Reduction Reaction Research Articles

Revealing Crucial Influences of Boron Support on Regulating Geometric and Electronic Structures of 3D Catalyst for Hydrogen Evolution and Oxygen Reduction Reactions

Revealing Crucial Influences of Boron Support on Regulating Geometric and Electronic Structures of 3D Catalyst for Hydrogen Evolution and Oxygen Reduction Reactions

Exploring the Active Site and Catalytic Activity of N-Coordinated Ni2 Dual-Atom Catalysts for Oxygen Reduction Reaction

Exploring the Active Site and Catalytic Activity of N-Coordinated Ni₂ Dual-Atom Catalysts for Oxygen Reduction Reaction

Effect of the Electrolyte on the Oxygen Reduction Reaction with PCN‐224(Co)

Electrocatalysis in metal‐organic frameworks is an interplay between the diffusion of charges, the intrinsic catalytic rate, and the mass‐transport of reactants through the pores. Here a systematic study is carried out to investigate the role of the electrolyte nature and concentration on the oxygen reduction reaction (ORR) with the PCN‐224(Co) MOF in aqueous electrolyte. It was found that the ORR activity is slightly influenced by the nature of the ions in solution, providing that the ionic strength is high enough to minimize the resistivity during the measurement. The ORR activity was found to be 1.3–1.5 times lower in lithium acetate compared to sodium acetate, while the ORR activity in cesium acetate was 1.3–1.6 times higher compared to the activity in sodium acetate. Moreover, there was no dependency found of the ORR catalysis on the size of the anion, buffer concentration, or oxygen concentration. These findings suggest that ORR catalysis in PCN‐224(Co) is limited by the intrinsic ORR rate at the active site rather than charge transport through the porous structure or substrate transport in the pores. Therefore, optimization of ORR catalysis with this MOF might be achieved by the optimization of the electronics at the cobalt active site.

Mesoporous Nitrogen-Doped Carbon Support from ZIF-8 for Pt Catalysts in Oxygen Reduction Reaction

Zeolitic imidazolate framework-8 (ZIF-8) has been extensively studied as a precursor for nitrogen-doped carbon (NC) materials due to its high surface area, tunable porosity, and adjustable nitrogen content. However, the intrinsic microporous structure of the ZIF-8 limits mass transport and accessibility of reactants to active sites, reducing its effectiveness in electrochemical applications. In this study, a soft templating approach using a triblock copolymer was used to prepare mesoporous ZIF-8-derived NC (Meso-ZIF-NC) samples. The hierarchical porous structure was investigated by varying the ratios of Pluronic F-127, NaClO4, and toluene. The resulting Meso-ZIF-NC exhibited widespread pore size distribution with an enhanced mesopore (2–50 nm) volume according to the composition of the reaction mixtures. Pt nanoparticles were uniformly dispersed on the Meso-ZIF-NC to form Pt/Meso-ZIF-NC catalysts, which presented a high electrochemical surface area and improved oxygen reduction reaction activity. The study highlights the important role of mesopore structure and nitrogen doping in enhancing catalytic performance, providing a pathway for advanced fuel cell catalyst design.

Recent advances on support materials for enhanced Pt-based catalysts: applications in oxygen reduction reactions for electrochemical energy storage

Abstract As the demand for sustainable energy solutions grows, developing efficient energy conversion and storage technologies, such as fuel cells and metal-air batteries, is vital. Oxygen Reduction Reaction (ORR) is a significant limitation in electrochemical systems due to its slower kinetics. Although Pt-based catalysts are commonly used to address this challenge, their high cost and suboptimal performance remain significant obstacles to further development. This review offers a comprehensive overview of advanced support materials aimed at improving the efficiency, durability, and cost-effectiveness of Pt-based catalysts. By examining a range of materials, including mesoporous carbon, graphene, carbon nanotubes, and metal oxides, the review clarifies the relationship between the structural properties of these supports and their influence on ORR performance. Additionally, it discusses the fundamental characteristics of these materials, their practical applications in fuel cells, and explores potential solutions and future directions for optimizing Pt-based catalysts to advance sustainable energy conversion technologies. Future research could focus on nano-engineering and composite material development to unlock the full potential of Pt-based catalysts, significantly enhancing their economic viability and performance in energy applications.

Single-atom vs. single-superatom as catalysts for ammonia production.

A new class of single-superatom catalyst (TiO, ZrO, and WC) supported on graphene is shown to outperform the stability and activity of their corresponding single-atom catalysts (Ni, Pd and Pt) for the electrochemical nitrogen reduction reaction. The results based on density functional theory point to a paradigm shift in catalyst design.

Titanium Dioxide and Photocatalytic CO2 Reduction: A Detailed Review of the Current Status and Future Prospects

A significant amount of carbon dioxide is released into the atmosphere as a result of the extensive usage of fossil fuels. The photocatalytic reduction and conversion of CO2 under visible light into alternative renewable solar fuels or other oxygenated products (methane, formaldehyde, methanol, and formic acid) are practical and efficient methods for reducing atmospheric carbon pollution. Functional materials containing titanium dioxide (TiO2) have attracted significant interest for the photocatalytic reduction of CO2. In this direction, many studies have been conducted in recent years, especially on solar energy harvesting and the charge separation, adsorption, activation, and reduction of CO2 on enhanced TiO2. Recent studies have shown that brookite TiO2 (BT) was the most active photocatalyst, followed by rutile and anatase. Therefore, this study aims to review in detail the recent advances in the development of selective and active catalysts for photocatalytic CO2 reduction using titanium dioxide with a brookite structure. This review evaluates the most common methods for obtaining BT. It discusses various engineered strategies, including doping with metallic or non-metallic heteroatoms, addition of a co-catalyst, formation of heterojunctions, and other algorithms to improve the CO2 reduction mechanism. The influence of another phase and crystal facets on the photocatalytic CO2 reduction reaction are discussed in detail. The problems associated with BT-based photocatalysts, namely, their modest visible-light absorption, slow interfacial charge separation, and poor surface catalytic dynamics, are further discussed, along with possible solutions. To stimulate additional research in this field, the difficulties and potential advantages of photocatalytic CO2 conversion methods are discussed.

Regulative Fe‐3d Orbitals via Lying‐Down Conformation of Metalorganic Molecules‐Axially Coordinated MXene for Rechargeable Zn–Air Batteries

AbstractA bifunctional electrocatalyst is developed, exhibiting high catalytic activity and reversibility for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through a regulative Fe d‐orbital engineering strategy. In this strategy, iron phthalocyanine organic molecule (FeOM) crystals are axially coordinated onto multilayer Mo2CTx MXene (FeOM‐Mo2CTx), adopting a lying‐down conformation. This hybridization fosters unique electronic guest–host interactions, with FeOM donating charge to Mo2CTx via Fe−O bonding, leading to symmetry breaking in electronic distribution and modified delocalization of Fe‐3d charge, accompanied by a Fe(II) spin‐state transition. These transformations enhance the adsorption and desorption toward oxygenated intermediates, optimizing the *OOH−*O transition to boost the reversibility of ORR and OER kinetics. The FeOM‐Mo2CTx exhibits a favorable ORR half‐wave potential of 0.961 V and a minimal OER overpotential of 349 mV at 10 mA cm−2 in 1.0 m KOH. The assembled aqueous zinc‐air battery (ZAB) achieves a peak power density of 155.3 mW cm−2 and exceptional charge–discharge durability over 1500 h, outperforming a conventional (Pt/C + RuO2) system. Overall, the findings underscore the significance of electronic structural engineering of FeOM with Mo2CTx, paving the way for innovative air cathodes in the development of rechargeable ZABs with enhanced performance and cost‐effectiveness.

Oxygen Reduction Reaction Catalysts for Zinc-Air Batteries Featuring Single Cobalt Atoms in a Nitrogen-Doped 3D-Interconnected Porous Graphene Framework.

Single-atom catalysts (SACs) with high activity and efficient atom utilization for oxygen reduction reactions (ORRs) are imperative for rechargeable Zinc-air batteries (ZABs). However, it is still a prominent challenge to construct a noble-metal-free SAC with low cost but high efficiency. Herein, a novel nitrogen-doped graphene (NrGO) based SAC, immobilized with atomically dispersed single cobalt (Co) atoms (Co-NrGO-SAC), is reported for ORRs. In this 3D NrGO, the Co-N4 sites endow high-efficiency ORR activity, and the 3D-interconnected porous architectures of NrGOs guarantee numberous active sites accessibility. Compared to commercial Pt/C catalyst (≈5.8mA cm-2), as-prepared Co-NrGO-SACs presents considerable limiting current density of ≈5.9mA cm-2, prominent half-wave potential of ≈0.84V, onset potential of ≈1.05V, and as well as superior methanol resistance. Particularly, ZABs with Co-NrGO-SACs deliver remarkable power density (≈240mW cm-2), super durability of over 233h at 5mA cm-2, outperforming noble-metal-based benchmarks. This work provides an effective noble-metal free carbon-based SAC nano-engineering for superdurable ZABs.

Tuning the electronic structure and SMSI by integrating trimetallic sites with defective ceria for the CO2 reduction reaction

Heterogeneous catalysts have emerged as a potential key for closing the carbon cycle by converting carbon dioxide (CO 2 ) into value-added chemicals. In this work, we report a highly active and stable ceria (CeO 2 )-based electronically tuned trimetallic catalyst for CO 2 to CO conversion. A unique distribution of electron density between the defective ceria support and the trimetallic nanoparticles (of Ni, Cu, Zn) was established by creating the strong metal support interaction (SMSI) between them. The catalyst showed CO productivity of 49,279 mmol g −1 h −1 at 650 °C. CO selectivity up to 99% and excellent stability (rate remained unchanged even after 100 h) stemmed from the synergistic interactions among Ni-Cu-Zn sites and their SMSI with the defective ceria support. High-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) confirmed this SMSI, further corroborated by in situ electron energy loss spectroscopy (EELS) and density functional theory (DFT) simulations. The in situ studies (HERFD-XAS & EELS) indicated the key role of oxygen vacancies of defective CeO 2 during catalysis. The in situ transmission electron microscopy (TEM) imaging under catalytic conditions visualized the movement and growth of active trimetallic sites, which completely stopped once SMSI was established. In situ FTIR (supported by DFT) provided a molecular-level understanding of the formation of various reaction intermediates and their conversion into products, which followed a complex coupling of direct dissociation and redox pathway assisted by hydrogen, simultaneously on different active sites. Thus, sophisticated manipulation of electronic properties of trimetallic sites and defect dynamics significantly enhanced catalytic performance during CO 2 to CO conversion.

Mesoporous Boron-Doped Carbon with Curved B4C Active Sites for Highly Efficient H2O2 Electrosynthesis in Neutral Media and Air-Supplied Environments.

Hydrogen peroxide (H2O2) electrosynthesis via the 2e- oxygen reduction reaction (ORR) is considered as a cost-effective and safe alternative to the energy-intensive anthraquinone process. However, in more practical environments, namely, the use of neutral media and air-fed cathode environments, slow ORR kinetics and insufficient oxygen supply pose significant challenges to efficient H2O2 production at high current densities. In this work, mesoporous B-doped carbons with novel curved B4C active sites, synthesized via a carbon dioxide (CO2) reduction using a pore-former agent, to simultaneously achieve excellent 2e- ORR activity and improved mass transfer properties are introduced. Through a combination of experimental analysis and theoretical calculations, it is confirmed that the curved B4C configuration, formed by mesopores in the carbon, demonstrates superior selectivity and activity for 2e- ORR due to its weaker interaction with *OOH intermediates compared to planar B4C in neutral media. Moreover, the mesopores facilitate oxygen supply and suppress the hydrogen evolution reaction, achieving a Faradaic efficiency of 86.2% at 150mA cm-2 under air-supplied conditions, along with an impressive O2 utilization efficiency of 93.6%. This approach will provide a route to catalyst design for efficient H2O2 electrosynthesis in a practical environment.

Progress in the Application of PtCo Alloy Catalysts in Oxygen Reduction Reactions for Fuel Cells

Proton Exchange Membrane Fuel Cells (PEMFCs) are considered an effective way to address energy shortages and environmental pollution due to their high efficiency, low-temperature operation, and environmental friendliness. However, the oxygen reduction reaction (ORR) at the cathode in PEMFCs is very slow and needs rare and expensive Pt-based catalysts, which limits their commercialization process. To reduce costs while maintaining efficient catalytic performance, researchers have developed various technological strategies, among which PtCo alloy catalysts have garnered widespread attention due to their excellent ORR catalytic performance. This article reviews the latest progress and current status of PtCo alloy catalysts in PEMFC oxygen reduction catalysis, discusses the impact of catalyst component control, particle size regulation, crystal face regulation, doping, and other regulatory strategies on the catalytic activity of fuel cells, and provides a detailed introduction to the most promising PtCo alloy structures, such as polyhedra, core-shell, nanoframes, and ordered intermetallic structures. At the same time, the research on catalyst supports is discussed, and the challenges and future prospects of PtCo alloy catalysts in their applications are pointed out.

Graphene Quantum Dot‐Modified Mn0.2Cd0.8S for Efficient Overall Photosynthesis of H2O2

AbstractThe photosynthesis of hydrogen peroxide (H2O2) via the selective two‐electron oxygen reduction reaction (ORR) is emerging as a promising method for producing this important chemical. However, the reliance on sacrificial agents has limited the practical application of many photocatalysts. Herein, nitrogen‐doped graphene quantum dots (NGQDs) are loaded onto the surface of MnxCd1‐xS solid solution nanowires to enable overall H2O2 photosynthesis in pure water under an air atmosphere. The optimized Mn0.2Cd0.8S/NGQDs (M0.2NG5) composite achieves a high yield of 6885 µmol g−1 h−1, which is 10.4 times and 4.5 times higher than that of CdS (661 µmol g−1 h−1) and Mn0.2Cd0.8S (1522 µmol g−1 h−1), respectively. The NGQDs act as co‐catalysts, enhancing the conductivity of the system. The strong electronegativity and polarity of the incorporated nitrogen and functional groups on the NGQDs edges enhance the ability of carbon atoms to activate O2 into ·O2−. The mechanism of H2O2 photosynthesis is investigated using in situ Fourier transform infrared spectroscopy, intermediate trapping experiments, and theoretical calculations. This work offers new insights into the design of non‐noble metal co‐catalyst‐modified photocatalysts for sacrificial‐agent‐free H2O2 production.

Conventional versus Unconventional Oxygen Reduction Reaction Intermediates on Single Atom Catalysts.

The oxygen reduction reaction (ORR) stands as a pivotal process in electrochemistry, finding applications in various energy conversion technologies such as fuel cells, metal-air batteries, and chlor-alkali electrolyzers. Hereby, a comprehensive density functional theory (DFT) investigation is presented into the proposed conventional and unconventional ORR mechanisms using single-atom catalysts (SACs) supported on nitrogen-doped graphene (NG) as model systems. Several reaction intermediates have been identified that appear to be more stable than the ones postulated in the conventional mechanism, which follows the *OOH, *O, and *OH intermediates. This finding particularly holds for adsorbed *O2, which can have different adsorption geometries, ranging from η1Ο2 or η2Ο2 superoxo complexes as well as sin and anti complexes, with the two O-related ligands binding on the same or opposite sides, respectively. In the case of M@NG (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Pt), the ORR follows these unconventional *O2 intermediates, whereas for Cr@NG and Cu@NG classical and unconventional *O2 intermediates compete. We approximate the electrocatalytic activity using the concept of the thermodynamic overpotential and demonstrate that the conventional mechanism gives rise to a smaller overpotential compared to mechanisms following unconventional intermediates during the four proton-coupled electron transfer steps. Our trend study indicates that transition metals with fewer d electrons reveal smaller electrocatalytic activity due to a larger thermodynamic overpotential. Among the investigated SAC systems, Co emerges as a promising candidate, with thermodynamic overpotential and limiting potential values of 0.38 and 0.85 V vs the standard hydrogen electrode, respectively, with the conventional mechanism being favored, and with Cu appearing as the second-best candidate.

Ni-Catalyzed Enantioselective Desymmetrization: Development of Divergent Acyl and Decarbonylative Cross-Coupling Reactions.

Ni-catalyzed asymmetric reductive cross-coupling reactions provide rapid and modular access to enantioenriched building blocks from simple electrophile precursors. Reductive coupling reactions that can diverge through a common organometallic intermediate to two distinct families of enantioenriched products are particularly versatile but underdeveloped. Here, we describe the development of a bis(oxazoline) ligand that enables the desymmetrization of meso-anhydrides. When secondary benzylic electrophiles are employed, doubly stereoselective acyl cross-coupling proceeds to give ketone products with catalyst control over three newly formed stereogenic centers. Alternatively, the use of primary alkyl halides in the presence of an additional halogen atom transfer catalyst results in decarbonylative alkylation to give enantioenriched β-alkyl acids. Analysis of reaction rates for a range of both catalysts and substrates supports the notion that tuning the different electrophile activation steps with the two catalysts is required for enhanced reaction performance. These studies illustrate how reaction design can diverge a common Ni-acyl intermediate to either acyl or decarbonylative coupling products and highlight how dual ligand systems can be used to engage unactivated alkyl halides in Ni-catalyzed asymmetric reductive coupling.

In Situ Spectroscopic Probing of the Hydroxylamine Pathway of Electrocatalytic Nitrate Reduction on Iron-Oxy-Hydroxide.

Crystalline γ-FeO(OH) dominantly possessing ─OH terminals (𝛾-FeO(OH)c), polycrystalline γ-FeO(OH) containing multiple ─O, ─OH, and Fe terminals (𝛾-FeO(OH)pc), and α-Fe2O3 majorly containing ─O surface terminals are used as electrocatalysts to study the effect of surface terminals on electrocatalytic nitrate reduction reaction (eNO3RR) selectivity and stabilization of reaction intermediates. Brunauer-Emmett-Teller analysis and electrochemically determined surface area suggest a high active surface area of 117.79 m2 g-1 (ECSA: 0.211 cm2) for 𝛾-FeO(OH)c maximizing the surface accessibility for nitrate adsorption and exhibiting selective eNO3RR to NH3 at pH 7 with a yield rate 18.326mg h-1 cm-2, >85% Faradaic efficiency (FE), and at least nine-times catalyst-recyclability. 15N- and D-labeling combined with in situ IR and Raman studies validate the adsorption of nitrate ions on the ─OH terminals of 𝛾-FeO(OH)c and the generation of nitrite and hydroxyl amine as eNO3RR intermediates. A kinetic isotope effect (KIE) value of 2.1 indicates H2O as the proton source and proton-coupled electron transfer as the rate-limiting step. The rotating-ring disk electrochemical (RRDE) study and subsequent Koutecký-Levich analysis reveal the electron-transfer rate constant (k) for the 2e- reduction of nitrate to nitrite is 5.7 × 10-6cm s-1. This study provides direct evidence of the hydroxyl amine formation as the dominant pathway of eNO3RR on γ-FeO(OH).

Smart Flow Micro‐Reaction Device Integrated with Oxygen Reduction Catalysts for Gaseous Electrochemiluminescence Sensing

AbstractThe sensitive detection of low‐concentration gases has significant implications for environmental monitoring, clinical diagnosis, and other fields of scientific inquiry. Electrochemiluminescence (ECL) is a widely accepted analytical technique known for its high sensitivity, precision, and minimal background interference. Nevertheless, it has rarely been documented in the context of gas‐oriented sensing. This study presents an innovative paradigm for gas sensing, which integrates oxygen reduction reactions (ORR) and a gas diffusion electrode (GDE) into a gas flow micro‐reaction device. The integration aims to optimize mass transfer, ensure adequate electrochemical contact, facilitate efficient electron transfer, and ultimately enhance ECL emission. The viability of this effective in situ gas sensing strategy under mild conditions without pre‐treatments is substantiated by experimental and model calculation evidence. This homemade micro‐reaction device enables the efficient quantification of formaldehyde with a limit of determination (LOD) as low as 12.7 ppb and paves the way for universal gaseous ECL sensing.

Revealing the Potential-Dependent Rate-Determining Step of Oxygen Reduction Reaction on Single-Atom Catalysts.

Single-atom catalysts (SACs) have attracted widespread attention due to their potential to replace platinum-based catalysts in achieving efficient oxygen reduction reaction (ORR), yet the rational optimization of SACs remains challenging due to their elusive reaction mechanisms. Herein, by employing ab initio molecular dynamics simulations and a thermodynamic integration method, we have constructed the potential-dependent free energetics of ORR on a single iron atom catalyst dispersed on nitrogen-doped graphene (Fe-N4/C) and further integrated these parameters into a microkinetic model. We demonstrate that the rate-determining step (RDS) of the ORR on SACs is potential-dependent rather than invariant within the operative potential range. Specifically, under the charge-neutral condition, the RDS is calculated to be water desorption with the highest barrier, while as the potential increases, it gradually transitions to the protonation of *OH species, O2* species, and O* species, regardless of the protonation of *OH species as the potential-determining step. Moreover, we reveal the critical role of the dynamic adsorption of axially adsorbed water in facilitating the release of the single-atom site, thus enhancing the ORR rate. Our work has resolved the long-standing controversies over the RDS of ORR on SACs and implies that the step with the lowest exothermicity is not always synonymous with the RDS, highlighting the importance of examining the kinetic barriers under realistic potential conditions for understanding the electrocatalytic performance.

Theoretical Insight into the Transition-Metal-Embedded Boron Nitride-Doped Graphene Single-Atom Catalysts for Electrochemical Nitrogen Reduction Reaction

Theoretical Insight into the Transition-Metal-Embedded Boron Nitride-Doped Graphene Single-Atom Catalysts for Electrochemical Nitrogen Reduction Reaction

V‐/O‐Doping to Endow Ag2S‐based Bimetal Oxysulfide with Sulfur Vacancies and Heterovalent States for Rapid Reduction of Organic and Cr(VI) Pollutants in the Dark

AbstractA novel AgVOS oxysulfide catalyst for rapid catalytic reduction of toxic organic substances and Cr(VI) under dark is synthesized by a facile method. With the V/O co‐doping, the doped Ag2S catalyst has the effectively regulated electron transfer performance, the hydrazine‐driven V5+‐to‐V4+ reduction to disturb charge equilibrium, and the formed sulfur vacancy balanced by oxygen doping to maintain charge equilibrium. The formed sulfur vacancy acts as the active site for electrophilic nucleophilic reaction, while the orbital hybridization of O2p and S3p stabilizes the valence state of S2−. A suitable ratio of n(V4+/V5+) is regulated during the hydrazine‐driven synthesis to facilitate the electron transfer and enhance the V5+‐to‐V4+ reduction reaction. V/O co‐doped AgVOS‐3 prepared by a suitable hydrazine content exhibits super catalytic reduction performance of organic 4‐NP (4‐nitrophenol), MB (methyl blue), MO (methyl orange), and RhB (Rhodamine B, 20 ppm, 100 mL) dyes, which are completely reduced within 8, 8, 10, and 8 min, respectively. In comparison, Cr6+ (50 ppm, 100 mL) is also completely reduced within 6 min by AgVOS‐3, indicating its good catalytic reduction activity for organic and inorganic mixture pollutants. Furthermore, AgVOS‐3 has good stability after cyclic tests to maintain a reduction efficiency of 96.5%. Therefore, the AgVOS catalyst shows a promising application for industrial wastewater treatment.