) catalysts crucially affects their lifetime. The choice of carbon support is important in terms of increasing the stability of catalysts. In this research, Pt/C samples were obtained using the polyol synthesis method on two types of carbon supports: the standard support, Vulcan XC-72, and carbon support with a high degree of graphitization, ECS-002402. One method for assessing structural characteristics is through transmission electron microscopy (TEM), according to which materials G1 and G2 showed an average nanoparticle size of 3.7 and 4.2 nm, respectively. On all catalysts, the oxygen reduction reaction proceeded according to the four electron mechanism. Durability was assessed by changes in ESA and activity in the ORR after 1000 cycles, with changes in the upper potential values: 0.7; 1.0; 1.2; and 1.4 V. After accelerated stress testing, the G1 material showed the greatest residual activity at a potential of 1.4 V (165 A/g (Pt). Based on the results of comparing various ADT protocols, the optimal mode of 0.4 and 1.4 V was chosen, and should be used for further studies comparing the durability of Pt/C catalysts. [ABSTRACT FROM AUTHOR]

N-doping and sulfonation is prepared on the reduced graphene oxide (rGO) support for PtNi nanoparticles (PtNi/S-(N)rGO) by a simple method of hydrothermal synthesis and thermal decomposition. The specific surface area increases from 180.7 m2/g of PtNi/rGo to 293.5 m2/g of PtNi/S-(N)rGO. The surface morphology shows wrinkles sites, which are separated by the sulfonated groups. The catalytic stability and efficiency are improved by the anchoring effect of sulfonated groups and evenly distribution of nanoparticles, respectively. The synergistic effect of N-doping and sulfonation can be in favor of catalytic efficiency by the increase of number of electron transfer. The half-wave potential of the PtNi/S-(N)rGO catalyst is up to 0.632 V, a small positive shift compared to the Pt/C catalyst. The durability of the PtNi/S-(N)rGO is 2.6 times higher than of the Pt/C catalyst after 5000 repeated cycles. The peak power of the PtNi/S-(N)rGO catalyst increased 37.5% compared to the Pt/C catalyst. Therefore, the stability and catalytic efficiency are improved by the PtNi/S-(N)rGO catalyst applied in proton exchange membrane fuel cell (PEMFC) compared to the commercial Pt/C catalyst. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is paid much more attention because of the high overpotential required for driving the four-electron process in the field of storage and sustainable energy conversion, including fuel cell applications. In this paper, PtCo nanoparticles encapsulated on carbon supports were prepared by a simple modified polyol method with ethylene glycol. Structural as well as electrochemical characterizations illustrated that the PtCo/C electrocatalysts had a minimum particle size of 4.8 nm, which is close to the commercial 40 wt% Pt/JM. Moreover, the electrochemical measurements indicated that ORR activity was competitive with the commercial 40 wt% Pt/JM catalyst. The synthesis method is a critical way to produce PtCo/C catalysts for use in polymer electrolyte membranes in fuel cells (PEMFCs). [ABSTRACT FROM AUTHOR]

Proton exchange membrane (PEM) fuel cells using Pt-based materials as electrocatalysts have achieved a decent performance, represented by the launched Toyota Mirai vehicle. The ideal PEM fuel cells consume stored pure hydrogen and air. However, SO2, as a primary air contaminant, may be fed along with air at the cathode, leading to Pt site deactivation. Therefore, it is important to improve the SO2 tolerance of catalysts for the stability of the oxygen reduction reaction (ORR). In this work, we develop the Pt/C-TiO2 catalyst against SO2 poisoning during ORR. Impressively, the hybrid Pt/C-TiO2 catalyst with 20 mass % TiO2 shows the best ORR and anti-toxic performance: the kinetic current density of ORR is 20.5% higher and the degradation rate after poisoning is 50% lower than Pt/C. The interaction between Pt and TiO2 as well as the abundant hydroxyl groups on the surface of TiO2 are both revealed to account for the accelerated removal of poisonous SO2 on Pt surfaces. [ABSTRACT FROM AUTHOR]

The development of non-precious metal electrocatalysts towards oxygen reduction reaction (ORR) is crucial for the commercialisation of polymer electrolyte fuel cells. In this work, cobalt-containing nitrogen-doped porous carbon materials were prepared by a pyrolysis of mixtures of saccharides, cobalt nitrate and dicyandiamide, which acts as a precursor for reactive carbon nitride template and a nitrogen source. The rotating disk electrode (RDE) experiments in 0.1 M KOH solution showed that the glucose-derived material with optimised cobalt content had excellent ORR activity, which was comparable to that of 20 wt% Pt/C catalyst. In addition, the catalyst exhibited high tolerance to methanol, good stability in short-time potential cycling test and low peroxide yield. The materials derived from xylan, xylose and cyclodextrin displayed similar activities, indicating that various saccharides can be used as inexpensive and sustainable precursors to synthesise active catalyst materials for anion exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

Platinum (Pt) nanoparticles on various supports, such as commercial carbon powder, titanium dioxide (TiO2), and reduced graphene oxide (rGO), were synthesized using a continuous flow microfluidic system. First, the support materials were separately synthesized using the sonochemical technique followed by the loading of Pt. The Pt nanoparticles on different supports were characterized using Brunauer–Emmett–Teller (BET) for surface area and porosity analysis; X‐ray diffraction (XRD) for structural confirmation; Fourier transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS) for surface composition; and transmission electron microscopy (TEM) for morphological investigation. Further, polymer electrolyte membrane (PEM) fuel cells were fabricated using the Pt nanoparticles on different supports, and cyclic voltammetry (CV), linear sweep voltammetry (LSV), and power density were performed. Among the three electrocatalysts, Pt/rGO showed the highest electrochemical performance. Pt/rGO showed higher specific activity (119 mA/cm2), mass activity (238 mA/mg), current density (1274 mA/cm2), and power density (497 mW/cm2). We also determined the mass activity and specific activity of the electrocatalysts based on the electrochemical data. This work shows the potential of the microfluidic system to continuously synthesize the technologically important nanomaterials and their application for energy conversion devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Developing a novel technique for synthesizing highly active and low-Pt catalysts. • Directional preparation of smaller size Pt NPs with (1 1 1) crystal faces. • The addition of NaOH significantly influences ORR activity of the catalyst. • Single-cell of PEMFC with designed catalyst outperforms commercial Pt/C. One important approach to address the cost issue of fuel cells is to maximize the utilization of Pt by reducing its loading and enhancing the performance for the oxygen reduction reaction (ORR) as well as durability of catalysts. In this work, a one-step synthesis of highly dispersed low-Pt (1 1 1) electrocatalysts (p-Pt/KBs) supported by Ketjenblack is conducted using interaction between solution and nonthermal plasma (SNP). The results show that the plasma-treated platinum precursor dispersion efficiently avoids particle agglomeration and increases more defects of the support surface, which are conducive to the trapping and anchoring of platinum nanoparticles (Pt NPs). The catalyst (p-Pt/KB-NaOH) with a platinum load of 10.8 wt% is obtained by adding sodium hydroxide to the platinum precursor dispersion solution, showing better ORR performance (E 1/2 = 0.88 V) and stability compared to the commercial platinum on carbon (Pt/C) catalyst (20 wt%, E 1/2 = 0.86 V). This improvement is attributed to the fact that neutralizing chloroplatinic acid slows down the reduction rate of the platinum precursor, effectively controlling the rapid nucleation and slow crystal growth of platinum. As the cathode catalyst for PEMFCs, p-Pt/KB-NaOH exhibits remarkable mass-transfer performance in the high-current density domain (HCD), with maximum power density (P max) of 1131 mW cm−2 at 2500 mA cm−2, which is 9.1 % higher than commercial Pt/C. Moreover, the single-cell operates stably for at least 100 h at 1000 mA cm−2 with a negligible decay (1.9 %) of the working voltage, ensuring long-term durability. [ABSTRACT FROM AUTHOR]

Functionalization of the carbon support is a promising strategy for lowering platinum loadings at the cathode of proton exchange membrane fuel cells. Here, nitrogen-containingmoieties are introduced directly onto carbon black by a simple and easily tunable graftingmethod initiated by the thermal decomposition of azo compounds in water. X-ray photoelectron spectroscopy (XPS) and elemental analysis confirm the successful functionalization. After deposition of Pt nanoparticles onto the carbon supports, the electrocatalysts are characterized in thin film rotating disk electrode (RDE) configuration towards the acidic oxygen reduction reaction (ORR). The grafting does not influence the Pt intrinsic ORR activity when the thin film does not include ionomer. However, the functionalization modifies the ionomer/carbon material interaction, leading to higher apparent ORR activity when the ionomer is included in the thin film. Moreover, accelerated stress testing shows durability enhancement as the result of grafting. [ABSTRACT FROM AUTHOR]

Hydrogen has the potential to be one of the solutions that can address environmental pollution and greenhouse emissions from traditional fossil fuels. However, high costs hinder its large-scale commercialization, particularly for enabling devices such as proton exchange membrane fuel cells (PEMFCs). The precious metal Pt is indispensable in boosting the oxygen reduction reaction (ORR) in cathode electrocatalysts from the most crucial component, i.e., the membrane electrode assembly (MEA). MEAs account for a considerable amount of the entire cost of PEMFCs. To address these bottlenecks, researchers either increase Pt utilization efficiency or produce MEAs with enhanced performance but less Pt. Only a few reviews that explain the approaches are available. This review summarizes advances in designing nanocatalysts and optimizing the catalyst layer structure to achieve low-Pt loading MEAs. Different strategies and their corresponding effectiveness, e.g., performance in half-cells or MEA, are summarized and compared. Finally, future directions are discussed and proposed, aiming at affordable, highly active, and durable PEMFCs.

[Display omitted] • Model Sn-Pt catalytic surfaces were prepared using electroless deposition. • The most promising model Sn-Pt catalytic surface has Sn/Pt ratio of 1:3. • Alloy-type SnPt/C electrocatalysts were prepared by Controlled Surface Reactions. • Correlation of optimal surface composition with oxygen reduction reaction activity. • Catalyst with the highest content of the Pt 3 Sn alloy phase was the most promising. Model Sn-Pt catalytic surfaces were prepared using electroless deposition of adsorbed tin atoms (via catalytic disproportion of Sn2+) onto smooth polycrystalline Pt disc to clarify the relationship between the Sn/Pt surface composition and the oxygen reduction reaction (ORR) activity. According to the optimization results the most promising surface Sn/Pt atomic ratio was ca. 1:3. Based on the ORR results obtained on model Sn-Pt catalytic surfaces alloy-type Sn-Pt/C catalysts with Sn/Pt 1:3, 1:2.5 and 1:2 ratios were prepared by Controlled Surface Reactions (CSRs). The selective incorporation of Sn onto Pt sites was achieved resulting in exclusive formation of Pt-Sn alloy phases without decoration of the support with tin species. According to the results the most promising surface Sn/Pt atomic ratio was observed on the SnPt(1:2.5)/C catalyst pre-treated in H 2 at 350 °C with the highest content of the fcc Pt 3 Sn alloy phase. The increased activity of the SnPt(1:2.5)/C catalyst in the ORR compared to the catalysts with Sn/Pt 1:3 and 1:2 ratios can be attributed to the optimal ratio between the interfacial surface sites with oxophilic and metallic chemical nature. [ABSTRACT FROM AUTHOR]

• α-MnO 2 nanorods have been in-situ supported on 3D-G via a facile hydrothermal method. • α-MnO 2 nanorods are evenly deposited on 3D-G surface which possesses more defects. • The synergistic interaction between α-MnO 2 nanorods and 3D-G improve ORR performance. • α-MnO 2 /3D-G catalyst exhibites excellent activity and durability for ORR in MFCs. Magnesium-air fuel cells are considered as a potential energy conversion device owing to a high theoretical specific capability, economic viability and environmental friendliness. In this work, α-MnO 2 nanorods are supported on three-dimensional graphene (3D-G) which is fabricated with coal tar pitch as the carbon precursor and MgO as the template via hydrothermal reaction. The synergistic interactions between α-MnO 2 nanorods and 3D-G improve the activity and durability performance for oxygen reduction reaction in 0.1 mol L−1 KOH solution. α-MnO 2 /3D-G exhibits a high half-wave potential (0.81 V) and superior to α-MnO 2 /C (0.72 V) and α-MnO 2 /rGO (0.76 V), and close to 20 wt% Pt/C (0.83 V). α-MnO 2 /3D-G also possesses higher durability than commercial Pt/C. Furthermore, the magnesium-air fuel cells based on α-MnO 2 /3D-G, air-cathode display the peak power density (106.2 mW cm−2), and continuously durability (discharge for 16 h at 50 mA cm−2 with the mere decay of cell voltage by 7.6%). These results prove that α-MnO 2 /3D-G catalyst with high activity and durability can be a promising electrocatalyst in magnesium-air fuel cells. [ABSTRACT FROM AUTHOR]

• The electrocatalyst has a PtCo@Pt core-shell structure. • PtCo nanoparticles were encapsulated in a Pt shell using an organic hydride donor. • PtCo@Pt with the unique Pt shell demonstrates enhanced catalytic activity. • PtCo@Pt performed well in both half- and single-cell system tests. Platinum alloys with other transition metals are widely used as catalysts as a promising strategy to improve the activity. However, the vulnerability of transition metals to the liquid electrolyte and fuel gases present during the device operation results in degradation of the catalytic activity. Highly stable catalyst is achieved by encapsulating the carbon-supported PtCo intermetallic core nanoparticles in a robust Pt shell. The hydride from Hantzsch ester reduces the residual Cl on the surface of the Pt skeleton and slowly forms negatively charged defect sites without damaging the core structure. Then, a secondary Pt reduction reaction via the hydride is employed to cover the activated surfaces of the Pt skeleton to optimize the shell thickness without the formation of isolated Pt nanoparticles. The PtCo@Pt with the unique Pt shell shows higher catalytic activity and durability than commercial Pt/C for oxygen reduction reaction electrocatalysts in proton exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

Abstract The exploration of cheap and stable electrocatalysts with high activity towards oxygen reduction reaction in the acidic and alkaline medium is a vital activity for large-scale applications of fuel cells. In recent years, one-dimensional nanofibrous electrode materials with high surface area and specific porosities have been drawing great attention in energy conversion devices such as fuel cells and metal-air batteries. Nanofibers with a one-dimensional nanostructure can be produced by electrospinning, which has been considered as a particularly low-cost and versatile method. In this review, we summarize the properties of electrospun nanofibers and the recent progress in designing of non-precious nanostructured electrocatalysts for oxygen reduction reaction in fuel cells. More importantly, we also highlight the interesting nanostructures, new synthetic approaches, and the electrocatalytic performance including active sites and stability of electrospun-based electrocatalysts. In addition, we describe the research challenges and future developmental perspectives of electrospun materials in energy technology. Highlights • Non-precious nanostructured electrocatalysts by electrospinning are summarized. • The active sites and reaction mechanism of the electrocatalysts are discussed. • Research challenges and future perspectives are described. [ABSTRACT FROM AUTHOR]

1 1 1 08/03/23 20230801 NES 230801 B The Front Cover b shows a schematic representation of the oxygen reduction reaction on our gas diffusion electrode. EN CeO2 electrocatalysts oxygen reduction reaction PEM fuel cell. The composite catalyst is based on Pt/C and non-stoichiometric CeO SB 2. sb The high hygroscopicity of the latter plays a crucial role in optimizing the water drainage and the cathode/Nafion interface, resulting in a considerable improvement in proton conductivity and Fuel Cell performances. [Extracted from the article]

Abstract Presently, the practical application of Fe/N/C catalysts as replacements of Pt for oxygen reduction reaction is still limited by insufficient activity. Herein, we demonstrate a novel design for such catalyst. On one hand, the obtained Fe/N/C SiO 2 ZnCl 2 catalyst owns high densities of well-exposed active-sites derived from three-dimensional well-balanced macro-, meso-, and microporous structures constructed by adopting ZnCl 2 salt and SiO 2 microspheres as combined templates. On the other hand, simulation reveals that a high loading of catalyst in cathode catalyst layer would not benefit cell performance and fast oxygen reduction reaction process occurs only inside a limited thickness of catalyst layer. Particularly, the Fe/N/C SiO 2 ZnCl 2 shows a maximal output power density as high as 480 mW cm−2 at an ultra-low loading of 0.5 mg cm−2. This study firstly exhibits that development of catalysts with high-density active sites and construct of ultra-thin catalyst layer are of great significance for improving the performance of fuel cell. Highlights • Fe/N/C SiO 2 ZnCl 2 was synthesized using ZnCl 2 templating and silica templating. • Fe/N/C SiO 2 ZnCl 2 shows superior ORR activity in both alkaline and acidic medium. • The P max of Fe/N/C SiO 2 ZnCl 2 is as high as 480 mW cm−2 at a 0.5 mg cm−2 loading. [ABSTRACT FROM AUTHOR]

It is still a grand challenge to develop a highly efficient nonprecious-metal electrocatalyst to replace the Pt-based catalysts for oxygen reduction reaction (ORR). Here, we propose a surfactant-assisted method to synthesize single-atom iron catalysts (SA-Fe/NG). The half-wave potential of SA-Fe/NG is only 30 mV less than 20% Pt/C in acidic medium, while it is 30 mV superior to 20% Pt/C in alkaline medium. Moreover, SA-Fe/NG shows extremely high stability with only 12 mV and 15 mV negative shifts after 5,000 cycles in acidic and alkaline media, respectively. Impressively, the SA-Fe/NG-based acidic proton exchange membrane fuel cell (PEMFC) exhibits a high power density of 823 mW cm-2. Combining experimental results and density-functional theory (DFT) calculations, we further reveal that the origin of high-ORR activity of SA-Fe/NG is from the Fe-pyrrolic-N species, because such molecular incorporation is the key, leading to the active site increase in an order of magnitude which successfully clarifies the bottleneck puzzle of why a small amount of iron in the SA-Fe catalysts can exhibit extremely superior ORR activity. [ABSTRACT FROM AUTHOR]

Carbon-supported hollow PdCu 2 @Pt core@shell nanoparticles with ordered intermetallic cores were prepared as an efficient and durable oxygen reduction reaction (ORR) electrocatalyst for polymer electrolyte membrane fuel cells (PEMFCs). PdCu 2 cores prepared using a chemical reduction method were thermally treated to produce ordered intermetallic structures. A Pt shell was then deposited via a galvanic displacement process. The effect of the galvanic displacement conditions on the properties and structure of the obtained core–shell nanoparticles was investigated by varying the solution pH and anion concentration. Acidic conditions and low Cl − concentrations were found to provide a uniform Pt layer with a hollow core, while maintaining the ordered intermetallic core structure. These hollow PdCu 2 @Pt core@shell nanoparticles showed high activity and stability for ORR electrocatalysis in PEMFCs. [ABSTRACT FROM AUTHOR]

Non-precious Fe/N/S-composited hierarchically porous carbon materials (Fe(x)/N/S-PAD, PAD: poly(acrylamide-co-diallyldimethyl ammonium chlor), x : the weight ratio of FeSO 4 7H 2 O/PAD) are synthesized using a facile silica colloid template approach with FeSO 4 7H 2 O as Fe and S sources, and PAD as N source, respectively. A simultaneous creation of porous structures and surface functionalities (Fe, N and S) of such catalysts is realized just by simply tuning the weight ratio of FeSO 4 7H 2 O and PAD in the synthetic precursors. As a result, a series of catalyst samples with high oxygen reduction reaction (ORR) activity/stability are obtained, demonstrating the promotion role of FeSO 4 /PAD ratio in synthesizing high-performing catalysts. Particularly, a catalyst (Fe(1.5)/N/S-PAD) with a trace Fe content down to 1.0 wt.% is tested to be superior to a commercial Pt/C catalyst in alkaline media and exhibits impressive ORR performance in acidic media. Combined with characterization results such as TEM, Raman spectra, BET and XPS analysis, it is found that the well-defined micro- and meso-porous structure play the key role in enhancing catalytic ORR performance rather than the final total N contents in the carbon. Regarding the stability of such a catalyst, test using cyclic voltammetry for 5000 cycles in O 2 -saturated solution shows a negligible degradation rate when compared with Pt/C one, suggesting that this catalyst could be used for catalyzing the high-performing cathode ORR in proton-exchange membrane fuel cells, alkaline fuel cells and metal–air batteries. [ABSTRACT FROM AUTHOR]

The possibility of using plasma deposited thin films of iron oxides as electrocatalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC) was examined. Results of energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis indicated that the plasma deposit consisted mainly of FeOX structures with the X parameter close to 1.5. For as deposited material iron atoms are almost exclusively in the Fe3+ oxidation state without annealing in oxygen containing atmosphere. However, the annealing procedure can be used to remove the remains of carbon deposit from surface. The single cell test (SCT) was performed to determine the suitability of the produced material for ORR. Preliminary results showed that power density of 0.23 mW/cm2 could be reached in the tested cell. [ABSTRACT FROM AUTHOR]

Pt-based electrocatalysts with higher activity and durability are necessary for cost-competitive polymer electrolyte membrane fuel cells. We have combined the high utilization and activity of core@shell nanostructures with the high surface area and stability of atomically thin nanosheets to afford electrocatalysts that show enhanced activity and durability for both cathode and anode reactions. Ru-core@Pt-shell nanosheets with an average thickness of 1.5–4.5 Pt monolayers have an electrochemically active Pt surface area of 112–151 m 2 (g-Pt) −1 , 1.4–1.9 times larger than typical Pt/C catalysts. A catalyst with a monolayer Ru-core and an average 3.5 monolayer Pt-shell supported on carbon (Ru@Pt-3.5ML(ns)/C) shows 4.5 times higher mass activity than benchmark Pt/C catalyst for the oxygen reduction reaction with a slower degradation rate, making this nanomaterial one of the most active and durable Pt-based catalysts. For the anode reactions, Ru@Pt-1.5ML(ns)/C shows 2 times higher apparent mass activity for the hydrogen oxidation activity in pure H 2 as well as 300 ppm CO containing H 2 , and better stability against potential cycling. [ABSTRACT FROM AUTHOR]

The present study focused on a development of a buckypaper [a 45-µm-thick film composed of entangled Carbon nanotube (CNTs)] electrode or electrocatalyst support for oxygen reduction reaction (ORR). The surfaces of the pristine nanotubes in the buckypapers were functionalized by three well-known oxidative approaches: chemical, thermal, and electrochemical. Physical properties of the buckypapers and supported Pt electrocatalysts were characterized by thermogravimetric analysis, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy (TEM). Electrochemical oxidation created the highest defect density as indicated by Raman data. In contrast, no significant change in surface functional group was observed after thermal oxidation. The TEM images revealed the successful deposition of Pt particles onto the buckypapers (35 wt% Pt/CNT) by an impregnation-reduction method, with average particle size between 2.5 and 3.5 nm. Electrocatalytic activity of the Pt electrocatalysts toward oxygen reduction was evaluated using a rotating disk electrode. The ORR results showed Pt electrocatalysts supported on the modified buckypaper displayed substantially enhanced ORR activity in comparison to the pristine Pt/buckypaper. The highest ORR activity at 0.85 V was ~5.3 mA cm. Our results demonstrated that buckypaper may be a potential catalyst support for fuel cell applications. Graphical Abstract: [ABSTRACT FROM AUTHOR]

Reducing human reliance on inefficient energy systems and fossil fuels has become more urgent due to the consequences of global climate change. However, traditional trial-and-error approaches have hampered our ability to accelerate the discovery and implementation of functional materials for efficient energy conversion devices, such as polymer electrolyte fuel cells (PEFCs). To address this, we develop an adaptive learning framework that integrates machine learning and state-of-the-art capabilities in high-throughput synthesis to achieve expedited optimization of iron-nitrogen-carbon PEFC oxygen reduction reaction (ORR) electrocatalysts. We use statistical inference, uncertainty quantification, and global optimization to build a computational design-of-experiment tool that identifies the optimum compositions to be investigated next to reduce the demands placed on experimental materials discovery. We benchmark the ability of the proposed strategy to discover optimum catalyst synthesis conditions in a six-dimensional search space when starting with a thirty-six-sample database. By following the adaptive learning strategy, we synthesize fourteen new catalysts from approximately ten billion unique compositions and discover four catalysts that outperform all original samples. The best machine learning-optimized catalyst is 33% more active than the highest-performing one in the initial database, showing an ORR activity seven times larger than those typically reported for the same class of materials. [Display omitted] • Optimized Fe–N–C oxygen reduction reaction catalysts via adaptive learning. • Elucidated the role of high-throughput synthesis conditions on catalyst activity. • Developed a computational design-of-experiment tool to pick catalysts to test next. • Discovered four catalysts that outperform the best materials in the initial dataset. • Demonstrated an activity increase of ∼33% relative to the previous best sample. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of melamine-phloroglucinol-formaldehyde (MPF) for N -doped porous carbon. • Catalyst materials possess hierarchical porous structure, high specific surface area. • MPF/M = Fe, Co catalysts show high ORR activity in 0.1 M KOH (E 1/2 up to 0.81 V) • M N C catalysts show excellent electrochemical stability for 10,000 potential cycles. • Excellent AEMFC performance (P max = 347, 324 mW cm−2) with MPF/Fe and MPF/Co catalysts. Delving into highly active and cost-efficient electrocatalysts for oxygen reduction reaction (ORR) is crucial for the large-scale application of polymer electrolyte fuel cells. Anion exchange membrane fuel cells (AEMFCs) are promising clean energy devices owing to their mild reaction conditions and the high probability of employing Pt-free catalysts for ORR. Developing the promising non-Pt ORR catalysts for AEMFC is still of great importance. Herein, we report the transition metal (Fe, Co, Mn, and Cu) impregnated melamine-phloroglucinol-formaldehyde (MPF) polymeric networks to derive metal-nitrogen-carbon (M N C) electrocatalysts via a robust synthesis route. The catalysts are screened through variable metal contents and different pyrolysis temperature optimizations by virtue of their ORR activity. The controlled synthesis method resulted to the prominent textural properties of the catalysts with efficient active centers to enhance the ORR performance. Amongst, iron-doped (MPF/Fe), and cobalt-doped (MPF/Co) catalysts are performing better in terms of half-wave potential (E 1/2) values of 0.81 and 0.80 V vs RHE which is attributed to the highly active M−N x sites and hierarchical porous structure of catalysts. Outstanding electrochemical stability in half-cell and high-power density in an AEMFC (up to 347 mW cm−2) made the present work drive to the development of highly efficient M N C catalysts for fuel cell applications. [ABSTRACT FROM AUTHOR]

Metal-nitrogen-carbons (M-N-Cs) as a reliable substitution for platinum-group-metals (PGMs) for oxygen reduction reaction (ORR) are emerging candidates to rationalize the technology of fuel cells. The development of M-N-Cs can further be economized by consuming waste biomass as an inexpensive carbon source for the electrocatalyst support. Herein, we report the simple fabrication and in-depth characterization of electrocatalysts using lignin-derived activated char. The activated char (LAC) was functionalized with metal phthalocyanine (FePc and MnPc) via atmosphere-controlled pyrolysis to produce monometallic M-N-Cs (L_Mn and L_Fe) and bimetallic M1-M2-N-Cs (L_FeMn) electrocatalysts. Raman spectroscopy and transmission electron microscopy (TEM) revealed a defect-rich architecture. XPS confirmed the coexistence of various nitrogen-containing active moieties. L_Fe and L_FeMn demonstrated appreciable ORR in both acidic and alkaline conditions whereas L_FeMn helped in restricting the peroxide yield, particularly in alkaline media. L_Fe and L_FeMn demonstrated remarkable onset potential (E onset) of ∼0.942 V (vs RHE) with an E 1/2 of 0.874 V (vs RHE) in 0.1 M KOH. In acid, L_FeMn had an E onset of 0.817 V (vs RHE) and an E 1/2 of ∼0.76 V (vs RHE). Finally, the L_FeMn as a cathode electrocatalyst was integrated and tested in PEMFC and AEMFC. AEMFC demonstrated optimistic performance with a peak power density of 261 mW cm−2 at the current density of ∼577 mA cm−2. • Waste lignin was valorized through pyrolysis and high surface area char was synthesized. • The biochar was functionalized by Fe-, Mn- and Fe–Mn phthalocyanine. • Fe- and FeMn- catalysts showed superior ORR compared to Mn-catalyst. • Integration of PGM-free FeMn-catalyst in PEMFC reached a P max of ∼72 mW cm−2. • Integration of PGM-free FeMn-catalyst in AEMFC reached a P max of ∼261 mW cm−2. [ABSTRACT FROM AUTHOR]

This report presents the interplay between the synthesis parameters, physicochemical properties, and electrochemical performance of core-shell low-Pt electrocatalysts (ECs) for the oxygen reduction reaction (ORR) based on Pt x Ni active sites stabilized on a carbon nitride shell. The impact of the pyrolysis temperature (T f), of the support core (H) composition and of an electrochemical dealloying-activation step on the EC morphology and on the accessibility and stability of the active sites are studied in detail. Three supports are employed based on carbon nanoparticles and/or graphene platelets. The ORR performance of activated ECs measured by cyclic voltammetry with the thin-film rotating ring-disk electrode approach is strongly affected by T f and H. The best performing ECs are tested in single proton exchange membrane fuel cells under operating conditions. The simultaneous presence of graphene and carbon in H improves the dispersion of active sites, resulting in a vastly improved mass activity and durability in comparison with a benchmark state-of-the-art Pt/C EC. [Display omitted] • Hierarchical core-shell Pt–Ni ORR electrocatalysts (ECs) are obtained. • Interplay between synthesis, properties, and performance of ECs is discussed. • Hierarchical Pt–Ni ECs exhibit mass activities surpassing DOE targets. • Hierarchical Pt–Ni ECs are more durable than Pt/C reference ECs. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks were used as metal-nitrogen-carbon templates to synthesize Co–N–C catalysts through a facile synthesis approach that combined a cobalt-based zeolitic imidazolate framework (ZIF) structure and conductive carbon support. The spectroscopic, structural, and thermogravimetric analysis confirmed the synthesis of the Co-based ZIF, used to prepare catalysts with different ZIF/carbon support ratios by pyrolysis under inert atmosphere. Electrochemical characterization at alkaline pH demonstrated high activity towards oxygen reduction reaction (ORR). In addition to ORR activity, the Co–N–C electrocatalysts showed high methanol tolerance in the preliminary tests in a half-cell configuration. When assembled at the cathode side of both a hydrogen-fed anion exchange membrane fuel cell and an alkaline direct methanol fuel cell (ADMFC), the Co–N–C electrocatalysts showed competitive performance with the state-of-the-art Pt/C and other platinum-group-metal-free materials, using a FUMASEP® FAA-3-50 membrane. Exceptionally high performance (higher than 45 mW cm−2) was achieved in ADMFC fed with high methanol concentration (up to 10 M), due to the high methanol tolerance of Co–N–C electrocatalysts. Normalizing the performance to Pt loading, a value of 31.0 mW mg Pt −1 was obtained, which is the highest power up to now recorded with this kind of membrane and one of the highest values in the literature for ADMFCs. [Display omitted] • Metal-organic-framework-derived Co–N–C electrocatalysts. • High catalytic activity towards oxygen reduction in an alkaline environment. • Remarkable methanol tolerance of Co–N–C electrocatalysts. • Application in H 2 -fed anion exchange membrane fuel cells cathodes. • Application in alkaline direct methanol fuel cells cathodes with high power output. [ABSTRACT FROM AUTHOR]

A 3D multi-physics, multi-component and not isothermal model is developed to analyze the effects of catalyst structures on the performance of a gas diffusion electrode (GDE) cell toward the oxygen reduction reaction using dry oxygen as a reactant. The model includes Stokes–Brinkman, Maxwell–Stefan, and modified Butler–Volmer equations for simulating the performance of the GDE cell, solved by Comsol® Multiphysics v4.4a platform. The model is validated against experimental data, showing congruent and convergent responses for different electrodes based on noble and non-noble metals catalysts, confirming the accuracy of the model and the equations applied. The use of a 3D model incorporating porous materials can be used for evaluating mass transport and diffusivity parameters of the electrocatalyst, identifying the controlling variable in the process. The model can be used as an optimization tool for further improvement of catalyst synthesis, suggesting which properties can be tuned to improve the overall performance in the catalyst design phase. [ABSTRACT FROM AUTHOR]

Aimed at developing a highly active and stable non-precious metal electrocatalyst for oxygen reduction reaction (ORR), a novel FexNy/NC nanocomposite--that is composed of highly dispersed iron nitride nanoparticles supported on nitrogen-doped carbon (NC)--was prepared by pyrolyzing carbon black with an iron-containing precursor in an NH3 atmosphere. The influence of the various synthetic parameters such as the Fe precursor, Fe content, pyrolysis temperature and pyrolysis time on ORR performance of the prepared iron nitride nanoparticles was investigated. The formed phases were determined by experimental and simulated X-ray diffraction (XRD) of numerous iron nitride species. We found that Fe3N phase creates superactive non-metallic catalytic sites for ORR that are more active than those of the constituents. The optimized Fe3N/NC nanocomposite exhibited excellent ORR activity and a direct four-electron pathway in alkaline solution. Furthermore, the hybrid material showed outstanding catalytic durability in alkaline electrolyte, even after 4,000 potential cycles. [ABSTRACT FROM AUTHOR]

Hollow nanomaterials composed of a Pt-rich shell surrounding a central void have demonstrated promising electrocatalytic activity for the oxygen reduction reaction (ORR). However, their long-term stability remains understudied, and is the focus of the present paper. Here, we followed the temperature-dependent morphological and compositional trajectories of hollow PtNi/C nanoparticles during accelerated stress tests (AST) of interest for proton-exchange membrane fuel cells (PEMFC) applications. The combined physical, chemical and electrochemical results showed that: (i) the PtNi/C nanoparticles preserve a hollow nanostructure during accelerated stress testing at T = 25 °C, but collapsed in real PEMFC operating conditions (solid electrolyte – T = 80 °C), (ii) the dissolution of Ni atoms is drastically enhanced with an increase of the temperature, almost all Ni atoms being leached after the AST conducted in a single PEMFC, (iii) a lattice strain of ca. 0.4% persists in the aged hollow PtNi/C nanocatalysts, (iv) whatever the AST conditions, hollow PtNi/C nanocatalysts show improved ORR activity over solid Pt/C nanocatalysts of the same crystallite size. The catalytic enhancement is believed to result from the presence of subsurface vacancies in the dealloyed hollow PtNi/C nanoparticles. In a more global perspective, the present contribution emphasizes the crucial role of temperature on the stability of shape-controlled particles (far from their equilibrium shape). [ABSTRACT FROM AUTHOR]

A series of low-platinum-content platinum–nickel (Pt–Ni), platinum–cobalt (Pt–Co) binary alloys and platinum–nickel–cobalt (Pt–Ni–Co) ternary alloys electrocatalysts were successfully prepared by a three-step process based on electrodeposition technique and studied as electrocatalysts for oxygen reduction reaction (ORR) in polymer-electrolyte fuel cells. Kinetics of ORR was studied in 0.5 M H 2 SO 4 solution on the Pt–Ni, Pt–Co and Pt–Ni–Co alloys catalysts using rotating disk electrode technique. Both the series of Pt–Ni, Pt–Co binary alloys and the Pt–Ni–Co ternary alloys catalysts exhibited an obvious enhancement of ORR activity in comparison with pure Pt. The significant promotion of ORR activities of Pt–Ni and Pt–Co binary alloys was attributed to the enhancement of the first electron-transfer step, whereas, Pt–Ni–Co ternary alloys presented a more complicated mechanism during the electrocatalysis process but a much more efficient ORR activities than the binary alloys. [ABSTRACT FROM AUTHOR]

Electrocatalyst support affects not only catalytic activity of a catalyst, but also mass transportation and electron transfer in the catalyst layers of an electrode for proton exchange membrane fuel cells. Multi-dimensional and combined carbon materials such as Vulcan XC-72, carbon nanotubes (CNTs), and home-made coiled carbon nanotubes (CCNTs) are applied to enhance the catalyst activity and utilization. Three-dimensional CCNTs with large specific surface area and graphitic characteristic are synthesized by solid-state catalytic method. This obtained CCNTs and commercial CNTs are used as support to prepare platinum catalysts via modified ethylene glycol method, respectively. And the electrochemical surface areas (ECSAs) of the as-prepared Pt/CNTs, Pt/CCNTs and commercial Pt/C (JM) catalyst are evaluated by cyclic voltammetry. Then each two and three kinds of above catalysts mixed with different mass ratios are investigated. The ECSAs of Pt/C–Pt/CCNTs (95:5) and Pt/C–Pt/CNTs–Pt/CCNTs (80:10:10) are calculated to be 106 m 2 g Pt −1 and 111 m 2 g Pt −1 , with respect to 70 m 2 g Pt −1 of Pt/C (JM) catalyst. And these mixed catalysts also demonstrate improved oxygen reduction reaction activities. This is mainly attributed to the unique structure of CCNTs, which can construct a multi-dimensional network to facilitate the mass transportation and electrons/protons transfer. [ABSTRACT FROM AUTHOR]

A cost-effective chemical, N,N′-bis(salicylidene)ethylenediamine (salen), is used as a ligand to form a carbon-supported Co-salen complex (Co-salen/C) by a simple solid-sate reaction. The Co-salen/C is then pyrolyzed at 600, 700, 800, 900, and 1000 °C to form carbon-supported Co–N–S/C catalysts for the oxygen reduction reaction (ORR). XRD, EDX, TEM, and XPS are used to characterize the catalysts' composition, crystalline nature, morphology, and possible surface groups induced by heat-treatment. Investigation of the catalytic activity and the ORR mechanisms using rotating disk electrode and rotating ring-disk electrode techniques demonstrates that all of these Co–N–S/C catalysts are highly active for the ORR in an O2-saturated 0.1 M KOH solution, but the catalyst heat treated at 700 °C gives the best ORR activity. The overall electron transfer number for the catalyzed ORR was determined to be 3.6–3.9, with 3.7–19.9% H2O2 production over the potential range of −0.05 to −0.60 V, suggesting that the ORR catalyzed by Co–N–S/C catalysts is dominated by a 4-electron transfer pathway from O2 to H2O. In addition, these catalysts exhibit superior methanol tolerance to commercial 40% Pt/C catalyst, thus the Co–N–S/C catalysts are promising for use as electrocatalysts in alkaline polymer electrolyte membrane fuel cells. [ABSTRACT FROM AUTHOR]

A series of non-precious metal electrocatalysts, namely pyrolyzed carbon-supported cobalt-polypyrrole, Co-PPy-TsOH/C, are synthesized with various cobalt precursors, including cobalt acetate, cobalt nitrate, cobalt oxalate, and cobalt chloride. The catalytic performance towards oxygen reduction reaction (ORR) is comparatively investigated with electrochemical techniques of cyclic voltammogram, rotating disk electrode and rotating ring-disk electrode. The results are analyzed and discussed employing physiochemical techniques of X-ray diffraction, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma, elemental analysis, and extended X-ray absorption fine structure. It shows that the cobalt precursor plays an essential role on the synthesis process as well as microstructure and performance of the Co-PPy-TsOH/C catalysts towards ORR. Among the studied Co-PPy-TsOH/C catalysts, that prepared with cobalt acetate exhibits the best ORR performance. The crystallite/particle size of cobalt and its distribution as well as the graphitization degree of carbon in the catalyst greatly affects the catalytic performance of Co-PPy-TsOH/C towards ORR. Metallic cobalt is the main component in the active site in Co-PPy-TsOH/C for catalyzing ORR, but some other elements such as nitrogen are probably involved, too. [ABSTRACT FROM AUTHOR]

A new platinum group metal (PGM)-free proton exchange membrane fuel cell (PEMFC) cathode catalyst materials, synthesized using the VariPore™ method by Pajarito Powder, LLC, are characterized for their structure and activity. The physico-chemical analysis of the iron-nitrogen-carbon (Fe-N-C) electrocatalysts show mesoporous carbon material effectively doped with iron and nitrogen. The materials have an average pore size of 7–8 nm and high specific surface area. The Fe-N-C catalysts exhibit good oxygen reduction reaction (ORR) activity in 0.5 M H 2 SO 4 electrolyte with high half-wave potential and sustainable electrochemical stability over 10,000 repeated potential cycles with insignificant losses in their activities. As cathode catalysts in a PEMFC, the Fe-N-C materials deliver remarkably good fuel cell performance at low overpotential approaching that of the commercial Pt catalyst. The high ORR electrocatalytic activity of these Fe-N-C catalysts is credited to the synergy between nitrogen-moieties, specifically pyrrolic-N, pyridinic-N, and graphitic-N, and iron in addition to the high mesoporosity that facilitate an effective reaction path in boosting the electrocatalytic activity and stability. [Display omitted] • State-of-the-art commercial PGM-free catalysts for ORR were characterized and evaluated. • Was shown that active centres are atomically dispersed. • Performance of electrocatalysts was evaluated in industrially manufactured MEA form-factor. • The fuel cell performance is close to the state-of-the-art R&D PGM-free catalysts. [ABSTRACT FROM AUTHOR]

Abstract: The catalytic layers of Proton Exchange Membrane (PEM) fuel cells use carbon-supported Pt-based nanoparticles, which are classically synthesized by impregnation with a metal precursor usually based on chloride counter-ions. However, the literature points out that chloride ions poison the catalytic activity. The purpose of this work is to compare the surface reactivity and the electrocatalytic activity of Pt/carbon xerogel nanoparticles contaminated with different amount of chlorine. The catalysts were synthesized using the Strong Electrostatic Adsorption (SEA) method and H2PtCl6 as a metal precursor. The Cl content in the catalysts was changed by varying the gas atmosphere and the duration of the reduction step. The effect of Cl contamination was investigated on two model reactions: the electrochemical COads oxidation and the O2 reduction. Evidences are provided that the Cl− ions issued from the incomplete decomposition/removal of the metal precursor partially block the Pt catalytic sites, and limit the rate of the COads + OHads recombination and of the diffusion of COads molecules in CO stripping experiments. The adsorption of Cl− ions also depreciates the ORR kinetics. In search for efficient catalysts, chloride-containing metal precursors must therefore be avoided. [Copyright &y& Elsevier]

Abstract: Non-Pt based oxygen reduction catalyst H2-air fuel cell performance is reported for various electrode compositions. Ink formulations for pyrolyzed Co porphyrin based cathode electrocatalysts were evaluated in a membrane electrode assembly (MEA) configuration and X-ray photoelectron spectroscopy was performed on the MEA catalyst layers. The effect of cooling time trajectories of the catalysts after pyrolysis as well as Nafion content in the ink formulation were studied. By building statistical structure-to-property relationships between XPS and MEA performance using multivariate analysis we have determined that the higher stability of fast-cooled containing inks is mainly associated with better preserved graphic carbon from the carbon black and C–F moieties of the Nafion, while better MEA performance is a result of the presence of these moieties as well as pyridinic nitrogen and nitrogen associated with metal in the pyropolymer. Optimal Nafion content is determined at 1:1 catalyst:Nafion weight ratio, while higher Nafion concentrations causes oxidation of the Nafion backbone itself as well as leaching of the Co x O y particles from the catalyst and formation of oxidized species of Co, O, C and F. Further, we report 1500 h of continuous fuel cell operation for two different non-platinum cathode catalysts in the optimized MEA. [Copyright &y& Elsevier]

Abstract: In this study, a novel core–shell structured Pd3Fe@Pt/C electrocatalyst, which is based on Pt deposited onto carbon supported Pd3Fe nanoparticles, is prepared for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). The carbon supported Pd3Fe nanoparticles act as seeds to guide the growth of Pt. The formation of the core–shell structured Pd3Fe@Pt/C is confirmed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and electrochemical characterization. The higher surface area of the synthesized catalyst suggests that the utilization of Pt in the Pd3Fe@Pt/C catalyst is higher than that in Pt/C. Furthermore, better electrocatalytic performance than that of Pt/C and Pd3Fe/C catalyst is observed in the ORR which follows a four-electron path. Consequently, the results indicate that the Pd3Fe@Pt/C catalyst could be used as a more economically viable alternative for the ORR of PEMFCs. [Copyright &y& Elsevier]

Fluorination is considered as a means of reducing the degradation of Fe/N/C, a highly active FeNx-doped disorganized carbon catalyst for the oxygen reduction reaction (ORR) in PEM fuel cells. Our recent experiments have, however, revealed that fluorination poisons the FeNx moiety of the Fe/N/C catalytic site, considerably reducing the activity of the resulting catalyst to that of carbon only doped with nitrogen. Using the density functional theory (DFT), we clarify in this work the mechanisms by which fluorine interacts with the catalyst. We studied 10 possible FeNx site configurations as well as 2 metal-free sites in the absence or presence of fluorine molecules and atoms. When the FeNx moiety is located on a single graphene layer accessible on both sides, we found that fluorine binds strongly to Fe but that two F atoms, one on each side of the FeNx plane, are necessary to completely inhibit the catalytic activity of the FeNx sites. When considering the more realistic model of a stack of graphene layers, only one F atom is needed to poison the FeNx moiety on the top layer since ORR hardly takes place between carbon layers. We also found that metal-free catalytic N-sites are immune to poisoning by fluorination, in accordance with our experiments. Finally, we explain how most of the catalytic activity can be recovered by heating to 900 °C after fluorination. This research helps to clarify the role of metallic sites compared to non-metallic ones upon the fluorination of FeNx-doped disorganized carbon catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe-N X /C-NC1100 with high graphitization is prepared via a stepwise pyrolysis method. • Fe-N X /C-NC1100 achieves a high density of active sites under harsh thermal treatment. • Fe-N X /C-NC1100 shows superior ORR stability with 25 mV loss of E 1/2 after 30 K cycles. • Fe-N X /C-NC1100 reserves 71 % of activity after 100 h at 0.5 V in H 2 -air fuel cell test. • Stability enhancement is ascribed to the strong antioxidant ability of NC support. Metal-nitrogen/carbon (M-N X /C) materials have been hailed as promising electrocatalysts toward oxygen reduction reaction (ORR). However, most reported promising Fe-N X /C catalysts are prohibited by their low stability in acidic media. Here we report a rational stepwise pyrolysis strategy for stabilizing isolated Fe-N X sites on highly graphitized N-doped carbon (NC) supports. The NC support derived from a harsh thermal treatment of 1100 °C can apparently enhance the graphitization degree of catalysts. The targeted catalyst, Fe-N X /C-NC1100 achieved a half-wave potential (E 1/2) of 0.811 V and displayed superior stability in both ORR (only 25 mV loss of E 1/2 after 30000 cycles) and fuel cell (71 % current retention at a voltage of 0.5 V after 100 h) tests. High graphitization degree of carbon support was responsible for the enhancement of stability, which empowers strong antioxidant ability to Fe-N X /C catalyst. [ABSTRACT FROM AUTHOR]