Mechanism Of Hydrogen Evolution Research Articles

Corrosion Inhibition Performance of Brachystegia eurycoma Leaf Extract on Mild Steel in Acid Media

The aim of this work is to investigate the corrosion inhibition of B. eurycoma leaves extract as a natural inhibitor for mild steel corrosion in 3 M H2SO4 solution. The corrosion inhibitory activity was analyzed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The surface roughness and its properties through scanning electron microscopy (SEM). The obtained result from EIS divulges that the gradual increase in inhibitor concentration and time of immersion leads to progressive increase in inhibition efficiency. At the end of 8 hours immersion time and inhibitor concentration of 1000 mg/l the highest inhibition efficiency of (88%) was obtained. The potentiodynamic polarization results indicated that addition of B. eurycoma leaves extracts hindered the reaction rates of anodic and cathodic reactions thereby performing as mixed- type inhibitor. The corrosion current density also revealed that in the presence of B. eurycoma leaves extracts the value of corrosion density reduced considerably from 265.2 \(\mu\) A/cm2 for sample without inhibitor to 67.8 \(\mu\) A/cm2 for sample with inhibitor. Again, it was observed that in the presence B. eurycoma leaves extracts the mechanism of hydrogen (effervescence) evolution was unique whereas the anodic dissolution of iron mechanism experienced the impact of the inhibitor. SEM inspection revealed that the mild steel surface showed smoother and lower damage in the presence of inhibitor. Obvious correlations were found between corrosion inhibition efficiency and some quantum chemical parameters such as energy of highest occupied molecular orbital (EHOMO), energy of lowest unoccupied molecular orbital (ELUMO), energy gap (EL–H) and electronic density etc. The obtained results were further elucidated with frontier molecular orbital theory.

Applying Nuclear Forward Scattering as In Situ and Operando Tool for the Characterization of FeN4 Moieties in the Hydrogen Evolution Reaction.

Nuclear forward scattering (NFS) is a synchrotron-based technique relying on the recoil-free nuclear resonance effect similar to Mössbauer spectroscopy. In this work, we introduce NFS for in situ and operando measurements during electrocatalytic reactions. The technique enables faster data acquisition and better discrimination of certain iron sites in comparison to Mössbauer spectroscopy. It is directly accessible at various synchrotrons to a broad community of researchers and is applicable to multiple metal isotopes. We demonstrate the power of this technique with the hydrogen evolution mechanism of an immobilized iron porphyrin supported on carbon. Such catalysts are often considered as model systems for iron-nitrogen-carbon (FeNC) catalysts. Using in situ and operando NFS in combination with theoretical predictions of spectroscopic data enables the identification of the intermediate that is formed prior to the rate-determining step. The conclusions on the reaction mechanism can be used for future optimization of immobilized molecular catalysts and metal-nitrogen-carbon (MNC) catalysts.

Visible‐Light‐Induced Photocatalytic Hydrogen Evolution Performance of Graphdiyne‐Alkyne Phosphating Mo–Metal‐Organic Frameworks Heterojunction

Herein, the application of graphdiyne (GDY) in photocatalytic splitting of water and hydrogen evolution is explored. In this article, GDY is prepared by ball milling using calcium carbide as raw material, and it is compounded with phosphating Mo–metal‐organic frameworks (MOFs), to explore the photocatalytic hydrogen evolution performance and hydrogen evolution mechanism of composite catalysts. In the results, it is shown that the P–Mo–MOFs (PMF)/G‐25 composite photocatalyst has the best hydrogen evolution activity, and the hydrogen evolution rate is highest at pH = 9, reaching 1668.5 μmol g−1 h−1. Through the four‐cycle hydrogen evolution cycle stability test, the PMF/G‐25 composites still has good hydrogen evolution stability. It is shown that the combination of phosphating Mo–MOFs and GDY can enhance the hydrogen evolution activity and has excellent hydrogen evolution performance. In the Mott–Schottky test, it is found that PMF and GDY are n‐type semiconductors. The conduction and valence values are −0.56 and 1.10 eV for GDY, and −0.68 and 0.97 eV for PMF, respectively. The mechanism of photocatalytic hydrogen evolution is analyzed, and it is speculated that S‐Scheme heterojunction is formed between PMF and GDY to further promote photocatalytic hydrogen evolution.

Energy band engineering over phosphorus-doped CdS/graphdiyne S-scheme heterojunction for enhance photocatalytic hydrogen production

The high recombination rate of photoelectron-hole pairs and the limited REDOX capacity of a single photocatalyst restrict the broader application of photocatalytic water splitting for hydrogen generation. This necessitates the design of an efficient multicomponent photocatalyst. In this work, phosphate-doped cadmium sulfide (CP) was designed by energy band engineering to have a wider band gap and reduce the recombination rate of photogenerated electrons and holes. Graphdiyne, prepared through a straightforward ball milling method, exhibits high conductivity and specific surface area. It pairs well with CP morphologically, effectively reducing CP aggregation and exposing more active sites. Compared with the original CdS (CS), the changes in the conduction and valence band positions of CP can form S-scheme heterojunction with graphdiyne, which effectively improves the interfacial charge migration effect, improves the photogenerated carrier separation efficiency, and maintains a high reduction capacity. Additionally, the mechanism of photocatalytic hydrogen evolution was verified by in-situ XPS. This work provides a feasible scheme for the design and construction of graphdiyne in heterojunction photocatalyst.

Rational Design of Three Dimensional Hollow Heterojunctions for Efficient Photocatalytic Hydrogen Evolution Applications.

The efficiency of photocatalytic hydrogen evolution is currently limited by poor light adsorption, rapid recombination of photogenerated carriers, and ineffective surface reaction rate. Although heterojunctions with innovative morphologies and structures can strengthen built-in electric fields and maximize the separation of photogenerated charges. However, how to rational design of novel multidimensional structures to simultaneously improve the above three bottleneck problems is still a research imperative. Herein, a unique Cu2O─S@graphene oxide (GO)@Zn0.67Cd0.33S Three dimensional (3D) hollow heterostructure is designed and synthesized, which greatly extends the carrier lifetime and effectively promotes the separation of photogenerated charges. The H2 production rate reached 48.5mmolg-1h-1 under visible light after loading Ni2+ on the heterojunction surface, which is 97 times higher than that of pure Zn0.67Cd0.33S nanospheres. Furthermore, the H2 production rate can reach 77.3mmolg-1h-1 without cooling, verifying the effectiveness of the photothermal effect. Meanwhile, in situ characterization and density flooding theory calculations reveal the efficient charge transfer at the p-n 3D hollow heterojunction interface. This study not only reveals the detailed mechanism of photocatalytic hydrogen evolution in depth but also rationalizes the construction of superior 3D hollow heterojunctions, thus providing a universal strategy for the materials-by-design of high-performance heterojunctions.

Sugars induced exfoliation of porous graphitic carbon nitride for efficient hydrogen evolution in photocatalytic water-splitting reaction

Photocatalytic hydrogen evolution holds great promise for addressing critical energy and environmental challenges, making it an important area in scientific research. One of the most popular photocatalysts is graphitic carbon nitride (gCN), which has emerged as a noteworthy candidate for hydrogen generation through water splitting. However, ongoing research aims to enhance its properties for practical applications. Herein, we introduce a green approach for the fabrication of porous few-layered gCN with surface modifications (such as oxygen doping, carbon deposition, nitrogen defects) with promoted performance in the hydrogen evolution reaction. The fabrication process involves a one-step solvothermal treatment of bulk graphitic carbon nitride (bulk-gCN) in the presence of different sugars (glucose, sucrose, and fructose). Interestingly, the conducted time-dependent process revealed that porous gCN exfoliated in the presence of fructose at 180 °C for 6 h (fructose_6h) exhibits a remarkable 13-fold promotion of photocatalytic hydrogen evolution compared to bulk-gCN. The studied materials were extensively characterized by microscopic and spectroscopic techniques, allowing us to propose a reaction mechanism for hydrogen evolution during water-splitting over fructose_6h. Furthermore, the study highlights the potential of employing a facile and environmentally friendly fructose-assisted solvothermal process to improve the efficiency and stability of catalysts based on graphitic carbon nitride.

Mechanisms of hydrogen evolution by six-coordinate cobalt complexes: a density functional study on the role of a redox-active pyridinyl-substituted diaminotriazine benzamidine ligand as a proton relay.

The hydrogen evolution reaction is an important process for energy storage. The six-coordinate cobalt complex [CoIII(L1-)(LH)]2+ (LH = N-(4-amino-6-(pyridin-2-yl)-1,3,5-triazin-2-yl)benzamidine) was found to catalyze photocatalytic hydrogen evolution. In this work, we performed density functional calculations to obtain the reduction potentials and the proton-transfer free energy of possible intermediates to determine the preferred pathways for proton reduction. The mechanism involves the metal-based reduction of Co(III) to Co(II) before the protonation at the amidinate N on the pyridinyl-substituted diaminotriazine benzamidinate ligand L1- to form [CoII(LH)(LH)]2+. Essentially, the subsequent electron transfer is not metal-based reduction, but rather ligand-based reduction to form [CoII(LH)(LH˙1-)]1+. Through a proton-coupled electron transfer process, the cobalt hydride [CoIIH(LH)(LH2˙)]1+ is formed as the key intermediate for hydrogen evolution. As the cobalt hydride complex is coordinatively saturated, a structural change is required when the hydride on Co is coupled with the proton on pyridine. Notably, the redox-active nature of the ligand results in the low acidity of the protonated pyridine moiety of LH2˙, which impedes its function as a proton relay. Our findings suggest that separating the proton relay fragment from the electron reservoir fragment of the redox-active ligand is preferred for fully utilizing both features in catalytic H2 evolution.

Elucidating the performance of hexamethylene tetra-amine interlinked bimetallic NiCo-MOF for efficient electrochemical hydrogen and oxygen evolution.

Bimetallic metal-organic frameworks (MOFs) play a significant role in the electrocatalysis of water due to their large surface area and availability of increased numbers of pores. For the inaugural time, we examine the effectiveness of a hexamethylene tetra-amine (HMT)-induced 3D NiCo-MOF-based nanostructure as a potent bifunctional electrocatalyst with superior performance for overall water splitting in alkaline environments. The structural, morphological, and electrochemical properties of the as-synthesized bifunctional catalyst were examined thoroughly before analyzing its behavior towards electrochemical water splitting. The HMT-based NiCo-MOF demonstrated small overpotential values of 274 mV and 330 mV in reaching a maximum current density of 30 mA cm-2 for hydrogen and oxygen evolution mechanisms, respectively. The Tafel parameter also showed favorable HER/OER reaction kinetics, with slopes of 78 mV dec-1 and 86 mV dec-1 determined during the electrochemical evaluation. Remarkably, the NiCo-HMT electrode exhibited a double-layer capacitance of 4 mF cm-2 for hydrogen evolution and 23 mF cm-2 for oxygen evolution, while maintaining remarkable stability even after continuous operation for 20 hours. This research offers a valuable blueprint for implementing a cost-effective and durable MOF-based bifunctional catalytic system that has proven to be effective for complete water splitting. Decomposition of water under higher current densities is crucial for effective long-term generation and commercial consumption of hydrogen.

Photocatalytic hydrogen evolution mechanisms mediated by stereoactive lone pairs of Sb2VO5 in quantum dot heterostructures

Photocatalytic hydrogen evolution mechanisms mediated by stereoactive lone pairs of Sb2VO5 in quantum dot heterostructures

Nickel-based composites using tungsten carbides as enhancers for electroactivity for the hydrogen evolution reaction

This study explores the impact of incorporating tungsten carbides into a Watts bath on the fabrication of Ni/WC and Ni/W2C composites, comparing them with conventional Ni Watts electrodeposited electrodes. Results indicate that adding tungsten carbides to the conventional nickel bath forms rougher and more porous structures in the deposited composites. Composite electrodes exhibit significantly enhanced current density for hydrogen evolution in alkaline media compared to nickel Watts electrodes. Differential Electrochemistry Mass Spectrometry (DEMS) elucidates the hydrogen evolution mechanism, providing accurate data for Tafel plots. X-ray photoelectron spectroscopy (XPS) shows minimal impact on nickel's surface chemistry. X-ray diffractograms demonstrate that tungsten carbide particles maintain crystalline structure. X-ray dispersive spectroscopy (EDS) reveals an uneven chemical composition, with Ni/WC and Ni/W2C composites containing approximately 17% tungsten carbides. Electrochemical impedance spectroscopy (EIS) indicates higher electrochemical areas and lower charge transfer resistances in Ni/WC and Ni/W2C composites than in Ni Watts. This study contributes insights for the efficient and economical development of electrolysis systems. Notably, Ni/WC and Ni/W2C composites show promising electrochemical performance, emphasizing their potential in advancing electrolysis technology.

Self-assembly, structure and catalytic activity of Ni3 on TiO2: A triple-atom catalyst for hydrogen evolution

Triple-atom catalysts (TACs), structurally derived from single-atom catalysts (SACs) but beyond SACs in the active sites, have received increasing attention but are still in their infant stage. Using density functional theory, we study the self-assembly of the Ni3 trimer on TiO2 (Ni3/TiO2) by atom-by-atom deposition. Coordinatively unsaturated sites on the TiO2 surface are responsible for this self-assembly, resulting in different configurations of Ni3. According to the orientation relationship and lattice mismatch, an embryo of Ni crystal is thought to be born of triangle Ni3 trimer on TiO2. The hydrogen evolution reaction activity and mechanism of Ni3/TiO2 with different H coverages are evaluated using thermochemistry and kinetics calculations. Only at high H coverage would Ni3/TiO2 TACs exhibit a hydrogen production activity higher than that of Ni1/TiO2 SACs, indicating the matching relationship between multiple active sites and multi-step reaction intermediates for the active-site utilization. The quantum confinement effect throughout Nin/TiO2 (n = 1–3) is evidenced by the localization of metallic states of Nin. Our results not only open the possibility for synthesizing multimers on oxides by self-assembly, but also enrich the quantum control toolbox in few-atom catalysts by coordination modulation.

Study of the reaction mechanism in hydrogen production using metal-free Schiff base as a catalyst

Understanding the hydrogen evolution reaction and its mechanism is crucial for numerous practical applications in the realm of green energy. The development and discovery of new technologies or alternatives hold great significance in generating hydrogen at a low cost. In this study, we propose a novel catalyst, N, N'-bis(2-hydroxy-1-naphthaldehyde)-o-phenylenediamine ([naph]2-o-ph), which is a Schiff base, for hydrogen production. The novelty lies in utilizing the organic Schiff base system and the proposed mechanism for hydrogen evolution, involving protonation and electron exchange on the Schiff base. Both experimental and theoretical results highlight the high capability of the Schiff base in generating hydrogen, providing valuable insights for potential applications in water electrolysis.

Alternative to Conventional Solutions in the Development of Membranes and Hydrogen Evolution Electrocatalysts for Application in Proton Exchange Membrane Water Electrolysis: A Review.

Proton exchange membrane water electrolysis (PEMWE) represents promising technology for the generation of high-purity hydrogen using electricity generated from renewable energy sources (solar and wind). Currently, benchmark catalysts for hydrogen evolution reactions in PEMWE are highly dispersed carbon-supported Pt-based materials. In order for this technology to be used on a large scale and be market competitive, it is highly desirable to better understand its performance and reduce the production costs associated with the use of expensive noble metal cathodes. The development of non-noble metal cathodes poses a major challenge for scientists, as their electrocatalytic activity still does not exceed the performance of the benchmark carbon-supported Pt. Therefore, many published works deal with the use of platinum group materials, but in reduced quantities (below 0.5 mg cm-2). These Pd-, Ru-, and Rh-based electrodes are highly efficient in hydrogen production and have the potential for large-scale application. Nevertheless, great progress is needed in the field of water electrolysis to improve the activity and stability of the developed catalysts, especially in the context of industrial applications. Therefore, the aim of this review is to present all the process features related to the hydrogen evolution mechanism in water electrolysis, with a focus on PEMWE, and to provide an outlook on recently developed novel electrocatalysts that could be used as cathode materials in PEMWE in the future. Non-noble metal options consisting of transition metal sulfides, phosphides, and carbides, as well as alternatives with reduced noble metals content, will be presented in detail. In addition, the paper provides a brief overview of the application of PEMWE systems at the European level and related initiatives that promote green hydrogen production.

Suppressing gas swelling in self-assembled Li4Ti5O12 (4 0 0) for high-performance rechargeable batteries

Lithium titanate is a promising anode material for lithium-ion batteries due to its high-rate capability and long-cycle duration. However, gas swelling during electrochemical reactions has hindered its industrial application. Here, we synthesize self-assembled (400)-orientation lithium titanate (SA-LTONF) with ultrafine nanoparticles using a feasible thermal method. The SA-LTONF with an organic carbon coating exhibited superior electrochemical performance. To understand such high-rate capability, we perform density functional theory (DFT) calculations which elucidate the orientation-dependent electrochemical mechanism of hydrogen evolution and the atomically dynamic mechanism of lithium-ion migration in Li4Ti5O12 and Li7Ti5O12. Our findings provide a unique insight into the gas generation and ultrafast lithium-ion transportation in lithium titanate and offer guidance for nanoarchitecture construction and materials design of lithium titanate for commercial applications.

The incorporation of cocatalyst cobalt sulfide into graphitic carbon nitride: Boosted photocatalytic hydrogen evolution performance and mechanism exploration

2D-layered graphitic carbon nitride (g-C 3 N 4 ) is regarded as a great prospect as a photocatalyst for H 2 generation. However, g-C 3 N 4 's photocatalytic hydrogen evolution (HER) activity is significantly restricted by the recombination of photocarriers. We find that cobalt sulfide (CoS 2 ) as a cocatalyst can promote g-C 3 N 4 nanosheets (NSs) to realize very efficient photocatalytic H 2 generation. The prepared CoS 2 /g-C 3 N 4 hybrids display highly boosted photocatalytic H 2 generation performance and outstanding cycle stability. The optimized 7%-CoS 2 /g-C 3 N 4 hybrids show a much improved photocatalytic H 2 generation rate of 36.2 ​μmol −1 ​h −1 , which is about 180 times as much as bare g-C 3 N 4 (0.2 ​μmol −1 ​h −1 ). In addition, the apparent quantum efficiency (AQE) of all the samples was computed under light at λ=370 ​nm, in which the AQE of 7%-CoS 2 /g-C 3 N 4 hybrids is up to 5.72%. The experimental data and the DFT calculation suggest that the CoS 2 /g-C 3 N 4 hybrid's excellent HER activity is attributable to the lower overpotential and the smaller Co-H bond activation energy for HER. Accordingly, the CoS 2 cocatalyst loading effectively boosts the photocatalytic performance of g-C 3 N 4 for H 2 evolution. The project promotes fast development of high-efficiency photocatalysts and low-cost for photocatalytic H 2 generation.

Evaluation of the polarization resistance of protonic ceramic electrolysis cells with a triple-component composite electrode

Steam-electrolysis performance of protonic ceramics cells with Ni-cermet and triple-component composite electrodes composed of protonic ceramics, mixed proton–electron conductor, and catalysts was evaluated under different operating atmospheres at 500 °C to determine the effects of the catalysts on the electrode performance and electrochemical reaction mechanisms of steam splitting and hydrogen evolution. Here, Ba(Ce0.3Zr0.5Y0.1Yb0.1)O3-δ, (Ba0.95La0.05) (Fe0.8Zn0.2)O3-δ, and La0.8Sr0.2CoO3-δ were used as the protonic ceramics, mixed proton–electron conductor, and catalyst, respectively. Under a fuel-cell atmosphere, the steam vapor pressure (pH2O) at the airside and hydrogen partial pressure (pH2) at the fuel side were held constant at equal levels. In contrast, pH2O was higher and pH2 was lower under the electrolysis atmosphere. The higher pH2O at the airside decreased the air electrode impedance, but the lower pH2 at the fuel side significantly increased the fuel electrode impedance. The La0.8Sr0.2CoO3-δ catalyst facilitated the adsorption and dissociation of steam. Based on the study results, the mechanisms for steam splitting/dissociation at the triple-component composite electrode and hydrogen evolution at the Ni-cermet electrode are suggested.

Study of the Mechanism of Photoactivated Hydrogen Evolution on a Silicon Photocathode with a-MoSx Thin-Film Catalyst

Study of the Mechanism of Photoactivated Hydrogen Evolution on a Silicon Photocathode with a-MoSx Thin-Film Catalyst

Mechanical activation-enhanced doping and defect strategy to construct Fe–S co-doped carbon nitride for efficient photocatalytic tetracycline degradation and hydrogen evolution

Achieving a simultaneous increase in the redox performance of carbon nitride (CN) remains a challenge owing to the low utilization efficiency of photogenerated carriers. Herein, a novel “mechanical activation (MA)-enhanced doping and defect” strategy was proposed for structural modification of CN to enhance its performance. Specifically, CN, FeCl3, and thiourea were treated by MA to prepare a precursor with uniform dispersion and anchoring of Fe and S components in CN, and then the MA-treated precursor was calcinated to obtain a Fe–S co-doped CN composite (MA-Fe-S-CN) with abundant N vacancies. Under visible light illumination, MA-Fe-S-CN displayed outstanding photocatalytic performance for tetracycline (TC) removal (92.7%) and hydrogen evolution (2965 µmol g−1h−1) within 120 min, which was 3.3 and 4.1 times higher than those of CN, respectively. The superlative redox performance of MA-Fe-S-CN was attributed to that MA-enhanced Fe–S co-doping and N vacancies effectively modified the built-in electric field, electronic structure, and redox potential of CN. Experimental and theoretical analysis revealed that photogenerated electrons were trapped by N vacancies and directed to Fe active sites through efficient charge transfer channels (Fe–N and Fe–S), resulting in rapid charge transfer and effective separation and utilization of carriers. On this basis, possible mechanisms of photocatalytic TC degradation and hydrogen evolution were proposed. This work provides a green and economically feasible way for improving the redox performance of CN.

Mo‐Modified ZnIn2S4@NiTiO3 S‐Scheme Heterojunction with Enhanced Interfacial Electric Field for Efficient Visible‐Light‐Driven Hydrogen Evolution

AbstractDesigning and developing visible‐light‐responsive materials for solar to chemical energy is an efficient and promising approach to green and sustainable carbon‐neutral energy systems. Herein, a facile in situ growth hydrothermal strategy using Mo‐modified ZnIn2S4 (Mo‐ZIS) nanosheets coupled with NiTiO3 (NTO) microrods to synthesize multifunctional Mo‐modified ZIS wrapped NTO microrods (Mo‐ZIS@NTO) photocatalyst with enhanced interfacial electric field (IEF) effect and typical S‐scheme heterojunction is reported. Mo‐ZIS@NTO catalyst possesses wide‐spectrum light absorption properties, excellent visible light‐to‐thermal energy effect, electron mobility, charges transfer, and strong IEF and exhibits excellent solar‐to‐chemical energy conversion for efficient visible‐light‐driven photocatalytic hydrogen evolution. Notably, the engineered Mo1.4‐ZIS@NTO catalyst exhibits superior performance with H2 evolution rate of up to 14.06 mmol g−1 h− 1 and the apparent quantum efficiency of 44.1% at 420 nm. The scientific explorations provide an in‐depth understanding of microstructure, S‐scheme heterojunction, enhanced IEF, Mo‐dopant facilitation effect. Moreover, the theoretical simulations verify the critical role of Mo element in promoting the adsorption and activation of H2O molecules, modulating the H adsorption behavior on active S sites, and thus accelerating the overall catalytic efficiency. The photocatalytic hydrogen evolution mechanism via S‐scheme heterojunction with adjustable IEF regulation over Mo1.4‐ZIS@NTO is also demonstrated.

Promotion of photocatalytic hydrogen evolution induced by graphitic carbon nitride transformation from 2D flakes to 1D nanowires

In this contribution, a sustainable approach to fabricate one-dimensional (1D) graphitic carbon nitride (gCN) for photocatalytic hydrogen generation is reported. The strategy was based on L-ascorbic acid (LAA) modification of two-dimensional (2D) gCN leading to the formation of a 1D structure. The resultant gCN_1D exhibits an increased photocatalytic hydrogen generation rate of ∼18-fold and 4-fold with respect to 2D bulk-gCN and exfoliated gCN (ex-gCN), respectively. The photocatalytic mechanism of hydrogen evolution from water splitting was proposed based on a detailed physiochemical investigation of the catalyst prior and after the process. The enhanced photocatalytic H2 generation of the gCN_1D is achieved due to enhanced light harvesting, the better position of valance and conduction bands, higher porosity, faster transfer and charge separation of photogenerated carriers, and lower recombination rate resulting from 1D nanostructure. Additionally, promoted stability is assigned to the formation of an additional phase of the CN4O8 during the photocatalytic process.