Cell Catalyst Research Articles

Correlating oxygen functionalities and electrochemical durability of carbon supports for electrocatalysts

Achieving high durability of the polymer electrolyte membrane (PEM) fuel cell catalysts remains a major challenge. While most of the research focuses on the active phase, carbon support remains overlooked. In this study durability of carbon support materials for Pt alloy nanoparticles is critically evaluated. First graphene derivative (GD) based carbon supports with different chemical properties are prepared and utilized along with widely used commercial carbon black (CB) material. High-temperature electrochemical accelerated degradation tests (HT-ADTs) combined with X-ray photoelectron spectroscopy (XPS) show that the total amount of oxygen functionalities, the type of oxygen functionalities, and sp2 carbon content play a crucial role in carbon support durability. The observations were confirmed with the direct online measurements of carbon corrosion via an advanced in-situ technique – an electrochemical cell coupled with a mass spectrometer (EC-MS). We report that increasing the content of sp2 carbon and decreasing carboxyl functional groups have the most beneficial effect on stability. The study provides important guidelines for tailoring the carbon support properties and their relationship to the durability of the electrocatalyst, which could be crucial for producing more stable catalysts and achieving the Department of Energy's fuel cell system lifetime targets. Moreover, the innovative carbon design approach presented here could be applied in other fields such as batteries, supercapacitors, sensors and others.

Hydrogen-intercalation enhanced the anti-CO poisoning ability of palladium-copper metallene for direct formate fuel cells

The direct formate fuel cells (DFFCs) are energy conversion devices that use formate as fuel. However, COads generated from formate dehydration accumulate on the Pd surface and cause catalyst poisoning and deactivation. Here, we constructed a hydrogen intercalated palladium-copper metallene (PdCuH metallene) to enhance the anti-CO poisoning ability. For formate oxidation, the mass and specific activities of PdCuH metallene/C were 3.4 and 3.2 times those of Pd/C. While in ORR, the mass and specific activities of PdCuH metallene reached 12.4 and 13.9 times that of Pt/C. When we assembled PdCuH metallene/C as an electrode material for DFFC, the peak power and limiting current density of PdCuH metallene/C || PdCuH metallene/C were 79.5% and 159.7% higher than that of Pt/C || Pd/C, respectively. This study provides a new resolution to address the CO poisoning deactivation of direct formate fuel cell catalysts.

Synthesis and characterization of nickel boride nanoparticles for energy conversion catalyst materials – The effect of annealing temperature

In the recent technology development, fuel cell has been widely used in many applications, including transportation and industry. Platinum catalysts are used to catalyst the reaction at the oxygen electrode, but they are expensive and has limited supply. A nickel-boron nanoparticle catalyst is proposed as a substitute for fuel cell catalyst material. The objectives are to evaluate the effect of the annealing process and to determine the characteristics of the annealed nanoparticles using scanning electron microscopy - energy dispersive X-ray (SEM-EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis, total organic carbon (TOC) analysis and X-ray diffraction (XRD). A wet chemical method was used to synthesize nickel-boron nanoparticles by chemical reduction (co-reduction) of nickel chloride and sodium borohydride. As-synthesized nickel-boron nanoparticles were annealed at temperatures of 200, 300, 400, 500, and 700 °C in an argon atmosphere for 2 h. From the experimental results, nickel-boron nanoparticles annealed at 300 °C with equal dispersion of crystalline Ni and crystalline Ni3B showed the highest catalyst performance. The yield of nickel-boron nanoparticles sized 1.1364 nm was smaller than in the literature (37 nm). The size of Ni-B nanoparticles was calculated by using the Scherrer equation with the values of full width half maximum (FWHM) obtained by peak fitting following the Gaussian model. Smaller Ni-B nanoparticles have a higher surface-area-to-volume ratio, which increases the exposure of the active sites (crystalline Ni and crystalline Ni3B phase) to the reactants (methanol) and improves catalytic activity.

Effects of carbon aggregates and ionomer distribution on the performance of PEM fuel cell catalyst layer: A pore-scale study

An in-depth understanding of the structure-performance relationship of the catalyst layer is crucial for its optimal design. In this work, the effects of carbon aggregation and ionomer distribution morphologies on the performance of the catalyst layer are investigated by pore-scale simulation. First, an optimized stochastic algorithm that can control the carbon aggregation degree and ionomer morphology is proposed to reconstruct realistic catalyst layer structures. The structural characteristics of the catalyst layer, such as pore size distribution, agglomerate size, and ionomer connectivity, are analyzed. A pore-scale model based on the lattice Boltzmann method is developed to simulate the reactive transport processes in the catalyst layer. The results indicate that the reasonable aggregation degree of carbon supports can balance the pore and cross-ionomer transport resistances of the oxygen to achieve optimal catalyst layer performance. The uniform ionomer coating in the catalyst layer can further improve the performance, and the optimal ionomer content is determined by balancing the electrochemical active surface area and the oxygen transport resistance. Based on the simulation results, a key principle for the optimal design of the catalyst layer is also proposed.

Structure and conductivity of ionomer in PEM fuel cell catalyst layers: a model-based analysis

Efforts in design and optimization of catalyst layers for polymer electrolyte fuel cells hinge on mathematical models that link electrode composition and microstructure with effective physico-chemical properties. A pivotal property of these layers and the focus of this work is the proton conductivity, which is largely determined by the morphology of the ionomer. However, available relations between catalyst layer composition and proton conductivity are often adopted from general theories for random heterogeneous media and ignore specific features of the microstructure, e.g., agglomerates, film-like structures, or the hierarchical porous network. To establish a comprehensive understanding of the peculiar structure-property relations, we generated synthetic volumetric images of the catalyst layer microstructure. In a mesoscopic volume element, we modeled the electrolyte phase and calculated the proton conductivity using numerical tools. Varying the ionomer morphology in terms of ionomer film coverage and thickness revealed two limiting cases: the ionomer can either form a thin film with high coverage on the catalyst agglomerates; or the ionomer exists as voluminous chunks that connect across the inter-agglomerate space. Both cases were modeled analytically, adapting relations from percolation theory. Based on the simulated data, a novel relation is proposed, which links the catalyst layer microstructure to the proton conductivity over a wide range of morphologies. The presented analytical approach is a versatile tool for the interpretation of experimental trends and it provides valuable guidance for catalyst layer design. The proposed model was used to analyze the formation of the catalyst layer microstructure during the ink stage. A parameter study of the initial ionomer film thickness and the ionomer dispersion parameter revealed that the ionomer morphology should be tweaked towards well-defined films with high coverage of catalyst agglomerates. These implications match current efforts in the experimental literature and they may thus provide direction in electrode materials research for polymer electrolyte fuel cells.

Strain Relaxation and Activity in PtCo Fuel Cell Catalyst Nanoparticles

Interest is growing in applying fuel cells to heavy duty transportation applications, which requires the fuel cell design to prioritize efficiency and durability to provide a low lifetime cost of ownership. This motivates further development of catalysts for the oxygen reduction reaction (ORR), as ORR kinetics are a key factor in fuel cell efficiency and catalyst degradation is a major factor limiting lifetime. Pt-alloy catalysts have seen success in light-duty fuel cell applications, where they provide enhanced activity believed to originate (at least in part) from strain of the active Pt surface by the underlying Pt-alloy core. Concerns remain regarding the viability of PtCo catalysts for heavy duty applications, as they may not sustain their activity advantage over extended lifetimes and leaching of the base metal can lead to additional performance degradation. These concerns motivate investigation into the fundamental mechanisms of strain-induced activity enhancements to guide further catalyst development and understand the ultimate limits for the performance and stability of PtCo catalysts. However, practical Pt-alloy fuel cell catalysts are complex, and understanding of real strain effects in these systems remains elusive.Here we will present an investigation into strain effects in Pt-Co ORR catalysts for fuel cells, combining scanning nanobeam electron diffraction (NBED), continuum elastic strain modelling, and full-cell electrochemistry measurements. We leverage recent developments in NBED to make high-throughput strain maps in heterogeneous, carbon-supported PtCo catalysts and identify different mechanisms of strain relaxation, including dislocations and geometric effects. Supported by continuum elastic modelling, we correlate shell thickness, strain state, and activity of PtCo catalysts. Finally, we will comment on how these results provide rational guidance to optimize stable, efficient Pt-alloy catalysts.

Effects of Bifunctional Oxygen Catalyst Layer Composition on Unitized Regenerative Fuel Cell Performance

Proton exchange membrane unitized regenerative fuel cells (PEM-URFCs) can generate storable fuel (hydrogen) and oxidant (oxygen) which can then be used to produce power from the same cell. Combining electrolysis and fuel cell modes within the same cell allows PEM-URFCs to have the potential for lower mass, volume, and cost compared with discrete fuel cell and electrolyzer systems. The bifunctional oxygen catalyst layer (BOCL) catalyzes the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) at the same electrode, and there are wide potential differences and opposing mass transport phenomena involved within the BOCL when operating in electrolyzer or fuel cell mode. The BOCL composition, structure and morphology significantly affect performance and stability of PEM-URFCs. In our prior work, we showed bimetallic nanoframes provide bifunctional oxygen electrocatalysts with significantly higher activity compared with monometallic structures, evaluated using a rotating disk electrode configuration.1 We will present our investigation of the effects of the BOCL composition, structure and morphology on URFC membrane electrode assemblies (MEAs) prepared using ultrasonic spraying. Catalyst composition and loading were determined to influence URFC performance, and there are tradeoffs between fuel cell performance, electrolyzer performance, and catalyst cost. In addition to the effects of the active catalyst (either Pt for ORR or IrO2 for OER), our work supports the non-catalytically active component influences MEA performance, which is in agreement with our finding of synergistic effects of Pt and IrO2 within rotating disk electrode measurements.1 We are also evaluating the effects of porous transport layers and different operating conditions on URFC MEA performance and durability over repeated cycling. References Godínez-Salomón, F.; Albiter, L.; Mendoza-Cruz, R.; Rhodes, C.P. Bimetallic Two-dimensional Nanoframes: High Activity Acidic Bifunctional Oxygen Reduction and Evolution Electrocatalysts. ACS Appl. Energy Mater. 2020, 3, 2404-2421.

Advanced Analytical Electron Microscopy Techniques for Probing Individual PGM-Free Catalyst Sites

Hydrogen fuel cells currently utilize expensive platinum group metal nanoparticles as catalysts [1]. To reduce the cost of catalyst materials, large efforts to develop viable platinum group metal-free (PGM-free) catalyst materials, which often consist of single transition metal atoms embedded in nitrogen-doped graphitic carbon structures, are being undertaken [2]. Given the atomic-scale nature of the metal sites in these materials, their performance and stability are highly dependent on the local coordination environment and consequently electronic structure of the sites [3]. A detailed understanding of the local elemental composition and lattice structure of individual sites, and how these properties vary between sites, is therefore needed to further develop improved PGM-free catalyst materials. While many bulk techniques are available that can provide average properties of these sites, such as Mössbauer and X-ray absorption spectroscopies, techniques with high spatial resolution are needed to measure the properties of individual sites. As a result, scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDS) has proven an invaluable tool for characterization of these materials due to its ability to probe structural and electronic properties at the atomic scale [4]. However, combined with the instability of many metal sites under the electron probe, the quantity and type of information accessible by conventional STEM instrumentation and acquisition methods is limited. To better understand the local coordination environment and electronic structure of individual sites, as well as how these properties vary site to site, new techniques and hardware are therefore needed.Here, we demonstrate advancements in STEM-EELS and -EDS that allow the quality and quantity of spectroscopic information obtained from individual sites to be significantly improved over conventional method. First, we demonstrate direct real-space mapping of metal sites by using a direct electron detector in the EELS spectrometer. This increases the data acquisition rate and signal-to-noise ratio sufficiently to map metal atom positions at the atomic scale. In addition, we show how automated metal atom position identification and subsequent probe positioning allow the rate at which metal sites are probed to be increased by another order of magnitude while simultaneously increasing the quantity of data obtained from each site. Using EELS and EDS signals acquired in parallel, this automated acquisition method enables a wide range of metal site elements to be identified, as well as the local coordination environment around the sites to be determined. Combined with electronic structure measurements of the metal atoms themselves, this technique provides significantly more information about individual sites than conventional methods. The techniques presented here are therefore poised to significantly improve our understanding of the local coordination environment and electronic structure of individual PGM-free metal sites, as well how these properties vary site to site, accelerating development of these low-cost hydrogen fuel cell catalyst materials [5].

Elucidating the Voltage-Cycling Induced Degradation Mechanism of PEM Fuel Cell Catalysts with Porous Carbon Supports

In order to reach the target of climate neutrality by the end of 2050, an increasing interest in the application of proton exchange membrane fuel cells (PEMFCs) for heavy duty vehicles (HDVs), such as trucks and buses has developed recently. However, HDVs require highly stable and durable cathode catalyst materials, which retain sufficient performance for at least 30,000 h of load-cycling during normal operation.1 It is well known that the concomitant voltage cycling of the cathode leads to severe losses in electrochemically active surface area (ECSA) due to Pt-dissolution that results in both Pt particle growth by Ostwald ripening and Pt loss into the ionomer phase.2 In general, employing high surface area carbons (HSACs) with Pt-particles located mostly in the internal pores of the primary carbon particles, reduces the loss of ECSA due to Pt-dissolution.3 Furthermore, it has been shown that catalyst degradation due to particle coalescence is mitigated using HSACs due to the larger inter-particle distance compared to catalysts with solid carbon supports.3 However, it is still not clear how the loss and growth of internal Pt-nanoparticles is promoted throughout voltage cycling, i.e., if they grow inside the pores or if they move outward to the external C-surface and get subsequently lost in the ionomer or grow due to Ostwald ripening.4, 5 Therefore, voltage-cycling based accelerated stress tests (ASTs) were performed using 5 cm2 membrane electrode assemblies (MEAs) with cathode loadings of 0.1 mgPt cmMEA -2, made with Pt/C catalysts based on different supports: i) solid Vulcan carbon (Vu, TEC10V20E, TKK); ii) porous Ketjenblack (KB, TEC10E20E, TKK); and, iii) a partially oxided Pt/KB catalyst (Pt/KBmod) in order to study the effect of the accessibility of internal Pt particles on catalyst degradation. The latter was produced by heat-treating a commercial Pt/KB catalyst under an air/Ar mixture at 250 °C for 12 h to induce Pt-catalyzed local C-support oxidation of the bottleneck pore entrance, as described by Lazaridis et al.6 A full MEA characterization was included to measure the ECSA by CO-stripping, the H2/air and H2/O2 performance, and the O2 and H+ transport resistance in the cathode by limiting current measurements and electrochemical impedance spectroscopy (EIS), respectively. Finally, Pt-particle location prior and after voltage-cycling ASTs was investigated using scanning transmission electron microscopy (STEM).It was found that after the same number of voltage cycles, a smaller loss in H2/air performance can be observed using porous carbon supports (see. Fig. 1, Vu vs KB/KBmod), concomitant with a superior ECSA retention that we ascribe to a reduced dissolution/sintering of the Pt particles located with the pores of the carbon support. Furthermore, a performance increase for the unmodified Pt/KB cathode is shown during the first 300 cycles (see. Fig. 1), which can be attributed to facilitated transport of O2 and H+ to the Pt sites. Lastly, Pt-utilization measured by CO-stripping increased significantly after extended aging, indicating that the share in external particles has risen over voltage-cycling.

Waste Tire Derived Carbon Support for Non-Platinum-Group Metal Catalyst Materials for Oxygen Reduction Reaction in Alkaline Medium

Extensive use of non-renewable energy sources and excessive accumulation of hard-to-recycle waste, such as end-of-life tires, are among the most significant environmental problems today. For a more sustainable future, it is essential to find alternative solutions to energy and special waste management. For example, waste tires can be used to synthesize high-tech porous carbon materials, which can be used as a carbon support in fuel cell catalysts. [1] While fuel cells offer a promising alternative to some fossil fuel-based technologies, low temperature fuel cell catalysts rely on expensive platinum. Non-platinum-group metal (NPGM) catalysts, such as iron and nitrogen co-doped carbon materials are good contenders to platinum-based catalysts for the oxygen reduction reaction. Synthesizing porous carbon materials for more economically viable NPGM fuel cell catalysts could provide one way to use waste tires more sustainably and lower the cost of efficient fuel cell catalysts.For this work, a carbon material was synthesized by pyrolyzing tire granules (Imdex A/S) at 1000 °C for three hours in Ar [2]. Based on this carbon material, several iron and nitrogen co-doped catalyst materials were synthesized using Fe(NO3)3 as the iron source, dicyandiamide or guanidine as the nitrogen source, and ZnCl2 as a pore modifier. All synthesized materials were acid washed overnight to remove redundant elements such as Zn from the pore modifier and various impurities originating from the tire granules (mainly Si, S, Ca, and Zn). Finally, the materials pyrolyzed for a second time. The pyrolysis temperature, choice of nitrogen compound, and precursor ratios were varied for the syntheses described in this work.The NPGM catalyst materials were characterized by various physical and electrochemical methods to describe the relationship between the catalyst structure and the activity of the oxygen reduction reaction. SEM and SEM-EDX were used to evaluate the morphology and composition of the catalyst materials. N2 sorption data suggested that the specific surface area ranged from 77 to 194 m2 g-1 for all materials. Electrochemical characterization was performed in 0.1M KOH solution using the rotating disk electrode method. The highest onset potential (Eon = 920 mV vs RHE) was reached by a material using guanidine as the nitrogen source pyrolyzed at 900 °C, which is comparable to other recently described NPGM materials [3], including waste-tire derived NPGM catalysts [4]. Acknowledgements: This work was supported by the following projects: PRG676 “ Development of express analysis methods for micro-mesoporous materials for Estonian peat derived carbon supercapacitors” (1.01.2020- 31.12.2024)"Advanced materials and high-technology devices for sustainable energetics, sensorics and nanoelectronics” (TK141) (1.01.2016−1.03.2023) References [1] J. S. Gnanaraj et al., Sustainability 10(8), 2840 (2018)[2] J. Laanemäe, R. Jäger, P. Teppor, O. Volobujeva, and Enn Lust, ECS Transactions, 108, p. 39 (2022)[3] R. Gutru et al., International Journal of Hydrogen Energy, 47 (2022)[4] M. Muhyuddin et al., Electrochemica Acta, 433, 141254 (2022)

(Invited) Modeling Two-Phase Transport in the Cathode Catalyst Layer of a PEM Fuel Cell with a Focus on the Ionomer Phase Structure and Its Effect on Oxygen Transport

A hydrophobic treatment was developed to reduce the liquid water saturation level and increase its removal rate from the cathode catalyst layer (CL) of a PEM fuel cell. If this was achieved, the transport rate of oxygen to the reactive sites would be expected to increase and the fuel cell performance would be improved, especially in the high current-density mass-transport controlled region. The performance of the fuel cells with the hydrophobically treated cathode CLs tested with humidified air at 70oC shows significant improvement (> 200% increase in peak power).[1,2] The polarization curves obtained show improvements over the entire curve from the kinetic-controlled region to the mass-transport affected and mass-transport limited regions instead of only the mass-transport limited region as originally expected. A mathematical model was developed to provide insight into the causes for the observed responses with a focus on the oxygen-water two-phase transport phenomena in the catalyst layer. It suggests the hydrophobic treatment affects the CL in two ways. First, the interface of the ionomer layer exposed to the gas pores becomes more hydrophobic and facilitates less coverage and faster water drainage from the CL resulting in better performance at high current densities. Second, it reduces the hydration level in the ionomer phase which results in higher oxygen concentration in the ionomer phase on top and in the catalyst agglomerates leading to higher performance over the whole polarization curve. This presentation will discuss the major features of the new model and the findings obtained in this study.[3] These efforts show that the modeling work is not just a simulation of the experimental results using established theories and equations. It requires researching, finding, and understanding the mechanisms and phenomena that govern the physical processes in the fuel cell and result in the measured fuel cell performance. The modeling work provides insights that could not be gained from fuel cell testing.References Regis P. Dowd Jr., Cynthia S. Day, and Trung Van Nguyen, “Engineering the Ionic Polymer Phase Surface Properties of a PEM Fuel Cell Catalyst Layer,” J. Electrochem. Soc., 164 (14), F138-F146 (2017). 10.1149/2.1081702jesRegis P. Dowd, Yuanchao Li, and Trung Van Nguyen, “Controlling the Ionic Polymer/Gas Interface Property of a PEM Fuel Cell Catalyst Layer During Membrane Electrode Assembly Fabrication,” J. Appl. Electrochem., 50 (10) 993-1006 (2020). 10.1007/s10800-020-01453-wYuanchao Li and Trung Van Nguyen, “A One-Dimensional Model of the Cathode Catalyst Layer of a PEM Fuel cell Hydrophobically Treated for Water Management,” J. Electrochem. Soc., 169 114505 (2022). 10.1149/1945-7111/ac9bdf

(Digital Presentation) Synthesis of Proton Exchange Membrane Fuel Cell Catalyst and Optimization of Membrane Electrode Assembly Preparation Parameters

Reducing platinum content in proton exchange membrane fuel cells (PEMFCs) is one of the most essential development directions to secure the economic viability of PEMFC. Efforts are being made to synthesise new, more active catalysts and to optimise PEMFC assembly parameters. (1–4)The study aimed to synthesise 60 wt% Pt/C catalyst and optimise catalyst loading on the electrodes, gasket thickness and coating strategy.The catalyst was synthesised by depositing Pt nanoparticles on carbon black (Ketjenblack EC-300J) using ethylene glycol as a reducing agent and solvent (5–7). The studied catalyst was characterised by thermogravimetric analysis, X-ray diffraction and N2 sorption analysis. The synthesized catalyst material contained approximately 60 wt% of Pt, and the average platinum crystallite size was under 3 nm. The catalyst had a micro-mesoporous structure with a specific surface area of 320 m2 g−1.For electrochemical characterisation, the measurements were performed in H2/air PEMFC. Using an ultrasonic coating system, the catalyst was deposited on the Nafion membrane or gas diffusion layer. A suitable gasket thickness was found using electrochemical measurements. The catalyst loading was varied on the anode between 0.05 and 0.50 mg cm−2 and on the cathode between 0.40 and 1.00 mg cm−2, leaving the catalyst loading constant on the non-variable electrode. Electrodes thickness depended linearly on the catalyst loading. The results showed that electrochemically active surface area does not depend on catalyst loading. Varying catalyst loading on the anode did not show a decrease in electrochemical activity; thus, the anode catalyst loading could be reduced to 0.05 mg cm−2. However, the electrochemical activity decreased at low cathode catalyst loadings. It was found that the cathode catalyst loading can be reduced to 0.60 mg cm−2.Under optimised conditions, the electrochemical activity of the investigated material was excellent. The PEMFC current density was 0.81 A cm−2 at 670 mV, the maximum achieved power density 0.80 W cm−2 and the electrochemically active surface area 56 mPt 2 gPt −1. Acknowledgements This work was supported by the EU through the European Regional Development Fund TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011) and the Estonian Research Agency project (personal research support group grant project No. PRG676). References R. Alink, R. Singh, P. Schneider, K. Christmann, J. Schall, R. Keding, and N. Zamel, Molecules, 25, E1523 (2020).Á. Kriston, T. Xie, D. Gamliel, P. Ganesan, and B. N. Popov, Journal of Power Sources, 243, 958 (2013).J. Lee, C. Seol, J. Kim, S. Jang, and S. M. Kim, Energy Technol., 9, 2100113 (2021).H. A. Gasteiger, J. E. Panels, and S. G. Yan, Journal of Power Sources, 127, 162 (2004).Y. Shao, S. Zhang, R. Kou, X. Wang, C. Wang, S. Dai, V. Viswanathan, J. Liu, Y. Wang, and Y. Lin, Journal of Power Sources, 195, 1805 (2010).W. Li, C. Liang, W. Zhou, J. Qiu, Zhou, G. Sun, and Q. Xin, J. Phys. Chem. B, 107, 6292 (2003).R. Kou, Y. Shao, D. Mei, Z. Nie, D. Wang, C. Wang, V. V. Viswanathan, S. Park, I. A. Aksay, Y. Lin, Y. Wang, and J. Liu, J. Am. Chem. Soc., 133, 2541 (2011).

Pt Nanoparticles on Atomic-Metal-Rich Carbon for Heavy-Duty Fuel Cell Catalysts: Durability Enhancement and Degradation Behavior in Membrane Electrode Assemblies

Pt Nanoparticles on Atomic-Metal-Rich Carbon for Heavy-Duty Fuel Cell Catalysts: Durability Enhancement and Degradation Behavior in Membrane Electrode Assemblies

Efficient synthesis of 2'-deoxyguanosine in one-pot cascade by employing an engineered purine nucleoside phosphorylase from Brevibacterium acetylicum.

2'-deoxyguanosine is a key medicinal intermediate that could be used to synthesize anti-cancer drug and biomarker in type 2 diabetes. In this study, an enzymatic cascade using thymidine phosphorylase from Escherichia coli (EcTP) and purine nucleoside phosphorylase from Brevibacterium acetylicum (BaPNP) in a one-pot whole cell catalysis was proposed for the efficient synthesis of 2'-deoxyguanosine. BaPNP was semi-rationally designed to improve its activity, yielding the best triple variant BaPNP-Mu3 (E57A/T189S/L243I), with a 5.6-fold higher production of 2'-deoxyguanosine than that of wild-typeBaPNP(BaPNP-Mu0). Molecular dynamics simulation revealed that the engineering of BaPNP-Mu3 resulted in a larger and more flexible substrate entrance channel, which might contribute to its catalytic efficiency. Furthermore, by coordinating the expression of BaPNP-Mu3 and EcTP, a robust whole cell catalyst W05 was created, capable of producing 14.8 mM 2'-deoxyguanosine (74.0% conversion rate) with a high time-space yield (1.32g/L/h) and therefore being very competitive for industrial applications.

Directional manipulation of electron transfer in copper/nitrogen doped carbon by Schottky barrier for efficient anodic hydrazine oxidation and cathodic oxygen reduction

Development of bifunctional hydrazine oxidation and oxygen reduction electrocatalysts with high activity and stability is of great significance for the implementation of direct hydrazine fuel cells. Combining zero-dimensional metal nanoparticles with three-dimensional nitrogen-doped carbon nanosheets is an attractive strategy for balancing performance and cost. However, the precise construction of these composites remains a significant challenge, and thorough study of their interaction mechanisms is lacking. Herein, the CuNPs/CuSA-NPCF catalyst was constructed by anchoring copper nanoparticles on a three-dimensional nitrogen-doped porous carbon nanosheet framework through coordination of polyvinyl pyrrolidone and copper ions. The Schottky barrier of metal–semiconductor matched the Fermi level of the rectifying contact, thus enabling directional electron transfer. The resulting electron-deficient Cu nanoparticles surface exhibited Lewis acidity, which was beneficial to adsorption of hydrazine molecule. While the electron-enriched Cu–N4/carbon surface improved the adsorption of oxygen molecule, and accelerated electron supply from Cu-N4 active sites to various oxygen intermediates. The CuNPs/CuSA-NPCF Mott-Schottky catalyst exhibited excellent catalytic activity for hydrazine oxidation reaction and oxygen reduction reaction in an alkaline media. The directional manipulation of electron transfer in heterogeneous materials was an attractive universal synthesis method, providing new approach for the preparation of efficient and stable hydrazine fuel cell catalysts.

PdPt Alloy Nanoframes with Rugged Surfaces: Efficient Bifunctional Fuel Cell Catalysts in a Broad pH Range

PdPt Alloy Nanoframes with Rugged Surfaces: Efficient Bifunctional Fuel Cell Catalysts in a Broad pH Range

Milestones of Electrocatalyst Development for Direct Alcohol Fuel Cells

AbstractWith increasing energy demands and environmental issues, renewable energy‐related conversion systems have gained significant attention as a potential substitute for traditional fossil fuel‐based energy technologies. First introduced by S.W.Grove in 1838, fuel cells have been extensively developed into many different types, and direct alcohol fuel cells (DAFCs) are of interest as a potential power source because of their large power density, quick start, simplicity, and nearly zero emission. However, the high cost and poor catalytic efficiency of current catalysts are primary barriers to commercializing DAFCs. Designing advanced nanocatalysts for both anode and cathode electrodes is of crucial importance for practical DAFC development; however, a brief evaluation of current progress in electrocatalyst development for the alcohol oxidation reaction (AOR) and oxygen reduction reaction (ORR) is still very little. Herein, recent advances in fuel cell catalysts, mainly focusing on several most active areas (i.e., Pt‐ and Pt‐free‐based catalysts, metal‐free carbon, carbon‐based nonprecious metal composites) are concisely summarized. Also, challenges and prospects for DAFCs are highlighted to supply a comprehensive view for further designing high‐performance DAFC catalysts.

Surface enrichment of ionomer in fuel cell catalyst layer prepared using slot-die coating method

The surface enrichment process of the ionomer during the drying of catalyst ink film produced by the slot-die coating method and its effect on fuel cell performance were investigated, wherein the solvent composition of the ink was considered. The slot-die-coated catalyst layer (CL) surface was observed using helium ion microscopy, conductive atomic force microscopy, and X-ray photoelectron spectroscopy, and ionomer enrichment was observed on the slot-die-coated CL surface. Furthermore, spontaneous adsorption of the ionomer at the air–solution interface was observed in the water-rich dispersion by measuring the surface tension of water–alcohol mixed solvents with and without an ionomer. Therefore, two ionomer enrichment mechanisms were proposed based on the alcohol content of the ink: an evaporation-dominated mechanism for alcohol-rich ink and an adsorption-dominated mechanism for water-rich ink. The effect of surface ionomer enrichment on proton conduction depends on the alcohol content of the catalyst ink. In addition, ionomer enrichment is conducive to the reduction of the oxygen transport resistance because of the reduction in the ionomer distributed inside the CL. These findings provide novel insights into the structural evolution and engineering of the CL.

Facile synthesis of RuCoOx/N-CNT@PEDOT-SH/Pt for high catalytic performance of the methanol electro-oxidation

The exploration of direct methanol fuel cell (DMFC) catalysts has always been a great challenge. We present a facile method to prepare RuCoOx/N-CNT, composited with PEDOT-SH and supported Pt nanoparticles (Pt NPs) as catalyst for methanol oxidation reaction (MOR). Bimetallic oxide carbon nanotubes (RuCoOx/N-CNT) serve as a carrier and a cocatalyst, especially the introduction of RuOx into CoOx can also generate a large number of oxygen vacancies, which can be used as highly active centers as reactants to provide adsorption (or coordination) sites, facilitating electron transfer between reactants and improving the hydrophilicity of catalysts, thereby promoting redox reaction kinetics. A series of structural characterizations show that alloying and charge redistribution exist in RuCoOx/[email protected]/Pt, and oxygen vacancies can effectively change the electronic structure and improve the exposure of active sites density, thereby enhancing MOR activity. Performance tests such as CV、i-t、stability test show that the electrocatalytic activity of RuCoOx/[email protected]/Pt (2003.3 mA mg-1Pt) is far superior to that of RuCoOx/N-CNT/Pt (1324.8 mA mg-1Pt) and commercial Pt/C (279.6 mA mg-1Pt) catalysts. This strategy can provide a scheme for high-performance, low-cost anode catalyst design in MOR.

Carboligation of 5-(hydroxymethyl)furfural via whole-cell catalysis to form C12 furan derivatives and their use for hydrazone formation

BackgroundBiobased 5-(hydroxymethyl)furfural (5-HMF) is an important platform that offers numerous possibilities for upgrading to a range of chemical, material and fuel products. One reaction of special interest is the carboligation of 5-HMF into C12 compounds, including 5,5’-bis(hydroxymethyl)furoin (DHMF) and its subsequent oxidation to 5,5’-bis(hydroxymethyl)furil (BHMF), due to their potential applications as building blocks for polymers and hydrocarbon fuels.ObjectivesThis study was aimed at evaluating the use of whole cells of Escherichia coli carrying recombinant Pseudomonas fluorescens benzaldehyde lyase as biocatalysts for 5-HMF carboligation, recovery of the C12 derivatives DHMF and BHMF, and testing the reactivity of the carbonyl groups for hydrazone formation for potential use as cross-linking agents in surface coatings. The effects of different parameters on the reaction were investigated to find the conditions for achieving high product yield and productivity.ResultsThe reaction with 5 g/L 5-HMF using 2 gCDW/L recombinant cells in 10% dimethyl carbonate, pH 8.0 at 30 °C resulted in DHMF yield of 81.7% (0.41 mol/mol) at 1 h, and BHMF yield of 96.7% (0.49 mol/mol) at 72 h reaction time. Fed-batch biotransformation generated a maximum DHMF concentration of 53.0 g/L (or 26.5 g DHMF/g cell catalyst) with productivity of 10.6 g/L.h, after five feeds of 20 g/L 5-HMF. Both DHMF and BHMF reacted with adipic acid dihydrazide to form hydrazone that was confirmed by Fourier-transform infrared spectroscopy and 1H NMR.ConclusionThe study demonstrates the potential application of recombinant E. coli cells for cost-effective production of commercially relevant products.