Earth-abundant Transition Metals Research Articles

Versatile applications of cobalt and copper complexes of biopolymeric Schiff base ligands derived from chitosan.

In the present study, biopolymeric Schiff base (SB) ligands were synthesized from chitosan and isatin. Consequently, their earth abundant transition metal complexes of cobalt and copper were synthesized. All compounds were extensively characterized using FTIR and UV spectroscopy, thermo-gravimetric (TG) analysis, X-ray powder diffraction (XRD) and FESEM (field emission scanning electron microscopy). The impetus of this study was to explore different applications of the same transition metal complexes, thereby converting them to broad spectrum antimicrobial drugs and to useful chemical catalysts. Thus, these cobalt and copper complexes were applied as anti-bacterial and anti-fungal agents and in reductive degradation of common pollutants. Specifically, chitosan, and all synthesized compounds were investigated against fungal species, namely, Candida and Aspergillus, and bacterial species, like Pseudomonas syringae, Escherichia coli, Staphylococcus aureus and Staphylococcus epidermis. All compounds demonstrated promising antimicrobial activity. Chitosan-modified compounds demonstrated a high antifungal activity against Candida albicans and possessed superior antibacterial action than free chitosan. Additionally, catalytic ability in reductive degradation of common dyes, methylene blue (MEB), Congo red (CR) and methyl orange (MO), was investigated. These dyes were conveniently degraded in presence of metal complexes, whereas neither chitosan nor the Schiff base ligand derived from it could carry out similar reaction.

Operando Nanoscale Characterization Reveals Fe Doping of Ni Oxide Enhances Oxygen Evolution Reaction via Fragmentation and Formation of Dual Active Sites.

Efficient catalytic water splitting demands advanced catalysts to improve the slow kinetics of the oxygen evolution reaction (OER). Earth-abundant transition metal oxides show promising OER activity in alkaline media. However, most experimental information available is either from post-mortem studies or in-situ space-averaged X-ray techniques in the micrometer range. Therefore, the composition of the active centers under operando conditions is still under debate. In this work, we combine nanoscopic and spectroscopic measurements on the hydroxylation of molecular beam epitaxy (MBE)-prepared Ni and NiFe oxides nanoislands with operando local investigations of Ni and NiFe hydroxide electrocatalysts under OER conditions to reveal the nature of the active centers in 2D OER catalysts. Our results reveal that Fe doping increases the active surface area by island fragmentation, and boosts the intrinsic activity by creating optimized active centers consisting of both Ni and Fe atoms. In addition, our findings show that operando characterization at the nanoscale is crucial to reveal the dynamic nature of the interface of 2D catalysts under reaction conditions.

Earth-abundant transition metal complexes in light-emitting electrochemical cells: successes, challenges and perspectives.

Light-emitting electrochemical cells (LECs) are an attractive technology in the field of solid state light devices (SSLDs) as their simple architectures allow the preparation of cost-effective lighting devices. Consequently, low-cost and sustainable emitters are highly desirable. Transition metal complexes are attractive in this field as they have been proved to possess compatible optoelectronic properties. Nowadays, the best emitters are based on platinum and iridium class metals, which is a limitation for industrial production. Due to this concern, researchers have turned their attention to Earth-abundant metal complexes. However, the abundance of these metals should not blind us to a consideration of their cost. Herein, the photophysical properties of the most interesting Earth-abundant metal complexes and their performance in LECs are put into context with respect to their real cost based on their metal precursors, revealing some surprises.

Dehydrogenative Coupling of Alcohols with Hydrazines under Nickel Catalysis.

The development of efficient and robust catalytic systems based on earth-abundant transition metals for fundamentally new transformations is crucial for sustainable chemical synthesis. Herein, an effective and selective Ni-catalyzed dehydrogenative coupling of alcohols with hydrazines with the liberation of ammonia gas is reported. Although several methods were documented for the N-alkylation reaction, the present strategy is conceptually novel, and the reaction proceeds through a pathway involving N-N bond cleavage of phenylhydrazine followed by hydrogen autotransfer. This unprecedented method demonstrates a wide substrate scope, allowing for the synthesis of C-N coupled products from arylhydrazines using various types of alcohols, including aryl, fused aryl, heteroaromatic, cyclic, and aliphatic alcohols, both primary and secondary alcohols. The present catalytic approach was expanded to facilitate selective deuterium incorporation reactions by employing deuterated alcohols at the α-methyl position of the resulting N-alkylated products. It is noteworthy that we have broadened the applicability of the current catalytic systems to facilitate the ketazine synthesis of hydrazine monohydrate by employing secondary alcohols. The reaction utilizes an inexpensive, abundant, and renewable alcohol that serves as both an alkylating and (transfer) hydrogenating agent. Kinetic studies reveal that the reaction rate depends on the concentration of arylhydrazine and the nickel catalyst, following fractional order.

In Situ Unravelling NiOOH Species on Flower-Like NiFeCo LDH/Nb2CTx for Ameliorated Solar-Powered Bifunctional Electrocatalytic Benzyl Alcohol Oxidation Coupled with Hydrogen Evolution.

Developing bifunctional electrocatalysts from earth-abundant first-row transition metals for large-scale hydrogen production through water electrolysis is both promising and challenging. This study presents a ternary layered double hydroxide (LDH) as a bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and benzyl alcohol oxidation (BAOR). The synergy between 2D NiFeCo LDH and non-Ti-based Nb2CTx MXene enhances electrochemical performance. The electrocatalyst achieves excellent results with a low potential of 1.5V versus RHE at 100mAcm⁻2 for BAOR, an overpotential of 320mV at 50mAcm⁻2 for HER, and stability over 100 h. A solar cell-powered HER||BAOR system shows faradaic efficiency of ≈73.92% for benzaldehyde production and solar-to-hydrogen (STH) efficiency of ≈39.67%. In situ Raman analysis identifies the oxyhydroxide group as the real catalytic active site during BAOR. These findings offer valuable insights for linking fundamental research with technological innovation to address global challenges.

Bifunctional heterostructure ZnWO4@ZnO nanocomposite for high-performance electrocatalysis and supercapacitor applications

Earth-abundant transition metal oxides (TMOs) represent a versatile class of electrode materials that excel in energy and environmental applications. Strategically incorporating additional metal oxides to form heterostructures significantly enhances electrical conductivity and cyclic stability, paving the way for better performance in energy storage and conversion technologies. In this study, we developed a ZnWO4@ZnO nanocomposite heterostructure using a straightforward solid-state synthesis method, positioning it as a bifunctional electroactive material for supercapacitor and catalytic applications. Importantly, the heterostructure’s increased surface area allows for more active sites for electrochemical reactions, which can boost current generation. The synergistic interaction between ZnO and ZnWO4 significantly enhances the electrochemical properties of the heterostructure, resulting in an impressive specific capacitance of 363 Fg−1 and exceptional cyclic stability over 10,000 charge–discharge cycles. These results underscore the potential of this material in energy storage and conversion technologies, making it a compelling candidate for high-performance supercapacitor and catalytic applications.

Crystallography of Intermetallic Pt Nanoparticle Catalysts on Engineered Carbon Supports

Platinum-based electrocatalysts represent the state-of-the-art for many fuel cell and electrolyzer applications due to their relatively high activity for both the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR). Due to the high cost of Pt metal, Pt utilization is maximized by dispersing the Pt on a carbon support as nanoparticles, but further improvements to catalyst activity and durability, as well as further cost reductions, are required for commercialization of fuel cell and electrolyzer technologies. Essential to the improvement of such catalysts is the design and preparation of Pt-based crystalline nanostructures, which can enhance the activity and durability of an electrocatalyst without increasing Pt loading. Furthermore, by alloying Pt with other, more earth-abundant transition metals, ordered intermetallic nanoparticles can be prepared which display not only enhanced electrocatalytic properties, but also require less of the expensive Pt metal for fabrication. Here, we crystallographically describe various intermetallic Pt catalysts supported on a new class of carbon materials developed by Pajarito Powder known as the Engineered Catalyst Support (ECS). ECS materials can disperse up to 50% Pt by weight of the catalyst by virtue of the high support surface area (400-900 m2/g), ideal for structural study by bulk crystallographic methods. Through correlation of crystalline Pt structures with electrochemical performance data, structure/function relationships are established to inform the high performance of Pt/ECS catalysts.

Composition-Activity-Stability Relationship Investigation of Trimetallic Pt-Ni-Au Oxygen Reduction Reaction Catalyst

Hydrogen-fuelled proton-exchange membrane fuel cells (PEMFCs) offer a promising path towards zero-emission energy, but their commercialization is hindered by challenges, particularly in the cathode catalysts responsible for the oxygen reduction reaction (ORR). Current catalysts rely heavily on expensive platinum, which degrades quickly in the harsh cathodic environment. Efforts are thus focused on developing cost-effective and stable catalysts. Recent research has shown that alloying platinum with earth-abundant transition metals can reduce costs and improve ORR activity. Bimetallic Pt-M (M=Ni, Cu, Co, Fe, etc.) alloy catalysts, particularly those incorporating gold, have demonstrated superior performance. However, achieving both high activity and long-term stability remains a challenge. Our recent work emphasizes the importance of precise catalyst engineering to optimize both activity and durability, highlighting the need for a balanced alloy structure and compositional profile in Pt–Au catalysts.In this work, a magnetron co-sputtering technique was utilized to introduce a small amount of Au (5, 10, and 20 at%) into Pt50Ni50 alloy. The resulting ternary PtNiAu alloy demonstrated enhanced stability compared to PtNi, as evidenced by reduced platinum and nickel dissolution with increasing Au content, confirmed over a wide potential range up to 1.5 VRHE. On the other hand, at elevated concentrations, Au showed a detrimental effect on the ORR activity. Despite showing lower activity than PtNi, the ternary PtNiAu alloy still displayed superior activity compared to pure Pt. The investigation employed robust characterization methods, including synchrotron radiation photoelectron spectroscopy (SRPES), in-situ scanning flow cell coupled with inductively coupled plasma mass spectrometer (SFC-ICP-MS), and rotating disc electrode (RDE), to probe the composition-activity-stability relationship and identify the optimal Pt-Ni-Au composition meeting both high activity and stability requirements.

PGM-Free Oer Catalyst for Water Splitting – an Interrogation on the Structural Dynamics of Catalyst during Reaction

Green hydrogen production through proton exchange membrane water electrolyzer (PEMWE) offers the advantages of high current density and high H2 purity with low footprint. At present, the platinum group metal (PGM) such as Ir are the catalysts of choice for the oxygen evolution reaction (OER) at PEMWE anode. The high cost and limited reserve of Ir add a significant cost to broad implementation of PEM electrolyzer.Replacing Ir with earth-abundant transition metals could help to reduce the electrolyzer system cost. For PEMWE application, a PGM-free anodic catalyst must be highly active to match the performance of Ir. Furthermore, it must be stable against oxidative acid corrosion. At Argonne, we recently developed a nanofibrous cobalt spinel OER catalyst prepared from cobalt zeolitic methyl-imidazolate framework (Co-ZIF) doped with manganese and lanthanum. [1] A PEMWE containing this catalyst with the anodic loading of ~2.0 mg/cm2 demonstrated a current density of 2A/cm2 at 2.47 volts or 4A/cm2 at 3.00 volts. The catalyst also showed a promising stability under accelerated-stress-test (AST) through voltage cycling as well as galvanostatic tests at different current densities.To better understand the structure-function relationship, we conducted extensive structural characterizations and computational modeling. For example, our high-resolution electron microscopy study showed a catalyst morphology mimicking that of ZIF precursor but composed of cobalt spinel crystallites with an average size of 3.5 nm. The oxygen atoms on the top layer of the spinel surface are in the relaxed mode. X-ray absorption spectroscopy showed strong oxygen deficiencies around cobalt compared to standard spinel reference. Such deficiency became more predominant at higher cell voltage. Contrary to general perception, the cobalt oxidation state actually decreased instead of increasing at the escalating OER potential and fast turnover rate. Accompanying the change of oxidation state, reduction of oxygen coordination number surrounding Co and growth of Debby-Weller factor of Co-O shell were observed, indicating rapid exchange of the lattice oxygen in spinel during OER. On the other hand, no such changes were observed for the atomically dispersed Mn ion in the spinel as the dopant.In this presentation, we will discuss in our detailed findings and offer our perspective on the future research direction for PGM-free OER catalyst for PEM water electrolyzer application. Acknowledgement: This work is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewal Energy, Hydrogen and Fuel Cell Technologies Office, and by Laboratory Directed Research and Development funding of Argonne National Laboratory, provided by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DEAC02-06CH11357. Work performed at the Center for Nanoscale Materials and Advanced Photon Source, both U.S. Department of Energy Office of Science User Facilities, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.[1] “La- and Mn-doped cobalt spinel oxygen evolution catalyst for proton exchange membrane electrolysis” Lina Chong, Guoping Gao, Jianguo Wen, Haixia Li, Haiping Xu, Zach Green, Joshua D. Sugar, A. Jeremy Kropf, Wenqian Xu, Xiao-Min Lin, Hui Xu, Lin-Wang Wang, Di-Jia Liu, Science 380, 609–616 (2023)

Understanding High Voltage Electrolyte Reactivity on Cation-Disordered Rock Salt Cathodes

Li-ion battery demand is expected to increase dramatically to meet rapidly increasing energy storage demands. To address the expense and scarcity of cobalt and nickel used in current layered oxide cathodes, alternative cathode materials that rely on earth-abundant transition metals must be explored. Promising such materials are cation-disordered rocksalt (DRX) oxides, particularly those that are comprised of manganese and titanium, along with lithium excess to allow for high reversible capacities (>300 mAh/g). A substantial fraction of extractable lithium capacity in DRX materials occurs at high voltages, creating high energy density, but also leading to deleterious degradation processes. Recent studies have observed reactivity of the DRX surface when cycled to high voltages: >25% of transition metals migrating out of the cathode and continuous evolution of CO2 after 150 cycles [1]. 13C labeling has identified the carbonate electrolyte as the primary source of the CO2 after the first cycle [2]. This reactivity leads to a sharp increase in impedance and rapid capacity fade [1]. However, the exact cause of high voltage reactivity is still not fully understood for the electrolyte – DRX interface.In this study, we quantify the surface reactivity of select electrolyte – DRX systems using operando gas measurements and inductively coupled plasma – optimal emission spectrometry (ICP-OES). Through this method, we can identify what electrolyte and DRX properties have the largest influence on surface reactivity. To monitor surface reactivity of the electrolyte, differential electrochemical mass spectrometry (DEMS) was used to quantify evolution of CO2 and other gaseous products during cycling. To track the surface reactivity of the DRX, ICP-OES was used to quantify transition metal dissolution. We show that ethylene carbonate oxidation is particularly problematic above 4.4 V, and that processes involving the conductive carbon, as well as Mn and O redox are culpable. The results of this study provide insight into the primary causes of capacity fade in DRX-based batteries, informing future designs of the electrolyte, DRX, and other cathode materials.[1]: Matthew J. Crafton et al 2024 J. Electrochem. Soc. 171 020530[2]: Manuscript in Preparation: Tzu-Yang Huang et al 2024. Chem. Of Mat. (Manuscript ID: cm-2024-007563)

Similarity between oxygen evolution in photosystem II and oxygen reduction in cytochrome c oxidase via proton coupled electron transfers. A unified view of the oxygenic life from four electron oxidation–reduction reactions

Basic concepts and theoretical foundations of broken symmetry (BS) and post BS methods for strongly correlated electron systems (SCES) such as electron-transfer (ET) diradical, multi-center polyradicals with spin frustration are described systematically to elucidate structures, bonding and reactivity of the high-valent transition metal oxo bonds in metalloenzymes: photosystem II (PSII) and cytochrome c oxidase (CcO). BS hybrid DFT (HDFT) and DLPNO coupled-cluster (CC) SD(T0) computations are performed to elucidate electronic and spin states of CaMn4Ox cluster in the key step for oxygen evolution, namely S4 [S3 with Mn(IV) = O + Tyr161-O radical] state of PSII and PM [Fe(IV) = O + HO-Cu(II) + Tyr161-O radical] step for oxygen reduction in CcO. The cycle of water oxidation catalyzed by the CaMn4Ox cluster in PSII and the cycle of oxygen reduction catalyzed by the CuA-Fea-Fea3-CuB cluster in CcO are examined on the theoretical grounds, elucidating similar concerted and/or stepwise proton transfer coupled electron transfer (PT-ET) processes for the four-electron oxidation in PSII and four-electron reduction in CcO. Interplay between theory and experiments have revealed that three electrons in the metal sites and one electron in tyrosine radical site are characteristic for PT-ET in these biological redox reaction systems, indicating no necessity of harmful Mn(V) = O and Fe(V) = O bonds with strong oxyl-radical character. Implications of the computational results are discussed in relation to design of artificial systems consisted of earth abundant transition metals for water oxidation.Graphical abstract

Nanostructured NiMoO4 as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Electrocatalysts derived from earth-abundant transition metals offer a viable alternative to noble metals for water electrolysis, yet they often suffer from poor catalytic behaviour and limited lifespan. In this study, nanostructured nickel molybdate on nickel foam (NiMoO4/NF) were synthesized via a straightforward hydrothermal process at three different durations (6, 12, and 24 h) to assess their oxygen evolution reaction (OER) performance. The electrodes, specifically NiMoO4-6h, NiMoO4-12h, and NiMoO4-24h, demonstrated significant OER activity in 1.0 M KOH solution, achieving overpotentials of 315 mV, 290 mV and 320 mV for respectively. Notably, the NiMoO4-12h electrode showed an exceptional stability, with only a 1.28% activity decrease after 200 hours at a current density of 10 mA cm-2. This study presents a novel approach to enhancing the electrocatalytic efficiency of these catalysts through optimizing their electrical conductivity, active surface sites, and surface reaction dynamics. Figure 1 (a) LSV curves at 2 mV s-1 and (b) Tafel plot of NiMoO4 catalysts. Figure 1

Using Theory to Understand the Origins of the High Activity of Earth-Abundant Transition Metal Oxide Electrocatalysts for the Hydrogen and Oxygen Evolution Reactions in Alkaline Media

A global hydrogen economy (GHE) was envisioned by Haldane in 1923 but has only recently captured wide attention. As the movement toward a GHE accelerates, the supply vs. demand of precious metals such as platinum and iridium will inevitably force their prices skyward. In order to ensure the future of the GHE, it is crucial to intensify the R&D of earth-abundant element-based electrocatalysts. We have recently focused on electrocatalysts for the oxygen evolution and hydrogen evolution reactions (OER, HER) based on Fe, Co, Ni and Mo-containing oxides.1-3 The use of density functional theory (DFT) calculations has enabled us to understand more deeply the origins of high catalytic activity.From OER experimental results, we have found that the activity is higher for Ni-Co oxides with lower structural order.1 This was explained by calculations indicating that the edges of NiOOH sheets are the active sites, at which the rate-determining step M-O + MOH  M-OOH-M is facilitated by the favorable geometry, in which the initial ) O—O distance is significantly shorter than that in the ideal structure (Fig. 1A). The presence of Co ("b" structure) further lowers the activation energy, to 0.15 eV. With the addition of Mo to NixCo1-xOOH, the rds M-O + M-O  M-O-O-M at the layer edges was found to become spontaneous, due to the electron-withdrawing effect of Mo.2 However, it was found that Mo slowly leached out of the structure during actual long-term operation. Ni-Fe oxide was found to be much more stable, and the corresponding DFT calculations showed that the activation energy for the M-O + M-OH  M-OOH-M step was lowered to 0.042 eV.3 In our work on the HER with Ni-Fe alloy/Ni-Fe oxide, we found experimentally that the activity was highest when the alloy was present in contact with a more crystalline form of the oxide.3 The DFT calculations showed that it is necessary to consider both the water dissociation step on the surface of the NixFe1-x(OH)2 sheets and the transfer of a proton to a metallic Ni-Fe alloy particle, on which two adsorbed hydrogens combine to produce H2 (Fig. 1B). This mechanism, which is similar to the bifunctional mechanism proposed by Markovic and coworkers for Pt/NiO,4 we have termed "reverse spillover."Thus, through the combination of experiment and theory, we are developing an understanding of how further increases in electrocatalytic activity for the OER and HER can be achieved with earth-abundant element-based materials.AcknowledgmentsThis work was partially based on results obtained from project JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan and a JSPS grant, KAKENHI (23H02059).References G. Shi, et al., ACS Catal., 12, 14209 (2022).G. Shi, et al., ACS Appl. Energy Mater., 6, 10742 (2023).G. Shi, et al., ACS Omega, 8, 13068 (2023).Z. Zeng, et al., Nature Energy, 2, 17070 (2017). Figure 1. (A) Reaction profile for the rate-determining step M-O + M-OH  M-O-OH-M on defective NixCo1-xOOH sheets with (a) only Ni and (b) Ni and Co in the active site (taken from Ref 1). (B) Reverse spillover reaction in which a proton is transferred from a water molecule at the surface of the Ni(OH)2 sheet to the Ni7Fe cluster that has a high coverage of H, from which H2 can subsequently desorb (taken from Ref. 3). Figure 1

Iron-Catalyzed sp3 C-H Alkylation of Fluorene with Primary and Secondary Alcohols: A Borrowing Hydrogen Approach.

The utilization of earth-abundant, cheap, and nontoxic transition metals in important catalytic transformations is essential for sustainable development, and iron has gained significant attention as the most abundant transition metal. A mixture of FeCl2 (3 mol %), phenanthroline (6 mol %), and KOtBu (0.4 eqivalent) was used as an effective catalyst for the sp3 C-H alkylation of fluorene using alcohol as a nonhazardous alkylating partner, and eco-friendly water was formed as the only byproduct. The substrate scope includes a wide range of substituted fluorenes and substituted benzyl alcohols. The reaction is equally effective with challenging secondary alcohols and unactivated aliphatic alcohols. Selective mono-C9-alkylation of fluorenes with alcohols yielded the corresponding products in good isolated yields. Various postfunctionalizations of C-9 alkylated fluorene products were performed to establish the practical utility of this catalytic alkylation. Control experiments suggested a homogeneous reaction path involving borrowing hydrogen mechanism with the formation and subsequent reduction of 9-alkylidene fluorene intermediate.

Influence of Annealing Temperature on the OER Activity of NiO(111) Nanosheets Prepared via Microwave and Solvothermal Synthesis Approaches.

Earth-abundant transition metal oxides are promising alternatives to precious metal oxides as electrocatalysts for the oxygen evolution reaction (OER) and are intensively investigated for alkaline water electrolysis. OER electrocatalysis, like most other catalytic reactions, is surface-initiated, and the catalyst performance is fundamentally determined by the surface properties. Most transition metal oxide catalysts show OER activities that depend on the predominantly exposed crystal facets/surface structure. Therefore, the design of synthetic strategies to obtain the most active crystal facets is of significant research interest. In this work, rock salt NiO OER catalysts with (111) predominantly exposed facets were synthesized by a solvothermal (ST) method either heated under supercritical or microwave-assisted (MW) conditions. Particular emphasis was placed on the influence of the post annealing temperature on the structural configuration and OER activity to compare their catalytic performances. The as-prepared electrocatalysts are pure α-Ni hydroxides which were converted to rock salt NiO (111) nanosheets with hexagonal pores after heat treatment at different temperatures. The OER activity of the electrodes has been evaluated in 0.1 M KOH using geometric and intrinsic current densities via normalization by the disk area and BET area, respectively. The lowest overpotential at a geometric current density of 10 mA/cm2 is found for samples pretreated by heating between 400 and 500 °C with a catalyst loading of 115 μg/cm2. Despite the very similar nature of the catalysts obtained from the two methods, the ST electrodes show a higher geometric and intrinsic current density for 500 °C pretreatment. The MW electrodes, however, achieve an optimal geometric current density for 400 °C pretreatment, while their intrinsic current density requires pretreatment over 600 °C. Interestingly, pretreated electrodes show consistently higher OER activity as compared to the poorly crystalline/less ordered hydroxide as-prepared electrocatalysts. Thus, our study highlights the importance of the synthesis method and pretreatment at an optimal temperature.

DFT analysis of the concerted metalation-deprotonation in earth-abundant 3d-transition-metal mediated C–H activations

Methane activation and functionalization under catalytic conditions remains a challenge that must be addressed to make this abundant alkane, the primary component of natural gas, into a more useful resource. One possible method of methane activation is concerted metalation-deprotonation (CMD), which thus far has been largely limited to precious metals and more reactive substrates. In this DFT study, CMD activation of methane is assessed employing more earth-abundant 3d transition metal complexes to assess the effects of metal, ligands, etc. upon the kinetics and thermodynamics of methane C–H activation via CMD mechanisms. Key findings from this study reveal the strong influence spin states as well as ligand modification have on the activation energy barriers. Moreover, an unexpected observation pertaining to ligand modification was seen where the acetate ligand exhibited higher computed free energy barriers compared to the trifluoroacetate ligand. Although acetate is more basic than trifluoroacetate, the ligand directing effects ultimately had a greater influence on the thermodynamic control of the CMD mechanism being studied here.

Redox-mediated synthesis of Cu2O/CuO/Mn3O4/C quaternary nanocomposites as an efficient electrode material for oxygen reduction reaction and supercapacitor application

Earth-abundant transition metal oxides (TMOs) hold significant promise as electroactive materials in various electrochemical energy conversion and storage applications, offering economic and environmental advantages over their less abundant counterparts. In this work, a simple and cost-effective redox-mediated reaction strategy under hydrothermal conditions has been adopted to synthesize the quaternary nanocomposites Cu2O/CuO/Mn3O4/C with variable amounts of carbon. The synthesized nanocomposites have been characterized using various analysis techniques, including powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Brunauer–Emmett–Teller (BET). The synthesized COM5 nanocomposite (Cu2O/CuO/Mn3O4/C-50), when used as an electrocatalyst for the oxygen reduction reaction (ORR), demonstrates a good limiting current density (JL), half-wave potential (E1/2), and onset potential (Eonset) of −5.50 mA/cm2, 0.75 V, and 0.95 V, respectively, as per the polarization curve. The COM5 nanocomposite exhibits a four-electron transfer mechanism, calculated using the Koutecky-Levich (K-L) equation. In an O2-saturated 0.1M KOH solution, the COM5 nanocomposite has shown a superior relative current durability of 84.46% over 14,000 s compared to the commercially available 10 wt% Pt/C, indicating its potential application in the ORR. However, for supercapacitor applications, the COM3 nanocomposite (Cu2O/CuO/Mn3O4/C-20) as active electrode material in galvanic charge-discharge (GCD) study shows superior performance (201 F/g at 1 A/g) compared to the COM2 nanocomposite (117 F/g at 1 A/g) in neutral aqueous electrolyte, possibly due to the lower charge transfer resistance (Rct) of 24.04 Ω compared to COM2 (34.63 Ω). In two-electrode studies, the COM3 nanocomposite exhibits a good energy density of 24.19 Wh/kg at 1 A/g and a 4.7 kW/kg power density at 5 A/g. Additionally, the COM3 nanocomposite shows excellent long-term durability (74% capacitance retention) at the current density of 5 A/g for 8000 cycles. The electrochemical findings indicate that the COM3 nanocomposite stands out as a superior electrode material for supercapacitors, while the COM5 nanocomposite proves to be an effective electrocatalyst for the oxygen reduction reaction.

Cobalt-Catalyzed Divergence in C(sp3)-H Functionalization of 9H-Fluorene: A Streamlined Approach Utilizing Alcohols.

Sustainable chemical production demands the creation of innovative catalysts and catalytic technologies. While the development of coherent and robust catalytic systems using earth-abundant transition metals is essential, it remains a significant challenge. Herein, an expedient divergence strategy for tandem dehydrogenative C(sp3)-H alkylation and cyclization reactions of 9H-fluorene using a newly developed N,N-bidentate cobalt catalytic system is developed. This method capitalizes on the use of abundant and readily accessible alcohol. Demonstrating wide-ranging applicability, the catalytic protocol successfully integrated a diverse array of fluorenes and alcohols. This includes benzylic, heteroaromatic, and aliphatic primary and secondary alcohols, amassing a total of 75 distinct examples. When applied to sterically bulky alcohols, the reaction preferentially undergoes alkenylation, yielding a tetrasubstituted olefin as the main product. In the case of diols, the expected outcome is Dual-fluorescence at both terminal positions. This process leads to difluorination, followed by a cyclization step, culminating in the formation of a relatively unprecedented spiro compound. The scalability of this method has been validated through gram-scale synthesis. Control experiments have shed light on the reaction mechanism, indicating that it progresses through an unsaturated intermediate and adheres to the borrowing hydrogen pathway.

Nanostructured NiMoO4 as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Electrocatalysts derived from earth-abundant transition metals offer a viable alternative to noble metals for water electrolysis, yet they often suffer from poor catalytic behaviour and limited lifespan. In this study, nanostructured nickel molybdate on nickel foam (NiMoO4/NF) were synthesized via a straightforward hydrothermal process at three different durations (6, 12, and 24 h) to assess their oxygen evolution reaction (OER) performance. The electrodes, specifically NiMoO4-6h, NiMoO4-12h, and NiMoO4-24h, demonstrated significant OER activity in 1.0 M KOH solution, achieving overpotentials of 315 mV, 290 mV and 320 mV for respectively. Notably, the NiMoO4-12h electrode showed an exceptional stability, with only a 1.28% activity decrease after 200 hours at a current density of 10 mA cm-2. This study presents a novel approach to enhancing the electrocatalytic efficiency of these catalysts through optimizing their electrical conductivity, active surface sites, and surface reaction dynamics.

Nanostructured NiMoO4 as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Electrocatalysts derived from earth-abundant transition metals offer a viable alternative to noble metals for water electrolysis, yet they often suffer from poor catalytic behaviour and limited lifespan. In this study, nanostructured nickel molybdate on nickel foam (NiMoO4/NF) were synthesized via a straightforward hydrothermal process at three different durations (6, 12, and 24 h) to assess their oxygen evolution reaction (OER) performance. The electrodes, specifically NiMoO4-6h, NiMoO4-12h, and NiMoO4-24h, demonstrated significant OER activity in 1.0 M KOH solution, achieving overpotentials of 315 mV, 290 mV and 320 mV for respectively. Notably, the NiMoO4-12h electrode showed an exceptional stability, with only a 1.28% activity decrease after 200 hours at a current density of 10 mA cm-2. This study presents a novel approach to enhancing the electrocatalytic efficiency of these catalysts through optimizing their electrical conductivity, active surface sites, and surface reaction dynamics.