Dissociation Step Research Articles

Efficient generation of human cerebral organoids directly from adherent cultures of pluripotent stem cells

Human cerebral organoids (hCOs) offer the possibility of deepening the knowledge of human brain development, as well as the pathologies that affect it. The method developed here describes the efficient generation of hCOs by going directly from two-dimensional (2D) pluripotent stem cell (PSC) cultures to three-dimensional (3D) neuroepithelial tissue, avoiding dissociation and aggregation steps. This has been achieved by subjecting 2D cultures, from the beginning of the neural induction step, to dual-SMAD inhibition in combination with CHIR99021. This is a simple and reproducible protocol in which the hCOs generated develop properly presenting proliferative ventricular zones (VZs) formed by neural precursor and radial glia (RG) that differentiate to give rise to mature neurons and glial cells. The hCOs present additional cell types such as oligodendrocyte precursors, astrocytes, microglia-like cells, and endothelial-like cells. This new approach could help to overcome some of the existing limitations in the field of organoid biotechnology, facilitating its execution in any laboratory setting.

Photoprocessing of cationic triazacoronene: dissociation characteristics of polycyclic aromatic nitrogen heterocycles in interstellar environments.

Polycyclic aromatic nitrogen heterocycles (PANHs) are present in various astronomical environments where they are subjected to intense radiation. Their photodissociation pathways give crucial insights into the cycle of matter in the universe, yet so far only the dissociation characteristics of few PANHs have been investigated. Moreover, most experiments use single photon techniques that only reveal the initial dissociation step, and are thus unsuited to replicate astronomical environments and timescales. In this work, we use the Instrument for the Photodynamics of PAHs (i-PoP) at the Laboratory for Astrophysics to simulate the interstellar photodissociation of a model PANH, cationic triazacoronene (TAC˙+, C21H9N3). Comparing the observed fragments to similar PAHs such as the isoelectronic coronene can give mechanistic insight into PAH dissociation. For coronene the major photodissociation products were found to be C9H+, C10+, and C11+. In contrast, fragmentation in TAC˙+ is initiated by up to three HCN losses often in combination with H- or H2 losses. In the lower mass region, the fragments show similarities to comparable PAHs like coronene, but for TAC˙+ the inclusion of nitrogen atoms into the ionic fragments in the form of e.g. (di)cyanopolyynes is also observed. These nitrogen-containing species may be important tracers of regions in interstellar space where interstellar PANHs are being photodissociated.

Revealing The Role of Electronic Asymmetricity on Supported Ru Nanoclusters for Alkaline Hydrogen Evolution Reaction

AbstractModulating the electronic asymmetricity of catalysts is an effective method for optimizating the elementary steps of water dissociation and hydrogen adsorption/desorption process for the alkaline hydrogen evolution reaction (HER). Herein, uniform Ru nanoclusters anchored on N doped ultrathin carbon nanosheets (Ru/NC) are synthesized to optimize the asymmetricity electronic properties of supported Ru for efficient HER. It is found that Ru and NC with a large work function difference (ΔΦ) leading to the formation of stronger asymmetrical charge distributions of Ru that electron‐deficient high‐valence Ru (Run+) coupling with low‐valence Ru (Ru0). Experimental and theoretical studies indicate the Run+ sites lowered the energy barrier for water dissociation and provided enough hydrogen proton to promote the hydrogen spillover from the Run+ to Ru0 sites, and Ru0 sites can enhance H desorption process, thus synergistically enhancing the hydrogen evolution activity. Notably, the Ru/NC catalyst exhibits a high alkaline HER activity (21.9 mV@10 mA cm−2, 29.03 mV dec−1). The role of electronic asymmetricity on supported Ru nanoclusters for the alkaline HER are demonstrated, which will provide guidelines for the rational design of high‐efficiency alkaline HER catalysts.

First-principles study of H2S adsorption and dissociation on the Ni(111) and Cl-covered Ni(111) surfaces

This article is based on density functional theory to calculate and study the adsorption and dissociation of H2S on Ni(111) and Cl-covered Ni(111) surfaces. The calculation results show that H2S is stably adsorbed at the Top site on both surfaces. There is a certain repulsive effect between Cl and H2S, which leads to a decrease in the adsorption strength of H2S. The dissociation energy barriers of the first step for H2S are higher than those of the second step on both surfaces, indicating that the first step of dissociation is the rate-determining step. In the presence of Cl, the energy barrier for the first step of H2S dissociation decreases from 0.27 eV to 0.19 eV, while the energy barrier for the second step of H2S dissociation increases from 0.01 eV to 0.11 eV. This means that the presence of Cl accelerates the first step of H2S dissociation and hinders the second step. The increase energy barrier for the second step of H2S dissociation implies greater difficulty in breaking the SH bond during this step, so the presence of Cl can inhibit the breaking of the SH bond in the second step. Additionally, the decomposition of H2S on both Ni(111) and Cl-covered Ni(111) surfaces is an exothermic process and a spontaneous one.

ERK2-topoisomerase II regulatory axis is important for gene activation in immediate early genes

The function of the mitogen-activated protein kinase signaling pathway is required for the activation of immediate early genes (IEGs), including EGR1 and FOS, for cell growth and proliferation. Recent studies have identified topoisomerase II (TOP2) as one of the important regulators of the transcriptional activation of IEGs. However, the mechanism underlying transcriptional regulation involving TOP2 in IEG activation has remained unknown. Here, we demonstrate that ERK2, but not ERK1, is important for IEG transcriptional activation and report a critical ELK1 binding sequence for ERK2 function at the EGR1 gene. Our data indicate that both ERK1 and ERK2 extensively phosphorylate the C-terminal domain of TOP2B at mutual and distinctive residues. Although both ERK1 and ERK2 enhance the catalytic rate of TOP2B required to relax positive DNA supercoiling, ERK2 delays TOP2B catalysis of negative DNA supercoiling. In addition, ERK1 may relax DNA supercoiling by itself. ERK2 catalytic inhibition or knock-down interferes with transcription and deregulates TOP2B in IEGs. Furthermore, we present the first cryo-EM structure of the human cell-purified TOP2B and etoposide together with the EGR1 transcriptional start site (–30 to +20) that has the strongest affinity to TOP2B within –423 to +332. The structure shows TOP2B-mediated breakage and dramatic bending of the DNA. Transcription is activated by etoposide, while it is inhibited by ICRF193 at EGR1 and FOS, suggesting that TOP2B-mediated DNA break to favor transcriptional activation. Taken together, this study suggests that activated ERK2 phosphorylates TOP2B to regulate TOP2-DNA interactions and favor transcriptional activation in IEGs. We propose that TOP2B association, catalysis, and dissociation on its substrate DNA are important processes for regulating transcription and that ERK2-mediated TOP2B phosphorylation may be key for the catalysis and dissociation steps.

Evaluating the influence of Ar/N2 flow rate and pressure on the conversion efficiency of a solar-assisted Fe2O3 – FeO WS cycle for hydrogen production: A thermodynamic approach

A thermodynamic analysis is carried out to evaluate the effects of oxygen partial pressure (PO2) and molar flow rate of reduction agents (m˙N2/Ar) on the performance of Fe2O3−FeO solar thermochemical cycle (STC|Fe2O3−FeO). The chemical equilibrium and efficiency analysis parameters such as enthalpy, Gibbs free energy and entropy are calculated as a function of thermal dissociation temperature (TH). The chemical equilibrium analysis suggests that the thermal dissociation step is feasible above 1250 K while the re-oxidation step is practicable at 550 K. The efficiency analysis revealed that the highest value of conversion efficiency (ηsolar−to−fuel) reached up to 44.42% for N2 based cycle and 45.46% for Ar based cycle without using the recuperation technique. However, the conversion efficiency (ηsolar−to−fuel) attained the highest value of 57.84% for N2 based cycle and 59.14% for Ar based cycle with 50% heat recuperation.

TMIC-74. SPATIAL LANDSCAPE OF MELANOMA BRAIN METASTASES WITH AND WITHOUT PRE-SURGICAL IMMUNE CHECKPOINT BLOCKADE

Abstract We recently characterized the immune populations of brain metastases samples with or without immune checkpoint blockade (ICB) treatment. In that study, we utilized single cell RNAseq (scRNAseq) and multiplex immunofluorescence (mIF) to demonstrate that ICB induced T cell infiltration and the migration of a unique MRC1+ macrophage subset from the perivascular space into the tumor parenchyma. However, scRNAseq’s tissue dissociation step loses spatial information of cells while mIF has low dimensionality, covering only a few markers for each tissue section. Thus, we applied sequencing-based Visium spatial transcriptomics (ST) to study the spatial architecture of melanoma brain metastases with/without ICB treatment and developed a pipeline that leverages public scRNAseq data as a reference to resolve fine-grained cell types on each Visium spot. ICB was associated with an increased CXCL13+ terminally exhausted T cell subset in close spatial proximity to tumor cells, suggestive of tumor specificity. ICB also reduced multiple MRC1+ macrophage subtypes in the blood vessel regions, supporting our mIF observation. Furthermore, we discovered that MRC1+ macrophages in close proximity to blood vessels expressed elevated TIMP1. TIMP1 is a known inhibitor of MMP9 that prevents ECM degradation and blood vessel damage, thus limiting T cell extravasation. In contrast, MRC1+ macrophages that migrated into the tumor had higher interferon activation and expressed CXCL9 and CXCL12 chemokines, which could recruit T cells via CXCR3 and CXCR4. Such findings could explain the increased T cell infiltration with ICB even in metastatic brain tumors. However, these MRC1+ macrophages also had an M2 signature and expressed multiple immune checkpoint ligands. Such data suggest these cells might also increase immunosuppressive interactions with T cells. In summary, our study reveals how ICB affects the spatial architecture and crosstalk of different cell types within melanoma brain metastases and will provide insights into new therapeutic strategies for brain metastases patients.

Theoretical Approach toward a Mild Condition Haber-Bosch Process on the Zeolite Catalyst with Confined Dual Active Sites.

The Haber-Bosch (H-B) process is today's dominant technology for ammonia production, but achieving a mild reaction condition is still challenging. Herein, we combined density functional theory (DFT) calculations and microkinetic modeling (MKM) to demonstrate the feasibility of conducting the H-B process under ambient conditions on a zeolite catalyst with confined dual active sites. Our designed dual Mo(II) cation-anchored ferrierite [2Mo(II)-FER] catalyst shows an energy barrier of only 0.58 eV for N≡N bond breaking due to the enhanced π-back-donation. Meanwhile, the three hydrogen sources (BH, FMH, and NMH) within 2Mo(II)-FER greatly enrich the hydrogenation mechanisms of NHx species, resulting in barriers of <1.1 eV for NHx (x = 0-2) hydrogenations. This dual-site catalyst properly decouples the N2 dissociation and NHx hydrogenation steps, which elegantly circumvents the linear scaling relation between the N2 dissociation barrier and the nitrogen binding energy. It is worth noting that our MKM results show 4 orders of magnitude higher reaction rates on 2Mo(II)-FER than the stepped sites of the FCC Ru catalyst at low temperatures, paving a solid basis to conduct the H-B process at low temperatures. We believe that our strategy will provide crucial guidance for synthesizing state-of-the-art zeolite catalysts to achieve the near-ambient condition H-B process and other chemical reactions in heterogeneous catalysis.

Fullerene Fragment Restructuring: How Spatial Proximity Shapes Defect-Rich Carbon Electrocatalysts.

Fullerene transformation emerges as a powerful route to construct defect-rich carbon electrocatalysts, but the carbon bond breakage and reformation that determine the defect states remain poorly understood. Here, we explicitly reveal that the spatial proximity of disintegrated fullerene imposes a crucial impact on the bond reformation and electrocatalytic properties. A counterintuitive hard-template strategy is adopted to enable the space-tuned fullerene restructuring by calcining impregnated C60 not only before but also after the removal of rigid silica spheres (∼300 nm). When confined in the SiO2 nanovoids, the adjacent C60 fragments form sp3 bonding with adverse electron transfer and active site exposure. In contrast, the unrestricted fragments without SiO2 confinement reconnect at the edges to form sp2-hybridized nanosheets while retaining high-density intrinsic defects. The optimized catalyst exhibits robust alkaline oxygen reduction performance with a half-wave potential of 0.82 V via the 4e- pathway. Copper poisoning affirms the intrinsic defects as the authentic active sites. Density functional theory calculations further substantiate that pentagons in the basal plane lead to localized structural distortion and thus exhibit significantly reduced energy barriers for the first O2 dissociation step. Such space-regulated fullerene restructuring is also verified by heating C60 crystals confined in gallium liquid and a quartz tube.

Breaking the Activity and Stability Bottlenecks of Electrocatalysts for Oxygen Evolution Reactions in Acids.

Oxygen evolution reaction (OER) is a cornerstone reaction for a variety of electrochemical energy conversion and storage systems such as water splitting, CO2 /N2 reduction, reversible fuel cells, and metal-air batteries. However, OER catalysis in acids suffers from extra sluggish kinetics due to the additional step of water dissociation along with its multiple electron transfer processes. Furthermore, OER catalysts often suffer from poor stability in harsh acidic electrolytes due to the severe dissolution/corrosion processes. The development of active and stable OER catalysts in acids is highly demanded. Here, we review the recent advances in OER electrocatalysis in acids and summarise the key strategies to overcome the bottlenecks of activity and stability for both noble-metal-based and noble metal-free catalysts, including i) morphology engineering, ii) composition engineering, and iii) defect engineering. Recent achievements in operando characterization and theoretical calculations are summarised which provide an unprecedented understanding of the OER mechanisms regarding active site identification, surface reconstruction, and degradation/dissolution pathways. Finally, we offer our views on the current challenges and opportunities to break the activity-stability relationships for acidic OER in mechanism understanding, catalyst design, as well as standardised stability and activity evaluation for industrial applications such as proton exchange membrane water electrolysers and beyond. This article is protected by copyright. All rights reserved.

Atomic-Scale Insights into Carbon Dioxide Hydrogenation over Bimetallic Iron–Cobalt Catalysts: A Density Functional Theory Study

The conversion of carbon dioxide to fuels and chemicals is a promising long-term approach for mitigating CO2 emissions. Despite extensive experimental efforts, a fundamental understanding of the bimetallic catalytic structures that selectively produce the desired products is still lacking. Here, we report on a computational surface science approach into the effect of the Fe doping of Co(111) surfaces in relation to CO2 hydrogenation to C1 products. Our results indicate that Fe doping increases the binding strength of surface species but slightly decreases the overall catalytic activity due to an increase in the rate-limiting step of CO dissociation. FeCo(111) surfaces hinder hydrogenation reactions due to lower H coverages and higher activation energies. These effects are linked to the Lewis basic character of the Fe atoms in FeCo(111), leading to an increased charge on the adsorbates. The main effect of Fe doping is identified as the inhibition of oxygen removal from cobalt surfaces, which can be expected to lead to the formation of oxidic phases on bimetallic FeCo catalysts. Overall, our study provides comprehensive mechanistic insights related to the effect of Fe doping on the catalytic behavior and structural evolution of FeCo bimetallic catalysts, which can contribute to the rational design of bimetallic catalysts.

Outstanding inhibition of H2O2 generation in doubly doped graphene: The synergy of two heteroatoms opens a new chemical path

Dual sulfur-nitrogen (SN) doped graphene surfaces have been revealed as a powerful active material in fuel cell applications. The experimental results presented in this work show a clear preference of the material doped with SN towards a 4-electron mechanism, almost completely inhibiting the formation of H2O2. However, materials doped only with nitrogen (N) or sulfur (S) favor the 2-electron mechanism, and therefore, the production of H2O2. A reasonable theoretical explanation is proposed to justify the inhibition of the H2O2 reaction with the use of SN doped graphenes in accordance with the experimental results. The interactions and charge transfer between N and S are the origin of an alternative dissociative step that inhibits the generation of H2O2, which is energetically favored, according to Density Functional Theory (DFT) calculations. These two dopant atoms generate a frustrated Lewis pair (FLP), resulting in an enhancement of the catalytic activity of the graphene. Atomic Dipole Corrected Hirshfeld charges (ADCH model) and Non-Covalent Interactions (NCI) are employed to identify the most active sites and support the explanation of the dissociative pathway which inhibits H2O2 formation.

Sustainable assessment of an integrated energy system coupled with solar thermochemical cycle

The energy transition globally makes the development of carbon-free and low-carbon fuels obligatory as these fuels cannot only be utilized as energy carriers but also for long-term energy storage. This paper presents the energy, technoeconomic, and environmental assessment of a new hybrid renewable energy integrated system with a novel concept of the thermochemical cycle for methanol production. For this purpose, a thermochemical cycle based on CeO2/Ce2O3 oxides is integrated with the methanol synthesis system. It consists of two chemical steps: (1) oxygen carrier reduction step where metal oxide reduction Ce (IV) to Ce (III) (endothermic phase) is performed employing renewable thermal energy and chemical energy originated from ultra-high concentrated photovoltaics and fossil methane respectively and (2) waste gas dissociation step where oxidation of Ce(III) takes place with dissociation of water and carbon dioxide (exothermic phase) and resulting syngas is converted to methanol. Plant design and simulation are performed in ASPEN plus commercial software. MATLAB was employed for the programming of thermal data to perform pinch analysis. The technical feasibility of the second step was investigated comprehensively in terms of temperature, input molar ratio and the potential operating conditions that were identified (TOXI = 900 °C and H2O/CO2 = 3.7) based on methanol production performance. Overall energy efficiency, solar-to-fuel efficiency and thermal efficiency are calculated to be 77.2%, 38% and 44.1% respectively. The findings of the environmental analysis show that carbon utilization of 20.85%, carbon storage of 79.14%, carbon capture of 100% and carbon avoidance of 19.6% are achieved. Economic analysis shows that the net project capital expenditure (CAPEX) and operating expenditure (OPEX) are estimated to be $186.49M and $218.67M. It was found that the best-case scenario of natural gas (NG) price is 40$/MWh, where the breakeven point is achieved during the 5th year of the project lifetime.

Unveiling the Structural Self-Reconstruction and Identifying the Reactive Center of a V, Fe Co-Doped Cobalt Precatalyst toward Enhanced Overall Water Splitting by Operando Raman Spectroscopy.

The development of efficient and stable bifunctional electrocatalysts based on non-noble metals for water electrolysis is both urgent and challenging. However, unresolved issues remain regarding the challenge of identifying the active phase and gaining a comprehensive understanding of its surface reconstruction and functionality throughout the reaction process. In this study, we have combined doping and heterostructure construction by a one-step electrodeposition and a subsequent activation treatment to synthesize Fe, V co-doped Co3O4/Co(OH)2 and Co/Co(OH)2 heterointerfaces (referred to as A-Co60Fe1.1V). These heterointerfaces, composed of Co/Co(OH)2 and Co3O4/Co(OH)2, are proposed to facilitate charge transfer process during catalysis. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the introduction of V and Fe dopants increases the valence state of Co centers in Co3O4 and Co(OH)2. Further operando Raman spectroscopy reveals that Co(OH)2 and Co3O4 with the high-valence Co centers remain stable during the hydrogen evolution reaction (HER) process. These high-valence Co centers are believed to promote the crucial water dissociation step and therefore enhance the overall HER catalysis. On the other hand, during the oxygen evolution reaction (OER), Fe, V co-doping leads to an earlier formation of the active CoOOH species, while Fe doping can further help stabilize the more reactive β-CoOOH species instead of the less reactive γ-CoOOH. As a result, the A-Co60Fe1.1V catalyst exhibits significantly improved catalytic activity for both HER and OER that it requires low overpotentials of 51 and 250 mV, respectively, to attain a current density of 10 mA cm-2. Moreover, when utilized as both the cathode and anode in alkaline water electrolysis, the A-Co60Fe1.1V catalyst can operate at a mere 1.54 V voltage while maintaining 10 mA cm-2, surpassing the majority of non-noble metal catalysts. Remarkably, it also exhibits stability for at least 40 h at ∼100 mA cm-2.

Mechanistic Insight into the Propane Oxidation Dehydrogenation by N2O over Cu-BEA Zeolite with Diverse Active Site Structures

The present work theoretically investigated propane oxidation dehydrogenation by utilizing N2O as an oxidant (N2O-ODHP) over Cu-BEA with three different types of active site, including monomeric Cu ([Cu]+), dimeric Cu ([Cu−Cu]2+), and distant monomeric Cu sites ([Cu]+—[Cu]+). Energetically, we calculated that the monomeric [Cu]+ is favorable for the αH dehydrogenation step (∆E = 0.05 eV), which, however, suffers from high barriers of N2O dissociation and βH dehydrogenation steps of 1.40 and 1.94 eV, respectively. Although the dimeric [Cu−Cu]2+ site with a Cu—Cu distance of 4.91 Å is much more favorable for N2O dissociation (0.95 eV), it still needs to overcome an extremely high barrier (∆E = 2.15 eV) for βH dehydrogenation. Interestingly, the distant [Cu]+—[Cu]+ site with the Cu—Cu distance of 5.82 Å exhibits low energy barriers for N2O dissociation (0.89 eV) and ODHP steps (0.01 and 0.33 eV) due to the synergistic effect of distant [Cu]+. The microkinetic analyses quantitatively verified the superior activity of the distant [Cu]+—[Cu]+ site with a reaction rate being eight to nine orders of magnitude higher than those of the monomeric and the dimeric Cu sites, and this is related to its ready charge-transfer ability, as shown by the partial Density of State (PDOS) analysis and the static charge differential density analysis in this study. Generally, the present work proposes that the distance between the [Cu]+ sites plays a significant and important role in N2O-ODHP over the Cu-based zeolite catalyst and modulates Cu—Cu distance, and this constitutes a promising strategy for highly-efficient Cu-zeolite catalyst design for N2O-ODHP.

Mean field model parameterization to recover coverage-dependent kinetics

Lateral interactions between adsorbates introduce coverage dependence into adsorption energies and activation barriers of surface reactions. Lattice-based kinetic Monte Carlo (kMC) simulations can capture these interactions quantitatively but are laborious to parameterize and solve. Mean field models are more tractable, but protocols to construct and parameterize them are unclear. Here we explore the ability of a coverage-aware mean-field model to map to a lattice-kMC model of a generic two-step reaction network, including quasi-equilibrated adsorption and rate-limiting dissociation steps. We derive expressions for mean-field and coverage-dependent adsorption energies and dissociation barriers and parameterize against lattice-kMC predictions. We show that the parameterized mean-field rates correlate with ground truth lattice-kMC results across a wide range of reaction conditions and identify regions where the mean field fails. The mean field model similarly captures kMC-derived rate-order, Arrhenius and Sabatier plots at a greatly reduced computational cost. The results provide guidance for parameterizing mean-field models, benchmarked against explicit lattice-based approaches for incorporating the influence of coverage effects.

Theoretical assessments of CO2 activation and hydrogenation pathways on transition-metal surfaces

Carbon dioxide (CO2) hydrogenation on transition-metal active sites offers a promising carbon utilization route toward mitigating greenhouse gas emissions. C1 products are often formed in parallel during CO2 hydrogenation, prompting investigations into the intrinsic properties of transition metals that drive activity and product selectivity. In this work, close-packed surfaces of a selection of transition-metal catalysts (Ni, Co, Rh, Ru, Pd, and Pt) were studied with density functional theory (DFT) calculations to understand their fundamental reactivities for CO2 transformation reactions. Results indicate that CO2 conversion proceeds through CO* formation and hydrogenation to form C1 products (* denotes an adsorbed species). Ni, Co, Rh, and Ru favor CO/CH4 formation, while Pd and Pt favor CO/CH3OH formation. The ability of a metal to dissociate C-O bonds drives selectivity between CH4 and CH3OH, while competition between CO* desorption and surface hydrogenation describes CO selectivities. The C-O bond dissociation steps often impose the highest barrier along CH4 formation reaction profiles, suggesting their kinetic relevance for CH4 formation rates. The provided DFT-derived data sets detail a comprehensive reaction network of elementary steps relevant to C1 chemistries, ultimately offering a benchmark for insights into design strategies for materials that exploit transition-metal active sites in carbon capture or utilization processes.

O-vacancy-rich and heterostructured Cu/Cu2O/NiO@NiCu foam self-supported advanced electrocatalyst towards hydrogen evolution: An experimental and DFT study

Defect-engineering and heterojunction-creating on a catalyst have been endorsed as effective approaches to enhance the hydrogen evolution reaction (HER) behavior. By skillfully employing the transformation of Cu2S/Ni3S2 to NiO/Cu2O and the electroreduction of partial Cu2O to Cu/Cu2O for the O-vacancy (Ov) production and in-situ reactions for the heterostructure construction, we fabricated a self-supported heterostructured hybrid with Ov-rich Cu/Cu2O coupled with few NiO grown in-situ on the NiCu bimetallic foam (named as Cu/NiO/Cu2O@NCF). Cu/NiO/Cu2O@NCF records a low overpotential of 79 mV at 10 mA cm−2 with a small Tafel slope of 60 mV dec−1 and sustained the activity without distinct decay for 100 h towards catalyzing HER in 1.0 M KOH. More profoundly, density functional theory computations reveal that Ov-Cu2O holds a much lower energy barrier for the rate-determining step of the H2O dissociation and a more electron density with respect to Ov-NiO, thereby accelerating the alkaline HER kinetics.

Fe and Mo dual-site single-atom catalysts for high-efficiency wide-pH hydrogen evolution and alkaline overall water splitting

The limitations of single-atom catalysts (SACs) hinder their application in wide-pH range of hydrogen evolution reaction (HER) and overall water-splitting in alkaline solution. Herein, we fabricate a rod-like Ni3S2 material wrapped by single-atom Fe-Mo co-modified CoNi-based nanosheets (FeMo@CoNi-OH/Ni3S2). The introduction of Fe-SAs and Mo-SAs into CoNi-hydroxyl compounds effectively changes their electronic structure and enhances their conductivity, thereby improving HER and OER performance. FeMo@CoNi-OH/Ni3S2 catalyst endows HER with overpotentials of 89, 176 and 177 mV in alkaline, acidic and neutral solutions, respectively, as well as good oxygen evolution reaction (OER) performance with 160 mV in alkaline to achieve 10 mA cm−2. The combination of the experiments and theoretical calculations reveals that the synergistic effect of Mo-SAs with Fe-SAs effectively reduces the intermediate energy barrier of the water dissociation step. This work contributes to the understanding of the catalytic mechanisms of dual single-atomic active sites in HER and OER processes.

Hydrogen production using aluminum-water splitting: A combined experimental and theoretical approach

Hydrogen generation from aluminum hydrolysis with NaOH as an activator is investigated experimentally. A theoretical model is developed using the Density Functional Theory (DFT) and a one-dimensional transport model formalism. The effects of NaOH concentration and reaction temperature on hydrogen production rates are investigated. The kinetic parameters calculated by DFT are used in the COMSOL transport equations and compared. A transport model is implemented for a reaction-diffusion problem of water over the Al surface. The activation barrier increases as the reaction progresses and adsorption of H2O molecules is limited due to space constraints. The reaction rate constants depend on temperature, species convection, and vibrational frequency. The three chemical reaction steps have activation barriers ranging from 7.72 to 61.75 kJ/mol. The activation barrier of the first H2O dissociation step is Ea,1 = 7.72 kJ/mol, whereas the second and third steps have activation barriers of Ea,2 = 15.44 kJ/mol and Ea,3 = 61.75 kJ/mol, respectively. The estimated DFT harmonic vibrational frequency of H2O stretching mode is 3788 cm−1.