Gibbs Free Energy Of Adsorption Research Articles

Nitrate Reduction Reaction on Zr-Doped TiO2 (101) Surfaces Investigated by First-Principles Calculations

Electrochemical nitrate reduction to ammonia is an efficient strategy for nitrate removal and ammonia production in ambient conditions. TiO2 is a promising electrocatalyst for such a reaction, but chemical doping is still needed to further improve the electrocatalytic properties of TiO2. Here, we investigated the effect of Zr-doping on the nitrate reduction reaction processes on the (101) surface of anatase TiO2 using first-principles calculations. Two models with different Zr-doping levels were built. The reaction pathways and the potential-determining steps were established based on a thorough investigation of the variation in Gibbs free energy of each possible elementary step. The results show that a high level of Zr doping was effective to lower the Gibbs free energy for nitrate adsorption; however, Zr doping may promote the competing hydrogen evolution reaction (HER) by reducing the adsorption Gibbs free energy of H. Moreover, Zr doping also increases the adsorption Gibbs free energies for the intermediate products NO2 and NO, which may result in an earlier termination of the reaction, by releasing the intermediates as the final products without producing ammonia. Therefore, Zr doping may decrease the Faradaic efficiency and selectivity of TiO2 for the reaction and should be treated with caution experimentally.

Synthesis of a nanocomposite with holocellulose extracted from barley straw and montmorillonite, and optimization of the removal of methylene blue dye using the synthesized adsorbent

In this study, holocellulose was extracted from milled barley straw with different mesh sizes using Laccase enzyme. After extraction, a dual composite was made using montmorillonite clay to remove methylene blue dye from synthetic effluent. Results of different analysis methods including scanning electron microscope, Fourier transform infrared spectroscopy, and BET revealed that prepared nanocomposite presented desired specifications, and for smaller mesh sizes, derived holocellulose had higher quality due to high specific surface area. Response surface methodology was employed to reduce the number of experiments for methylene blue adsorption experiments and to achieve an empirical model for prediction of adsorption efficiency at different operating conditions. The effect of different factors including solution temperature, pH, initial dye concentration, and mesh size of milled barley straw on dye adsorption performance by prepared composite was examined. Maximum removal efficiency was obtained about 95% at temperature of 32 °C, pH of 8, initial dye concentration of 4 mg L−1, and mesh size of 70. Also, isotherm studies were performed on experimental data using Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models and results revealed that the adsorption process follows Langmuir model with maximum predicted adsorption capacity of 159 mg g−1, which implies monolayer adsorption. Moreover, thermodynamic study revealed that adsorption of methylene blue is endothermic and spontaneous while enthalpy and Gibbs free energy of adsorption are positive and negative, respectively. Finally, adsorption kinetic study determined that the pseudo-second-order kinetics model with correlation coefficient of about 1 best fitted the experimental results which is the characteristic of chemisorption process.

Synthesis of Magnetite Coated Oleic Acid: Sequestration of Toluene and Xylene from Aqueous Solution and Cost Analysis

Toluene and xylene are carcinogenic and toxic compounds, and their presence in excessive amounts in the environment has an adverse impact on water quality, thus affecting public health. In this study, magnetite coated oleic acid, (MNP-OA) nanocomposite was synthesized, characterized and applied as an effective nano-adsorbent for the efficient removal of toluene and xylene from aqueous solutions. Magnetite nanoparticles were coated with oleic acid via the microwave method and characterized using BET surface area, XPS, SEM-EDX and pHpzc analysis. Batch adsorption studies were performed to optimize operating parameters including solution pH, adsorbent dose, contact time, and initial concentration. The impact of hydrophobic coating on the kinetics, equilibrium, and the mechanism of toluene and xylene uptake were determined. Characterization confirmed the surface coating of magnetite with oleic acid which evidenced from the additional oxygenated functional groups such as hydroxyl and carboxylic groups. The morphological analysis showed spherically shaped magnetite nanoparticles. Maximum adsorption capacity of 133.57 mg/g for toluene and 161.01 mg/g for xylene were attained at solution pH of 8, adsorbent dose of 0.1 g and concentration of 100 mg/dm3 at 298 K. The pseudo-second-order and Langmuir models best explained the kinetics and adsorption isotherm, respectively. The thermodynamic parameters, including Gibbs free energy, enthalpy change, and entropy change of adsorption indicated that the adsorption process was endothermic and spontaneous in nature. The MNP-OA nanocomposites can be applied as a reusable, cost-effective, and efficient adsorbent for toluene and xylene remediation and could be considered for other volatile organic compounds in future application.

Improvement of corrosion resistance for brass in 3.5% NaCl media by using 4- fluorophenyl-2, 5-dithiohydrazodicarbonamide

Corrosion poses a significant challenge for numerous industries. The use of corrosion inhibitors is essential within these industries. The efficacy of environmentally friendly corrosion inhibitors should remain high even when used at low concentrations. In the present study, the compound 4- fluorophenyl-2,5- dithiohydrazodicarbonamide (FTSC) was used as a corrosion inhibitor for brass in 3.5% NaCl solution. The inhibitor efficiency was determined by using a series of electrochemical techniques such as open circuit potential (OCP), potential dynamic polarisation (PDP), linear polarisation resistance (LPR), and electrochemical impedance spectroscopy (EIS). All experimental tests have been done in stagnant conditions. The findings of the experiments revealed that the compound FTSC looked to be of the cathodic type. Furthermore, the maximum inhibitor efficiency was reached at 98.28% at 1 × 10-3 and at an immersion time of 1 h. The current density was reduced from 16.5 to 0.284 A.cm-2. The adsorption of compound on the brass surface in 3.5% NaCl solution obeyed the Langmuir isotherm with a low negative value of the standard Gibbs free energy of adsorption (-33.8 kJ/mol ΔGads (chemisorption and physisorption). The results confirmed that the compound FTSC can be used as a corrosion inhibitor for brass in 3.5% NaCl.

Machine learning assisted screening of doped metals phosphides electrocatalyst towards efficient hydrogen evolution reaction

Transition metals (TM) doped metal phosphides usually exhibits promising reactivity towards acidic hydrogen evolution reaction (HER). However, the experimental screening of highly active TM-doped metal phosphides catalyst is time-consuming and challenging. In this study, a density functional theory combined machine learning (DFT-ML) framework is proposed to accelerate the screening and predicting TM-doped metal phosphides-based HER electrocatalysts. In this framework, the ML database is constructed using critical catalyst features and DFT-calculated adsorption energy of HER intermediates. Also, local average electronegativity of the adsorption site and the surrounding atoms as catalyst feature is proposed to describe the reaction sites in this ML model. Using the HER energetics on the state-of-art highly active Pt (111) as benchmark catalyst model, a set of 10 potential active HER catalysts is predicted. By performing the H* adsorption Gibbs free energy change analysis on these ML-predicted catalysts, six promising TM-doped metal phosphides HER catalysts are determined in the sample space. This study provides a facile and effective approach for the quick screening of high-performance HER electrocatalysts.

Simple activation effect on the EC hydrolysis performance of MOF structure

Transition metal-based metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) are considered as the ideal substitutes or supports for electrochemical catalysis field. However, due to the limited number of surface-active sites and the low conductivity of the bulk of MOFs/COFs, their electrocatalytic (EC) performance is usually promoted by the complicated multi-step decoration procedures. In this paper, a simple sequential-activation-step was verified to have the ability to improve considerably the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance of pristine Co-MOF (ZIF-67) material. For example, NC@Co from the carbonized and electrochemical activated ZIF-67 exhibited enhanced OER properties, while NC@CoxOy obtained via a sequential carbonize-oxidized-electrochemical activated procedure on ZIF-67 exhibited outstanding HER performance relatively. Density Functional Theory (DFT) calculations indicated that the in situ generated CoOOH was attributed to the improved HER/OER performance of the corresponding ZIF-67 activated derivatives with the redistribution of electron density, increased conductivity, and the optimized adsorption Gibbs free energy of hydrolysis intermediates. This work presents potential directions for the application of MOFs or COFs in the fields of electrochemical energy conversion through the electrochemical pathways.

Evidence for an Interface of Hybrid Cocatalysts Favoring Photocatalytic Hydrogen Evolution Kinetics.

Hybrid cocatalysts have great application potential for improving the photocatalytic hydrogen evolution performance of semiconductors. The interfaces between components of hybrid cocatalysts make a great contribution to the improvement, but the associated mechanisms remain unclear. Herein, we prepared and tested three comparative CdS-based photocatalysts with NiS, NiS/Ni9S8, and Ni9S8 as the cocatalysts separately. The emphasis is placed on investigating the effect of the NiS/Ni9S8 interfaces on the photocatalytic hydrogen evolution performance of CdS. NiS/Ni9S8 exhibits a higher ability than NiS and Ni9S8 in making CdS a more active photocatalyst for water splitting. It shows that NiS, NiS/Ni9S8, and Ni9S8 perform similarly in terms of promoting the charge transfer and separation of CdS based on steady-state and time-resolved photoluminescence studies. At the same time, the linear sweep voltammetry and electrochemical impedance spectroscopy tests combined with the density functional theory calculations reveal that the component interfaces of NiS/Ni9S8 enable us to lower the water splitting activation energy, the charge-transfer resistance from the cocatalyst to sacrificial agent, and hydrogen adsorption Gibbs free energy. It is evidenced from this work that component interfaces of hybrid cocatalysts play a vital role in accelerating the dynamics of hydrogen evolution reactions.

Cefalexin adsorption on the surface of pristine and Al-doped boron nitride nanocages (B12N12 and AlB11N12): A theoretical study

In this study, the capability of pristine and Al-doped BN nanocages (B12N12 and AlB11N12) as sensor and adsorbent for the detection and removal of cefalexin antibiotic as an emerging environmental contaminant was investigated by infra-red (IR), frontier molecular orbital (FMO) and natural bond orbital (NBO) computations. The obtained negative values of adsorption energies, adsorption enthalpy changes and Gibbs free energy changes showed cefalexin interaction with both nanostructures is experimentally possible, exothermic, and spontaneous. The NBO results showed cefalexin adsorption on the B12N12 surface is a chemisorption but its interaction with AlB11N12 is a physisorption and the calculated values of thermodynamic constants also confirmed this subject. The influence of temperature on the adsorption processes was also scrutinized and the obtained results demonstrated cefalexin interaction with both adsorbents is more favorable at lower temperatures. The computed density of states (DOS) spectrums showed when cefalexin adsorbs on the surface of B12N12, the bandgap of nanostructure declined -39.052 % from 14.908 (eV) to 9.130 (eV). But in the case of Al-doped nanocage, the bandgap decreased -63.718 % from 12.830 (eV) to 4.655 (eV). The strong and chemisorption nature of cefalexin interaction with B12N12 and relatively subtle decline of nanostructure bandgap suggested that B12N12 can be a potential adsorbent for the removal of cefalexin but it cannot be a suitable sensing material for its detection. However, the semi-chemisorption nature of cefalexin interaction with AlB11N12 and tangible decreasing of adsorbent bandgap showed AlB11N12 is an ideal sensing material for the development of new disposable electrochemical sensors for detection of cefalexin.

Modulating electronic structure and sulfur p-band center by anchoring amorphous Ni@NiSx on crystalline CdS for expediting photocatalytic H2 evolution

Photocatalytic water splitting is a prospective approach to address the energy and environmental challenges. Herein, an amorphous Ni@NiSx cocatalyst has been fabricated and simultaneously assembled onto CdS to form amorphous-crystalline Ni@NiSx-CdS photocatalyst via a partial reduction strategy. Comprehensive experiments and theoretical calculations demonstrate that the synergistic effects between the electronic coupling of amorphous-crystalline interface and the gradient work function variation induced by Ni nanocluster encapsulation achieve the deeper downshift of the S p-band center to optimize H* intermediate adsorption, enhance charge extraction ability though Schottky junction and lower H* adsorption Gibbs free energy (ΔGH*). Accordingly, the optimal Ni@NiSx-CdS photocatalyst delivers a remarkable photocatalytic H2 production rate of 78.7 mmol·g−1·h−1 with an apparent quantum efficiency (AQE) of 36.74% at 420 nm, which is approximately 18.3 and 1.5 times than that of CdS and NiSx-CdS, respectively. This work offers a novel insight into the development of amorphous nanocomposite cocatalysts for promoting solar-to-H2 energy conversion.

Synergistic experimental and computational approaches for evaluating pyrazole Schiff bases as corrosion inhibitor for mild steel in acidic medium

In this investigation, the efficiency of a pyrazole Schiff base as a corrosion inhibitor for mild steel in an acidic setting (1 M HCl) was examined. Several tests, including electrochemical impedance spectroscopy (EIS), weight loss (WL), and potentiodynamic polarization (PDP), showed the inhibitor's strong efficiency in averting corrosion on the metal surface. Inhibition efficiencies for CPMNA and CMPMA at 300 ppm and 298 K, respectively, were 94.60 % and 91.99 %. Inhibition efficiencies varied with temperature and inhibitor concentration. At 318 K, their efficiency marginally declined to 89.17 % and 88.20 %.We also delved into the kinetic and thermodynamic properties of inhibitor sorption and mild steel deterioration. The Gibbs free energy of adsorption (Gads), which includes chemisorption and physisorption, indicates multimodal adsorption. Surface data further confirmed these observations. Research performed on surface morphology, including contact angle (CA) measurements, electron dispersive X-ray (EDX), and scanning electron microscopy (SEM), provided additional support for these inferences. Fukui functions, Density Functional Theory (DFT), Molecular Dynamics Simulation (MDS), and RDF analysis were several instances of computational simulation strategies that verified good agreement with experimental results. Overall, this research offers pertinent information to scientists seeking to create stronger organic corrosion inhibitors.

In-situ fabrication of vertical heterogeneous nickel diselenide-molybdenum diselenide architectures as bifunctional overall water-splitting electrocatalyst

Despite the rapid advances in electrocatalysts based on two-dimensional (2D) transition metal dichalcogenides (TMDs) materials, they are subject to serious aggregation, poor conductivity and the presence of inactive basal planes. Herein, we have successfully demonstrated the in-situ construction of NiSe2–MoSe2 heterostructure arrays on carbon cloth (NiSe2–MoSe2/CC) by a facile two-step hydrothermal process. The presence of the synergistic effect in the heterostructures effectively optimizes the poor conductivity and hydrophilicity, and thus enables fast electron transfer, leading to enhanced electrochemical reaction. Furthermore, density functional theory calculations reveal that the electrons redistribution at the heterojunction interface and the reduced Gibbs free energy of hydrogen adsorption for hydrogen evolution reaction (HER)/the Gibbs free energy change value of rate-determining step for oxygen evolution reaction (OER), thus enhancing the HER/OER catalytic activity. Importantly, the device displays a good performance with a low overpotential of 98 and 310 mV for HER and OER, respectively, and a low cell voltage of 1.59 V for its corresponding electrolyzer (10 mA cm−2). This work presents the high-performance water splitting of bifunctional electrocatalysts based on 2D TMDs materials and offers a novel design concept of interface engineering.

N‐(4‐Chloromethylbenzyl)‐N, N‐dimethyldodecan‐1‐aminium Chloride: A Quaternary Ammonium Surfactant as Corrosion Inhibitor

AbstractThis study used a quaternary surfactant, N‐(4‐Chloromethylbenzyl)‐N, N‐dimethyldodecan‐1‐aminium chloride (CMBDAC), as an excellent corrosion inhibitor of C1018 carbon steel (C1018 CS) in harsh 15 % HCl acidizing condition. CMBDAC was synthesized with an excellent yield and characterized by NMR, FTIR, and TGA. Gravimetric weight loss (WL), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) studies were employed to measure the efficacy of CMBDAC. At a relatively low concentration of 15 ppm, CMBDAC surpassed 90 % inhibition efficiency, with a maximum inhibition efficiency of 99.25 % being reached just for 50 ppm of CMBDAC. The inhibitor showed an efficacy of 96.16 % even at a temperature of 60 °C via the WL technique, showing potential to be used as a high‐temperature corrosion inhibitor. The adsorption isotherm study revealed that CMBDAC followed Langmuir adsorption isotherm. The Gibbs free energy of adsorption ( was calculated to be −40.43 kJ mol−1, indicating that CMBDAC was adsorbed via chemisorption. A very high value (1.68×105 L mol−1) of equilibrium constant ( ) suggested very strong adsorption of the inhibitor. PDP study disclosed that CMBDAC acted as a mixed‐type inhibitor. SEM‐EDX study demonstrated the adsorption of CMBDAC on the C1018 surface. Different DFT‐optimized parameters have been discussed in detail to support the superb inhibitory action indicated by CMBDAC.

Adsorption and desorption of acetone by TiO2 clusters: Transition state theory and sensing analysis

TiO2 cluster sensitivity to acetone adsorption using transition state theory is investigated. Ti10O20 cluster is used to perform the calculations using density functional theory with dispersion corrections. Adsorption state and transition state are calculated via thermodynamic energies, i.e., Gibbs free energy of adsorption and activation. Reaction rate, response, response time, and recovery time as a function of temperature and acetone concentration are calculated. Acetone burning in the air due to autoignition is considered using a logistic function. The results of the theory are compared with available experimental findings that revealed the quality of both theoretical and experimental results. The response time decreases with respect to acetone concentration. On the other hand, the recovery time in the desorption phase increases with acetone concentration. The temperature of maximum response is 356 °C, while the maximum response value is 2.9.

Immobilization of Co nanoparticles into N-doped carbon nanotube on g-C3N4 via coordination-polymerization integrated strategy for efficient H2 evolution reaction at all pH values

Constructing Co-based carbon nanotubes/g-C3N4 structure via integrated strategy remains a challenge in cobalt-based electrocatalysis. We firstly proposed a coordination-polymerization integrated strategy for the preparation of Co@N-CNT@g-C3N4 with efficient hydrogen evolution reaction at all pH values. In Co@N-CNT@g-C3N4, Co nanoparticles were encapsulated in the tip of carbon nanotubes and carbon nanotubes grew on g-C3N4 to bridge Co particles and g-C3N4. More importantly, Co particles, carbon nanotubes, and g-C3N4 were assembled simultaneously skillfully to construct a closely integrated interface, thereby enhancing electron transfer efficiency. Electrochemical tests showed that the structure has high catalytic activity, with overpotentials of 61, 145, and 170 mV in 1 M KOH, 0.5 M H2SO4 and 1.0 M phosphate buffer saline (PBS), respectively, to drive 10 mA cm−2. Additionally, the Gibbs free energy for hydrogen adsorption (∆GH*) on the Co surface of Co@N-CNT@g-C3N4 was only − 0.13 eV, which was conducive to H2 formation.

Agglomeration Drives the Reversed Fractionation of Aqueous Carbonate and Bicarbonate at the Air-Water Interface.

In the course of our investigations of the adsorption of ions to the air-water interface, we previously reported the surprising result that doubly charged carbonate anions exhibit a stronger surface affinity than singly charged bicarbonate anions. In contrast to monovalent, weakly hydrated anions, which generally show enhanced concentrations in the interfacial region, multivalent (and strongly hydrated) anions are expected to show a much weaker surface propensity. In the present work, we use resonantly enhanced deep-UV second-harmonic generation spectroscopy to measure the Gibbs free energy of adsorption of both carbonate (CO32-) and bicarbonate (HCO3-) anions to the air-water interface. Contrasting the predictions of classical electrostatic theory and in support of our previous findings from X-ray photoelectron spectroscopy, we find that carbonate anions do indeed exhibit much stronger surface affinity than do the bicarbonate anions. Extensive computer simulations reveal that strong ion pairing of CO32- with the Na+ countercation in the interfacial region results in the formation of near-neutral agglomerate clusters, consistent with a theory of interfacial ion adsorption based on hydration free energy and capillary waves. Simulated X-ray photoelectron spectra predict a 1 eV shift in the carbonate spectra compared to that of bicarbonate, further confirming our experiments. These findings not only advance our fundamental understanding of ion adsorption chemistry but also impact important practical processes such as ocean acidification, sea-spray aerosol chemistry, and mammalian respiration physiology.

Ru-Cu Nanoheterostructures for Efficient Hydrogen Evolution Reaction in Alkaline Water Electrolyzers.

Combining multiple species working in tandem for different hydrogen evolution reaction (HER) steps is an effective strategy to design HER electrocatalysts. Here, we engineered a hierarchical electrode for the HER composed of amorphous-TiO2/Cu nanorods (NRs) decorated with cost-effective Ru-Cu nanoheterostructures (Ru mass loading = 52 μg/cm2). Such an electrode exhibits a stable, over 250 h, low overpotential of 74 mV at -200 mA/cm2 for the HER in 1 M NaOH. The high activity of the electrode is attributed, by structural analysis, operando X-ray absorption spectroscopy, and first-principles simulations, to synergistic functionalities: (1) mechanically robust, vertically aligned Cu NRs with high electrical conductivity and porosity provide fast charge and gas transfer channels; (2) the Ru electronic structure, regulated by the size of Cu clusters at the surface, facilitates the water dissociation (Volmer step); (3) the Cu clusters grown atop Ru exhibit a close-to-zero Gibbs free energy of the hydrogen adsorption, promoting fast Heyrovsky/Tafel steps. An alkaline electrolyzer (AEL) coupling the proposed cathode and a stainless-steel anode can stably operate in both continuous (1 A/cm2 for over 200 h) and intermittent modes (accelerated stress tests). A techno-economic analysis predicts the minimal overall hydrogen production cost of US$2.12/kg in a 1 MW AEL plant of 30 year lifetime based on our AEL single cell, hitting the worldwide targets (US$2-2.5/kgH2).

Carbon dots tailoring the interfacial proton and charge transfer of iridium nanowires with stress strain for boosting bifunctional hydrogen catalysis

The effective harnessing of hydrogen energy relies on the development of bifunctional electrocatalysts that facilitate hydrogen evolution/oxidation reactions (HER/HOR) with high catalytic activity. The design of such electrocatalysts requires the consideration of not only the volcano relationship with hydrogen binding energy (HBE) or hydrogen adsorption Gibbs free energy (ΔGH) but also the regulation of catalytic kinetics such as interfacial proton/electron transfer. In this work, unique one-dimensional iridium nanowires with compressive stress are successfully prepared and combined with carbon dots (Ir NWs/CDs). Acting as an electrocatalyst for HER in 0.5 M H2SO4, the optimal Ir NWs/CDs only requires an 18 mV overpotential to achieve a current density of −10 mA cm−2. Furthermore, the optimal Ir NWs/CDs shows high HOR performance with a mass activity (@ 50 mV versus RHE) 1.5 times that of 20% Pt/C and excellent anti-CO toxicity ability which is twice the level of the PtRu/C catalyst. Ir NWs/CDs exhibit enhanced HER/HOR activity due to (1) the appropriate modulation of the binding energy to hydrogen intermediate facilitated by the compressive stress applied to the Ir structure and (2) the improved proton/electron transfer kinetics by optimizing the electronic properties and surface structures through tailored CDs. This study delivers a new strategy for designing and synthesizing efficient acidic HER/HOR bifunctional catalysts.

Exploring the catalytic properties of Ti2CO2 MXene decorated with Cu-cluster for Hydrogen evolution reaction

Catalysts based on non-noble and cost-effective metals are crucial for the hydrogen evolution reaction (HER) to obtain a viable source of renewable energy in the form of hydrogen. MXene is one of the 2D materials that has recently drawn much interest due to its intriguing catalytic properties. In this work, employing density functional theory we have systematically studied and compared the HER activity of Ti2CO2 MXene with adsorbed Cu3 and Cu5 clusters on top. Our findings suggest that the Ti2CO2 MXene with adsorbed Cu3 cluster exhibits significant enhancement in catalytic activity towards HER. The Gibbs free energy of hydrogen adsorption (ΔGH∗) is found to be −0.08 eV, which is close to the ideal value, suggesting comparable catalytic activity to platinum. In contrast, the Ti2CO2-Cu5 catalyst exhibits a higher Gibbs free energy value of 0.105 eV for HER. The stability of the structures was evaluated by assessing the cohesive and binding energies, supported by Ab Initio Molecular Dynamics (AIMD) simulations. A thorough analysis of the electronic structure and bonding nature of the catalysts are presented. These analyses suggest that the boost in catalytic activity could be ascribed to the accumulated charge at the centre of the Cu3 cluster. Based on our comparison, the Ti2CO2-Cu3 catalyst emerges as a more suitable candidate for the HER process, highlighting its potential as a cost-effective and efficient HER catalyst.

Modulation of chalcogen‐functionalized MXenes Ti2CT2 (T = O, S, Se, and Te) as catalysts for hydrogen evolution reaction

AbstractExploration and exploitation of efficient and nonprecious catalysts for hydrogen evolution reaction (HER) is one of the key solutions to energy problems. Two‐dimensional (2D) MXenes have attracted extensive attention as potential catalysts and supports due to their unique structure and customizable properties. In this work, we have systematically investigated the structural stability and electronic properties of chalcogen‐functionalized MXenes Ti2CT2 (T = O, S, Se, and Te) and Pt‐anchored Ti2CT2 MXenes (Pt‐Ti2CT2). Density functional theory calculations have discovered that all Ti2CT2 exhibit metallic electronic structures except Ti2CO2 with an indirect bandgap. Additionally, the electronic densities of states at Fermi level for Pt‐Ti2CT2 are greatly enhanced after anchoring Pt atoms. The reduction of chalcogen electronegativity is recognized to mainly contribute to weaker bond strength but greater electronic activity. Moreover, Pt‐Ti2CTe2 is predicted to exhibit near‐zero Gibbs free energy of hydrogen adsorption especially at high hydrogen coverage, indicating its significant potential as HER catalysts. It is also revealed that Ti2CT2 and Pt‐Ti2CT2 MXenes are not only ideal candidates of catalyst materials but also could serve as good catalyst substrates. This work provides insights into the structural and chemical complexity of MXenes for catalyst applications but also demonstrates a new strategy to modulate high‐efficiency and low‐cost catalyst and support materials.

Mo2C nanocrystalline coupling with Ni encapsulated in N-doped fibrous carbon network as bifunctional catalysts towards advanced anion exchange membrane electrolyzers

Anion exchange membrane water electrolysis (AEMWE) has been considered to be the promising approach for cost-effective hydrogen production. However, the noble metal catalysts of AEM enable it still under the early stage of development. Herein, Mo2C nanocrystalline coupling with Ni have been successfully encapsulated into robust carbonaceous network (Mo2C/NC@0.5Ni) as inexpensive transition metal catalysts for AEM electrolyzers. The Mo2C nanocrystals are uniformly confined in N doped porous carbon network which is derived from the decomposition of PVP and urea during carbonation process. Importantly, rational designed Ni layers are also coated on the surface of the network structure. When utilized as bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the Mo2C/NC@ 0.5Ni can achieve desirable overpotentials of 103 mV and 307 mV at a current density of 10 mA cm−2 in 1 M KOH, respectively. Furthermore, the Mo2C/NC@ 0.5Ni‖Mo2C/NC@ 0.5Ni AEM electrolyzers requires only a voltage of 1.9 V to reach a current density of 110.5 mA cm−2 with remarkable durability over 50 h. Numerous interconnected porous structure and defects caused by N doping can provide abundant active sites, facilitate electrons transportations and suppress the aggregation of inner Mo2C. Particularly, the conductive Ni layers could effectively improve the structural strength and induce the synergistic effect with Mo2C component, thereby, improving the catalytic activity and stability. In addition, the DFT calculation results indicate that the Mo2C/NC@ 0.5Ni catalyst has a lower Gibbs free energy of hydrogen adsorption (ΔGH*=−0.21 eV), which is beneficial to its HER catalytic activity. This work provides an insight in developing advanced AEMWE for high efficient and green hydrogen production.