High Catalyst Loading Research Articles

Salt template-assisted polymer tethering strategy to achieve high dispersed cobalt single atoms/clusters on porous carbon catalysts for effective Fenton-like reactions

The exploration of the synthesis of porous carbon-supported metal nanocatalysts with high metal loading and dispersion for the development of heterogenous catalysts is important. However, this remains a challenging subject. In this paper, a salt template-assisted polymer tethering strategy was proposed to prepare Co single atom and ultrafine cluster anchored on porous carbon (Co-NPC) with a high-loading of 16.9wt%, thereby exposing high density of reaction sites. The obtained Co-NPC catalyst exhibited excellent catalytic performance for almost 100% degradation of bisphenol A (BPA) within 20min, which is much faster than the CoSA-NPC catalyst with only single atom sites and Co-NC without salt template added. Radical quenching experiments and electron paramagnetic resonance tests verified that both the nonradical oxidation pathway by 1O2, the electron transfer and radical oxidation pathway by •OH, SO4•- appeared during the degradation process. After 3 cycles, the removal rate of BPA did not decrease significantly. The fixed bed experiment revealed that Co-NPC could realize the continuous degradation of methylene blue (MB) with almost 100% degradation efficiency. This research indicated that the strategy by pyrolyzing metal coordinated polymer is a potential method for the synthesis of high metal loading catalyst at gram scale, meeting the requirement of practical applications.

Chemoselective Ring-Opening Polymerization of α-Methylene-δ-valerolactone Catalyzed by a Simple Organoaluminum Complex to Prepare Closed-Loop Recyclable Functional Polyester.

α-Methylene-δ-valerolactone (MVL) as a bio-renewable bifunctional monomer has shown great promise to prepare closed-loop recyclable polyester with pendent functionalizable double bond. However, the chemoselective ring-opening polymerization (ROP) of MVL still faces challenges including low polymerization temperature, expensive catalyst as well as high catalyst loading. In this contribution, we present the chemoselective and controlled ROP of MVL using a simple organoaluminum complex [MeAl(BHT)2] (BHT=2,6-di-tert-butyl-4-methylphenoxy), which can be easily prepared from commercially available trimethylaluminum and 2,6-di-tert-butyl-4-methylphenol without purification. MeAl(BHT)2 exhibits much higher catalytic activity (TOF=668 h-1) than that of MeAl[Salen] (TOF=89 h-1), a commonly used organoaluminum catalyst. The high chemoselectivity and activity of MeAl(BHT)2 is proposed to originate from the cooperative activation of propagating chain-ends and monomers via the "coordination-insertion" mechanism. Remarkably, high-molecular-weight P(MVL)ROP can be prepared in bulk using MeAl(BHT)2, which is not accessible by the previous catalysts. This study may advance the development of closed-loop recyclable polymers considering the easy preparation, low cost and good catalytic performance of MeAl(BHT)2.

Insights to the differences in catalytic performance of under-rib and under-channel regions for PEM water electrolysis

The difference in catalyst utilization in different regions of proton exchange membrane electrolyzer cell (PEMEC) is often overlooked, yet it holds significant implications for understanding the electrochemical reactions in electrolysis and designing novel electrode structures. In this study, we creatively designed catalyst coated membrane (CCM) with non-uniform distribution of catalytic layers in the under-rib and under-channel regions. Combined with the gradient design method of catalytic layers, the electrochemical reactions in the different regions were explored experimentally. The difference in reactant supply between the under-rib and under-channel catalytic layer was revealed by the water starvation experiment. Moreover, a three-dimensional two-phase non-isothermal model was constructed to study the differences in the current density distribution between ribs and channels. The results show that the current density under the rib is higher than under the channel. At the rib: channel catalyst loading of 3:1, the CCM performance is optimal. Based on the findings, the CCM with non-uniform, gradient catalytic layer was designed, which can achieve an 18.33 % reduction in precious metal loading without significant performance loss. This study reveals the genuine differences in catalysis reactions within PEMEC, thus providing new insights for realizing the electrode designs with high electrolysis performance and low catalyst loading.

Challenges and Opportunities in Preparing Fe-N-C Layers Supported on Non-Carbon Supports

Global energy demand will be continuously rising in the foreseeable future. To mitigate the results of climate change it is necessary to reduce the emittance of greenhouse gases. One promising approach is to switch to hydrogen as energy carrier and use proton exchange membrane fuel cells (PEMFCs) to efficiently convert H2 into electric power. Here, hydrogen and oxygen/air are used to directly generate electrical energy with only water as byproduct. Both reactions need to happen efficiently at the same time. The oxygen reduction reaction (ORR), however, is a very sluggish four-electron-reaction and needs efficient catalysts.The state-of-the-art ORR catalyst in PEMFC is platinum but that is a very scarce and expensive metal. Hence, it is important to switch to precious-metal-group (PGM) free catalysts. In recent years, bio inspired iron-based FeNC catalysts have been shown to approach ORR activities that are competitive with those of platinum, even though they need a higher catalyst loading than Pt to reach the desired high current densities.1–3 Those catalysts feature single Fe atoms surrounded by four N atoms in graphitic carbon. The drawback of those materials is their lower stability compared to PGM materials. In a nutshell, the carbon matrix oxidizes during operation in PEMFCs, changing the morphology of the catalytic center and rendering it less active, or inactive, depending on the carbon oxidation extent. Direct demetallation phenomena are also possible, leaving a N4 cavity without metal cation center. It was shown recently by Wu et al.4 that it is possible to raise durability by adding an additional carbon layer on the catalyst. One alternative approach to reduce those degradations is to interface Fe-N4 sites with a carbon-free support. The targeted support material must be immune to corrosion in acid and withstand the typical ORR electrochemical potentials. It also has to be electrically conductive to facilitate electron transfers, both locally and on long scale.In this work, conductive ceramic metal oxide materials (Ta doped SnO2, TTO) was investigated as a possible alternative catalyst supports. This material is resistant to acid and can withstand prolonged potentials at operating conditions in PEMFCs.5 During the synthesis of the FeNC catalysts, high temperatures are generally applied. Such treatments can be detrimental to the conductivity of ceramics due to metal aggregation (in case of doped materials) and may also lead to morphological changes as well as the reduction of the ceramics to metallic materials. A robust method to synthesize FeNC catalysts is by mixing the separate Fe, N and C precursors and using optimized thermal treatment. In this study, the effect of the pyrolysis conditions as well as the ratio of FeNC precursors to TTO was investigated with various characterization methods, e.g. X-ray absorption spectroscopy, Mossbauer spectroscopy, and high resolution TEM. The characterization techniques confirm the presence of single atom Fe as well as different Sn species that might contribute to the activity. The resulting materials were electrochemically characterized with rotating disc electrode techniques and in PEM fuel cells for their ORR-activity and durability. It was shown that the activity of materials with a high FeNC precursor content relative to TTO can outperform a reference FeNC synthesized similarly but without TTO, in both RDE (Figure) and PEMFC.The presentation will report in detail the effects of pyrolysis conditions and FeNC precursor/TTO content on the structure, activity and stability of materials.(1) Mehmood, A. et al. High Loading of Single Atomic Iron Sites in Fe–NC Oxygen Reduction Catalysts for Proton Exchange Membrane Fuel Cells. Nat. Catal. 2022, 5 (4), 311–323. https://doi.org/10.1038/s41929-022-00772-9.(2) Gasteiger, H. A.; Marković, N. M. Just a Dream—or Future Reality? Science 2009, 324 (5923), 48–49. https://doi.org/10.1126/science.1172083.(3) Zion, N. et al.. Electrocatalysis of Oxygen Reduction Reaction in a Polymer Electrolyte Fuel Cell with a Covalent Framework of Iron Phthalocyanine Aerogel. ACS Appl. Energy Mater. 2022, 5 (7), 7997–8003. https://doi.org/10.1021/acsaem.2c00375.(4) Liu, S.et al. Atomically Dispersed Iron Sites with a Nitrogen–Carbon Coating as Highly Active and Durable Oxygen Reduction Catalysts for Fuel Cells. Nat. Energy 2022, 7 (7), 652–663. https://doi.org/10.1038/s41560-022-01062-1.(5) Jiménez-Morales, et al. Strong Interaction between Platinum Nanoparticles and Tantalum-Doped Tin Oxide Nanofibers and Its Activation and Stabilization Effects for Oxygen Reduction Reaction. ACS Catal. 2020, 10 (18), 10399–10411. https://doi.org/10.1021/acscatal.0c02220. Figure 1

Enhancing Stability and Activity of Transition Metal Chalcogenides: Development of Carbon-Based Hydrochar Supported Nickel-Cobalt Selenide Electrocatalyst for Oxygen Evolution Reaction

Transition metal chalcogenides (TMCs) have long been regarded as cost-substitutes for traditional noble metal electrocatalysts, exhibiting comparable activity in the oxygen evolution reaction (OER). However, stability and activity remain crucial factors influencing the broader applicability of the catalysts. Therefore, enhancing the stability of transition metal chalcogenides is a key area of interest. This study delves into the development of carbon-based hydrochar support, serving as an alternative scaffold for depositing TMCs. Specifically, it aims to explore the application of scaffold for nickel-cobalt selenide (NiCoSe), a TMC exhibiting significant potential in accelerating the OER rate by increasing extrinsic activity through higher catalyst loading, enhanced porosity, and ensuring stability of the supported catalyst. The activity and stability of the NiCoSe/hydrochar are determined from cyclic voltammogram and chronoamperometric curves. Characterization of the synthesized NiCoSe on hydrochar show porous microstructure and well-dispersed electrocatalyst on hydrochar scaffold which allowed enhanced transport of species and aided electron transport through the electrolyte-electrode interface. SEM-EDS spectra show uniform distribution of NiCoSe which is advantageous for enhanced performance of the catalyst. This study elucidated the effect of hydrochar to enhance the extrinsic activity of NiCoSe towards the oxygen evolution reaction.

Boosting the Oxygen Reduction Performance of Fe–N–C Catalyst Using Zeolite as an Oxygen Reservoir

Non-precious metal electrocatalysts (such as Fe–N–C materials) for the oxygen (O2) reduction reaction demand a high catalyst loading in fuel cell devices to achieve workable performance. However, the extremely low solubility of O2 in water creates severe mass transport resistance in the thick catalyst layer of Fe–N–C catalysts. Here, we introduce silicalite-1 nanocrystals with hydrophobic cavities as sustainable O2 reservoirs to overcome the mass transport issue of Fe–N–C catalysts. The extra O2 supply to the adjacent catalysts significantly alleviated the negative effects of the severe mass transport resistance. The hybrid catalyst (Fe–N–C@silicalite-1) achieved a higher limiting current density than Fe–N–C in the half-cell test. In the H2–O2 and H2–air proton exchange membrane fuel cells, Fe–N–C@silicalite-1 exhibited a 16.3% and 20.2% increase in peak power density compared with Fe–N–C, respectively. The O2-concentrating additive provides an effective approach for improving the mass transport imposed by the low solubility of O2 in water.

Room temperature catalytic upgrading of unpurified lignin depolymerization oil into bisphenols and butene-2

Lignin is the largest source of renewable aromatics on earth. Despite numerous techniques for lignin depolymerization into mixtures of valuable monomers, methods for their upgrading into final products are scarce. The state of the art upgrading methods generally rely on catalytic funneling, requiring high temperatures, catalyst loadings and hydrogen pressure, and lead to the loss of functionality and bio-based carbon content. Here an alternative approach is presented, whereby the target monomers are selectively converted in unpurified mixtures into easily separable final products under mild conditions. We use reductive catalytic fractionation of wood to convert lignin into iso-eugenol and propenyl syringol enriched oil followed by an olefin metathesis to yield bisphenols and butene-2, thus, valorizing all bio-based carbons. To further demonstrate the synthetic utility of the obtained bisphenols we converted them into polyesters with a high glass transition temperature (Tg = 140.3 °C) and thermal stability (Td50% = 330 °C).

Synthesis of Hydrochars via Hydrothermal Carbonization of Zinc Chloride Activated Cotton Textile Waste

Anthropogenic pollution from fossil fuel combustion due to increasing global populations and emerging industries poses a serious threat to the environment. Therefore, it is vital to explore alternative green energy sources. Hence, this study synthesized renewable solid fuel hydrochars by utilizing biomass of cotton textile waste (CTW) as feedstock. ZnCl2 was selected as a catalyst due to its Lewis acid properties promoting hydrolysis and dehydration of raw materials towards hydrochar formation. The ZnCl2-activated cotton textile waste (ZnCl2-CTW) was prepared via the wet impregnation method at different ZnCl2 loading. The hydrochars were synthesized via hydrothermal carbonization of ZnCl2-CTW in a Parr batch reactor at the reaction temperature of 200 °C for 3 h. The hydrochars and CTW were characterized using a thermogravimetric analyser (TGA) to evaluate the proximate analysis, whereas an elemental analysis and determination of higher heating value (HHV) were conducted employing a CHNS analyser. The proximate analysis indicates the hydrochars volatile matter increases at higher catalyst loading, possibly due to the high content of bio-oil adsorbed on the hydrochars surface. The elemental analysis shows higher carbon and lower oxygen content for hydrochars compared to CTW, mainly due to the dehydration, decarboxylation, and aromatization reactions during HTC. Meanwhile, the HHV of hydrochars increases as catalyst loading increases to 1.5 g, which obtained the highest value of 18.41 MJ/kg, indicating good quality of solid fuel. This demonstrated that the ZnCl2 catalyst was useful in improving the energy density of hydrochars. Overall, ZnCl2 catalyst loading of 1.5 g has exhibited good performance in producing hydrochars via HTC of CTW. Thus, ZnCl2-CTW has the potential to produce hydrochar suitable as solid fuel, contributing to the conversion of waste into energy and the preservation of the environmental.

ProPhos: A Ligand for Promoting Nickel-Catalyzed Suzuki-Miyaura Coupling Inspired by Mechanistic Insights into Transmetalation.

Nickel-catalyzed Suzuki-Miyaura coupling (Ni-SMC) offers the potential to reduce the cost of pharmaceutical process synthesis. However, its application has been restricted by challenges such as slow reaction rates, high catalyst loading, and a limited scope of heterocycles. Despite recent investigations, the mechanism of transmetalation in Ni-SMC, often viewed as the turnover-limiting step, remains insufficiently understood. We elucidate the "Ni-oxo" transmetalation pathway, applying PPh2Me as the ligand, and identify the formation of a nickel-oxo intermediate as the turnover-limiting step. Building on this insight, we develop a scaffolding ligand, ProPhos, featuring a pendant hydroxyl group connected to the phosphine via a linker. The design preorganizes both the nucleophile and the nickel catalyst, thereby facilitating transmetalation. This catalyst exhibits fast kinetics and robust activity across a wide range of heteroarenes, with a catalyst loading of 0.5-3 mol %. For arene substrates, the catalyst loading can be further reduced to 0.1 mol %.

High-Strength and Ultrathin Photocatalytic Membranes with High-Loading Catalysts for Water Treatment

High-Strength and Ultrathin Photocatalytic Membranes with High-Loading Catalysts for Water Treatment

Organosulphur and organoselenium compounds as ligands for catalytic systems in the Sonogashira coupling.

Sonogashira coupling is a reaction of aryl/vinyl halides with terminal alkynes. It is used for the synthesis of conjugated enynes. Generally, copper (Cu) is required as a mediator for this reaction. It requires a long reaction time, high catalyst loading, or expensive ligands. Recently, homogeneous, heterogeneous, and nanocatalysts have been developed using organosulphur and organoselenium compounds as building blocks. Preformed complexes of metals with organosulphur and organoselenium ligands are used for homogeneous catalysis. Heterogeneous catalytic systems have also been developed using Cu, Pd, and Ni as metals. The nanocatalytic systems (synthesized using such ligands) include copper selenides and stabilized palladium(0) nanospecies. This article aims to cover the developments in the field of the processes and techniques used so far to generate catalytically relevant organic ligands having sulphur or selenium donor sites, the utility of such ligands in the syntheses of homogeneous, heterogeneous, and nanocatalytic systems, and critical analysis of their application in the catalysis of this coupling reaction. The results of catalysis are analyzed in terms of the effects of the S/Se donor, halogen atom of aryl halide, the effect of the presence/absence of electron-withdrawing or electron-donating groups or substituents on the aromatic ring of haloarenes/substituted phenylacetylenes, as well as the position (ortho or para) of the substitution. Substrate scope is discussed for all the kinds of catalysis. The supremacy of heterogeneous and nanocatalytic systems indicates promising future prospects.

A robust depolymerization route for polysiloxanes.

A versatile, robust, and stable tetrabutylammonium difluorotriphenylsilicate (TBAT) catalyst has been deployed for efficient depolymerization of silicones. This catalyst is soluble in a variety of organic solvents and is stable up to 170 °C, enabling a wide range of reaction conditions under which F--catalysed siloxane bond cleavage can be initiated. This effort offers significant advancement overcoming the traditional limitations of silicone depolymerization, such as high catalyst loading, storage and handling, and few viable reaction media.

Expedient alkyne semi-hydrogenation by using a bimetallic AgCu-C3N4 single atom catalyst.

Metal-catalyzed semi-hydrogenation of alkynes is an important step in organic synthesis to produce diverse chemical compounds. However, conventional noble metal catalysts often suffer from poor selectivity owing to over-hydrogenation. Here, we demonstrate a high-loading bimetallic AgCu-C3N4 single-atom catalyst (SAC) for alkyne semi-hydrogenation. The AgCu-C3N4 SACs exhibit higher activity and selectivity (99%) than their low-loading variants due to the synergistic interaction of heteronuclear Ag-Cu sites at small inter-site distances. Using a combination of techniques such as phenylacetylene-DRIFTS, H2-temperature programmed desorption and DFT calculations, we showed that the cooperative bimetallic interaction during alkyne semi-hydrogenation was achieved by isolated Ag centers as hydrogen activation sites and isolated Cu centers as alkyne activation sites. Our work highlights the importance of achieving high catalyst loading to reduce the inter-site distance in bimetallic SACs for cooperative interactions, which can potentially open new catalytic pathways for synthesizing fine chemicals and pharmaceuticals.

A high-loading catalyst of highly dispersed nickel species on acid-treated mesoporous clay layers for efficient CO and CO2 methanation

The catalyst, consisting of nickel-amino acid framework nanocrystals on acid modified clay layers, exhibited excellent activity and stability in CO and CO2 methanations due to its high content of dispersed Ni species.

(Invited) Membrane Degradation in Polymer Electrolyte Membrane Fuel Cells for Heavy Duty Applications

Polymer electrolyte membrane fuel cells (PEMFCs) are being considered for heavy duty applications, and the DOE has established various performance and durability targets to enable their adoption.1. The key differences between light and heavy-duty application of fuel cells is their increased durability and operating efficiency requirements for heavy duty applications when compared to the lower cost requirement for light duty applications. While higher catalyst loadings can be utilized to increase the fuel cell performance and catalyst lifetime, membrane durability could be a significant outstanding challenge. Membranes are expected to last 25,000 hours to 30,000 hours for heavy duty applications and the Million Mile Fuel Cell Truck Consortium (M2FCT) is evaluating various membrane technologies for use in heavy duty drive cycles. Current state of the art membranes with both mechanical and chemical stabilization have already met light-duty durability requirement of 5000+ hours and have the potential to meet 25,000+ hour lifetimes. This talk will describe the various membrane related accelerated stress tests (ASTs) developed by the consortium and will present membrane durability results obtained from long-term (500 hours) fuel cell operation at elevated temperature (90 oC). Both the mechanical and chemical durability of membranes will be discussed with particular emphasis and fluoride emission rates (FERs) and lifetime predictions. Acknowledgement: This work was supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE) through the Million Mile Fuel Cell Truck (M2FCT) consortia, technology managers G. Kleen and D. Papageorgopoulos.

Fe-N-C Catalysts Synthesized on Conductive Non-Carbon Support Materials for Improved PEMFC Durability

Global energy demand will be continuously rising in the foreseeable future. To mitigate the results of climate change it is necessary to reduce the emittance of green house gasses. One very promising approach is to switch to hydrogen as energy carrier and use proton membrane fuel cells (PEMFCs) as the primary energy generation technology. Here, hydrogen and oxygen/air are used to directly generate electrical energy with only water as byproduct. Both reactions need to happen efficiently at the same time. The oxygen reduction reaction (ORR), however, is a very sluggish four-electron-reaction and needs efficient catalysts.The state-of-the-art catalyst is platinum but that is a very scarce and expensive metal. Hence, it is important to switch to precious-metal-group (PGM) free catalysts. In recent years, bio inspired iron-based Fe-N-C catalysts have been shown to approach ORR activities that are competitive with those of platinum, even though they need a higher catalyst loading than Pt to reach the desired current densities.1-3 Those catalysts feature single Fe atoms surrounded by four N atoms in graphitic carbon. The drawback of those materials is their lower stability compared to PGM materials. In a nutshell, the carbon matrix oxidizes during operation in PEMFCs, changing the morphology of the catalytic center and rendering it less active, or inactive, depending on the carbon oxidation extent. Demetallation phenomena are also possible, leaving a N4 cavity without metal cation center. It was shown recently by Wu et al.4 that it is possible to raise durability by adding an additional carbon layer on the catalyst. One alternative approach to reduce those degradations is to interface Fe-N4 sites with a carbon-free support. The targeted support material must be immune to corrosion in acid and withstand the typical ORR electrochemical potentials. It also has to be electrically conductive to facilitate electron transfers, both locally and on long scale.In this work, conductive ceramic metal oxide materials were investigated as possible alternative catalyst supports. Those materials are resistant to acid and can withstand prolonged potentials at operating conditions in PEMFCs. The conductivity is usually raised by doping, since many of those ceramics are semi-conductors. However, during the synthesis of the Fe-N-C catalysts, high temperatures are generally applied. Such treatments can be detrimental to the conductivity of the ceramics due to metal aggregation (in case of doped materials) and may also lead to morphological changes. A robust method to synthesize Fe-N-C catalysts is by mixing the separate Fe, N and C precursors and using optimized thermal treatment at high temperatures. They can be further pyrolyzed with ammonia to introduce defects and basicity into the structure, which leads to higher catalytic activity but even lower stability in acid medium. In this study, the effect of the pyrolysis conditions on conductive oxide materials was investigated with various characterization methods, e.g. x-ray diffraction, scanning electron microscopy and N2 sorption isotherms. This gives insights into the changes that happen during the thermal treatment and can be used to find optimal synthetic conditions to keep most desired parameters of the ceramics preserved or only minimally lowered. Several different approaches were used to combine Fe-N-C catalysts with conductive ceramic metal oxide materials. The resulting materials were characterized and tested with rotating disc electrode techniques and in PEM fuel cells for their ORR-activity and durability.(1) F. Jaouen et al., Nature Catalysis, 2022, 5, 311–323(2) H. A. Gasteiger et al., Science, 2009, 324, 48−49(3) L. Elbaz et al., ACS Applied Energy Materials 2022, 5 (7), 7997-8003(4) G. Wu et al., Nature Energy, 2022, 7, 652–663

Platinum Group Metal-Free Catalyst Loading Optimization for Dry Cathode Operation in Anion Exchange Membrane Water Electrolysis

With an increasing interest for green hydrogen as an important fuel for the global energy transition and as a raw material for green chemistry, extensive research efforts are currently devoted to increase the performance of water electrolysis technologies. In this frame work, Anion Exchange Water Electrolysis (AEMWE) has a strategic role promising to boost electrolytic hydrogen production without relying on scarce resources as AEMWE does not need Iridium or other Platinum group metals (PGM) catalysts, unlike Proton Exchange Membrane Water Electrolysis (PEMWE), to reach high power density [1].In this work, the focus is on electrode optimization for dry cathode operation. Operating without a liquid feed on the cathode reduces the extent of the drying of hydrogen gas and simplifies the balance of the plant. However, water must be transported from the anode to the cathode where it is consumed by the hydrogen evolution reaction (HER) [2]. Also, ionic connection from the membrane to catalyst surface must be provided by the ionomer without a supporting electrolyte which is generally employed in AEMWE to improve performance [1]. Under these premises, it is clear that using high catalyst loading to compensate for the intrinsic low activity of Platinum group metals-free (PGM-free) catalysts will result in lower utilization of the catalyst layer as a function of the electrode thickness [3].To study how transport limitations hinder cathode performance, we manufactured catalyst coated membranes (CCMs) via decal transfer method and varied the cathode catalyst loading thereby adjusting catalyst layer (CL) thickness. RaneyTM Nickel served as the cathode catalyst and Super PTM Carbon as the conductive additive. It was found that increasing the catalyst loading between 0.65 mg/cm2 and 1.65 mg/cm2 greatly improved cell performance (Figure 1). However, cell voltage proved to be less sensitive to cathode loading for higher loadings. In fact, to reasonably improve the performance further, a loading of 4.55 mg/cm2 was necessary. Noticeably, the high frequency resistance (HFR) was found to be independent of catalyst loading (i.e. CL thickness) due to the high electronic conductivity of the cathode CL with carbon additive.This works sheds light on how AEMWE performance are related to cathode catalyst loading when the cathode is dry operated. It is found that performance improvement is limited at high loading (above 1.65 mg/cm2). This shows how the ionic conductivity of the electrode should be improved to mitigate the low mass activity of PGM-free catalyst.[1] Ayers, Katherine, Nemanja Danilovic, Ryan Ouimet, Marcelo Carmo, Bryan Pivovar, and Marius Bornstein. “Perspectives on Low-Temperature Electrolysis and Potential for Renewable Hydrogen at Scale.” Annual Review of Chemical and Biomolecular Engineering 10, no. 1 (June 7, 2019): 219–39.[2] Koch, Susanne, Joey Disch, Sophia K. Kilian, Yiyong Han, Lukas Metzler, Alessandro Tengattini, Lukas Helfen, Michael Schulz, Matthias Breitwieser, and Severin Vierrath. “Water Management in Anion-Exchange Membrane Water Electrolyzers under Dry Cathode Operation.” RSC Advances 12, no. 32 (2022): 20778–84.[3] Liu, Jiangjin, Zhenye Kang, Dongguo Li, Magnolia Pak, Shaun M. Alia, Cy Fujimoto, Guido Bender, Yu Seung Kim, and Adam Z. Weber. “Elucidating the Role of Hydroxide Electrolyte on Anion-Exchange-Membrane Water Electrolyzer Performance.” Journal of The Electrochemical Society 168, no. 5 (May 1, 2021): 054522.Figure 1 Polarization curve of CCMs with different cathode catalyst loading. The cathode contains 65 % catalyst (RaneyTM Nickel), 10% ionomer and 25% Super PTM Carbon. NiFe nanoparticles are used in the anode with 5% ionomer (AP-1-HNN5-00-X). The measurements are conducted at 60 °C feeding 1 M KOH to anode. Figure 1

Investigating Oxygen Reduction Performance of Fe-N-C Catalysts for Proton Exchange Membrane Fuel Cells

Non-precious Fe-N-C catalysts have reached high activity levels for acidic oxygen reduction reaction (ORR) in rotating ring disk electrode (RRDE) setup approaching to that of the platinum group metals (PGM) when compared at high catalyst loadings of 0.6-1.0 mgFe-N-C cm-2. The improvements in the ORR activity of Fe-N-Cs can be attributed to new synthetic routes developed in recent years that have led to increased Fe-N4 active site density and utilization and/or better intrinsic activity/turnover frequency (TOF) of those sites.1-3 Despite impressive activities in half-cells, Fe-N-Cs still require quite high loadings in the range of 4.0-5.0 mg cm-2 in proton exchange membrane fuel cells (PEMFCs), which makes the Fe-N-C cathodes 4-5x thicker than Pt-based cathodes (~100 µm for Fe-N-C layer vs ~10-20 µm for Pt layer). Thick Fe-N-C cathodes suffer from quick performance drop in medium to high current density region due to mass-transport related losses. Reducing the Fe-N-C loading levels in RRDE and in PEMFC without comprising the ORR activity would need further improvements in active site density, site utilization and TOF. In this talk, I will present our work on how morphological tailoring of carbon framework in Fe-N-Cs affects the utilization of active sites and water adsorption-desorption behaviour with the aim of improving the ORR performance and mass-transport properties. Active-site imprinted carbon frameworks are used to prepare Fe-N-Cs that consist of purely Fe-N4 sites without any other iron species.1,4,5 Besides activity, performance stability against extensive voltage cycling in RRDE and long-term durability in PEMFC single-cells is another important criterion that Fe-N-Cs need to fulfil for becoming a viable substitute to PGM catalysts. Very recently, encouraging results on the improvement of Fe-N-C durability in PEMFC tests have been reported using radical scavengers and by coating a thin carbon layer on the surface of Fe-N-C.6,7 However, significantly more efforts are required in that direction for reaching the durability targets of thousands of hours. Second part of the talk will discuss the performance stability of Fe-N-Cs.

Cu(II)-Catalyzed H/D exchange of indole derivatives

Cu(OTf)2 was explored as an efficient catalyst for hydrogen deuterium (H/D) exchange of indole derivatives. The advantage of this reaction is that deuteration selectivity can be adjusted by changing reaction parameters. When the reaction was performed with 10 mol% of Cu(OTf)2 as a catalyst in dioxane at 80 °C, deuteration preferentially occurred at C3 position of indole with high atom% deuterium incorporation. Furthermore, per-deuterated indole derivatives could be achieved by performing the reaction with higher catalyst loading in toluene at 120 °C. Performing the reaction on a continuous flow reactor facilitates the scale-up process, affording deuterated products with a throughput of 3.9 g/h.

Decoupling Activation and Transport by Electron-Regulated Atomic-Bi Harnessed Surface-to-Pore Interface for Vanadium Redox Flow Battery.

Vanadium redox flow battery (VRFB) promises a route to low-cost and grid-scale electricity storage using renewable energy resources. However, the interplay of mass transport and activation processes of high-loading catalysts makes it challenging to drive high-performance density VRFB. Herein, a surface-to-pore interface design that unlocks the potential of atomic-Bi-exposed catalytic surface via decoupling activation and transport is reported. The functional interface accommodates electron-regulated atomic-Bi catalyst in an asymmetric Bi─O─Mn structure that expedites the V3+ /V2+ conversion, and a mesoporous Mn3 O4 sub-scaffold for rapid shuttling of redox-active species, whereby the site accessibility is maximized, contrary to conventional transport-limited catalysts. By in situ grafting this interface onto micron-porous carbon felt (Bi1 -sMn3 O4 -CF), a high-performance flow battery is achieved, yielding a record high energy efficiency of 76.72% even at a high current density of 400mA cm-2 and a peak power density of 1.503W cm-2 , outdoing the battery with sMn3 O4 -CF (62.60%, 0.978W cm-2 ) without Bi catalyst. Moreover, this battery renders extraordinary durability of over 1500 cycles, bespeaking a crucial breakthrough toward sustainable redox flow batteries (RFBs).