High-throughput chainmail catalyst FeCo@C nanoparticle for oxygen evolution reaction

Oxygen evolution reaction (OER) is a key part of water electrolysis for hydrogen production. Non-noble-metal catalysts with high activity, stability, but low cost are prerequisites for practical application. In this work, sucrose char was synthesized and then chainmail catalysts were produced by in situ growth method, defined as M@C (M = Fe, Co and FeCo). FeCo@C showed great OER performance in both catalytic activity and durability tests. The overpotentials were 302 mV (at the current density of 10 mA cm⁻²) and 423 mV (at 50 mA cm⁻²), with a lowest Tafel slope of 75 mV dec⁻¹. The electrochemical surface area of catalysts were also analyzed by calculating the capacitance of the double layer to further investigate the catalytic activity. Furthermore, FeCo@C showed superior stability after 30 h test or 10,000 cycles of cyclic voltammetry. Theoretical calculation based on density functional theory (DFT) demonstrated that the overpotential of OER was determined by the Gibbs free energies of reaction intermediates HO1, O1 and HOO1. The adsorption of HO1 radicals onto the FeCo@C was weaker than Fe@C, which was favorable for reducing the overpotential, as the rate-determining step of the OER process over these catalysts was that HO1 dehydrogenated to form O1.     

Lithium-functionalized boron phosphide nanotubes (BPNTs) as an efficient hydrogen storage carrier

In this work we have carried out extensive Density Functional Theory (DFT) and ab-initio Molecular Dynamics (AIMD) simulations to study the structural and electronic properties, thermal stability, and the adsorption/desorption processes of hydrogen H₂ molecules on Lithium (Li) functionalized one-dimensional boron phosphide nanotubes (BPNTs), for possible use as materials of H₂-storage media. Our results show that Li atoms can be adsorbed on the hollow sites of (7,7)-BPNT with binding energy ranging from 1.69 eV, for one Li, to 1.65 eV/Li for 14 Li atoms adsorbed on (7,7)-BPNT. These large energies of Li prevent the formation of clusters on the nanotube sidewall. The investigation of the electronic behavior showed that (7.7)-BPNT semiconductor turns metallic upon the Li-adsorption. Furthermore, the average binding energy of H₂-molecules adsorbed on nLi@BPNT(mH₂) systems (with n = 1, 2, 4, 6, 8, 14 and m = 1, 2, 3, 4, with m the number of H₂ for each Li) lies within a range of 0.13–0.20 eV/H₂ which is compatible to the required range for adsorption/desorption of H₂-molecules at room conditions. A H₂-storage gravimetric capacity up to 4.63% was found for 14Li@BPNT(4H₂) system. In addition, AIMD simulation strongly indicates that given adequate monitoring of the temperature, the charge/release process of H₂-molecules can be controlled. Our findings suggest that Li-functionalized (7,7) boron phosphide nanotubes can provide a valuable underlying material for H₂-storage technologies and therefore must certainly be the subject of further experimental exploration.     

Catalytic activity and underlying atomic rearrangement in monolayer CoOOH towards HER and OER

For efficient hydrogen and oxygen production, design and synthesis of cost-effective, stable and active materials are inevitable. In this work, the catalytic activity of 2D CoOOH towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been investigated using first principles calculations based on density functional theory. The adatom induced structural rearrangement have been investigated from structural parameters as well as charge redistribution in 2D CoOOH. The preferred site for hydrogen and oxygen adsorption were found to be the top site of oxygen atom of 2D CoOOH. The catalytic activity of HER and OER towards 2D CoOOH was studied by calculating the Gibbs free energy. Our study revealed that the 2D CoOOH serve better as a catalyst for HER than OER with adsorption energy of −0.45 and −3.68 eV respectively suggesting its efficient use for hydrogen production. We further investigated the changes in electronic properties of 2D CoOOH on adsorption of hydrogen and oxygen atom.     

Hydrogen evolution and oxygen evolution reactions of pristine and alkali metal doped SnSe2 monolayer

Many transition metal di-selenides such as MoSe₂ and WSe₂ show good catalytic activity on their edges with limited active orientations. These metal di-selenides are actively being used as target material for increasing the number of electrocatalytic active sites and in turn to improve the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities by increasing the ratio of edges to the basal plane. In present work, we have studied the activity of pristine and alkali atoms (Na, K and Ca) doped-SnSe₂ for HER and OER catalyst. The state-of-art density functional theory (DFT) based computations are performed for estimating the catalytic activity of the pristine and doped SnSe₂ by means of evaluating the adsorption and Gibbs free energies subjected to hydrogen and oxygen adsorption. Further, to get better prediction of adsorption energy on the individual catalytic surface, we have included the dispersion correction term to exchange-correlation functional. Results show that the pristine SnSe₂ is not a good HER catalyst when hydrogen is adsorbed on its basal plane. However, edge-sites show the good hydrogen adsorption and indicates that the edges of SnSe₂ are the most preferential site for hydrogen adsorption. As far as the catalytic activity of SnSe₂ with dopants is concerned, the Na-doped SnSe₂ among all shows the best catalytic activity over its edge-site; whereas K and Ca doped SnSe₂ show basal plane as preferred catalytic site. It is interesting to note that the disadvantage of low catalytic activity on basal plane of SnSe₂ can be improved by selective doping of alkali metals.     

Orientated carbon nanotubes boosting faster charge transfer for bifunctional HER and OER

Orientated Carbon nanotubes would expose more active sites and have better electrical conductivity, while most of the carbon nanotubes are disordered, so it is necessary to align with the aid of external force. Hence, we obtain the stretchable films (denoted as PMC) by casting the solution of hydrothermal MWCNTs (ho-MWCNTs) and poly (vinyl alcohol) (PVA), following the Ni(OH)₂ deposited on PMC (denoted as PMC/Ni). XPS and XRD confirmed the charge transfer between ho-MWCNTs and PVA, which means generation of electronic delocalization center. Furthermore, the alignment of ho-MWCNTs could be observed by SEM. Meanwhile, PMC/Ni exhibited excellent catalytic performance for OER and HER in 1 M KOH. It only require 320 mV to achieve 20 mA cm^?2 for OER and a low overpotential of ?219 mV to achieve 10 mA cm^?2 for HER in 1 M KOH. The results verify that orientated ho-MWCNTs have a positive effect in promoting catalytic performance by promoting to faster electron transfer and more active sites. Hence, we believe that the catalytic performance of other hollow-tubes materials would show a strong relationship with the orientation, which needs more efforts to research.     

Mesoporous nickel-sulfide/nickel/N-doped carbon as HER and OER bifunctional electrocatalyst for water electrolysis

The development of non-precious metal-based highly active bi-functional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is critical factor for making water electrolysis a viable process for large-scale industrial applications. In this study, bi-functional water splitting electrocatalysts in the form of nickel-sulfide/nickel nanoparticles integrated into a three-dimensional N-doped porous carbon matrix, are prepared using NaCl as a porous structure-forming template. Microstructures of the catalytic materials are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and N₂ adsorption-desorption analysis. The most active catalyst synthesized in this study exhibits a low HER overpotential of 70 mV at 10 mA cm⁻² and a low Tafel slope of 45 mV dec⁻¹. In OER, the optimized sample performs better than a state-of-the-art RuO₂ catalyst and produces an overpotential of 337 mV at 10 mA cm⁻², lower than that of RuO₂. The newly obtained materials are also used as HER/OER electrocatalysts in a specially assembled two-electrode water splitting cell. The cell demonstrates high activity and good stability in overall water splitting.     

Hydrogen evolution reaction and electronic structure calculation of two dimensional bismuth and its alloys

We present a systematic ab initio study of atomic hydrogen and oxygen adsorption on bismuthene monolayer and its alloys with arsenic and antimony through electronic structure calculations based on density functional theory within generalized gradient approximation. We systematically investigated the preferable adsorption site for hydrogen and oxygen atom on 2D Bi, BiAs and BiSb. It was found that the hydrogen atom prefers top site of bismuth atom and oxygen atom prefers to reside in the hexagonal ring of these 2D bismuth alloys. The free energy calculated from the individual adsorption energy for each monolayer subsequently guides us to predict the best suitable catalyst among the considered 2D monolayers. The 2D BiSb serves better for hydrogen evolution reaction (HER) with hydrogen adsorption energy as ?1.384 eV while 2D BiAs is suitable for oxygen evolution reaction (OER) with oxygen adsorption energy as ?1.092 eV. We further investigated the effects of the adsorbate atom on the electronic properties of 2D Bi, BiAs and BiSb. The adsorption of oxygen on 2D BiAs and BiSb was shown to reduce the bulk band gap by 40.56 and 67.79% respectively which will be advantageous for the observation of Quantum Spin Hall effect at ambient conditions.     

Enhancement in the catalytic activity of two-dimensional α-CN by B,Si and P doping for hydrogen evolution and oxygen evolution reactions

Employing the Density Functional Theory investigations, we have designed 2D α-CN with the dopants P, Si and B as catalyst for HER and OER activities. Doping of P and B over α-CN modifies its electronic properties and reduces band gap (3.78 eV) of α-CN to the required band gap for HER and OER activities. The modification of electronic properties is discussed by the analysis of partial density of states, Löwdin charge and charge density plot. To understand HER and OER activities better, we computed Gibbs free energy change after adsorption of H/O in various doped α-CN systems. We observe that the P doping at C site and B doping at N site of α-CN are best suited for HER and OER respectively. The HER (OER) activity increases by 88.33% (29.35%) for P doped at C site (B doped at N site) of α-CN in comparison to pristine α-CN.     

In situ Raman spectroscopic study towards the growth and excellent HER catalysis of Ni/Ni(OH)2 heterostructure

The electrochemical water splitting to produce H₂ in high efficiency with earth-abundant-metal catalysts remains a challenge. Here, we describe a simple “cyclic voltammetry + ageing” protocol at room temperature to activate Ni electrode (AC-Ni/NF) for hydrogen evolution reaction (HER), by which Ni/Ni(OH)₂ heterostructure is formed at the surface. In situ Raman spectroscopy reveals the gradual growth of Ni/Ni(OH)₂ heterostructure during the first 30 min of the aging treatment and combined with polarization measurements, it suggests a positive relation between the Ni/Ni(OH)₂ amount and HER performance of the electrode. The obtained AC-Ni/NF catalyst, with plentiful Ni–Ni(OH)₂ interfaces, exhibits remarkable performance towards HER, with the low overpotential of only 30 mV at a H₂-evolving current density of 10 mA/cm² and 153 mV at 100 mA/cm², as well as a small Tafel slope of 46.8 mV/dec in 1 M KOH electrolyte at ambient temperature. The excellent HER performance of the AC-Ni/NF could be maintained for at least 24 h without obvious decay. Ex situ experiments and in situ electrochemical-Raman spectroscopy along with density functional theory (DFT) calculations reveal that Ni/Ni(OH)₂ heterostructure, although partially reduced, can still persist during HER catalysis and it is the Ni–Ni(OH)₂ interface reducing the energy barrier of H1 adsorption thus promoting the HER performance.     

Defects and doping engineered two-dimensional o-B2N2 for hydrogen evolution reaction catalyst: Insights from DFT simulation

In this work, a detailed investigation of the structural and electronic properties and hydrogen evolution reaction (HER) activity of the pristine, vacancy and carbon (C) doped o-B₂N₂ monolayer is carried out using first-principles based density functional theory. The creation of vacancy and C doping modulates structural and electronic properties of the monolayers and enhances the HER activity of o-B₂N₂. The BN vacancy defect, C doping at B and N sites in the monolayer enhances the magnitude of HER activity by 77.34%, 86.71% and 83.59% as compared to pristine monolayer. The modulation in the HER activity of the o-B₂N₂ is due to the redistribution of charge after induction of vacancy and dopant. Our results suggest that the C doping makes o-B₂N₂ metallic which can be utilized as an “electrocatalyst” whereas BN vacancy defected o-B₂N₂ monolayer is semiconducting with a band gap of ～1 eV and can be used as “photocatalyst” for HER activity.     

Hydrogen evolution reaction of metal di-chalcogenides: ZrS2, ZrSe2 and Janus ZrSSe

Transition metal di-chalcogenides with stoichiometry MX₂ (M: Mo, V, W, Pt and X: S, Se) are considered as one of the non-precious and effective catalysts for the production of clean hydrogen energy via water-splitting mechanism. The major drawback of these materials is their inactive basal plane as compared to their edge sites. Recently, Janus MoSSe-a novel sandwiched structure has been synthesized and predicted theoretically to obtain increased catalytic activity by applying strain, external electric field and by creating vacancy. In this work, we have used state-of-the-art density functional theory with dispersion correction (DFT-D3) to study the catalytic activity for hydrogen evolution reaction (HER) of ZrS₂, ZrSe₂ and Janus ZrSSe. From our calculations, we conclude that among these three systems, the Janus ZrSSe ($\Delta G=1.19eV;\Delta G:Gibb\text{s}\text{free}energy$) is a good catalyst and can be utilized for HER at edge site. Janus ZrSSe shows enhanced catalytic activity at S-edge as compared to its basal plane and Se-edge site; whereas ZrSe₂ shows good catalytic activity at Se-edge rather than at the basal plane. The ZrS₂ shows good catalytic activity at S-edge. Further, we have doped Nb, Pt and W atoms in ZrS₂, ZrSe₂ and Janus ZrSSe to see their effect on catalytic activity of pristine compounds and found that the Nb-doped ZrSe₂ shows good catalytic activity for HER and is best among all considered systems with $\Delta G=0.63eV$ followed by Pt-doped ZrS₂. This study provides a theoretical basis for future application of ZrS₂, ZrSe₂ and Janus ZrSSe based catalysts for HER.     

Theoretical study of single-nonmetal-modified V2CO2 MXene as an efficient electrocatalyst for overall water splitting

The electrocatalytic water splitting consists of two half-reactions, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which require low-cost and highly activity catalysts. Two-dimensional transition metal carbon-nitride (MXenes) are considered as the potential catalysts candidates for HER and OER due to their unique physical and chemical properties. In this work, using density functional theory (DFT), we have investigated the effect of single non-metal (NM, NM = B, N, P, and S) atoms doping, strain, and terminal types on the HER and OER activities of V₂CO₂ MXene. Results indicated that P doping V₂CO₂ (P/V₂CO₂) has best HER performance at hydrogen coverage of θ = 1/8, and N doping V₂CO₂ (N/V₂CO₂) has best OER performance among the studied systems. In addition, it can be found that there is a strong correlation between the ΔG_H and strain, ΔG_H and valence charges of the doped atoms after applying strain to the doping structures, with the correlation coefficient (R²) about equal 1. Moreover, the mixed terminal can enhance the performances of HER and OER, which obey the follow rules: mixed terminal (O1 and 1OH) > original terminal (O1) > 1OH terminal. The ab initio molecular dynamics simulations (AIMD) results revealed that the single non-metallic doped structures are stable and can be synthesized experimentally at different terminals.     

N-doped hollow porous carbon spheres@Co Cu Fe alloy nanospheres as novel non-precious metal electrocatalysts for HER and OER

In this work, a string of different proportion trimetallic loaded the N-doped hollow porous carbon nanospheres (N-HPCS@Co Cu Fe NSs) were successfully crafted by a simple and economical method. Herein, the hollow-carbon structure was formed by etching carbon nanospheres. Moreover, owing to the presence of the PDA and P123, high dispersed nano spheres with mesopores were obtained. By this way, the catalyst can expose unique internal cavity and short transport path. Meanwhile, trimetal-based metal-organic frameworks (MOFs) Co Cu Fe alloy nano spheres (Co Cu Fe NSs) are first prepared. Creatively, PDA acts as the carbon resource, nitrogen resource and metal grafting agent simultaneously. Through a series of tests, N-HPCS@Co₁ Cu₁ Fe NSs has the best electrocatalytic performance and durable stability. This work highlights the current advances of hollow porous carbon structure, trimetallic active sites and N-doping, as well as, endow high electrocatalytic activity and durability for HER and OER.     

The construction of defective FeCo-LDHs by in-situ polyaniline curved strategy as a desirable bifunctional electrocatalyst for OER and HER

Here, Fe, Co-layered double hydroxide and polyaniline composites onto nickel foam (NF) (FeCo-LDH/PANI) were fabricated via one-step co-electrodeposition method. The test results indicate the co-existence of the amorphous structure and the smaller size of crystal district with more defects in optimal FeCo-LDH/PANI. Importantly, it is found that there are more defects in FeCo-LDH/PANI compared to that of FeCo-LDH possibly attributed to the local etching of H⁺ released from the polymerization of aniline. Benefitting from the numerous defects, higher electrochemical surface area (ECSA), lower charge-transfer resistance and electron interaction, the optimized FeCo-LDH/PANI needs the overpotentials of 104, 246, 285 and 323 mV vs RHE for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) to achieve 10 and 100 mA cm⁻², and shows desirable stability. Noticeably, the optimal FeCo-LDH/PANI requires a cell voltage of 1.53 V to drive 10 mA cm⁻² for the whole water splitting.     

Graphene oxide guiding the constructing of nickel-iron layered double hydroxides arrays as a desirable bifunctional electrocatalyst for HER and OER

It is accepted that the electrocatalytic activity is correlated to the morphology. Here, graphene oxide guiding nickel and iron layered double hydroxides hybrid arrays (GO-FeNi-LDH) are firstly fabricated by one-step electro-deposition method. The pretty 3D arrays with sheets vertically growing on nickel foam (NF) are highlighted by controlling the quantity of GO. Furthermore, the electron transfer from Ni, Fe to graphene is detected, making the metals and graphene in high valence and electron-rich state, respectively. The optimal GO-FeNi-LDH presents pretty morphology, defects, electron interactions and good conductivity. Therefore, to achieve 10 and 100 mA cm⁻², it requires the overpotentials of 119, 210, 285 and 303 mV for HER and OER and excellent durability. Noticeably, the optimal GO-NiFe-LDH needs a cell voltage of 1.48 V to drive 10 mA cm⁻² for the whole water splitting, which are lower than that of most of advanced electrocatalysts, endowing it in first-rank electrocatalyst.     

Engineering bimetallic cactus-like NiFeOOH/CoNiSe2 heterostructure nanosheets for efficient oxygen evolution and overall water splitting

The development of structural stable, high-performance, inexpensive electrocatalysts for oxygen evolution reactions (OER) is essential to alleviate the energy crisis. Herein, cactus-like CoNiSe₂ was synthesized on nickel foam and NiFeOOH was electrodeposited on surface of CoNiSe₂ to form a core-shell structural electrode. The obtained NiFeOOH/CoNiSe₂/NF exhibited ultra-low overpotentials of 204 mV and 234 mV at 10 and 100 mA cm⁻², with a Tafel slope of 26.2 mV dec⁻¹ in 1 M KOH alkaline solution. Furthermore, the current density only decreased by 5% after a 100 h durability test at 200 mA cm⁻², showing excellent robust stability. A two-electrode system with NiFeOOH/CoNiSe₂/NF as anode and Ni/NiO@MoO_3-x/NF as cathode (NiFeOOH/CoNiSe₂/NF||Ni/NiO@MoO_3-x/NF) showed a low voltage of 1.47/1.56 V to deliver 10/100 mA cm⁻². According to the experimental and density functional theory (DFT) results, the strong electronic interactions at the NiFeOOH/CoNiSe₂/NF interface leads to an increase in the valence state of Fe and an optimisation of the adsorption free energy, which are favourable to reduce the energy consumption of the OER. This work obtained high performance OER electrocatalysts by engineering amorphous and crystalline heterointerfaces and structural design, which will provide some inspiration for similar work.     

Recent advancements in the cathodic catalyst for the hydrogen evolution reaction in microbial electrolytic cells

The microbial electrochemical technology is a foremost viable technology for hydrogen production from organic matter or wastewater catalyzed by electroactive microorganisms. Developing a high-efficient and low-cost cathode for hydrogen production is crucial for the practical applications of MEC. In the present article, cathode materials and catalysts for hydrogen evolution reaction (HER) in MECs are reviewed. There is an essential requirement of cost-effective HER catalysts for improving MEC performance and as the practical findings fell short of the ideal catalyst's expectations, the density functional theory (DFT) can give essential molecular knowledge and anticipate viable catalysts. Additionally, this article provides an overview of the development of density functional theory (DFT), as well as computer simulations for HER processes using DFT, and also computational designs and virtual screens of novel HER catalysts. The development of catalysts combined with DFT simulations offers significant advancements in the near future on the path to an ideal electrocatalyst in MEC.     

Highly efficient,cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst

In order to obtain a fuel cell with both enhanced power generation performance and cell reversal resistance, the composite catalyst consisting of the self-made PtNi/C octahedral and the oxygen evolution reaction (OER) catalyst IrO₂ and RuO₂ is mixed and applied in the anode, and the only octahedral catalyst is employed as the cathode to prepare the membrane electrode assembly (MEA). The electrochemical activity of the composite catalyst decreases slightly, but its performance retention after the accelerated durability test (ADT) is higher. In the single cell test, the MEA fabricated using the composite catalyst maintains good single cell power generation performance. Compared with the control fabricated with Pt/C (JM), the cell voltage at 1 A cm⁻² and the maximum power density are increased by 23 mV and 119 mW cm⁻², respectively. Especially, its durability under continuous cell reversal condition is also improved significantly, and the holding time is prolonged by 1 h. This work realizes the transformation of the octahedral catalyst from the laboratory research to the actual application, and solves the difficulties in fuel cell application, and promotes its commercialization.     

High performance material for hydrogen storage: Graphenelike Si2BN solid

Recently, two dimensional graphenelike i.e. Si₂BN solid monolayer have attracted much attention for the use of hydrogen developments. The work is based on first principles calculations using density functional theory with long range van der Waal (vdW) interactions. The optimized structure is energetically more stable due to high formation energy 45.39 eV with PBE and 50.82 eV with HSE06 functionals, respectively. Our ab-initio studies show that Pd (palladium) adatoms secured graphenelike Si₂BN solid via two types of interactions; physisorption and chemisorptions reactions, which engrossing up to 3H₂ molecules signifying gravimetric limits of ≈6.95–10.21 wt %. The absorption energies vary from ?0.31 eV to ?1.93 eV with Pd-adatom and without Pd-adatom respectively, and it varies up to ?1.24 eV. The work function of pure Si₂BN is 5.36 eV while metal-adatom on monolayer Si₂BN with (1 to 6)H₂ molecules is 3.53 eV–4.99 eV and reaches up to 5.85 eV. The theoretical study suggests that the functionalized graphenelike Si₂BN is efficient for hydrogen storage and propose a possible improvement for advantageous storage of hydrogen at ambient conditions.