Catalyst Active Sites Research Articles

Enhancing Ammonia Synthesis and CO Hydrogenation to Methanol via Nonthermal Plasma Catalysis: A Focus on Catalyst Pore Structure and Active Site Design

The increasing energy demand, climate change and sustainable development necessitate the transition from fossil fuels to renewable sources (such feedstock and energy). Green hydrogen is one of the key components in sustainable energies/fuels being crucial for reducing carbon emissions and achieving carbon neutrality. However, hydrogen storage and transportation are challenging, and chemical hydrogen storage reactions such as ammonia synthesis and CO2 hydrogenation (to methanol) are considered promising solutions. Nonthermal plasmas (NTPs) are partially ionized gases with various energetic species, which are produced under ambient conditions being able to facilitate efficient chemical reactions under mild conditions. Importantly, NTP technologies can theoretically utilize green electricity produced by renewable energies (such as solar and wind) showing significant low-carbon potential. Previous studies have shown the catalysts design has an important impact on the performance of catalytic reactions under NTP conditions, and hence this aspect deserves attention. Here this mini review comments on the application of NTP catalytic technologies in ammonia synthesis and CO2 hydrogenation to methanol, with a special focus on catalyst pore structure and active site design. The critical summary and perspective can serve as the most current snapshot of the relevant research fields in NTP technologies, helping their further development.

Exploiting graph theory in MD simulations for extracting chemical and physical properties of materials.

Some of our recent developments and applications of algorithmic graph theory for extracting the physical and chemical properties of materials from molecular dynamics simulations are presented. From the chemical viewpoint, the power of graph theory is illustrated in the search for a catalyst's active sites at a silica solid surface. From the physical viewpoint, we present graph algorithms that recognize the structural motifs that exist at the silica/liquid water interface. Statistical analyses of the instances of these surface-water motifs provide a detailed understanding of the structures and dynamics at the aqueous interface.

Mn Doping at High-Activity Octahedral Vacancies of γ-Fe2O3 for Oxygen Reduction Reaction Electrocatalysis in Metal-Air Batteries.

γ-Fe2O3 with the intrinsic cation vacancies is an ideal substrate for heteroatom doping into the highly active octahedral sites in spinel oxide catalysts. However, it is still a challenge to confirm the vacancy location of γ-Fe2O3 through experiments and obtain enhanced catalytic performance by preferential occupation of octahedral sites for heteroatom doping. Here, a Mn-doped γ-Fe2O3 incorporated with carbon nanotubes catalyst was developed to successfully achieve preferential doping into highly active octahedral sites by employing γ-Fe2O3 as the precursor. Further, the vacancy in γ-Fe2O3 was only located on octahedral sites rather than tetrahedral ones, which was first proved by direct experimental evidence through the clarification doping sites of Mn. Notably, the catalyst shows outstanding activity towards oxygen reduction reaction with the half-wave potential of 0.82 V and 0.64 V vs. reversible hydrogen electrode in alkaline and neutral electrolytes, respectively, as well as the maximum power density of 179 mWcm-2 and 403 mWcm-2 for Mg-air batteries and Al-air batteries, respectively. It could be attributed to the synergistic effect of the doping Mn on octahedral sites and the substrate γ-Fe2O3 along with the modification of the adsorption/desorption properties for oxygen-containing intermediates as well as the optimization of the reaction energy barriers.

In/Outside Catalytic Sites of the Pore Walls in One-Dimensional Covalent Organic Frameworks for Oxygen Reduction Reaction.

Pore channels play a decisive role in mass transport in catalytic systems. However, the influences of the location of catalytic sites inside or outside of the pore walls on the performance were still under-explored due, because it is difficult to construct sites anchored in or outside of pore walls. Herein, one-dimensional covalent organic frameworks with precisely anchored active sites were used to explore the effects of channels on a typical oxygen reduction reaction (ORR) catalysis. Electrocatalytic evaluations showed that single Pt sites located inside of the channels exhibited higher kinetic activity compared to those anchored outside. The in situ spectroscopic analysis revealed that local reconstruction of Pt-Cl breaking and potential-induced anion transport occurred more effectively inside the channels. The superior anion transportability and kinetic activity of the inside-channel active sites also facilitated *OH desorption during the ORR process outperforming their outside-channel counterparts. The results of this study provide strategies for designing active sites in porous catalysts for heterogeneous catalysis.

Highly Selective Hydrogenation of Nitriles to Primary Amines without an Additive Using Nanoscale Ni0-NiII/III-bTiO2 Heterojunctions.

Despite significant progress in the catalytic hydrogenation of nitriles, the persistent challenge of requiring additives to prevent condensation byproducts and achieve selectivity toward primary amines demands urgent attention. In this work, we present an integrated approach utilizing a ligand-bridged Ni-Ti bimetallic complex as a precursor to tune Ni0-NiO-NiO(OH) heterojunctions and phases of black titania (bTiO2) by controlling pyrolytic conditions. This tailored phase distribution and charge dynamics across heterojunctions create an effective balance of acidic and basic sites, enabling the direct hydrogenation of nitriles to primary amines without the need for additives. However, at elevated pyrolysis temperatures, this balanced composition begins to shift, with the loss of critical phases that alter the catalyst's structural and chemical properties. This shift reduces amphoteric behavior, resulting in decreased selectivity for primary amines and favoring the formation of condensation byproducts. The catalyst's structure, amphoteric nature, crystallinity, surface area, and active sites are comprehensively characterized using high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), temperature programmed desorption of ammonia (NH3-TPD), temperature programmed desorption of carbon dioxide (CO2-TPD), and CO2 adsorption techniques. The magnetically retrievable catalyst exhibited excellent functional group tolerance, high selectivity, multiple reusability, broad substrate scope, and high activity for nitrile hydrogenation to primary amines, with the potential for advanced catalytic hydrogenation of other functional groups.

In/Outside Catalytic Sites of the Pore Walls in One‐Dimensional Covalent Organic Frameworks for Oxygen Reduction Reaction

Pore channels play a decisive for mass transport in catalytic systems. However, the influences of the location of catalytic sites inside or outside of the pore walls on the performance were still under‐explored due, because it is difficult to construct sites anchored in or outside of pore walls. Herein, one‐dimensional covalent organic frameworks (COFs) with precisely anchored active sites were used to explore the effects of channels on a typical oxygen reduction reaction (ORR) catalysis. Electrocatalytic evaluations showed that single Pt sites located inside of the channels exhibited higher kinetic activity compared to those anchored outside. The in situ spectroscopic analysis revealed that local reconstruction of Pt–Cl breaking and potential‐induced anion transport occurred more effectively inside the channels. The superior anion transportability and kinetic activity of the inside‐channel active sites also facilitated *OH desorption during the ORR process outperforming their outside‐channel counterparts. The results of this study provide strategies for designing active sites in porous catalysts for heterogeneous catalysis.

Mn Doping at High‐Activity Octahedral Vacancies of γ‐Fe2O3 for Oxygen Reduction Reaction Electrocatalysis in Metal‐Air Batteries

γ‐Fe2O3 with the intrinsic cation vacancies is an ideal substrate for heteroatom doping into the highly active octahedral sites in spinel oxide catalysts. However, it is still a challenge to confirm the vacancy location of γ‐Fe2O3 through experiments and obtain enhanced catalytic performance by preferential occupation of octahedral sites for heteroatom doping. Here, a Mn‐doped γ‐Fe2O3 incorporated with carbon nanotubes catalyst was developed to successfully achieve preferential doping into highly active octahedral sites by employing γ‐Fe2O3 as the precursor. Further, the vacancy in γ‐Fe2O3 was only located on octahedral sites rather than tetrahedral ones, which was first proved by direct experimental evidence through the clarification doping sites of Mn. Notably, the catalyst shows outstanding activity towards oxygen reduction reaction with the half‐wave potential of 0.82 V and 0.64 V vs. reversible hydrogen electrode in alkaline and neutral electrolytes, respectively, as well as the maximum power density of 179 mWcm−2 and 403 mWcm−2 for Mg‐air batteries and Al‐air batteries, respectively. It could be attributed to the synergistic effect of the doping Mn on octahedral sites and the substrate γ‐Fe2O3 along with the modification of the adsorption/desorption properties for ORR oxygen‐containing intermediates as well as the optimization of the reaction energy barriers.

Two-Dimensional Bi2Se3 Nanosheets Synthesis for Efficient Electrocatalytic Production of Ammonia from Nitrate

Ammonia (NH3), a critical component for various industries, is produced through the Haber-Bosch process, which, despite its importance, is a significant source of carbon emissions and operates on a centralized model, emphasizing the need for innovative solutions to decarbonize and decentralize its production. Electrochemical nitrate (NO3–) reduction to NH3 presents a promising alternative to the Haber-Bosch process for NH3 synthesis, with the added advantage of transforming waste into a valuable resource while mitigating water pollution concerns. However, achieving a well-defined active center and catalytic selectivity in the electrochemically driven reaction remains a significant challenge. In this study, we successfully fabricated a highly selective and active 2D Bi2Se3 catalyst, which demonstrated better performance in reducing NO3– to NH3 with a Faradaic efficiency (FE) of approximately 80% (−0.3V (RHE)) and a significant yield rate of 45mgh−1mgcat−1 (0.46 mmolh−1cm−2). Furthermore, the fabricated material exhibited exceptional stability and durability, maintaining a high NO3– reduction of 80% FE even after 10 consecutive cycles of extended use and continuous operation, demonstrating its remarkable resilience and reliability. Our findings show that the prepared catalyst selectively promotes the electrochemical reduction of NO3– to NH3 while suppressing the competing hydrogen evolution reaction (HER). The charge density profile indicates a pronounced charge localization around the Se atoms, implying that the Se active sites in the 2D Bi2Se3 catalyst act as the active center for the NO3– reduction mechanism, playing a crucial role in facilitating the reaction kinetics.

Ciprofloxacin degradation over Co3O4 catalysts by the microwave-assisted persulfate oxidation: a critical role of coordination composition

The combination of catalysts and microwave (MW) effects presents an emerging approach for persulfate (PS) activation, while the effect of active sites of catalysts on the synergistic reaction remains poorly understood. Here, we regulated the coordination composition of Co3O4 by strategically controlling the oxygen atmosphere during fabrication. We found that Co3+ and Co2+ acted as reactive centers for microwave absorption and catalytic activation of persulfate, respectively. By altering the ratio between Co3+ and Co2+, we explored the Co3O4 (2.23)-550 catalysts with significantly improved synergistic activity for degrading ciprofloxacin (CIP), which was 33.0 and 26.8 times higher than PS- Co3O4 (2.23)-550 (without microwave) and MW- Co3O4 (2.23)-550 (without persulfate), respectively. Meanwhile, Co3O4 (2.23)-550 catalyst (0.5mgL-1) showed the highest degradation rate of CIP 92.6% (0.5mgL-1) within 10min under microwave. According to the radical identification and intermediate analysis, the efficient degradation of CIP was ascribed to both free radical and non-free radical pathways. Thus, this work raises new insights into the structure-activity relationship of catalysts, and provides an efficient way to eliminate antibiotics via synergistic catalysis.

Accurate location of Ni and W active sites in hierarchical zeolite catalyst for the conversion of cellulose to alcohols

The process of converting cellulose into short-chain alcohols is a critical component of biomass valorization. In this study, we utilized an anion-cation co-directed hydrothermal method and wet impregnation to synthesize a hierarchical MFI zeolite with isolated Ni and W sites. We employed linear correlation analysis to evaluate the influence of pore size, site accessibility, and acidity on product selectivity. Balancing hydrogenation and acidic sites on the catalyst enhanced retro-aldol condensation and hydrogenation during cellulose conversion. Surface acidic sites accelerated glucose retro-aldol condensation, while micropore acidic sites aided in ethylene glycol hydrogenolysis. The close proximity of Ni and W facilitated high selectivity and yield of ethanol through bimetallic synergy. This research presented a novel strategy for preparing hierarchical zeolites with isolated metal sites and provides clarity on the cooperative roles of active sites in Ni-W bimetallic catalysts for cellulose conversion.

Rational Design of Supported Metal Catalysts for Selective Hydrogenation of Sulfur‐Containing Compounds

AbstractHydrogenation of nitro, carbonyl groups, and unsaturated bonds of sulfur‐containing compounds over supported metal catalysts is a green process in the production of building blocks of bioactive natural compounds, drugs, pesticides, and so forth, but it is a challenging task due to the strong coordination and complexation of the lone pair electrons in sulfur atom with active sites in catalyst, leading to dramatically reduced activity. Previous studies emphasize the sulfur‐resistant properties of catalysts in the hydrogenation of industrial feedstocks, but the direct hydrogenation of sulfur‐containing compounds has received limited attention. In this concept, recent advances in the hydrogenation of sulfur‐containing compounds were reviewed, including the strategies to improve the resistance of supported metal catalysts to sulfur poisoning. Finally, we give future perspectives on the development of efficient catalysts for the hydrogenation of sulfur‐containing compounds, and key factors influencing the hydrogen dissociation and migration in the presence of sulfur atoms are highlighted.

PH-Dependent Oxygen Reduction on Metal Monoxide/Polypyrrole Hybrid Catalysts

The oxygen reduction reaction (ORR) is at the heart of many such fuel cell devices and holds a special place in the field of electrocatalysis, but it is notoriously slow. Various studies in the past decade have focused on determining a method to reduce the over potential of ORR and to replace the conventional costly Pt catalyst in both types of fuel cells.Theoretical approaches have been reported that dual-catalyst system in which two catalysts work simultaneously to decrease specific adsorption energies of intermediates, resultantly, linear scaling relationship were circumvented, could be an effective way to improve the catalytic activity. A calculation work suggested that combination of transition metal sites and hydrogen donor/acceptor sites were available to improve catalytic performances of ORR and OER beyond limitations originated from linear scaling relations. Polypyrrole, well known as a conductive polymer, is capable of deprotonation / deprotonation with adsorption and desorption of anions. It has been reported that pPy are easily and reversibly deprotonated and protonated in aqueous solution. The deprotonation / protonation of polypyrrole is reversible, suggesting that pPy can act as a proton donor in the ORRElectrocatalytic ORR in aqueous media proceeds along a pathway having multiple steps in which multiple surface intermediates are involved (* →*OO → *OOH → *O → *OH where * = active site of catalyst). Proton supplied from media plays a crucial role on the ORR mechanism. Therefore, pH of media affects the kinetics of ORR significantly. In the same vein, it is expected that the ORR activity is improved in the presence of proton donor (HD) around active sites of catalysts.In this work, we demonstrate a possibility that a series of proton donors are involved in protonation of the surface intermediates. we demonstrate the improvements of the ORR activities on various metal oxides through an additional organic compartment, polypyrrole (pPy), that can provide protons to oxygen intermediate. pPy has been well studied to modification of metal catalysts such as metal organic compounds, M-N-C for enhancing ORR kinetics. Herein, as a different role of pPy, it is studied that the interaction of polypyrrole with oxygen intermediate adsorbed on transition metal catalysts to provide protons. As an experimental result, it was confirmed that this change leads to an improvement of ORR kinetics.Moreover, we present pH dependency of overpotential reduction by the pPy also supported that the proton transfer from pPy to the metal monoxide catalyst would affect ORR kinetics. The ORR overpotential was improved by 50mV at pH 13 on transition metal oxide catalysts. The overpotential improvement was intensified as the pH of media decreased. It is suspected that the pH affects deprotonation of the proton donors (HD à H+ + D-). High pH deprotonates the proton donors so that the effects of proton donors decrease. However, the proton of HD survives in acidic media so that the proton transfer from HD to active site is facilitated. The ORR overpotential gain was as large as 295 mV at pH 4 even if the oxide catalyst was not stable at the acidic pH. At pH 7, the overpotential improvement was estimated at 254 mV. Figure 1

Pt Ternary Alloy with Rare Earth Metal - Pt5Ce-Co Intermetallic Nanoparticles as Highly Active Catalyst for Oxygen Reduction Reaction in PEMFCs

Platinum-based alloy catalysts have been extensively studied for oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs) because their superior enhancement in activity and durability. Alloying with rare earth (RE) elements is an important direction of exploring in Pt-based alloy design, due to its electronic configurations that can provide additional pathways for tailoring the electronic structures of active elements through alloying. Pt-RE alloys show more negative formation enthalpy than the widely applied late transition metal-based Pt alloys, which makes them thermodynamically and kinetically stable. The recently developed solid-phase synthesis strategy makes the nanoscale RE-based alloys more applicable. Here we reported a ternary intermetallic alloy of Pt5CeCo/C synthesized by two step-reduction method, annealing in diluted H2 under high temperature. Due to the unique 4f orbital of Lanthanoids Ce and the contraction effect, the electronic valence state of Pt alloys was modified, thus, optimizing the adsorption energy of the the reaction intermediates over the catalyst active sites, and effectively improving the electrocatalytic performance of the catalysts. It appears that the introduction of Ce greatly improves the ORR activity and fuel cell performance of Pt5CeCo/C, which achieved 2.8 A∙mgPt -1 of mass activity and 78.1 m2∙gPt -1 of ECSA using rotating disk electrode (RDE), while it is only 0.62 A∙mgPt -1 and 75.2 m2∙gPt -1 for Pt3Co/C, respectively. After 30k of accelerated stress test (AST) on RDE, Pt5CeCo/C can maintain 1.4 A∙mgPt -1 of mass activity, far exceeding Pt3Co/C and commercial Pt/C. For membrane electrode assembly (MEA) test, Pt5CeCo/C shows an initial mass activity of 724 mA∙mgPt -1, and a current density of 1876 mA∙cm-2 at 0.7 V under heavy-duty vehicle (HDV) testing conditions, while it still remains 1400 mA∙cm-2 at 0.7 V after 30k AST. This work provides an avenue to design advanced PGM ternary alloys by incorporating rare-earth metals to promote the catalyst performance.

Developing Catalysts for Proton and Anion Exchange Membrane Water Electrolyzers

To achieve carbon neutrality, extensive research is ongoing to produce green hydrogen via water electrolysis combined with renewable energy sources. Understanding and developing catalysts for membrane electrode assembly (MEA) type water electrolysis systems, such as proton exchange membrane water electrolysis (PEMWE) and anion exchange membrane water electrolysis (AEMWE), are critical steps toward this goal. Therefore, this presentation will focus on catalyst development for PEMWE and AEMWE, with emphasis on cost-effective catalysts.For oxygen evolution reaction (OER) catalysis in PEMWE, the primary challenge is to minimize iridium (Ir) usage for sustainable green hydrogen production. Layered monoclinic iridium nickel oxide (IrNiOx) platelets were synthesized using a molten salt method and employed for the OER. These platelets exhibited high OER activity with reduced Ni dissolution in acidic conditions. When applied in MEA, they demonstrated enhanced interconnectivity within the catalyst layer, promoting electron transfer. Even at low Ir loading (0.2 mgIr cm-2), the platelets showed good performance with an initial cell voltage of 1.70 V at 1 A cm-2 and minimal degradation over 100 hours. This highlights the effectiveness of incorporating transition metals into Ir oxide to reduce Ir usage in PEMWE.For oxygen evolution reaction (OER) catalysis in AEMWE, attention is focused on nickel iron (NiFe) hydroxide catalysts for their high activity and stability in alkaline conditions. However, the lack of initial electrical conductivity of as-prepared NiFe LDH limits its potential as an electrocatalyst. To address this issue, a monolayer structuring approach was proposed. This method improved mass transport to allow a high energy conversion efficiency of 72.6% with exceptional stability over 50 hours at 1 A cm-2. Additionally, lack of initial electrical conductivity hinders determination of electrochemically active surface area (ECSA) of NiFe LDH using conventional double layer capacitance method. Use of electrochemical impedance spectroscopy (EIS) at reactive OER potentials to extract the capacitance that is hypothesized to arise due to reactive OER intermediates (O*, OH*, OOH*) adsorbed on the catalyst surface was thus investigated. This allowed the estimation of ECSA and intrinsic activity of NiFe LDH, validating the methodology through rigorous catalyst loading and support studies.For hydrogen evolution reaction (HER) catalysis in AEMWE, replacing platinum (Pt) with Ni-based alloys containing molybdenum (Mo) species has shown promise. Dynamic active sites of Ni catalysts with Mo species require innovative approaches to maintain initial performance, warranting material innovation or careful manipulation of operating protocol. The approaches in which this is made possible is shortly presented, together with the innovations that allows probing of such phenomenon.

(Invited) Electrocatalytic Activity and Structural Insights of Cu, Fe and N-Doped Mesoporous Carbon for the Oxygen Reduction Reaction

For widespread applications of polymer electrolyte fuel cells, non-PGM electrocatalysts with high oxygen reduction reaction (ORR) activity and product selectivity to H2O need to be developed. Metal, nitrogen-doped carbon (M–N–C, M = Fe, Co, Cu, etc.) electrocatalysts have been intensively studied as non-PGM based electrocatalysts in acidic media for the ORR because they show relatively high ORR activity in the non-PGM-based electrocatalysts. Recently, heterometallic doping into nitrogen-doped carbon, which is known as dual-metal atom catalysts, can show the cooperative effect on the ORR activity and product selectivity. We have also developed such heterometallic non-PGM electrocatalysts of Cu, Fe, N-doped carbon nanotubes for the ORR in acidic media, inspired by the active site of a natural ORR catalyst of cytochrome c oxidase [1]. The co-doping of Cu and Fe in carbon nanotubes improves the ORR activity and product selectivity toward H2O via four-electron transfer. However, its ORR activity is relatively low (a turnover frequency of 0.40 e– site–1 s–1 at +0.80 V vs. RHE) and the structure of the active site remains unclear.We report the synthesis, activity and structural insight of a Cu, Fe, N-doped mesoporous carbon, (Cu,Fe)–N–mesoC, electrocatalyst for the ORR in acidic media. (Cu,Fe)–N–mesoC was prepared in pyrolysis from the composite of an iron complex of a 1,12-diazatriphenylene ligand [2], a multinuclear copper complex of 1,2,4-triazole [3] and mesoporous carbon. (Cu,Fe)–N–mesoC shows a turnover frequency of 1.35 e– site–1 s–1 at +0.80 V vs. RHE and a low hydrogen peroxide yield (< 5%). X-ray absorption and emission spectroscopy of (Cu,Fe)–N–mesoC was performed to understand the structure of the active site.References.[1] M. Kato, N. Fujibayashi, D. Abe, N. Matsubara, S. Yasuda, I. Yagi, ACS Catal., 11, 2356-2365 (2021).[2] K. Matsumoto et al., Chem. Eur. J., 28, e20210345 (2022).[3] M. Kato et al., ACS Appl. Energy Mater., 1, 2358-2364 (2018).

Shedding Light on Active Site Reconstruction and Structural Transformation of Oxygen Evolution Reaction Catalysts for Water Electrolysis

Designing efficient and stable electrolcatalysts for the demanding oxygen evolution reaction (OER) in water electrolysis is challenging and we are still lacking fundamental understanding of the underlying processes related to catalyst transformations governing their final activity and stability. Only the combination of operando spectroscopy techniques with electrochemical measurements can promote a deeper understanding on the interplay of different phenomena taking place during OER [1].In this work, we utilize operando techniques like X-ray Absorption Spectroscopy (XAS) and Surface Enhanced Raman Spectroscopy (SERS) [2], in combination with specifically designed electrochemical protocols to study i) the reconstruction/reactivation of active sites in Ir-based OER catalysts for acidic media (Fig. 1a-c) and Ni-based OER catalysts for alkaline media (Fig. 1d) and ii) the identification of the relevant OER active species which will eventually define the final electrocatalyst performance [3]. We show not only the formation of the active species for OER but also the dynamic operando transformation of the Ir- and Ni-based electrocatalysts before the onset of OER but also their structural transformation due to electro-oxidation during OER, processes that lead to the final active phase.The underlying mechanisms studied via our operando analysis provide fundamental understanding of reaction mechanism but also guidance for the design of efficient OER catalysts optimized for their operation in technical devices.

Enhanced Performance and Durability of Ruddlesden-Popper Oxide Anodes Decorated with Fe Nanoparticles for Direct Ammonia-Fed Solid Oxide Fuel Cells

Direct ammonia-fed solid oxide fuel cells (DA-SOFCs) efficiently convert ammonia into electricity, aligning with the necessary temperatures for thermal decomposition of ammonia. However, challenges such as nitridation of anode metal catalysts and decreased cell durability hinder further development. To address these issues, this study explores the partial substitution of Sr with Ba at the A-site of the Ruddlesden-Popper (RP) structure, enhancing the structure's mixed ionic and electronic conductivity (MIEC). This modification aims to improve ammonia's thermal decomposition and the overall electrochemical performance of SOFCs. Incorporating Ba modifies the RP crystal lattice to facilitate metal nanoparticle exsolution and increase basicity, crucial for enhancing nitrogen recombination and desorption during ammonia decomposition. This adaptation helps maintain active catalyst sites and improves durability against nitridation. The study focuses on in-situ exsolution of Fe nanoparticles (NPs) and partial Ba substitution, both of which enhance not only catalytic and electrochemical performance but also durability under operating conditions.Advanced characterization methods, including X-ray diffraction complemented by Rietveld refinement and high-resolution electron microscopy, elucidate the lattice changes and phase transitions induced by Ba. These modifications promote the exsolution of Fe NPs, pivotal for enhancing electrochemical performance. Electrochemical assessments show that the new Fe NPs exsolved La1.2Sr0.4Ba0.4Mn0.4Fe0.6O4- δ (R-LSBMF) anode material achieves nearly 100% ammonia decomposition conversion at 650oC and sustains this activity over time, demonstrating its durability. The in-situ reduced LSBMF mixed with GDC (Ce0.9Gd0.1O2) as a DA-SOFC anode shows a maximum power density (MPD) of 1.019 W cm-2 and significantly low ohmic resistance (0.154 Ω cm²) at 800 oC.This research advances the understanding of elemental substitution in anode materials and underscores the potential of Ruddlesden-Popper phase perovskites for high-efficiency, durable DA-SOFCs. It also enhances the prospects for ammonia as a viable fuel for SOFCs, driving the technology toward sustainable, eco-friendly energy solutions. Therefore, the outstanding catalytic and durability features of the R-LSBMF anode material open paths for commercializing DA-SOFCs, which is essential for addressing environmental challenges. Figure 1

Electrolyte Effects in Ethanol Electro-Reforming at Anode with Acetaldehyde As Target Product

Introduction The development of the electrolysis hydrogen production process has been vigorously promoted due to the widespread use of hydrogen energy. However, the oxygen produced as a byproduct during this process has not been effectively utilized. Therefore, this research focuses on the production of chemical compounds through organic electrosynthesis in place of oxygen generation as the anode reaction, examining selectivity and reaction rates. Specifically, this study targets the synthesis of acetaldehyde from the oxidation of ethanol. Currently, acetaldehyde is produced from ethylene through the Wacker process, but the synthesis of acetaldehyde from ethanol, which can be derived from biomass, is gaining attention due to concerns over the depletion of fossil resources. The energy losses in electrochemical processes are primarily due to Ohmic losses, requiring high electrolyte concentrations to achieve sufficient ion conductivity. Moreover, the adsorption of electrolyte anions on the catalyst surface can decrease catalytic activity. This study examines the relationship between the pH, anion adsorption, and reaction rate in the electrolytic oxidation reaction of ethanol in acid electrolytes. Experimental A schematic of the experimental setup is shown in Figs. 1 and 2. Platinum electrodes (De Nora Permelec Ltd, JL-510 coating DSE) were placed on silicone gaskets with flow channels, and the gaskets were sandwiched between silicone gaskets, PTFE plates, and stainless-steel endplates. A cation exchange membrane (Chemours, Nafion® NR-212) was placed in the center to separate the reactions at the two electrodes. An electrochemical measurement system (Hokuto Denko, HZ-pro) was used to measure current and solution resistance. In the experiments, sulfuric acid or perchloric acid was used as the electrolyte; solutions containing either ethanol or acetaldehyde were supplied to the anode, while plain sulfuric or perchloric acid solutions were supplied to the cathode. The reaction was performed at room temperature and pressure. High-performance liquid chromatography (Hitachi High-Tech Science, Chromaster®, ion exclusion column GL-C610-S, Hitachi High-Tech Science 5450 RI Detector) was used for product analysis. Results and Discussion The ethanol electro-oxidation reaction is a consecutive reaction in which acetaldehyde is formed and further oxidized to acetic acid. In addition, the parallel reaction of ethanol oxidizing into carbon dioxide also occurs simultaneously. The reaction equations are expressed by Eqs. (1)–(3), and the uncovered fraction of the catalyst active site is expressed as θ v in Table 1. Assuming the reaction mechanism involving Eqs. (1)–(4), the overall reaction rate equations r s1, r s2 and r s3 are expressed in Eqs. (5)–(11).Due to the oxidation of ethanol being a complex reaction, to better understand the entire reaction, the oxidation of acetaldehyde to acetic acid was first investigated using acetaldehyde as the reactant. The relationship between electrolyte concentrations and r s2 at potential differences of 1.2 V are shown in Figs. 3(a) and 3(b). The results shown in Fig. 3(a) indicate that when the concentration of perchloric acid is low, increasing the concentration of the electrolyte significantly enhances the reaction rate, which is believed to be due to improved proton transport. In contrast, as illustrated in Fig. 3(b), the presence of sulfate ions may lead to decrease in reaction rate due to their adsorption.In the ethanol electro-oxidation experiment, the impact of electrolyte concentration on reaction rate (r s1) at 0.6 V and 1.2 V is depicted in Figs. 4(a) and 4(b). At 0.6 V, anion adsorption is minimal, leading to lower OH•σ production from water electrolysis, and increase in r s1 due to enhanced proton transport. Conversely, at 1.2 V, stronger anion adsorption and greater OH•σ formation occur, reducing r s1 despite the positive effect of better proton transport. Fig. 5 illustrates the relationship between ethanol conversion and acetaldehyde selectivity for the two electrolytes. The findings show that acetaldehyde selectivity is higher when using perchloric acid compared to sulfuric acid as the electrolyte. The possible reason is that acetaldehyde and sulfate ions undergo co-adsorption, making acetaldehyde more likely to oxidize into acetic acid, resulting in a lower selectivity of acetaldehyde in sulfuric acid solution than in perchloric acid solution. Conclusions In the electrolytic reaction of ethanol or acetaldehyde, increasing the sulfuric acid concentration decreases the reaction rate. This may be due to the adsorption of sulfate ions occupying the active site of the catalyst. Higher acetaldehyde selectivity is obtained when perchloric acid is used as the electrolyte. The maximum reaction rate was obtained under 0.1 M perchloric acid, influenced by high proton transport and low anion adsorption. The result of this study illustrates that the selection of an appropriate electrolyte and its concentration is also important in optimizing the electrolytic oxidation reaction of ethanol to produce acetaldehyde. Figure 1

(Invited) Treated Perfluorosulfonic Acid Ionomer Layer with Dual Oxygen Transport Pathways for PEMFC Cathode Catalyst Layer

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 with the expected outcome to be higher performance in the transport-controlled region. However, test results show improvement (> 200% increase in peak power)[1] in both kinetic and transport-controlled regions. Further investigation by mathematical modeling and neutron reflectometry shows the treatment affects the CL in two ways. First, the ionomer/gas phase interface in the pores of the CL becomes more hydrophobic. This facilitates less liquid water coverage of the ionomer layer surface and faster water drainage from the CL that results in better performance at high current densities, which is as expected. Second, it affects the microstructures of the ionomer phase and causes it to separate into two regions, a larger more hydrophobic (or less hydrophilic) region with fewer sulfonic acid groups and therefore lower water hydration levels and a smaller less hydrophobic (or more hydrophilic) region with more ionic groups with higher hydration levels. The more hydrophobic region, which facilitates faster liquid water removal from its interface with the gas pores and direct access to the oxygen gas at higher current densities, provides a higher oxygen solubility pathway to the catalyst active sites in CL at both low and high current densities leading to higher fuel cell performance over the whole polarization curve. See image. The ratio of these two regions can be controlled by the treatment process. This presentation will discuss the hydrophobic treatment process and the major findings of this study.References Regis P. Dowd, Yuanchao Li, Trung Van Nguyen, “Controlling the Ionic Polymer/Gas Interface Property of a PEM Fuel Cell Catalyst Layer During Membrane Electrode Assembly Fabrication,” Appl. Electrochem., 50 (10) 993-1006 (2020).Yuanchao 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. Electrochemical Society, 169 114505 (2022). Figure 1

Oxide Encapsulated Ruthenium Oxide Catalysts for Selective Oxygen Evolution in Unbuffered pH Neutral Seawater

Direct seawater electrolysis is a promising approach to producing green hydrogen in water-scarce environments using renewable energy. However, the undesirable chlorine evolution reaction (CER) and hypochlorite evolution reaction (HCER) compete with the desired oxygen evolution reaction (OER) at the anode electrocatalyst. This issue is most pronounced in unbuffered pH neutral solutions due to local acidification resulting from the OER. To overcome this challenge, this study provides a comprehensive evaluation of the use of silicon oxide (SiOx) and titanium oxide (TiOx) nanoscale overlayers coated on metallic ruthenium (Ru) and ruthenium oxide (RuOx) thin film electrodes and their ability to block chloride ions from reaching active sites during operation in unbuffered 0.6 M NaCl electrolyte. Using a combination of (electro)analytical techniques, encapsulated RuOx anodes are shown to effectively suppress Cl- transport to buried catalyst active sites while allowing for the desired OER to occur, leading to increases in OER faradaic efficiency at moderate overpotentials. Evidence for the ability of SiOx overlayers to block Cl- ions from reaching the active buried interface was obtained by monitoring the OH stretching mode of OH adsorbates using in situ Raman spectroscopy. This study also reports trade-offs between the activity, selectivity, and stability of bare and encapsulated Ru and RuOx electrocatalysts, finding that the magnitude of these trade-offs strongly depends on the complex interplay between electrode architecture, material properties, and catalytic performance, especially in unbuffered pH neutral seawater.