Fuel Cell Reactions Research Articles

Hydrothermal synthesis of palladium nitrides as robust multifunctional electrocatalysts for fuel cells

An efficient hydrothermal synthesis has been reported for the preparation of PdNxnanocrystals with controllable stoichiometries, which can exhibit superior catalytic performance toward a wide range of fuel cell reactions.

In-Plane Structural Fluctuations in Differently Condensed Graphitic Carbon Nitrides

Graphitic carbon nitrides (g-CNxHy) are an important class of materials for driving energy conversion processes such as photocatalysis and fuel cell reactions. However, a poor understanding of stru...

Insights in to the Electrochemical Activity of Fe-Based Perovskite Cathodes toward Oxygen Reduction Reaction for Solid Oxide Fuel Cells

The development of novel oxygen reduction electrodes with superior electrocatalytic activity and CO2 durability is a major challenge for solid oxide fuel cells (SOFCs). Here, novel cobalt-free perovskite oxides, BaFe1−xYxO3−δ (x = 0.05, 0.10, and 0.15) denoted as BFY05, BFY10, and BFY15, are intensively evaluated as oxygen reduction electrode candidate for solid oxide fuel cells. These materials have been synthesized and the electrocatalytic activity for oxygen reduction reaction (ORR) has been investigated systematically. The BFY10 cathode exhibits the best electrocatalytic performance with a lowest polarization resistance of 0.057 Ω cm2 at 700 °C. Meanwhile, the single cells with the BFY05, BFY10 and BFY15 cathodes deliver the peak power densities of 0.73, 1.1, and 0.89 W cm−2 at 700 °C, respectively. Furthermore, electrochemical impedance spectra (EIS) are analyzed by means of distribution of relaxation time (DRT). The results indicate that the oxygen adsorption-dissociation process is determined to be the rate-limiting step at the electrode interface. In addition, the single cell with the BFY10 cathode exhibits a good long-term stability at 700 °C under an output voltage of 0.5 V for 120 h.

Fe–N–C Composite Catalyst Derived from Solid Digestate for the Oxygen Reduction Reaction in Microbial Fuel Cells

Transforming biomass waste into cost-effective non-precious-metal catalysts for the oxygen reduction reaction (ORR) provides a great opportunity for the development of microbial fuel cells (MFCs). ...

N-Doped CNT: Distribution Electron on Different Ratio N/C for Oxygen Reduction Reaction

Carbon nanotubes (CNTs) have the advantage to improve electrochemical fuel cell reactions by increasing the dispersion of nanoparticles as well as having high strength in mechanical and electrical properties. Therefore, this study presents the comparison of nitrogen doped CNT and other doping heteroatom on CNT as a catalyst support for application in the Direct Liquid Fuel Cell (DLFC). The doping ratio in CNT was conducted to determine the effect of the oxygen reduction reaction. In addition, the effect of CNT diameter in oxygen adsorption also has been tested. The models and calculations were done using density functional theory (DFT). The result showed that the ratio of N/C is decreases as the diameter of CNT decreases. The value is even dropped as the unit cell is increased to 1x1x2. The band gap value of CNT before doping is higher compared to after nitrogen doping. While increasing the diameter of doped CNT has increased the mulliken charge distribution and thus make the model more stable. In the adsorption energy of molecule oxygen, the 1x1x2 unit cell of CNT and large diameter show a remarkable and stable compared to in 1x1x1 unit cell and small diameter of CNT. Thus, the adsorption energy of the oxygen molecule shows a more stable value in the low doping ratio and high CNT diameter compared to a high doping ratio and a small diameter of the CNT. This result shows the potential of the CNT in helping to improve electrochemical reaction in DLFC.

Performance of Perovskite-Type Oxides for Oxygen Reduction Reaction in Direct Hydrazine Fuel Cell

Perovskite-type oxide-based La0.6Sr0.4Mn(1-x)Co x O3/carbon (x = 0, 0.1, 0.2, 0.3, 1) catalysts were prepared by calcination of a mixture of metal nitrates and PVP at 600 °C, followed by milling of the calcined powder with a carbon support. The catalytic activities for the oxygen reduction reaction (ORR) were tested in alkaline electrolyte by using a rotating ring-disk electrode (RRDE) at 25 °C. With an increase in the doping amount of Co, the onset potential of the La0.6Sr0.4Mn(1-x)Co x O3/carbon catalyst was found to be shifted in a positive direction and the ring current during ORR decreased. Especially, the La0.6Sr0.4Mn0.7Co0.3O3/carbon (x = 0.3) catalyst showed the highest ORR activity among the prepared catalysts. The La0.6Sr0.4Mn0.7Co0.3O3/carbon was tested as the cathode of an alkaline membrane-type direct hydrazine fuel cell (DHFC), and a maximum power density of 133 mW cm−2, which exceeded that for the MEA using Pt/C (73.4 mW cm−2), was obtained at 50 °C. In addition, the open circuit voltage (OCV) for the DHFC (0.846 V) was greater than that of a commercial Pt/C cathode (0.788 V). Thus, the perovskite-type La0.6Sr0.4Mn0.7Co0.3O3 catalyst is expected to be a good candidate for use as a catalytic material for a DHFC cathode as an alternative to Pt.

Acetonitrile Contamination and Recovery of Pemfcs

The proton exchange membrane fuel cell (PEMFC) is still considered a promising power source for transportation and stationary applications. Electrochemical catalysts and the proton exchange membrane (PEM) are the two key components that determine cell performance. The catalyst promotes fuel cell reactions generating electricity for the external load whereas the PEM completes the circuit by transporting protons. Air pollution is detrimental to both PEMFC performance and durability (1). Acetonitrile, is a critical pollutant that primarily originates from automobile exhausts and manufacturing facilities, where acetonitrile has been used as a solvent for spinning fibers and as an electrolyte in lithium batteries. The acetonitrile concentration in atmospheric air reaches values of up to 3 ppm in some areas (2). During PEMFC operation, acetonitrile is introduced into the cathode compartment by slippage through the air filter. The effects of acetonitrile on a PEMFC were investigated by in-situ operation and ex-situ electrochemical techniques (3,4). The results of in-situ tests showed that a trace amount of acetonitrile close to the atmospheric concentration caused significant short- and long-term damage, especially for MEAs with commercially relevant low Pt catalyst loadings (5,6). The ex-situ analysis indicated that acetonitrile not only impacted the oxygen reduction reaction by adsorbing on the Pt/C catalyst surface, but also affected the proton conductivity of ionomers and PEMs by ion exchange with its conversion products. Acetonitrile reaction products exhausted from an operating PEMFC were also identified by in-situ GC-MS and ex-situ water analysis (7). The acetonitrile reaction intermediates and products assisted the derivation of a contamination mechanism. Acetonitrile is hydrolyzed and reduced to NH3 and CH3CHO, and CH3COOH. Subsequent NH3 hydrolysis forming NH4 + gradually impacted the proton conductivity of the ionomer and PEM by accumulation. The other hydrocarbon products adsorbed on the surface of Pt catalysts competed with the main fuel cell reactions and were successively oxidized to harmless CO2.Automotive PEMFCs are exposed to variable operating conditions: startup, duty cycling, and shutdown. In this contribution, the effects of operating conditions on PEMFC contamination by acetonitrile are investigated. Contamination mechanisms are employed to analyze in detail cell performance degradation during contaminant injection and recovery after the contaminant injection was interrupted. Both steps involve at least two different processes. The adsorption and desorption of acetonitrile and/or its redox products dominate the fast cell voltage change occurring during the initial portion of both degradation and recovery steps. The ion exchange dominated the slower evolution in cell voltage during the latter part of both degradation and recovery steps. During cell contamination, the amount of water carried by reactant streams showed a considerable impact on performance degradation. The longer time needed to reach a steady state (see Figure 1) was attributed to ammonium scavenging by liquid water drops (8) delaying its accumulation. For the cell performance recovery step, the Pt catalyst activity and cathode potential only impact the earliest and shortest portion of the transient. As a result, the recovery duration is dominated by the ionomer and membrane ion exchange process, and is therefore less sensitive to contamination extent or operational history as previously observed (Figure 8 in (9)). Faster recovery strategies will be proposed based on the contamination mechanism and this detailed analysis of the operating condition effects.ACKNOWLEDGMENTSThis work was supported by the Department of Energy (DE-EE0000467) and the Office of Naval Research (N00014-19-1-2159). Authors are also grateful to the Hawaiian Electric Company for their ongoing support of the Hawaii Sustainable Energy Research Facility operations.REFERENCES J. St-Pierre, in Polymer Electrolyte Fuel Cell Durability, F. N. Büchi, M. Inaba, and T. J. Schmidt, Editors, p. 289, Springer (2009).http://www.epa.gov/airquality/airdata/index.html. Information accessed in August 2014.J. Ge, J. St-Pierre, Y. Zhai, Electrochim. Acta, 134 (2014) 272–280.Y. Zhai, J. Ge, J. St-Pierre, Electrochem. Commun., 66 (2016) 49–52.J. St-Pierre, Y. Zhai, Molecules, 25 (2020) article 1060.Y. Zhai, J. Ge, J. Qi, J. St-Pierre, J. Electrochem. Soc., 165 (2018) F3191–F3199.Y. Zhai, J. St-Pierre, Acetonitrile contamination reactions in PEMFCs, in preparation for ChemElectroChem.J. St-Pierre, B. Wetton, Y. Zhai, J. Ge, J. Electrochem. Soc., 161 (2014) E3357–E3364.Y. Zhai, J. St-Pierre, Appl. Energy, 242 (2019) 239–247. Figure 1. Cell voltage transients during the PEMFC contamination by acetonitrile for different combinations of reactant stream relative humidities. Figure 1

The Role of Local Heating and Phosphate Poisoning during the Oxygen Reduction Reaction in Solid Acid Fuel Cells

With the ongoing effort to decarbonize and decentralize the electricity infrastructure by shifting to renewable energy sources, fuel cells and in particular intermediate temperature fuel cells receive a growing interest as a promising technology for a highly efficient, on demand transformation of chemical into electrical energy. Since the 2000s, fuel cells have cycled from high expectations to disillusion, caused by the high production cost an insufficient stability. High temperature polymer electrolyte membrane fuel cells (HT PEM FC) are a prominent and well investigated candidate for the intermediate temperature range. However, the usage of concentrated, highly corrosive phosphorous acid as membrane dopant required expensive production materials and causes deterioration of the catalyst over time. Changing from a liquid to a solid electrolyte can simultaneously improve the long term stability and reduce the construction price. A suitable solid acid is CsH2PO4. It is a non-toxic and less corrosive electrolyte with a proton conductivity of 2*10-2 S/cm at 240°C.[1] Since first demonstrated for fuel cell fabrication in 2003,[2] the platinum utilization and power densities have been improved ever since.[3,4] Solid acid fuel cells (SAFC) are already used in industry in a small scale, but the development has been hampered by the poor stability of the cathode electrode. The rate limiting reaction step is the complex oxygen reduction reaction (ORR) at the cathode side. During operation, it is the largest source of overpotential and hence waste heat generation.[5] For an active site, the current collector, electrolyte and gas phase need to be in direct contact with each other to provide all necessary reactants, thereby the interface resistance between the current collector and the catalyst is crucial for the performance.In the work we are going to present, we investigated electrodes based on a platinum thin film catalyst layer.[6,7] These electrodes enable us to investigate degradation effects on a reasonable time scale. We will show that only a few areas close to the current collectors meet the requirements for active sites and consequently generating most of the measured current, leading to a localized heating. We observed a current density depended morphology chance of CsH2PO4 during operation at these active sites, located close to the current collector. While a variety of degradation processes can result from this process, we determined a phosphate adsorption on the catalyst as the most pronounced one. Similar to HT PEM FC, phosphate species from the electrolyte can adsorb at the platinum surface and act as catalyst poison.[8–10] We will present, that these poisoning effects can be reversed but not prevented by cyclic voltammetry (CV) measurements. After reactivating the cell by CV measurements, the cell performance increased to the initial value before degrading again. The reversibility of the process was shown for five reactivations over a period of 50 h. Overall, we identified the cause and nature of the main degradation mechanism in solid acid fuel cells with platinum thin film electrodes and will present different design optimizations for a stable, high performance fuel cell which arise from our findings.

AuCo3O4/C – Different Fabrication Methods and Application for Fuel Cell Reactions

Nanoscale materials are very important in many industries. There are many various synthesis methods such as adsorption, electroless deposition, galvanic displacement or microwave irradiation methods which let to fabricate nanomaterials. Lately, microwave irradiation is used as a rapid convenient method which gives excellent yields and higher purity of the products than conventional methods. Nanoparticles-based catalysts are usually heterogeneous catalysts broken up into metal nanoparticles in order to speed up the catalytic process. Metal nanoparticles have a higher surface area so there is increased catalytic activity because more catalytic reactions can occur at the same time. Nanoparticles catalysts can also be easily separated and recycled with more retention of catalytic activity than their bulk counterparts. Nanoparticles of gold are attractive for their interaction with other compounds and property to attract catalytic active groups.In this work, we investigated the influence of synthesis method to the electrocatalytic activity of catalyst. Therefore, Au nanoparticles were deposited on the Co3O4/carbon (Co3O4/C) substrate using microwave irradiation AuCo3O4/C-1, AuCo3O4/C-2 and impregnation AuCo3O4/C-3 methods. The composition, morphology and structure of the prepared catalysts were characterized using Inductively Coupled Plasma Optical Emission Spectroscopy, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy and X-ray diffraction. The electrocatalytic properties of prepared catalysts were investigated towards ethylene glycol electro-oxidation and oxygen electro-reduction reactions in an alkaline medium. Electrochemical analysis was performed using a rotating disc electrode and the Autolab electrochemical workstation.It has been determined, that in all cases modification of Co3O4/C catalyst by gold improved the electrocatalytic properties of synthesized AuCo3O4/C catalysts. As-prepared AuCo3O4/C catalysts showed an enhanced electrocatalytic activity towards the electro-oxidation of ethylene glycol and electro-reduction of oxygen in an alkaline medium compared with that obtained for the Co3O4/C or Au/C catalysts. The AuCo3O4/C catalysts prepared by microwave irradiation heating demonstrated up to 3 times higher electrocatalytic activity towards the electro-oxidation of ethylene glycol and up to 2 fold higher electrocatalytic activity towards electro-reduction of oxygen compared with that of the AuCo3O4/C catalyst prepared using impregnation.

Ultra-Low Platinum Nano-Alloy Encapsulated in Carbon Nanotube Matrix: A Practical PEM Fuel Cell Electrocatalyst

Hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) are the crucial PEM fuel cell reactions. However, the sluggish kinetics of these reactions particularly ORR require efficient catalysts to reduce the larger voltage losses and boost the electrochemical activity. Hence developing efficient and durable platinum (Pt)-based electrocatalysts is of enormous significance for practical PEM fuel cell. The state-of the-art carbon black supported Pt nanoparticles (Pt/C) catalyst has sever activity and stability issues. The tiny Pt nanoparticles often undergo the dissolution and redeposition under electrochemical operation, which would destroy their initial state of highly uniform dispersion and high activity. Meanwhile, the amorphous carbon support suffers from the corrosion and oxidation at the cathodic working conditions, which leads to the initial interaction disruption of Pt and carbon support. It causes Pt nanoparticles detachment and agglomeration with a consequent significant activity degradation. Herein we report an integrated ultra-low Pt nanoalloy encapsulated in nitrogen-doped carbon nanotubes matrix (PtCoNi@NCNTs) for efficient oxygen reduction in practical fuel cell. This hybrid Pt-based catalyst achieves a higher mass activity of 3.46 A mgPt -1 at 0.9 V vs. RHE with a negligible stability decay after 10,000 cycles. More importantly, this excellent half-cell activity can be fully transformed into practical full cell. The fuel cell based on this hybrid electrocatalyst delivers a power density of 11.2 W mgPt -1 cathode, which is 8 times of commercial Pt/C 20 % based cells (1.4 W mgPt -1 cathode). Furthermore, PtCoNi@NCNTs also demonstrates an excellent fuel-cell durability by retaining its initial current after 10 h operation at the constant voltage of 0.7 V without any loss. This excellent performance is ascribed to the synergetic response by the integration of encapsulated Pt nano-alloy and hierarchical nitrogen-doped carbon nanotube matrix. It is well acknowledged that the fine tuning of transition metals in the PtM alloy offers extra Pt structural strain that controls the weakening of surface bonds and results in a hike in the electrocatalytic activity. Moreover, the incorporation of metal-nitrogen-carbon (M-N-C) sites also additionally boosts catalytic activity, where the hierarchical architecture is not only the robust substrate to anchor/embed ternary alloy nanoparticles but also ensures sufficient contact of the reactant on the catalysts, which is always ignored in the previous catalysts for fuel cells. Respectable hydrophilic NCNTs matrix restricts comprehensive contact between electrolyte and active sites thereby regulating the oxygen diffusion to the active sites and avoid flooding, hence the enhanced mass transport boosts fuel cell performance. Decent hydrophilic nature of the PtCoNi@NCNTs catalyst facilitates the three-phase interface at the cathode that offers efficient mass transport and excellent conductivity for efficient oxygen reduction reaction. Higher graphitic properties offer advanced durability to the NCNTs support against corrosion and oxidation at cathodic working conditions, while few layers carbon coatings shield the Pt nanoalloy against dissolution in acidic conditions thereby offering pronounced durability for long term fuel cell operation. Therefore, such novel graphitic NCNTs support material endows superior durability to the electrocatalyst in real working conditions of PEM fuel cell. In this work the existing gaps between the RDE activity and fuel cell performance have been investigated and optimized magnificently, which endorses the complete transformation of RDE activity to the MEAs level. This work may provide significant insights in designing the low-Pt integrated highly durable electrocatalysts for practical PEM fuel cells. Figure 1

Room Temperature Synthesis of Ordered Intermetallic Electrocatalysts

The conversion of O2 to H2O is an important fuel cell reaction for the recovery of renewable electricity from chemical fuels. Alloys of Pt-group metals (PGMs) with transition metals have emerged as catalysts with enhanced activity and durability for the oxygen reduction reaction (ORR). To date, most studies focus exclusively on alloys that adopt a Face-centered cubic (FCC) or Face-centered tetragonal (FCT) crystal lattice. Under ORR operating conditions, these materials evolve from alloys to Pt core-alloy shell materials, in this case both the alloy core and Pt shell retains the FCC or FCT type crystal structure; indicating that materials can dynamically change during catalysis.Here we present the synthesis of Pd-Bi based ordered intermetallics by partial dealloying of a Bi rich alloy. We found that under ORR operation conditions, β-PdBi2 (I4/mmm space group) which adopts a tetragonal lattice, transforms to α-Pd3Bi (Pmma space group) which adopts an orthorhombic crystal structure; this transformation is mediated by oxidative Bi corrosion under potential cycling, and reconstruction of the atoms in the bulk. To the best of our knowledge, this is the first report of a material that exhibits an electrochemically driven, non-congruent phase transition among materials with different crystal structures. The resulting phase-converted Pd3Bi is stable and exhibits high performance for ORR. Phase-converted Pd3Bi outperform Pt and Pd metal, reaching mass activities of 2.6 A/mgPd, which is nearly 10X higher than Pt/C (~0.3 A/mgPt) and Pd/C (~0.2 A/mg) at 0.9 V vs the Real Hydrogen Electrode (RHE). The mass activity of Pd3Bi decreases by ~38% after 10,000 cycles, indicating that it is stable. Activation energy (Ea) determined by temperature dependent electro-kinetic measurements indicates that the activity enhancement on phase-converted Pd3Bi originates from anion-poisoning resistant behavior. These results establish that PGMs-based ordered intermetallics with low-symmetry crystal structures can be highly active and durable electrocatalysts.

Buoyancy Control Device Enabled by Reversible Proton Exchange Membrane Fuel Cells for Fine Depth Control

Abstract Fine buoyancy control is essential for underwater robots to maintain neutral buoyancy despite dynamic changes in environmental conditions. This paper introduces a novel buoyancy control system that uses reversible fuel cells (RFC) as a mass-to-volume engine to change the underwater robots' buoyancy. The RFC uses both the water electrolysis process and fuel cell reaction to produce and consume gases in a flexible bladder for volume change. Unlike conventional actuators such as motors and pistons used in buoyancy control, this mechanism is silent, compact, and energy-efficient. A dynamic model that described the dynamics of the RFC-enabled buoyancy change is presented. Then, a proportional-derivative (PD) controller is designed to position the device at any depth underwater. A prototype device is built to validate the dynamic model and the performance of the feedback controller. Experimental results demonstrate a fine depth control performance with 4 cm accuracy and 90 s settling time. The compact buoyancy design is readily integrable with small underwater robots for fine depth change allowing the robots to save actuation energy.

Nitrogen and Sulfur Codoped Graphene Macroassemblies as High-Performance Electrocatalysts for the Oxygen Reduction Reaction in Microbial Fuel Cells

Microbial fuel cells (MFCs) are receiving considerable attention for generating clean and sustainable electrical energy directly from wastewater. The development of highly efficient, durable, and i...

Synthesis and Performance of MOF-Based Non-Noble Metal Catalysts for the Oxygen Reduction Reaction in Proton-Exchange Membrane Fuel Cells: A Review.

Hydrogen is widely regarded as a prime energy carrier for bridging the gap between renewable energy supply and demand. As the energy-generating component of the hydrogen cycle, affordable and reliable fuel cells are of key importance to the growth of the hydrogen economy. However, the use of scarce and costly Pt as an electrocatalyst for the oxygen reduction reaction (ORR) remains an issue to be addressed, and in this regard, metal–organic frameworks (MOFs) are viewed as promising non-noble alternatives because of their self-assembly capability and tunable properties. Herein, recent (2018–2020) works on MOF-based electrocatalysts containing N-doped C, Mn, Fe, Co, multiple metals, and multiple sites are reviewed and summarized with a focus on ORR activity, and the principal physicochemical properties and electrochemical performance of these catalysts realized using rotating electrodes are compared.

Photo-responsive metal/semiconductor hybrid nanostructure: A promising electrocatalyst for solar light enhanced fuel cell reaction

Direct alcohol fuel cells (DAFCs) have received wide attention as a new type of clean energy device because of their high energy conversion efficiency, portability, non-toxicity and pollution-free. Anode catalysts are the key factors affecting the performance of DAFCs. Recently studies show that using the optical activity of semiconductor materials as the carriers of traditional precious metal electrocatalysts, under the illumination of light sources, can greatly improve the electrocatalytic activity and stability of electrodes. In this review, the research progress of photo-responsive metal/semiconductor hybrids as the electrocatalysts for DAFCs in recent years is summarized, including: (1) Mechanism and advantages of photo-assistant electrochemical alcohol oxidation reaction, (2) metal/semiconductor electrocatalyst for the different type of fuel cell reactions, (3) different kind of metals in photo-responsive metal/semiconductor hybrid nanostructure, (4) the personal prospects of the photo-responsive metal/semiconductor electrode for future application in DAFCs.

Mayenite Electrides and Their Doped Forms for Oxygen Reduction Reaction in Solid Oxide Fuel Cells

The oxygen reduction reaction is an important reaction at the cathode in solid oxide fuel cells. Materials that exhibit high chemical and mechanical stability, high ionic and electronic conductivity, and are non-toxic are of great interest as cathodes for the reduction of oxygen. Here, we use density functional theory simulations to examine the efficacy of 12CaO·7Al2O3 and 12SrO·7Al2O3 electrides and their doped forms for the conversion of O2 gas to form O2− in their nanocages via encapsulation. Calculations show that encapsulation is exoergic in the un-doped electrides, and the formation of O2− is confirmed by the charge analysis. A stronger encapsulation is noted for C12A7 electride than the S12A7 electride. The C12A7 electride doped with B or Ga also exhibits exoergic encapsulation, but its encapsulation energy is slightly lower than that calculated for the un-doped C12A7 electride. There is an enhancement in the encapsulation for the S12A7 electride doped with B compared to its un-doped form. Doping of Ga in S12A7 electride exhibits only a very small change in the encapsulation with respect to its un-doped form. The present results can be of interest in the design of cathode material for solid oxide fuel cells.

Applications of Artificial Intelligence for Analysis of Two-Phase Flow in PEM Fuel Cell Flow Fields

This work probes the use of machine learning to uncover complex relationships between liquid phase behavior and pressure drop in polymer-electrolyte fuel cell reactant channels. Using a supervised decision tree (DT) regression algorithm, the liquid distributions in an ex-situ experimental reactant channel are correlated to the two-phase pressure drop for a range of air flow rates. Liquid phase distribution data collection is accomplished by capturing 2D images via a CCD camera of a transparent flow channel simulating polymer-electrolyte fuel cell conditions. Pressure transducers measure pressure drop along the length of the channel and are synchronized with the image collection. The images are processed for noise reduction and feature extraction and then used with pressure data for training. Overall, the DTs predict pressure drop using liquid distributions as inputs at rates exceeding 88.9% accuracy and were able to capture complex behavior such as pressure changes due to breakup of liquid slugs.

Behavior of gold-enhanced electrocatalytic performance of NiPtAu hollow nanocrystals for alkaline methanol oxidation

The Pt-based catalyst tends to be poisoned by carbon monoxide (CO)-like intermediates produced in fuel cell reactions, which seriously deteriorates its catalytic performance. Herein, noble metal Au with the capacity of resistance to CO-like intermediates poisoning was employed to construct multi-element Pt-based catalysts. Two trimetallic NiPtAu hollow nanocrystals (HNCs) with different surface Au contents were synthesized to explore the role of Au in electrocatalysis for alkaline methanol oxidation reaction (MOR). The trimetallic NiPtAu-SRAu HNCs catalyst with the relative rich Au content (15.17 at%) on surface exhibits a much lower CO oxidation peak potential than the other HNCs counterpart and 20 wt% Pt/C, which indicates the more exceptional CO-resisting performance. Besides, the MOR specific activity of NiPtAu-SRAu HNCs (31.52 mA cm−2) is 7 times higher than that of 20wt% Pt/C (4.50 mA cm−2). This enhancement in catalytic activity as well as anti-CO poisoning capability for NiPtAu-SRAu HNCs can be mainly ascribed to the weakened CO adsorption due to the exposure of Au atoms on NiPt surface evidenced by the experimental data and density functional theory calculations. This study not only investigates the role of Au in MOR catalysis but also could be helpful for designing and optimizing the electrocatalysts for high-active and robust fuel cell applications.

N and S Co-doped Ordered Mesoporous Carbon: An Efficient Electrocatalyst for Oxygen Reduction Reaction in Microbial Fuel Cells

Background: Porous carbon materials are promising candidate supports for various applications. In a number of these applications, doping of the carbon framework with heteroatoms provides a facile route to readily tune the carbon properties. The oxygen reduction reaction (ORR), where the reaction can be catalyzed without precious metals is one of the common applications for the heteroatom-doped carbons. Therefore, heteroatom doped catalysts might have a promising potential as a cathode in Microbial fuel cells (MFCs). MFCs have a good potential to produce electricity from biological oxidization of wastes at the anode and chemical reduction at the cathode. To the best of our knowledge, no studies have been yet reported on utilizing Sulfur trioxide pyridine (STP) and CMK-3 for the preparation of (N and S) doped ordered porous carbon materials. The presence of highly ordered mesostructured and the synergistic effect of N and S atoms with specific structures enhance the oxygen adsorption due to improving the electrocatalytic activity. So the optimal catalyst, with significant stability and excellent tolerance of methanol crossover can be a promising candidate for even other storage and conversion devices. Methods: The physico-chemical properties of the prepared samples were determined by Small Angle X-ray Diffraction (SAXRD), N2 sorption-desorption, Transmission Electron Microscopy (TEM), Field Emission Scanning Electron Microscopy (FESEM) and X-ray Photoelectron Spectroscopy (XPS). The prepared samples were further applied for oxygen reduction reaction (ORR) and the optimal cathode was tested with the Microbial Fuel Cell (MFC) system. Furthermore, according to structural analysis, The HRTEM, and SAXRD results confirmed the formation of well-ordered hexagonal (p6mm) arrays of mesopores in the direction of (100). The EDS and XPS approved that N and S were successfully doped into the CMK-3 carbon framework. Results: Among all the studied CMK-3 based catalysts, the catalyst prepared by STP precursor and pyrolysis at 900°C exhibited the highest ORR activity with the onset potential of 1.02 V vs. RHE and 4 electron transfer number per oxygen molecule in 0.1 M KOH. The high catalyst durability and fuel-crossover tolerance led to stable performance of the optimal cathode after 5000 s operation, while the Pt/C cathode-based was considerably degraded. Finally, the MFC system with the optimal cathode displayed 43.9 mW·m-2 peak power density showing even reasonable performance in comparison to a Pt/C 20 wt.%.cathode. Conclusions: The results revealed that the synergistic effect of nitrogen and sulfur co-doped on the carbon substrate structure leads to improvement in catalytic activity. Also, it was clearly observed that the porous structure and order level of the carbon substrate could considerably change the ORR performance.

Study on the influence of the thickness of nanostructured rhodium films toward electrooxidation of adsorbed carbon monoxide

Carbon-supported rhodium thin films with various thicknesses are grown by varying the number of laser pulses, Nlp (from 5000 to 50,000) under 2 Torr of He background atmosphere using the pulsed laser deposition method. The thin films are characterized for their morphological features and structural properties. It is observed that smooth dense 2D nanosheets of Rh are obtained with 5000 Nlp, whereas higher Nlp yields to highly porous Rh films. X-ray photoelectron spectroscopy reveals that both metallic Rh and Rh3+ are present at the surface of the Rh films. Nevertheless, the amount of metallic Rh increased as the Nlp increased. The influence of the thickness of the Rh films on the tolerance to CO, a poison that strongly adsorbs on the surface of catalysts in fuel cells reactions, was investigated through anodic stripping voltammetry. It is found that Rh film deposited with 50,000 Nlp exhibits the highest electroactive surface area (27.90 cm2 vs. 1.20 cm2 of Pt), the lowest onset potential of CO electrooxidation (0.47 V vs. 0.60 V Pt), and a net charge corresponding to electrooxidation of the CO adlayer of 424 μC cm−2 (vs. 358 μC cm−2 of Pt). Such high tolerance to CO poisoning is explained on the basis of the elevated porosity and roughness of the Rh surface. Indeed, a roughness factor of 90.5 for Rh against about 3.8 for Pt grows under analogous deposition conditions of pressure and number of laser pulses.