Electrocatalysts For Fuel Cells Research Articles

Vesicular AuPd alloy nanowires for enhanced electrocatalytic activity

Developing excellent fuel cells requires complex design and precise tuning of catalyst structure and composition. This paper presents a simple approach to fabricate AuPd vesicular nanowires (VNWs) with controlled composition. The method uses homogeneous Te nanowires (NWs) as templates and reducing agents in the replacement reaction and NaClO as etching agent. Bimetallic synergism and rich catalytic sites in the vesicular nanowires give AuPd catalysts the excellent electrocatalytic performance for methanol oxidation. In particular, the Au28Pd71 VNWs showed the highest electrocatalytic activity for methanol oxidation, and its highest mass current density was1.278 A mg−1, which was 1.22 and 1.65 times that of Pt VNWs and commercial Pt/C, separately. Furthermore, Au28Pd71 VNWs exhibited good stability after 2000 cycles, maintaining an initial mass current density of 85.2%. As the optimal component ratio, Au28Pd71 exhibited superior electrocatalytic performance for methanol oxidation. This discovery demonstrated a new approach for the programming and fabrication of senior methanol fuel cells electrocatalysts.

Highly durable fuel cell electrocatalyst with low-loading Pt-Co nanoparticles dispersed over single-atom Pt-Co-N-graphene nanofiber

Highly durable fuel cell electrocatalyst with low-loading Pt-Co nanoparticles dispersed over single-atom Pt-Co-N-graphene nanofiber

Microwave application as an alternative method to increase the efficiency of PtC catalyst in PEMFCs

This study aims to develop a high-performance Pt/C catalyst for the cathode and anode parts of a modified Proton exchange membrane (PEM) fuel cell in nitrogen and argon gases at different microwave radiation powers. The pure and modified forms of the synthesized Pt/C catalysts were characterised using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results revealed that the crystal structure of the modified Pt/C catalyst was perfect and that the particle size of the catalytic material grew significantly as a consequence of the modification. Furthermore, the durability of PEM fuel cell electrocatalysts was investigated using the cyclic voltammetry (CV) technique. The experimental results indicated that microwave radiation had a significant effect on the particle size of the Pt/C catalyst. Additionally, the modified Pt/C catalyst exhibited a decreased activation potential loss and increased the cathode and anode power density values by 34% and 47%, respectively, compared to the Pt/C catalyst.

Materials for electrocatalysts in proton exchange membrane fuel cell: A brief review

Energy is a requisite factor for technological advancement and the economic development of any society. Currently, global energy demand and supply largely rely on fossil fuels. The use of fossil fuels as a source of energy has caused severe environmental pollution and global warming. To salvage the dire situation, research effort is geared toward the utilization of clean, renewable and sustainable energy sources and the hydrogen energy economy is among the most preferred choices. Hydrogen energy economy, which includes hydrogen production, storage and conversion has gained wide consideration as an ecofriendly future energy solution with a fuel cell as its conversion device. Fuel cells, especially, the proton exchange membrane category, present a promising technology that converts hydrogen directly into electricity with great efficiency and no hazardous emissions. Unfortunately, the current generation of proton exchange membrane fuel cells faces some drawbacks that prevent them from large-scale market adoption. These challenges include the high costs and durability concerns of catalyst materials. The main source of high cost in fuel cells is the platinum catalyst used in the electrodes, particularly at the cathode where the sluggish oxygen reduction reaction kinetics require high loading of precious metals. Many research efforts on proton exchange membrane fuel cells are directed to reduce the device cost by reducing or completely replacing the platinum metal loading using alternative low-cost materials with “platinum-like” catalytic behaviour while maintaining high power performance and durability. Consequently, this review attempts to highlight recent research efforts to replace platinum and carbon support with other cost-effective and durable materials in proton exchange membrane fuel cell electrocatalysts. Overview of promising materials such as alloy-based (binary, ternary, quaternary and high-entropy alloys), single atom and metal-free electrocatalysts were discussed, as the research areas are still in their infancy and have many open questions that need to be answered to gain insight into their intrinsic requirements that will inform the recommendation for outlook in selecting them as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell.

Innovative Electrocatalysts for Fuel Cell and Battery Applications

The development of sustainable energy systems is essential to hinder global warming and environmental pollution emergencies [...]

Kinetics of Oxygen Reduction Reaction of Polymer-Coated MWCNT-Supported Pt-Based Electrocatalysts for High-Temperature PEM Fuel Cell

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.

Platinum-Containing Nanoparticles on a Nitrogen-Doped Carbon Support as Highly Active Electrocatalysts for Low-Temperature Fuel Cells

Platinum-Containing Nanoparticles on a Nitrogen-Doped Carbon Support as Highly Active Electrocatalysts for Low-Temperature Fuel Cells

Nanostructured Electrocatalysts for Fuel Cell and Water Electrolysis Applications to Realize Sustainable Hydrogen Society

Nanostructured Electrocatalysts for Fuel Cell and Water Electrolysis Applications to Realize Sustainable Hydrogen Society

Electrocatalysts for Formic Acid-Powered PEM Fuel Cells: Challenges and Prospects

In view of the drawbacks of rechargeable batteries, such as low mass and volumetric energy densities, as well as slow charging rate, proton exchange membrane fuel cells (PEMFCs) are reckoned to be promising alternative devices for energy conversion. Currently, commercial PEMFCs mainly use H 2 as the fuel, but the challenges in generation, storage, and handling of H 2 limit their further development. Among the liquid fuels, formic acid possesses the merits of low flammability, low toxicity, slow crossover rate, faster reaction kinetics, and high volumetric H 2 storage capacity, thus being considered as the most promising energy carrier. It can be used as the energy source for direct formic acid fuel cells (DFAFCs) and formic acid-based H 2 -PEMFCs, which are also called indirect formic acid fuel cells (IFAFCs). A common issue hindering their commercialization is lacking efficient electrocatalysts. In DFAFCs, the anodic electrocatalysts for formic acid oxidation are suffering from stability issue, whereas the cathodic electrocatalysts for oxygen reduction are prone to poisoning by the permeated formic acid. As for IFAFCs, CO and CO 2 impurities generated from formic acid dehydrogenation will cause rapid decay in the catalytic activity. High working temperature can improve the CO and CO 2 tolerance of catalysts but will accelerate catalyst degradation. This review will discuss the mitigation strategies and recent advances from the aspect of electrocatalysts to overcome the above challenges. Finally, some perspectives and future research directions to develop more efficient electrocatalysts will be provided for this promising field.

Ultrastable Fe-N-C Fuel Cell Electrocatalysts by Eliminating Non-Coordinating Nitrogen and Regulating Coordination Structures at High Temperatures.

Pyrolyzed Fe-N-C materials have attracted considerable interest as one of the most active noble-metal-free electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Despite significant progress is made in improving their catalytic activity during past decades, the Fe-N-C catalysts still suffer from fairly poor electrochemical and storage stability, which greatly hurdles their practical application. Here, an effective strategy is developed to greatly improve their catalytic stability in PEMFCs and storage stability by virtue of previously unexplored high-temperature synthetic chemistry between 1100 and 1200°C. Pyrolysis at this rarely adopted temperature range not only enables the elimination of less active nitrogen-doped carbon sites that generate detrimental peroxide byproduct but also regulates the coordination structure of Fe-N-C from less stable D1 (O-FeN4 C12 ) to a more stable D2 structure (FeN4 C10 ). The optimized Fe-N-C catalyst exhibits excellent stability in PEMFCs (>80% performance retention after 30h under H2 /O2 condition) and no activity loss after 35 day storage while maintaining a competitive ORR activity and PEMFC performance.

Mixed-Dimensional Pt-Ni Alloy Polyhedral Nanochains as Bifunctional Electrocatalysts for Direct Methanol Fuel Cells.

Pt nanocatalysts play a critical role in direct methanol fuel cells (DMFCs) due to their appropriate adsorption/desorption energy, yet suffer from an unbalanced relationship between size-dependent activity and stability. Herein, mixed-dimensional Pt-Ni alloy polyhedral nanochains (Pt-Ni PNCs) with an ordered assembly of a nanopolyhedra-nanowire-nanopolyhedra architecture are fabricated as bifunctional electrocatalysts for DMFCs, effectively alleviating the size effect. The Pt-Ni PNCs exhibit 7.23 times higher mass activity for the anodic methanol oxidation reaction (MOR) than that of commercial Pt/C. In situ Fourier transform infrared spectroscopy and CO stripping measurements demonstrate the prominent stability of the Pt-Ni PNCs to resist CO poisoning. For the cathodic oxygen reduction reaction (ORR), a positive half-wave potential exceeding Pt/C is achieved by the Pt-Ni PNCs, and it can be well maintained for 10000 cycles with negligible activity decay. The designed nanostructure can alleviate the agglomeration and dissolution problems of 0D small-sized Pt-Ni alloy nanocrystals and enrich surface atom steps and active facets of 1D chain-like nanostructures. This work provides a proposed strategy to improve the catalytic performance of Pt-based nanocatalysts by constructing novel interfacial relationships in mixed dimensions to alleviate the imbalance between catalytic activity and catalytic stability caused by size effects.

Silver‐Free Synthesis of Concave Au Nanocubes with Enhanced Activity Towards Electro‐Oxidation of Ethanol: Experimental and Theoretical Studies

AbstractWe report a silver‐free synthesis of gold (Au) concave nanocubes (CNCs) that involves the direct deposition of Au atoms over spherical Au seeds under well‐controlled reaction kinetics and surface capping. The elementally‐pure composition makes them ideal research candidate towards validating structural advantage of concave surface in electrocatalytic oxidation of ethanol. In particular, the as‐obtained Au CNCs exhibited an enhanced specific activity and reaction kinetics, but weakened long‐term stability, as compared to quasi‐spherical counterparts. Theoretical simulations suggest that the high‐index planes represent a high catalytic performance for ethanol oxidation. The current work offers an effective synthetic strategy that successfully excludes the necessary and wide use of Ag+ ions in controlled synthesis of pure Au nanocrystals with a concave cubic shape, shedding light on the rational design of fuel cell electrocatalyst from the perspective of crystal facet effect.

Silicon-doped niobium suboxide (NbOS): A fuel cell electrocatalyst support with enhanced conductivity and corrosion-resistance

A novel carbon-free silicon-doped niobium suboxide was synthesized and tested as an electrocatalyst support for fuel cell applications. The promising Nb0·24O0·46Si0.30 (NbOS) metal oxide support exhibits a low structural band-gap with significantly high electronic conductivity. Furthmore, the NbOS support shows high corrosion-resistance in acidic media at high potentials. Pt nanoparticles were dispersed over the NbOS support (Pt/NbOS) to create an electrocatalyst with excellent electroactivity towards the oxygen reduction reaction (ORR). Likewise, in situ electrochemical analysis, and impedance spectroscopy (EIS) confirmed remarkable durability of the Pt/NbOS catalyst when subjected to harsh accelerated stress testing (AST) condtions. The enhanced stability and electrocatalytic activity and of Pt/NbOS is attributed to the strong metal-support interaction (SMSI) between the Pt nanoparticles (NPs) and the conductive NbOS support, which were confirmed via XRD and XPS measurements.

Particle Design and Evaluation for Electrocatalysts of Polymer Electrolyte Fuel Cells

Particle Design and Evaluation for Electrocatalysts of Polymer Electrolyte Fuel Cells

Investigation of the Influence of Selected Operating Modes on the Long-Term Stability of Electrocatalysts in the PEM Fuel Cell

The membrane electrode assembly (MEA) is the core component of the fuel cell stack. In it, the conversion of chemical energy into electrical energy takes place at the catalyst layers. The functional capability of the MEA is an indispensable prerequisite for the operation of the fuel cell stack and thus plays a decisive role in defining its stability. In addition to the selection of suitable materials, the mode of operation plays a major role in the durability of the MEA. It is known from the literature that electrochemical degradation reactions generally depend on operating parameters such as temperature, potential and dynamics. [1] Therefore, in order to derive a durability promoting mode of operation for the PEM Fuel Cell as well as to make lifetime predictions, it is necessary to identify and understand the processes occurring during the aging of the MEA.This work deals with the investigation of the influence of the operating parameters in the drive cycle as an important operating mode on the aging of the cathode catalyst layer in the MEA. According to the state of the art, nanoparticulate platinum supported on carbon (Pt/C) is usually used as the cathode catalyst. The degradation of Pt/C has been intensively studied in recent years. Platinum dissolution and Pt agglomeration are discussed as the main causes of Pt/C degradation during PEMFC operation. [2, 3]Studies have shown that the dissolution rate generally increases with potential and can accelerate under potentiodynamic conditions. [1] Dissolution of Pt from the catalyst, transport of Pt ions through the electrode, and precipitation of Pt in the membrane, possibly due to reduction of Pt ions by the H2 crossover from the anode can be associated with the loss of cathode electrochemical surface area (ECSA) and thus irreversible performance loss. [4]The primary objective of this work is to investigate the influence of different operating parameters such as temperature and potential range on the degradation rate of the cathode using an accelerated stress test (AST) which was developed to simulate an analogous to real drive cycle operation of a PEM fuel cell in a vehicle.A secondary objective is to evaluate the AST itself in order to determinate its capability of fuel cell lifetime prediction. For that the transferability of the observed degradation rates are to be evaluated on different integration levels such as single-cell PEM test bench and short-stack multi-cell test bench. As a measure to evaluate the transferability of the accelerated stress tests, the loss of electrochemical active surface area (ECSA) serves as an indirect measure of catalyst degradation and the resulting Pt particle size distribution which is determined by TEM serves as a direct measure. The derivation of acceleration factors for the lifetime tests of the different integration levels would allow an early estimation of the lifetime, this way test time and cost could be significantly saved in the evaluation of new materials.

Ternary PtZnCu Intermetallic Nanoparticles as an Efficient Oxygen Reduction Electrocatalyst for Fuel Cells with Ultralow Pt Loading

Ternary PtZnCu Intermetallic Nanoparticles as an Efficient Oxygen Reduction Electrocatalyst for Fuel Cells with Ultralow Pt Loading

Stepwise synthesis of “Pt-on-PdAg” hybrid trigonal/hexagonal nanocrystals for efficient electroxidation of methanol: Interface engineering for trimetallic electrocatalyst

We report the fabrication of “Pt-on-PdAg” heterogeneous nanocrystals in the form of trigonal/hexagonal plate (THNPs) and explored their applications in electroxidation of methanol (MOR) in alkaline medium. In particular, PdAg polyhedral nanoparticles are prepared in advance, followed by the addition of Pt salts to allow in situ galvanic replacement reaction (GRR) between them, leading to the formation of Pt nano-islands on PdAg particle surface and the transformation of the overall morphology into trigon/hexagon. The deliberately designed Pt-“PdAg alloy” interface arising from the hybrid structure greatly enriches the absorption sites, showing noticeable structural advantages in MOR electrocatalysis. Particularly, the carbon-supported Pt-on-PdAg THNPs exhibit nearly 30-fold increase in specific activity as compared to that of commercial Pt/C, as well as enhanced reaction kinetics and long-term durability. DFT calculations suggest that the reaction of CH 3 OH oxidation mediated by PtAgPd is energetically more favorable compared to the similar reaction promoted by Pt, which rationalizes the experimental observation that PtAgPd shows the improved catalytic performance. The present study offers a feasible route to construct trimetallic nanocrystals with successful interface engineering, and validates their promising use as fuel cell electrocatalyst from both experimental validation and fundamental insights. It may help enlighten the rational design of heterostructured electrocatalysts with regulated multiple active sites. • Stepwise synthesis of trigonal/hexagonal plate-like Pt-on-PdAg hybrid nanostructures is proved. • The density of Pt nano-islands and the overall elemental composition can be tuned. • Interface engineering, tensile strain and multimetallic synergy, contribute to enhanced MOR. • DFT calculations show that MOR mediated by PtAgPd is energetically more favorable.

Electrochemical studies and electrocatalytic applications of Zirconia-Polyaniline nanocomposite

• Ethanol and formic acid oxidation. • Electrocatalyst. • polyaniline/ZrO 2 nanocomposite. In recent days, conducting polymers with inorganic metal oxide shows interest in electrochemical and electro catalytic applications. Zirconia doped polyaniline (PANI) nanocomposites were synthesized through in situ polymerization method for both formic acid oxidation (FAO) and ethanol oxidation reaction (EOR). The synthesized nanocomposites were characterized by X-ray Diffraction Spectroscopy (XRD), High-Resolution Transmission Electron Microscope (HRTEM), Energy Dispersive Spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The electrochemical properties of nanocomposites were tested by cyclic voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) methods. Studies of differential Pulse Voltammetry and chronoamperometry shows the electro catalytic activity and stability of the ZrO 2 -PANI catalyst. The FAO of ZrO 2 -PANI demonstrates the highest electro catalytic performance with a high current density of 4.6 mA.cm −2 , which is higher than the EOR with the maximum of peak current of 2.8 mA.cm −2 . As per studies, ZrO 2 -PANI nanocomposites work well as a direct-formic acid fuel cell electrocatalyst.

Engineering Hollow Core-Shell N-C@Co/N-C Catalysts with Bits of Ni Doping Used as Efficient Electrocatalysts in Microbial Fuel Cells.

The sluggish and inefficient oxygen reduction reaction (ORR) of cathode catalysts in microbial fuel cells is widely accepted as the key restriction in implementing their large-scale actual production application. Recently, modification of nitrogen-doping carbon materials with some transition metal species (M-N-C) is expected to be reserve force to substitute commercial noble metal catalysts. However, long-term stability is always unable to solve effectively. We report a simple synthetic approach of metal-organic framework-derived hollow core-shell Co-nitrogen codoping-modified porous carbon catalysts (N-C@Co/N-C-n%Ni), which is introduced by bits of Ni substance, via the template method and vacuum-assisted impregnation method that exhibit similar catalytic activity to commercial Pt/C catalysts. The hollow core-shell H-N-C@Co/N-C-3%Ni catalyst shows excellent ORR performance and stability, which is 96.31% of the initial current after 125 h continuous reaction, and has been capable of yielding a maximum power density of 1.17 ± 0.01 W·m-2 with 2% decrease in 45 days for long-term continuous operation.

Superaerophobic CoP Nanowire Arrays as a Highly Effective Anode Electrocatalyst for Direct Hydrazine Fuel Cells

Superaerophobic CoP Nanowire Arrays as a Highly Effective Anode Electrocatalyst for Direct Hydrazine Fuel Cells