Reduction Reaction Research Articles

Probing Activation and Deactivation Mechanisms in Electrochemical CO2 Reduction Reaction and Water Splitting through In‐Situ/Operando Analysis

Probing Activation and Deactivation Mechanisms in Electrochemical CO₂ Reduction Reaction and Water Splitting through In‐Situ/Operando Analysis

Optimizing the electronic synergy of atomically dispersed dual-metal sites for high-efficiency oxygen evolution/reduction reaction.

We reported an exogenous nitrogen-doped method to synthesize a bifunctional electrocatalyst with oxygen reduction and evolution reaction activity. This electrocatalyst displays excellent ORR (E1/2 = 0.9 V vs. RHE) and OER (potential E = 1.57 V at 10 mA cm-2) activity.

Molecular Strain Accelerates Electron Transfer for Enhanced Oxygen Reduction.

Fe-N-C materials are emerging catalysts for replacing precious platinum in the oxygen reduction reaction (ORR) for renewable energy conversion. However, their potential is hindered by sluggish ORR kinetics, leading to a high overpotential and impeding efficient energy conversion. Using iron phthalocyanine (FePc) as a model catalyst, we elucidate how the local strain can enhance the ORR performance of Fe-N-Cs. We use density functional theory to predict the reaction mechanism for the four-electron reduction of oxygen to water. Several key differences between the reaction mechanisms for curved and flat FePc suggest that molecular strain accelerates the reductive desorption of *OH by decreasing the energy barrier by ∼60 meV. Our theoretical predictions are substantiated by experimental validation; we find that strained FePc on single-walled carbon nanotubes attains a half-wave potential (E1/2) of 0.952 V versus the reversible hydrogen electrode and a Tafel slope of 35.7 mV dec-1, which is competitive with the best-reported Fe-N-C values. We also observe a 70 mV change in E1/2 and dramatically different Tafel slopes for the flat and curved configurations, which agree well with the calculated energies. When integrated into a zinc-air battery, our device affords a maximum power density of 350.6 mW cm-2 and a mass activity of 810 mAh gZn-1 at 10 mA cm-2. Our results indicate that molecular strain provides a compelling tool for modulating the ORR activities of Fe-N-C materials.

H2O2 Mediated Photoreduction of Nitrates to Ammonia by Iron Filings under Ambient Conditions.

Herein, a simple ambient conditioned sunlight promoted photochemical reduction reaction is demonstrated for the of nitrate (NO3-) conversion to ammonia (NH3) with the maximum conversion yield of ∼16 mM using iron filings (f-Fe) in the presence of H2O2. Based on a radical scavenging study of reactive species and the characterization of catalyst f-Fe before and after the reaction, a plausible mechanism has been proposed for the ambient conditioned synthesis of NH3. The results associated with the NH3 synthesis have been verified using the 15N isotopic labeled nitrate (15NO3-), which supports the simpler viability of the reported procedure.

Nitrogen Electrochemical Reduction Reaction Pathways Evidenced by Online Electrochemical Mass Spectrometry and Isotope Labeling on the MoS2 Surface

Nitrogen Electrochemical Reduction Reaction Pathways Evidenced by Online Electrochemical Mass Spectrometry and Isotope Labeling on the MoS₂ Surface

Tuning Dual Catalytic Active Sites of Pt Single Atoms Paired with High-Entropy Alloy Nanoparticles for Advanced Li-O2 Batteries.

To achieve a long cycle life and high-capacity performance for Li-O2 batteries, it is critical to rationally modulate the formation and decomposition pathway of the discharge product Li2O2. Herein, we designed a highly efficient catalyst containing dual catalytic active sites of Pt single atoms (PtSAs) paired with high-entropy alloy (HEA) nanoparticles for oxygen reduction reaction (ORR) in Li-O2 batteries. HEA is designed with a moderate d-band center to enhance the surface adsorbed LiO2 intermediate (LiO2(ads)), while PtSAs active sites exhibit weak adsorption energy and promote the soluble LiO2 pathway (LiO2(sol)). An optimal ratio between LiO2(ads) and LiO2(sol) pathway was realized to modulate PtSAs and HEA active sites via regulating the etching conditions in the dealloying synthesis process for obtaining high-performance Li-O2 batteries. The ORR kinetics are accelerated, and the parasitic reactions are restrained in the Li-O2 batteries. As a result, Li-O2 batteries based on the HEA@Pt-PtSAs catalyst demonstrate an ultralow overpotential (0.3 V) and ultralong cycling performance of 470 cycles at 1000 mA g-1. The insights into the synthetic strategies and the importance of balancing the ORR pathways will offer guidance for devising multisite synergistic catalysts to accelerate redox-reaction kinetics for Li-O2 batteries.

Efficiently Re-Utilizing the High-Value Metals in the Spent LiNi1-x-yMnxCoyO2 for the Trifunctional Electrocatalysts by a Novel One-Pot Method.

Traditional hydrometallurgy methods for recycling the spent lithium-ion battery materials face some challenges, including the complex processes, and difficulties in separating Ni/Co/Mn. To address these issues, this work proposes a simple one-pot method to achieve a high Li leaching efficiency (99.2%) and simultaneously transform the majority of Ni (99.5%) and Co (99.9%) into a high-performance multifunctional electrocatalyst (LNMCO-HS-180). LNMCO-HS-180 with single-phase structure shows a hollow microsphere morphology. LNMCO-HS-180 can efficiently catalyze the oxygen reduction (ORR), oxygen evolution (OER), and methanol oxidation reactions (MOR), with the ORR half-wave potential of 0.732V and, OER potential of 1.469V at 10mA cm-2. This is mainly attributed to the unique hollow microsphere morphology, suitable Ni/Co/Mn oxidation states, and reduction in the free energy barriers for OER and ORR. Additionally, LNMCO-HS-180 exhibits an MOR potential of only 1.43V at 100mA cm-2 and excellent formate selectivity (>99%).

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

Building insights into the structure-performance relationship of catalysts has been emphasized recently. However, it remains a challenge due to catalysts' various and complex structures, especially the easily overlooked influence of the support material. Here, we reveal the crucial influences of boron introduction on synthesizing 3D carbon nanotube monoliths with embedded multistate Co metals, i.e., single atoms, clusters, and nanoparticles (Co-BNCNTs), by an interesting chemical blowing-assisted calcination method. The boron introduction can contribute to forming captivating boron-nitrogen pairs, shaping a 3D frame, and regulating electronic structure. The 3D Co-BNCNT monoliths present good catalytic performance for both the hydrogen evolution reaction (HER) at all pH values and the oxygen reduction reaction (ORR). The theoretical calculations indicate that the B incorporation in Co-NCNTs can optimize the free energy of adsorbed hydrogen and facilitate the O2 adsorption and the protonation of the O2* species. Furthermore, the Co-BNCNTs-based zinc-air battery provides great battery performance with a high power density and discharge-charge durability.

Ambient Temperature Isolation of a Monatomic Boron(0) Complex.

The first bottleable example of a neutral Group 13 atom bound only by neutral donor ligands (L) has been fully characterized by spectroscopic methods and its structure determined by a single-crystal X-ray diffraction study. A two-coordinate paramagnetic L2B0 complex can readily be accessed through a facile reduction reaction and is stabilized by π-accepting cyclic (alkyl)(amino)carbene (CAAC) ligands. Further reduction of (CAAC)2B leads to the isolation of a stable diamagnetic boride anion. In turn, oxidation leads to the putative formation of a transient two-coordinate cationic borylene, which has been trapped to form a stable boron(I) complex. Density functional theory calculations support the formulation of (CAAC)2B as a boron(0) complex stabilized by strong multiple bonding.

Constructing Interfacial B-P Bonding Bridge to Promote S-Scheme Charge Migration within Heteroatom-Doped Carbon Nitride Homojunction for Efficient H2O2 Photosynthesis.

The emerging step (S)-scheme heterojunction systems became a powerful strategy in promoting photogenerated charge separation while maintaining their high redox potentials. However, the weak interfacial interaction limits the charge migration rate in S-scheme heterojunctions. Herein, we construct a unique S-scheme carbon nitride (CN) homojunction with boron (B)-doped CN and phosphorus (P)-doped CN (B-CN/P-CN) for hydrogen peroxide (H2O2) photosynthesis. The B-CN/P-CN nanosheet composites revealed extensively tight interfacial contact, improved visible-light harvesting, and reduced carrier lifetime. The structural investigation results also indicate that the interfacial chemical B-P bonding is formed between B-CN and P-CN nanosheets, inducing an accelerated interfacial S-scheme charge migration. Density functional theory calculations further clarify the S-scheme charge transfer mechanism. Consequently, the 2e- oxygen reduction reaction was the predominant pathway of H2O2 production, facilitated by the B-CN/P-CN homojunction. The optimal H2O2 yield rate reached 2199.5 μmol L-1 h-1 over the B-CN/P-CN homojunction (S3) photocatalyst under monochromatic LED irradiation, increasing 2-8 times as against most of the C3N4 photocatalysts. This study highlights the crucial role of interfacial charge transfer between heterojunction/homojunction materials, accompanied by an unveiling reaction mechanism for solar-energy conversions.

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

Theoretical Investigation of Two-Dimensional FeC4 Structures with Surface Van Hove Singularity for Electrochemical Nitric Oxide Reduction Reaction.

The electrochemical nitric oxide reduction reaction (eNORR) is an efficient method for converting aqueous NO into NH3. The pursuit of innovative electrocatalysts with enhanced activity, selectivity, durability, and cost-effectiveness for NORR remains a research focus. In this study, using particle swarm optimization (PSO) searches, density functional theory (DFT), and the constant-potential method (CPM), we predict two stable two-dimensional FeC4 monolayers, designated as α-FeC4 and β-FeC4, as promising electrocatalysts for the NORR. Our results demonstrate that both α-FeC4 and β-FeC4 monolayers possess intrinsic metallicity with surface Van Hove singularity (SVHS), showing remarkable NORR catalytic performance. Additionally, the substantial disparity in adsorption free energies between NO and H atom at 0 V ensures the high selectivity of these novel FeC4 monolayers toward NORR. These findings not only contribute to the expanding family of two-dimensional transition metal carbides but also provide a new idea for the design of highly efficient NORR electrocatalysts.

Dry-Solid-Electrochemical Synthesis: A General Method for Large Scale Synthesis of Single-Atom Catalysts with High Metal loadings.

Single-atom catalysts (SACs) with high metal loadings are highly desirable but still challenging for large scale synthesis. Here we report a new technique named as dry-solid-electrochemical synthesis (DSES) for a general large-scale synthesis of SACs with high metal loadings in an energy-conservation and environment-friendly way. With it, a series of pure carbon-supported metal SACs (Platinum up to 35.0 wt%, Iridium 21.2 wt%, Ruthenium 20.4 wt% and Iron 17.6 wt%) with high metal loadings were obtained. Particularly, a Pt SAC with Pt 23.9 wt% and remarkable oxygen reduction reaction (ORR) performance in fuel cells is synthesized on kilogram scale. Based on multiple control experiments, a unique redox mechanism for DSES process is proposed: metal precursors on conductive supports are reduced to metals via a homolytic cleavage of metal-halogen bonds by the attacking of electrons flowing through the dry solid phase. Such versatile technique paves a new economical and environment-friendly pathway for fabricating high-metal-loading SACs or atomic dispersion catalysts.

Electronic Structure Modulation in N, P, S Tri‐Doped Nanofibers with Interpenetrated Pores for Enhanced Oxygen Reduction Reaction

AbstractMulti‐heteroatom‐doped metal‐free carbons with well‐tailored electronic structures are regarded as promising oxygen reduction reaction (ORR) catalysts. However, their active sites are often hindered by the carbon matrix, resulting in reduced catalytic activity. Herein, nitrogen, phosphorus, and sulfur tri‐doped hollow hierarchical porous carbon nanofibers (NPS‐HPCNFs) with interpenetrated pores are synthesized using a facile coaxial electrospinning method. The distinctive steric confinement induced by the interpenetrated pores created a positive microenvironment for the ORR. As a result, the resultant NPS‐HPCNF catalyst exhibits a half‐wave potential (E1/2) of 0.86 V (vs. RHE) and superb long‐term stability in 0.1 m KOH. Furthermore, the zinc‐air battery (ZAB) assembled with NPS‐HPCNF achieves a great peak power density of 210 mW cm−2 and a superior specific capacity of 795 mAh g−1, outperforming the commercial Pt/C candidate. In addition, density functional theory (DFT) calculations reveal that the synergistic effect of the N, P, S tri‐doping combined with defect sites effectively regulated the electronic structure and significantly enhanced the *OOH adsorption, thus accelerating the ORR process. Therefore, the tri‐doped carbon nanofibers with abundant interpenetrated pores represent a promising and eco‐friendly alternative to state‐of‐the‐art Pt/C electrocatalysts for various electrochemical energy applications.

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.

Atomically Dispersed Ni-N-C Catalysts for Electrochemical CO2 Reduction.

The atomic dispersion of nickel in Ni-N-C catalysts is key for the selective generation of carbon monoxide through the electrochemical carbon dioxide reduction reaction (CO2RR). Herein, the study reports a highly selective, atomically dispersed Ni1.0%-N-C catalyst with reduced Ni loading compared to previous reports. Extensive materials characterization fails to detect Ni crystalline phases, reveals the highest concentration of atomically dispersed Ni metal, and confirms the presence of the proposed Ni-Nx active site at this reduced loading. The catalyst shows excellent activity and selectivity toward CO generation, with a faradaic efficiency for CO generation (FECO) of 97% and partial current density for CO (jco) of -9.0 mA cm-2 at -0.9 V in an electrochemical H-type cell. CO2RR activity and selectivity are also studied by rotating disk electrode (RDE) measurements where transport limitations can be suppressed. It is expected that the utility of these Ni-N-C catalysts will lie with tandem CO2RR reaction schemes to multi-carbon (C2+) products.

Supramolecularly Built Local Electric Field Microenvironment around Cobalt Phthalocyanine in Covalent Organic Frameworks for Enhanced Photocatalysis.

The local electric field (LEF) plays an important role in the catalytic process; however, the precise construction and manipulation of the electric field microenvironment around the active site remains a significant challenge. Here, we have developed a supramolecular strategy for the implementation of a LEF by introducing the host macrocycle 18-crown-6 (18C6) into a cobalt phthalocyanine (CoPc)-containing covalent organic framework (COF). Utilizing the supramolecular interaction between 18C6 and potassium ion (K+), a locally enhanced K+ concentration around CoPc can be built to generate a LEF microenvironment around the catalytically active Co site. The COF with this supramolecularly built LEF realizes an activity of up to 7.79 mmol mmolCo-1 h-1 in the photocatalytic CO2 reduction reaction (CO2RR), which is a 180% improvement compared to its counterpart without 18C6 units. The effect of LEF can be subtly controlled by fully harnessing the K+@18C6 interaction by changing the potassium salts with different counterions. In situ spectroscopy and density functional theory calculations show that the complexation of K+ by 18C6 creates a positive electric field that stabilizes the critical intermediate *COOH involved in CO2RR, which can be tuned by the halide ion-mediated K+@18C6 interaction and hydrogen-bonding interaction, consequently leading to improved catalytic performance to varying degrees.

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.

Light-induced Enhancement of Energetic Charge Carrier Extraction and Modulation of Local Charge Density to Impact Selectivity in Plasmonic Nanometals.

Localized surface plasmon resonance (LSPR) metals exhibit remarkable light-absorbing property and unique catalytic activity, attracting significant attention in photocatalysts recently. However, the practical application of plasmonic nanometal is hindered by challenge of energetic electrons extraction and low selectivity. The energetic carriers generated in nanometal under illumination have extremely short lifetimes, leading to rapid energy loss. In this work, silver nanometals modified with five distinct sulfhydryl ligands (re-Ag-S-R) were synthesized via photoreduction of superlattice precursors. Modified surface efficiently extracts and preserves excited state electrons of plasmonic nanometals. By modulation the local charge density at catalytic active sites through substituents with varying electron-donating and electron-withdrawing properties, the selectivity of the photocatalytic carbon dioxide reduction reaction and hydrogen evolution reaction was influenced. The results demonstrated opposite selectivity between methoxy-modified re-Ag-S-OCH3 (CO selectivity of 96.73%) and amino-modified re-Ag-S-NH2 (H2 selectivity of 96.66%) despite their similar structures. The changes in excited states and surface contact potentials induced by LSPR were monitored using femtosecond transient absorption (fs-TA) spectroscopy and Kelvin probe force microscopy (KPFM). Meanwhile, the detailed discussion of the LSPR mechanism in plasmonic nanometals will serve as valuable references and foundational elements for future research in this area.