Platinum doped iron carbide for the hydrogen evolution reaction: The effects of charge transfer and magnetic moment by first-principles approach

In this work, the catalytic activity towards hydrogen evolution reaction (HER) was studied for hydrogen adsorption on Pt doped Fe₂C (001) surface configuration (Pt/Fe₂C) and compared with pure Pt (001). The adsorption of H on the pristine Fe₂C, Pt doped Fe₂C, and pure Pt in (001) slab was computed. The best and promising HER activity (ΔG_H1 = −0.02 eV) is obtained at the hollow site adsorption of Pt/Fe₂C (Fe₁₃Pt₃C₈) compared to the experimental value of pure Pt (ΔG_H1 = −0.09 eV) suggesting the possibility of the H₂ formation on the surface of Fe₁₃Pt₃C₈. The structural stabilities of Fe₂C and Pt/Fe₂C were investigated by the formation energy analysis. Also, it is observed that to enhance the HER mechanism, the modification of the d-electron structure of Pt atoms is essential which can be achieved by the increased Pt doping. The Bader charge analysis demonstrated the charge transfer between the substrate and the adsorbed H atoms. The density of states (DOS) of pure Fe₂C and optimal Pt/Fe₂C were calculated which revealed the magnetic and metallic nature of these materials. In addition, the adsorption and resulted activation of H₂ were facilitated by the elongation of H–H bond length in Fe₁₃Pt₃C_8. This work supports the HER over single atom catalysts (SACs) with lower Pt loading but with high catalytic activity and the maximum atom utilization of SACs.     

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.     

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.     

HER activity of MxNi1-x (M = Cr,Mo and W; x ≈ 0.2) alloy in acid and alkaline media

Reported are the synthesis and HER activity of M_xNi_1-x (M = Cr, Mo and W; x ≈ 0.2) alloy in acid and alkaline media. It was realized that doping group ⅥB element (Cr, Mo, W) in Ni metal matrix can greatly improve corresponding HER activity in both acid and alkaline electrolyte. Mo_xNi_1-x exhibits the highest HER activity among all samples in 1.0 M H₂SO₄ electrolyte, which it requires only 64 mV to reach current density of 10 mA/cm². Calculated free-energy of ΔG_H1 for M_xNi_1-x (M = Cr, Mo and W) well explained their HER activity trend in acid and it follows the order of Mo_xNi_1-x > W_xNi_1-x > Cr_xNi_1-x. In alkaline condition, their HER activities all deteriorate except Cr_xNi_1-x. HER activity of Cr_xNi_1-x in 1.0 M KOH (η_10(base) = 106 mV) surpasses that in 1.0 M H₂SO₄ (η_10(acid) = 160 mV) is quite unexpected. The DFT calculation suggesting the adsorbed OH holds the key and will alter the adsorption energy (ΔG_H1) of neighboring H atom on the surface in alkaline condition. This case study offers a good opportunity to investigate the factor to influence HER behavior of electrocatalyst in acid and alkaline media.     

Activation of metal-free porous basal plane of biphenylene through defects engineering for hydrogen evolution reaction

The biggest challenge in the commercial application of electrochemical reduction of water through the hydrogen evolution reaction (HER) is hampered due to the scarcity of inexpensive and efficient catalysts. Herein, we propose a metal-free biphenylene nanosheet, a recently proposed two-dimensional (2D) carbon allotrope, as an excellent HER electrocatalyst. The dynamical and thermal stability of biphenylene nanosheet is validated through phonon dispersion and abinitio molecular dynamics (AIMD) calculations, respectively. At a low H coverage (1/54), the biphenylene nanosheet shows excellent catalytic activity with the Gibbs free energy (ΔG_H1) of 0.082 eV. The Bdoping and C-vacancy in biphenylene further improve ΔG_H1 to −0.016 eV and 0.005 eV, respectively. The interactions between the H atom and the nanosheet are explained through the relative position of the p-band center. Our study opens new possibilities to use non-metallic porous materials as highly efficient electrocatalysts for HER.     

Heterostructure and phase engineering synergistically activated highly efficient alkaline hydrogen evolution in Mo2C/MoS2-rGO hybrids

Heterostructure and phase engineering are effective method to tune the electronic structure of MoS₂, which can activate and boost its intrinsic catalytic activity. Herein, the theoretical calculations reveal that the free energy of H1 adsorption (ΔG_H1) for Mo₂C (−0.65 eV) is lower than MoS₂ (2.05 eV), which is favorable for hydrogen adsorption. Inspired by the theoretical predictions, we develop a facile strategy to prepare nanostructured Mo₂C/MoS₂ dispersed on reduced graphene oxide (rGO) via a hydrothermal preparation and carburization reaction. Since the Mo₂C/MoS₂-rGO nanostructures with great deal of both MoS₂ and Mo₂C edges by heterostructure and phase engineering, which can induce massive active sites for HER on the surface of rGO, the intimate interfacial coupling effect between Mo₂C and MoS₂ can effectively improve the charge transfer rate. The Mo₂C/MoS₂-rGO catalyst exhibits exceptional HER properties, delivering a high turnover frequency (TOF) of 0.209 s⁻¹ at an overpotential of 200 mV in 0.1 M KOH. This work may open a new window for designing NPM electrocatalysts with highly efficient HER property based on earth-abundant materials.     

Improving the catalytic activity of two-dimensional Mo2C for hydrogen evolution reaction by doping and vacancy defects

Molybdenum carbide (Mo₂C) has high catalytic activities toward electrocatalytic hydrogen evolution reaction (HER) owing to its high surface activity and electrochemical properties. However, the defects modification of Mo₂C, which plays an important role in the HER activity, is relatively scarce in the theoretical research. Herein, in this work, based on first-principles calculations, we screen the influences of vacancies, nonmetal doping (X_C/T, X = N, O, F, P and S) and metal substitutional doping (Y_Mo, Y = Re and W) on HER of two-dimensional Mo₂C. The results reveal that vacancies of Mo₆C (0.02 eV) and Mo₃C (0.22 eV), substitutional dopants of O_C, S_C, Re_Mo (?0.33～0.08 eV) and adsorptive dopants of N_T, F_T, P_T, S_T (?0.26～0.14 eV) show enhanced catalytic activity with the absolute value of hydrogen adsorption free energy $(\Delta GH1)$ smaller than 0.33 eV. A negative linear relationship is observed between $\Delta GH1$ and d band center of transition metals in vacancies and metal dopants, but not in the configurations with nonmetal doping. The results provide more insight and guidance for the design of Mo₂C electrocatalyst.     

Two-dimensional B7P2: Dual-purpose functional material for hydrogen evolution reaction/hydrogen storage

It is well known that the development of dual-purpose materials is more significant and valuable than single-use materials due to the diversity of their use purposes. Based on density functional theory (DFT), the hydrogen evolution/hydrogen storage characteristics of two-dimensional (2D) B₇P₂ monolayer are systematically studied in this paper, focusing on the key word of clean energy-“hydrogen”. The results show that the B₇P₂ monolayer can be used as a stable metal-free decorated catalyst for hydrogen evolution reaction (HER), which is renewable and environmentally friendly. The calculated Gibbs free energy (ΔG_H1) is 0.06 eV, which is comparable or even better than that of Pt catalyst (ΔG_H1 = ?0.09 eV). In addition, we also found that the increase of hydrogen coverage and strain driving (?2%–2%) did not further enhance the HER activity of B₇P₂ monolayer, showing a poor ΔG_H1. In the aspect of hydrogen storage, we have investigated the hydrogen storage performances of alkali-metal (Li, Na and K) doped B₇P₂. It is found that in the fully loaded case, B₇P₂Li₆ is a promising hydrogen storage material with a 7.5 wt% H₂ content and 0.15 eV/H₂ average hydrogen adsorption energy (E_ave). Moreover, ab initio molecular dynamics (AIMD) calculations show that there is no dynamic barrier for H₂ desorption of Li-decorated B₇P₂ monolayer. In conclusion, our results indicate that the B₇P₂ monolayer is not only an excellent catalyst for HER, but also a promising hydrogen storage medium.     

Accelerate the alkaline hydrogen evolution reaction of the heterostructural Ni2P@Ni(OH)2/NF by dispersing a trifle of Ru on the surface

Electrocatalytic water splitting for hydrogen production plays a vital role in the development of new energy field, but there is still a lack of low-content precious metal or cost-effective non-noble metal catalysts for the hydrogen evolution reaction (HER). Therefore, how to develop the catalysts with a smaller amount of precious metal to achieve higher performance is still a major challenge. Herein, we have fabricated Ru–Ni₂P@Ni(OH)₂/NF-2 heterostructure by phosphating Ni(OH)₂/NF and then anchoring Ru on the surface through wet chemical strategy. Benefiting from its optimal ΔG_H1 and synergistic effect, this Ru–Ni₂P@Ni(OH)₂/NF-2 catalyst shows superior electrocatalytic HER kinetics in alkaline electrolyte. A small overpotential of 31 mV is needed for this electrocatalyst to obtain the current densities of 10 mA cm^?2 with remarkable durability over 24 h. This work provides a new strategy for the preparation of effective HER electrocatalyst with a low precious metal content.     

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.     

Theoretical study the component and facet dependence of HER performance on nickel phosphides surfaces

Energy depletion and environmental pollution are still serious challenges for human beings. The application of hydrogen energy should be a promising strategy to address this issue. However, the hydrogen production should be one shortcoming for hydrogen energy. The hydrogen evolution reaction (HER) based on electrocatalysis is an effective way to enhance the hydrogen generation with small energy consumption under ambient conditions. Many works have been devoted to develop high performance catalysts to satisfy the HER processes. Nevertheless, the mechanism about facet-dependence and composition-dependence influence is still need to deeply study. Hereon, based on density functional theory calculations, the [100], [110], and [111] facets of Ni_xP_y (Ni₃P, Ni₂P, NiP, NiP₂, NiP₃) systems were created and their HER catalytic activity were used to reveal the underline mechanism. By analyzing the variation of Gibbs free energy, it was found that the structural composition has a greater effect on HER than the facet. Significantly, the Ni₂P(111) surface with Ni/P-termination has the best HER performance for all samples in present work. Through exploring the electron transfer of H with surrounding atoms during the HER process, the H adsorption mechanism as well as its reaction mechanism has been revealed. The deep insights in this work provide an important fundamental that the contents of non-metal for compounds catalysts can heavily influence the performance of HER, which should give more guidance for designing new catalysts.     

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.     

Efficient overall water splitting using nickel boride-based electrocatalysts

Currently there is tremendous interest in the discovery of low cost and efficient electrocatalysts for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). In this work, iron-doped nickel boride (Fe_xNi_1-xB) and nickel boride (NiB) were successfully grown on 3D self-supporting graphene (SSG) electrodes via a one-step reduction approach. The Fe_0.2Ni_0.8B/SSG electrode required a very low overpotential of only 263 mV for OER (the best OER activity achieved to date for a metal boride). NiB/SSG showed modest OER performance but excellent HER activity. A water electrolyzer comprising Fe_0.2Ni_0.8B/SSG and NiB/SSG delivered a current density of 10 mA cm⁻² at a voltage of only 1.62 V. Further, the Fe_0.2Ni_0.8B/SSG and NiB/SSG catalysts showed excellent stability with no deactivation observed over 14 h of testing. Results demonstrate that nickel boride-based electrocatalysts are promising lost cost alternatives to precious metal-based electrocatalysts for OER, HER and overall water splitting.     

In situ growth of Ni0·85Se on graphene as a robust electrocatalyst for hydrogen evolution reaction

Seeking the efficient and robust electrocatalysts necessarily enhances performance of hydrogen evolution reaction (HER). Increasing the surface active sites is a means to improve the performance. Herein, we use the Ni_0·85Se anchored on reduction of graphene oxide (Ni_0·85Se/rGO) hybrid material skillfully established by one-step facile hydrothermal method as a robust and stable electrocatalyst applying to hydrogen evolution reaction (HER). In terms of morphology, Ni_0·85Se nanospheres composed of many nanosheets are uniformly distributed on the graphene sheet layer. We also detailedly analyze its properties. Based on the interaction between Ni_0·85Se and rGO, and the roles of graphene are as a substrate to heighten conductivity, possesses more active surface area by limiting growth of Ni_0·85Se, and increases dispersion for exposing more active surface area and enlarge ion/electron transfer rate. In HER, the Ni_0·85Se/rGO catalyst displays the overpotential of 128 mV with a common current density of 10 mA cm⁻², a small Tafel slope of 91 mV dec⁻¹, an extremely low onset potential of 37 mV, outstanding stability that a high current retention of 97.7% after 1000 cycles and well long-term stability for 18 h, outperforming the capability of Ni_0·85Se nanospheres in alkaline solution for HER. The above results indicate that the Ni_0·85Se/rGO hybrid material is a good HER ability and non-noble metal electrocatalyst has potential value in 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.     

Interface engineering of Ni0.85Se/Ni3S2 nanostructure for highly enhanced hydrogen evolution in alkaline solution

Interface engineering is considered as an effective strategy to improve the hydrogen evolution reaction (HER) performance of electrocatalysts. Herein, the Ni_0.85Se/Ni₃S₂ heterostructure grown on nickel foam (NF) is synthesized via successive wet-chemical processes. The obtained Ni_0.85Se/Ni₃S₂ heterostructure is firstly investigated as an HER electrocatalyst in alkaline media and exhibits more excellent electrochemical properties over Ni₃S₂. And it delivers a low overpotential of 145 mV at a current density of ?10 mA cm^?2, and superior stability. Based on the analysis of high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectra (XPS), the enhanced HER activity is due to the modulation of surface electronic structure, ascribing from the construction of heterointerface between Ni_0.85Se and Ni₃S₂. Meanwhile, the Ni_0.85Se/Ni₃S₂ heterostructure prepared in this work is also verified to be employed as a promising alternative to noble metal catalysts in HER.     

High-throughput screening of transition metal single-atom catalyst anchored on Janus MoSSe basal plane for hydrogen evolution reaction

Considerable efforts have been made to enhance the hydrogen evolution reaction (HER) catalytic performance of Janus MoSSe monolayer, which have been considered to be a promising candidate due to the unique asymmetry structure. However, the activation effect remains non-optimal for the inert Janus MoSSe basal plane at present. Herein, a train of transition metal (TM) atoms were anchored on the S-/Se-/Mo-defective MoSSe basal plane to screen effective TM single-atom catalysts for HER through density functional theory (DFT) computations. Interestingly, the single Co atom anchored on Mo-defective MoSSe and the single Zn or Cd atom anchored on S-defective MoSSe were judged to possess excellent HER performance yielding a near-zero ΔG_H (ΔG_H = ?0.050, ?0.095, ?0.098 eV, respectively), which is comparable to the optimized Pt-SACs. The enhanced HER activity is attributed to the doping of TM atoms (Co, Zn and Cd) which improves the conductivity of the original MoSSe and offers unoccupied states near the Fermi level decreasing the energy barrier of electrons transfer between H and TMs@MoSSe surface. In addition, the change of unoccupied antibonding states of active atoms leads to appropriate interaction between the active sites and H. The hybridization between H-s orbital and the TMs@MoSSe systems around the Fermi level also suggests the formation of stable bonding-antibonding hydrogen adsorption states. This work reveals an effective way of activating MoSSe basal plane for HER.     

Self-standing,hybrid three-dimensional-porous MoS2/Ni3S2 foam electrocatalyst for hydrogen evolution reaction in alkaline medium

Self-standing and hybrid MoS₂/Ni₃S₂ foam is fabricated as electrocatalyst for hydrogen evolution reaction (HER) in alkaline medium. The Ni₃S₂ foam with a unique surface morphology results from the sulfurization of Ni foam showing a truncated-hexagonal stacked sheets morphology. A simple dip coating of MoS₂ on the sulfurized Ni foam results in the formation of self-standing and hybrid electrocatalyst. The electrocatalytic HER performance was evaluated using the standard three-electrode setup in the de-aerated 1 M KOH solution. The electrocatalyst shows an overpotential of 190 mV at ?10 mA/cm² with a Tafel slope of 65.6 mV/dec. An increased surface roughness originated from the unique morphology enhances the HER performance of the electrocatalyst. A density functional approach shows that, the hybrid MoS₂/Ni₃S₂ heterostructure synergistically favors the hydrogen adsorption-desorption steps. The hybrid electrocatalyst shows an excellent stability under the HER condition for 12 h without any performance degradation.     

Amorphous MoS2 nanosheets on MoO2 films/Mo foil as free-standing electrode for synergetic electrocatalytic hydrogen evolution reaction

A facile oxidation-sulfidation strategy is proposed to fabricate the vertically aligned amorphous MoS₂ nanosheets on MoO₂ films/Mo foil (MF) as free-standing electrode, which features as the integration of three merits (high conductivity, abundant exposures of active sites, and enhanced mass transfer) into one electrode for hydrogen evolution reaction (HER). Density functional theory (DFT) calculations reveal the strong interaction between MoS₂ and MoO₂, which can enhance the intrinsic conductivity with narrow bandgap, and decreases hydrogen adsorption free energy (ΔG_H1 = ~0.06 eV) to facilitate the HER process. Benefiting from the unique hierarchical structure with amorphous MoS₂ nanosheets on conductive MoO₂ films/MF to facilitate the electron/mass transfer by eliminate contact resistance, controllable number of stacking layers and size of MoS₂ slabs to expose more edge sites, the optimal MoS₂/MoO₂/MF exhibits outstanding activity with overpotential of 154 mV at the current density of 10 mA cm⁻², Tafel slope of 52.1 mV dec⁻¹, and robust stability. Furthermore, the intrinsic HER activity (vs. ECSA) on MoS₂/MoO₂/MF is significantly enhanced, which shows 4.5 and 18.6 times higher than those of MoS₂/MF and MoO₂/MF at overpotential of 200 mV, respectively.     

Synthesis of Ni2P/Ni5P4 on porous N decorated rGO foam for efficiently electrocatalytic hydrogen evolution reaction

As a new generation of non-precious metal catalysts, nickel phosphide is regarded as an ideal substitute for precious metal platinum in electrochemical hydrogen evolution. Here, a hydrogen evolution reaction (HER) electrocatalyst is developed by in situ growth of Ni₂P/Ni₅P₄ heterostructures on porous N decorated rGO foam (named Ni₂P/Ni₅P₄/N-rGO). The porous rGO foam structure provides a larger surface area and abundant active sites. The Ni₂P/Ni₅P₄ nanoparticles with heterostructures are uniformly distributed on the rGO sheet, which enhance the charge transfer ability. The decorating of N element also correspondingly improves the HER performance. The as-prepared Ni₂P/Ni₅P₄/N-rGO exhibits excellent HER performance in alkaline medium. When the current density is 10 mA cm^?2, the overpotential is only 22 mV. No obvious loss of HER activity after 2000 cyclic voltammetry indicates that the composite has excellent stability. This work presents a valuable route for fabricating inexpensive and high-performance catalysts for electrocatalysis.