Modulation of the B4N monolayer as an efficient electrocatalyst for hydrogen evolution reaction

Exploring stable catalysts with an efficient hydrogen evolution reaction (HER) arises intense concerns due to its renewable and low-cost properties. In this work, we have systematically investigated a two-dimensional (2D) material, namely, B₄N monolayer as efficient HER electrocatalysts based on first-principles computations. When the material is metal-free, the calculated Gibbs free energy (ΔG_H1) corresponding to hydrogen coverages of 2/4 reaches to 0.005 eV, which is better than that of the Pt catalyst. Moreover, we also find that the HER activity of the B₄N monolayer is sensitive to the strains-driven. The single metal atom supported on B₄N can still make the value of ΔG_H1 close to 0 eV for Cr/B₄N and V/B₄N. These results reveal that the B₄N monolayer is a promising candidate for HER applications.     

Metal-nonmetal atom co-doping engineered transition metal disulfide for highly efficient hydrogen evolution reaction

The development of effective and non-precious electrocatalyts for hydrogen evolution reaction (HER) has attracted massive research interests. Herein, we report a density functional theory (DFT) investigation on the activation and optimization of Molybdenum disulfide (MoS₂) monolayer as efficient HER electrocatalysts by cobalt-nonmetal atom (X = B, C, N, P, Se) codoping. Our results show that three CoX-MoS₂ (X = C, N, and Se) catalysts display enhanced HER performance with |ΔG_H|s in the range of 0.12–0.23 eV. Careful electronic structure analysis manifests that the favorable H adsorption process on the MoS₂ basal plane is induced by suitable in-gap states upon codoping. Furthermore, appropriate biaxial strain can help optimize the HER performance of these co-doped systems, e.g, the ΔG_Hs of CoC@MoS₂, CoN@MoS₂, and CoSe@MoS₂ reaches 0.0 eV, ?0.04 eV, and ?0.01 eV at 1.86% tensile strain, 5% compressive strain, and 4% compressive strain, respectively. Our work offers a highly promising catalyst for HER and guides the atomic design of more efficient non-noble electrocatalysts.     

Li-decorated B2O as potential candidates for hydrogen storage: A DFT simulations study

Two-dimensional (2D) B₂O monolayer is considered as a potential hydrogen storage material owing to its lower mass density and high surface-to-volume ratio. The binding between H₂ molecules and B₂O monolayer proceeds through physisorption and the interaction is very weak, it is important to improve it through appropriate materials design. In this work, based on density functional theory (DFT) calculations, we have investigated the hydrogen storage properties of Lithium (Li) functionalized B₂O monolayer. The B₂O monolayer decorated by Li atoms can effectively improve the hydrogen storage capacity. It is found that each Li atom on B₂O monolayer can adsorb up to four H₂ molecules with a desirable average adsorption energy (E_ave) of 0.18 eV/H₂. In the case of fully loaded, forming B₃₂O₁₆Li₉H₇₂ compound, the hydrogen storage density is up to 9.8 wt%. Additionally, ab initio molecular dynamics (AIMD) calculations results show that Li-decorated B₂O monolayer has good reversible adsorption performance for H₂ molecules. Furthermore, the Bader charge and density of states (DOS) analysis demonstrate H₂ molecules are physically absorbed on the Li atoms via the electrostatic interactions. This study suggests that Li-decorated B₂O monolayer can be a promising hydrogen storage material.     

First principles of Si-doped BC2N single layer for hydrogen evolution reaction (HER)

Understanding the Hydrogen Evolution Reaction (HER) process is fundamental to use hydrogen as a sustainable (clean and renewable) energy source. Using first-principles calculations, we study the HER process when Si-doped a h-BC₂N single layer. The pristine BC₂N presents semiconducting properties with a band gap of 1.6–2.0 eV, being appropriate as a catalytic in the water splitting process. When Si is incorporated into the BC₂N monolayer, we obtain that the most stable site (lower formation energy) occurs when the Si atom replaces a C atom (Si_C). The Si atom moves out of the plane forming a buckling structure and the semiconducting properties are maintaining without spin effects. However, Si_B and Si_N give rise to two unpaired spin electronic levels inside the band gap and a magnetic moment of 1 μ_B. The adsorption energies of an H₂ molecule on the top of the Si atom are in the range of 50–100 meV, which are greater than the calculated ones for H₂ adsorbed on graphene and h-BN nanosystems but still low to be considered as an optimized medium for hydrogen storage. In addition, we observe that dispersive forces (van der Waals interactions) are responsible for half part of the adsorption energies. Strain due to the difference between the atomic radius of Si and C as well as the less stability of the Si–H bonds compared to the C–H ones leads to the Gibbs free energy (ΔG1) for hydrogen adsorbed on Si_C near zero, showing that Si-doped h-BC₂N is a potential system for HER.     

Catalytic activity for hydrogen evolution reaction of Janus monolayer MoXTe (X=S,Se)

At present, the precious metal Pt is a common catalyst for large-scale hydrogen evolution reaction (HER) production of hydrogen, but due to its high price and scarcity, finding an innovative catalyst has become the key to electrocatalytic hydrogen evolution. Here, the HER electrocatalytic activity of Janus MoXTe (X = S, Se) monolayers was investigated through first-principles calculations. Mo vacancy, X vacancy and Te vacancy were introduced into 2H, 1T, and 1T’ phase respectively and their stability was studied. The results show that the introduction of vacancy can improve the electrocatalytic hydrogen evolution performance. Particularly, the Gibbs free energies (ΔG_H) of Te vacancy of 2H phase MoSTe and MoSeTe are close to zero (ΔG_H = 0.03, −0.05 eV, respectively), and has the highest exchange current density. We further find that the conductivity of 2H phase MoSTe and MoSeTe is enhanced after introducing Te vacancy. In details, H get 1.86 and 1.43 e on V_Te in 2H phase MoSTe and MoSeTe. The bond between S and H is more stable, H is better adsorbed on the catalyst, and the performance is improved. Our research provides a strategy for designing MoXTe monolayer electrocatalysts, which are predicted to be employed in HER catalysts with low cost and high performance.     

Enhancement of hydrogen storage capacity on co-functionalized GaS monolayer under external electric field

Hydrogen storage properties of co-functionalized 2D GaS monolayer have been systematically investigated by first-principles calculations. The strength of the binding energy of hydrogen (H₂) molecules to the pristine GaS surface shows the physisorption interactions. Co-functionalized GaS sheet by Li, Na, K and Ca atoms enhanced the capacity of binding energies of hydrogen and strength of hydrogen storage considerably. Besides, DFT calculations show that there is no structural deformation during H₂ desorption from co-functionalized GaS surface. The binding energies of per H₂ molecules is found to be 0.077 eV for pristine GaS surface and 0.064 eV–0.37 eV with the co-functionalization of GaS surface. Additionally, in the presence of applied external electric field enhanced the strength of binding energies and it is found to be 0.09 eV/H₂ for pristine GaS case and 0.19 eV/H₂ to 0.38 eV/H₂ for co-functionalized GaS surface. Among the studied GaS monolayer is found to be the superior candidate for hydrogen storage purposes. The theoretical studies suggest that the electronic properties of the 2D GaS monolayer show the electrostatic behavior of hydrogen molecules which confirms by the interactions between adatoms and hydrogen molecules before and after hydrogen adsorption.     

C7N6 monolayer as high capacity and reversible hydrogen storage media: A DFT study

Searching advanced materials with high capacity and efficient reversibility for hydrogen storage is a key issue for the development of hydrogen energy. In this work, we studied systematically the hydrogen storage properties of the pure C₇N₆ monolayer using density functional theory methods. Our results demonstrate that H₂ molecules are spontaneously adsorbed on the C₇N₆ monolayer with the average adsorption energy in the range of 0.187–0.202 eV. The interactions between H₂ molecules and C₇N₆ monolayer are of electrostatic nature. The gravimetric and volumetric hydrogen storage capacities of the C₇N₆ monolayer are found to be 11.1 wt% and 169 g/L, respectively. High hardness and low electrophilicity provides the stabilities of H₂–C₇N₆ systems. The hydrogenation/dehydrogenation (desorption) temperature is predicted to be 239 K. The desorption temperatures and desorption capacity of H₂ under practical conditions further reveal that the C₇N₆ monolayer could operate as reversible hydrogen storage media. Our results thus indicate that the C₇N₆ monolayer is a promising material with efficient, reversible, and high capacity for H₂ storage under realistic conditions.     

Geometric structures and hydrogen storage properties of M2B7 (M=Be,Mg, Ca) clusters

Based on the density functional theory, we investigate the electronic properties of the clusters M₂B₇ (M = Be, Mg, Ca) and their hydrogen storage properties systematically in this paper. Extensive global search results show that the global minimal structures of the three systems (Be₂B₇, Mg₂B₇ and Ca₂B₇) are heptagonal biconical structure, and the two alkaline earth metals are located at the top of the biconical. Chemical bonding analyses show that M₂B₇ clusters have 6σ and 6π delocalized electrons, which are doubly aromatic. At the wB97XD level, the three systems have good hydrogen storage capabilities. The hydrogen storage density of Be₂B₇ is as high as 23.03 wt%, while Mg₂B₇ and Ca₂B₇ also far exceed the hydrogen storage target set by the U.S. Department of Energy in 2017. Their average adsorption energies of H₂ molecules all ranged from 0.1 eV/H₂ to 0.48 eV/H₂, which is fall in between physisorption and chemisorption. Extensive Born Oppenheimer molecular dynamics (BOMD) simulations show that the H₂ molecules of the three systems can be completely released at a certain temperature. Therefore, M₂B₇ systems can achieve reversible adsorption of H₂ molecules at normal temperature and pressure. It can be seen that the B₇ clusters modified by alkaline earth metals may become a promising new nano-hydrogen storage material.     

Hydrogen storage properties of Li-decorated B2S monolayers: A DFT study

Hydrogen storage properties of Li functionalized B₂S honeycomb monolayers are studied using density functional theory calculations. The binding of H₂ molecules to the clean B₂S sheet proceeds through physisorption. Dispersed Li atoms on the monolayer surface increase both the hydrogen binding energies and the hydrogen storage capacities significantly. Additionally, ab initio molecular dynamics calculations show that there is no kinetic barrier during H₂ desorption from lithiated B₂S. Among the studied B₈S₄Li_x (x = 1, 2, 4, and 12) compounds, the B₈S₄Li₄ is found to be the most promising candidate for hydrogen storage purposes; with a 9.1 wt% H₂ content and 0.14 eV/H₂ average hydrogen binding energy. Furthermore, a detailed analysis of the electronic properties of the B₈S₄Li₄ compound before and after H₂ molecule adsorption confirms that the interactions between Li and H₂ molecules are of electrostatic nature.     

Ultra-high capacity hydrogen storage of B6Be2 and B8Be2 clusters

The B₆Be₂ and B₈Be₂ clusters, adopting fascinating inverse sandwich-like geometries, were recently predicted with quantum chemical calculations. Both systems exhibit the high stability and double aromaticity with 4σ/6π or 6σ/6π delocalized electrons. The hydrogen storage of two systems is studied in the present paper. Our calculations show that B₆Be₂ and B₈Be₂ clusters have the ultra-high capacity hydrogen storage, each Be site can bound up with seven H₂ molecules, corresponding to a gravimetric density of 25.3 wt percentage (wt%) for B₆Be₂ and 21.1 wt% for B₈Be₂, respectively, which far exceeds the target (5.5 wt%) proposed by the US department of energy (DOE) in 2017. The average absorption energies of 0.10–0.45 eV/H₂ for B₆Be₂ and 0.11–0.50 eV/H₂ for B₈Be₂ at the wB97XD level suggest that both systems are ideal for reversible hydrogen storage and release. The reversibility of H₂ molecules on B₆Be₂ and B₈Be₂ complexes are faithfully demonstrated with the Born-Oppenheimer molecular dynamics (BOMD) simulations. The Be-doped boron nanostructure is a promising candidate for ultra-high hydrogen storage materials.     

First-principles study of superior hydrogen storage performance of Li-decorated Be2N6 monolayer

The potential application of pristine Be₂N₆ monolayer and Li-decorated Be₂N₆ monolayer for hydrogen storage is researched by using periodic DFT calculations. Based on the obtained results, the Be₂N₆ monolayer gets adsorb up to seven H₂ molecules with an average binding energy of 0.099 eV/H₂ which is close to the threshold energy of 0.1 eV required for practical applications. Decoration of the Be₂N₆ monolayer with lithium atom significantly improves the hydrogen storage ability of the desired monolayer compared to that of the pristine Be₂N₆ monolayer. This can be attributed to the polarization of H₂ molecules induced by the charge transfer from Li atoms to the Be₂N₆ monolayer. Decoration of Be₂N₆ monolayer with two lithium atoms gives a promising medium that can hold up to eight H₂ molecules with average adsorption energy of 0.198 eV/H₂ and hydrogen uptake capacities of 12.12 wt%. The obtained hydrogen uptake capacity of 2Li/Be₂N₆ monolayer is much higher than the target set by the U.S. Department of Energy (5.5 wt% by 2020). Based on the van't Hoff equation, it is inferred that hydrogen desorption can occur at T_D = 254 K for 2Li/Be₂N₆ (8H₂) system which is close to ambient conditions. This is a remarkable result indicating important practical applications of 2Li/Be₂N₆ medium for hydrogen storage purposes.     

Hydrogen storage capacity and reversibility of Li-decorated B4CN3 monolayer revealed by first-principles calculations

This work explored the feasibility of Li decoration on the B₄CN₃ monolayer for hydrogen (H₂) storage performance using first-principles calculations. The results of density functional theory (DFT) calculations showed that each Li atom decorated on the B₄CN₃ monolayer can physically adsorb four H₂ molecules with an average adsorption energy of ?0.23 eV/H₂, and the corresponding theoretical gravimetric density could reach as high as 12.7 wt%. Moreover, the H₂ desorption behaviors of Li-decorated B₄CN₃ monolayer at temperatures of 100, 200, 300 and 400 K were simulated via molecular dynamics (MD) methods. The results showed that the structure was stable within the prescribed temperature range, and a large amount of H₂ could be released at 300 K, indicative of the reversibility of hydrogen storage. The above findings demonstrate that the Li-decorated B₄CN₃ monolayer can serve as a favorable candidate material for high-capacity reversible hydrogen storage application.     

Density functional theory study of reversible hydrogen storage in monolayer beryllium hydride by decoration with boron and lithium

The hydrogen storage capacity of M-decorated (M = Li and B) 2D beryllium hydride is investigated using first-principles calculations based on density functional theory. The Li and B atoms were calculated to be successfully and chemically decorated on the Surface of the α-BeH₂ monolayer with a large binding energy of 2.41 and 4.45eV/atom. The absolute value was higher than the cohesive energy of Li and B bulk (1.68, 5.81eV/atom). Hence, the Li and B atoms are strongly bound on the beryllium hydride monolayer without clustering. Our findings show that the hydrogen molecule interacted weakly with B/α-BeH₂(B-decorated beryllium hydride monolayer) with a low adsorption energy of only 0.0226 eV/H₂ but was strongly adsorbed on the introduced active site of the Li atom in the decorated BeH₂ with an improved adsorption energy of 0.472 eV/H₂. Based on density functional theory, the gravimetric density of 28H₂/8li/α-BeH₂) could reach 14.5 wt.% higher than DOE's target of 6.5 wt. % (the criteria of the United States Department of Energy). Therefore, our research indicates that the Li-decorated beryllium hydride monolayer could be a candidate for further investigation as an alternative material for hydrogen storage.     

Transition metal atoms anchored 2D holey graphyne for hydrogen evolution reaction: Acumen from DFT simulation

Here, we report a theoretical design of transition metals (TMs) anchored two-dimensional (2D) holey graphyne (HGY) based catalyst for the hydrogen evolution reaction (HER) through state-of-art density functional theory (DFT) simulation. The studied TMs (Co, Fe, Cr) are bonded strongly on HGY surface due to charge transfer from d orbital of metal to C 2p orbital of HGY. The HGY+TMs systems are stable at room temperature as evident from ab-initio molecular dynamics (AIMD) simulation. We predicted that the Co, Fe and Cr anchored HGY are highly active for HER activity with Gibbs free energy (ΔG) value as low as −0.21, −0.14, and −0.05 eV respectively and which are close to the best-known HER catalyst (Pt metal). The enhanced HER performance is attributed to the increased conductivity as well as redistribution of electrons. As pristine HGY is experimentally synthesized, HGY+TMs (Co, Fe, Cr) systems can be as an efficient catalyst for H₂ production.     

Study of the reversible hydrogen storage performance of Ti-decorated hexagonal B36 by DFT calculations with van der Waals corrections

In this work, we report on the study of the hydrogen storage capability of titanium (Ti) decorated B₃₆ nanosheets using density functional theory (DFT) calculations with van der Waals corrections. Ti atoms are strongly bonded to the surface of B₃₆ with a binding energy of 6.23 eV, which exceeds the bulk cohesive energy of crystalline Ti. Ti-decorated B₃₆ (2Ti@B₃₆) can reversibly adsorb up to 12 H₂ molecules with a hydrogen storage capacity of 4.75 wt % and average adsorption energy between 0.361 and 0.674 eV/H₂. The values of desorption temperature and the results of molecular dynamics simulations enable to conclude that 2Ti@B₃₆ is a perspective reversible material for hydrogen storage under real conditions.     

Enhanced hydrogen evolution reaction performance of MoS2 by dual metal atoms doping

Molybdenum disulfide (MoS₂) has been considered a promising high-efficiency, low-cost hydrogen evolution reaction (HER) catalyst in acidic and alkaline media. However, the lack of active sites in the basal plane become the most significant obstacle hindering the widespread application of MoS₂. Here, we systematically studied the HER performance of MoS₂ plane or edge by co-doping Co atom and other 3d transition metals (TM = Ti–Fe, Ni) by density functional theory calculation methods. Interestingly, the dual atoms doping in both the basal plane and edges of MoS₂ is a feasible fabrication with small or negative formation energies. Compared with the pristine MoS₂ electrocatalyst, the HER performance in these doped systems is largely enhanced in both basal plane and edges due to the effective charge regulation on the S site by dual atom doping. Remarkably, close to zero H adsorption free energy (ΔG_H = ?0.161–0.119 eV) is identified for the TM-Co co-doped MoS₂ basal, indicating that they are potential alternate HER electrocatalysts of Pt. Our study provides a new strategy to design highly efficient non-noble metal electrocatalysts accessibility for energy-related applications.     

Mechanistic insights into hydrogen evolution reaction on Ni2B(001) facet using first-principle calculations

In this paper, first-principle calculations based on density functional theory (DFT) were used to investigate the performance and mechanism of the hydrogen evolution reaction (HER) on the typical active (001) facet of the novel electrocatalyst Ni₂B. There were two types of atomic distribution on the Ni₂B (001) surface, namely the B-rich surface and the Ni-rich surface. The investigation of the reaction mechanism revealed that the Volmer-Heyrovsky mechanism was easier to be realized on this Ni₂B (001) facet, and the Heyrovsky reaction was the reaction rate-determining step. The Gibbs free energy(ΔG_H) on the B-rich surface was - 0.02 eV, which was closer to 0 eV than that on the Ni-rich surface of Ni₂B (001). The HER reactivity on the Ni-rich surface was increased by Cr-doping (ΔG_H = - 0.01 eV), which indicated that the introduction of other transition metal atoms might effectively increase the HER electrocatalysis activity of Ni₂B (001) surface. This work paves a new avenue for exploring efficient and durable non-precious metal electrocatalysts for HER in acidic medium.     

Chemical hydrogen storage using polynuclear borane anion salts

The polynuclear borane anions nido-B₁₁H₁₄⁻, closo-B₁₀H₁₀²⁻ and closo-B₁₂H₁₂²⁻ undergo heterogeneous transition metal-catalyzed hydrolysis to generate hydrogen. The rate of hydrolysis is dependent upon the concentration of polynuclear borane anions and surface area of the metallic catalyst. The aqueous solutions of polynuclear borane anions, especially the closo-B₁₀H₁₀²⁻ and closo-B₁₂H₁₂²⁻ dianions, are very stable for an extended period of time (years) in the absence of catalyst and spontaneously generate hydrogen in the presence of a rhodium metal catalyst. These polynuclear borane anions have a high potential for use in portable hydrogen storage systems without requiring high pH aqueous media for storage as in the case of NaBH₄.     

Li decorated heteroborospherene C4B32 as high capacity and reversible hydrogen storage media: A DFT study

In this work, adsorption of H₂ molecules on heteroborospherene C_2v C₄B₃₂ decorated by alkali atoms (Li) is studied by density functional theory calculations. The interaction between Li atoms and C₄B₃₂ is found to be strong, so that it prevents agglomeration of the former. An introduced hydrogen molecule tilts toward the Li atoms and is stably adsorbed on C₄B₃₂. It is obtained that Li₄C₄B₃₂ can store up to 12H₂ molecules with hydrogen uptake capacity of 5.425 wt% and average adsorption energy of ?0.240 eV per H₂. Dynamics simulation results show that 6H₂ molecules can be successfully released at 300 K. Obtained results demonstrate that Li decorated C₄B₃₂ is a promising material for reversible hydrogen storage.     

Selective decorating of BC3 and C3N nanosheets with single metal atom for hydrogen storage

Employing first-principles calculations, we have studied the structure, stability and hydrogen storage efficiency of pristine and defective BC₃ and C₃N monolayer functionalized by a variety of single metal adatoms. It is found that single Sc adatom, acting as an optimal dopant on perfect BC₃ monolayer, is able to adsorb up to nine H₂ molecules as strongly as around 0.24 eV/H₂, which allows for a hydrogen storage capacity of 7.19 wt% for Sc atoms stably adsorbing on double sides of BC₃ monolayer with eighteen H₂ molecules (18H₂@2Sc/BC₃). Moreover, the desorption temperature and thermodynamical stability of multiple H₂ adsorbed Sc-decorated BC₃ sheet have been addressed and the saturate configuration of 18H₂@2Sc/BC₃ is predicted to be stable at mild temperatures and pressures, i.e. less than 250 K at 1 bar, or larger than 24 bar at room temperature. This study indicates that the Sc-decorated BC₃ monolayer could be a potential H₂ storage candidate, and provides an instructive guidance for designing metal-functionalized carbon-based sheets in hydrogen storage.