Hydrogen Adsorption Free Energy Research Articles

Surface reconstruction of RuO2/Co3O4 amorphous-crystalline heterointerface for efficient overall water splitting

The rational construction of amorphous-crystalline heterointerface can effectively improve the activity and stability of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, RuO2/Co3O4 (RCO) amorphous-crystalline heterointerface is prepared via oxidation method. The optimal RCO-10 exhibits low overpotentials of 57 and 231 mV for HER and OER at 10 mA cm−2, respectively. Experimental characterization and density functional theory (DFT) results show that the optimized electronic structure and surface reconstruction endow RCO-10 with excellent catalytic activity. DFT results show that electrons transfer from RuO2 to Co3O4 through the amorphous-crystalline heterointerface, achieving electron redistribution and moving the d-band center upward, which optimizes the adsorption free energy of the hydrogen reaction intermediate. Moreover, the reconstructed Ru/Co(OH)2 during the HER process has low hydrogen adsorption free energy to enhance HER activity. The reconstructed RuO2/CoOOH during the OER process has a low energy barrier for the elementary reaction (O*→*OOH) to enhance OER activity. Furthermore, RCO-10 requires only 1.50 V to drive 10 mA cm−2 and maintains stability over 200 h for overall water splitting. Meanwhile, RCO-10 displays stability for 48 h in alkaline solutions containing 0.5 M NaCl. The amorphous-crystalline heterointerface may bring new breakthroughs in the design of efficient and stable catalysts.

1D/3D dual carbon-supported Mott-Schottky-type Co-Co2P heterojunctions for pH-universal hydrogen evolution

The rational design of low-cost, efficient, and stable heterojunction catalysts for pH-universal hydrogen evolution is attracting increasing attention towards a sustainable hydrogen economy. Herein, a sequential spatial restriction-pyrolysis route is developed to confine Mott-Schottky-type Co-Co2P heterojunctions embedded in the one-dimensional (1D) carbon nanotube-modified three-dimensional (3D) N,P dual-doped carbon matrix (Co-Co2P@CNT//CM). The synergistic effect between the abundant Mott-Schottky heterointerfaces and the 1D/3D dual carbon confinement system enables fully exposed active sites and facilitated charge transfer dynamics, thus triggering favorable electronic structures of Co-Co2P@CNT//CM. As a result, Co-Co2P@CNT//CM heterojunctions exhibit excellent pH-universal hydrogen evolution reaction (HER) performance with overpotentials of 142, 205, and 262 mV at 10 mA cm−2 in 0.5 M H2SO4, 1.0 M KOH, and 1.0 M phosphate buffer saline (PBS), respectively. The theoretical results demonstrated that the Mott-Schottky effect can induce an oriented interfacial charge exchange between Co and Co2P. This can lower the reactive kinetic barrier and endow Co-Co2P@CNT//CM with ideal hydrogen adsorption free energy, which efficiently drives the production of H2 from electrolytic water.

Manipulating Electron Redistribution in Ni2 P for Enhanced Alkaline Seawater Electrolysis.

Developing bifunctional electrocatalyst for seawater splitting remains a persistent challenge. Herein, an approach is proposed through density functional theory (DFT) preanalysis to manipulate electron redistribution in Ni2 P addressed by cation doping and vacancy engineering. The needle-like Fe-doped Ni2 P with P vacancy (Fe-Ni2 Pv) is successfully synthesized on nickel foam, exhibiting a superior bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic activity for seawater electrolysis in alkaline condition. As a result, bifunctional Fe-Ni2 Pv achieves the industrially required current densities of 1.0 and 3.0 A cm-2 at low voltages of 1.68 and 1.73V, respectively, for seawater splitting at 60 °C in 6.0m KOH circumstances. The theoretical calculation and the experimental results collectively reveal the reasons for the enhancement of catalyst activity. Specifically, Fe doping and P vacancies can accelerate the reconstruction of OER active species and optimize the hydrogen adsorption free energy (ΔGH* ) for HER. In addition, the active sites of Fe-Ni2 Pv are identified, where P vacancies greatly improve the electrical conductivity and Ni sites are the dominant OER active centers, meanwhile Fe atoms as active centers for the HER. The study provides a deep insight into the exploration for the enhancement of activity of nickel-based phosphide catalysts and the identification of their real active centers.

Optimizing Co content in intermetallic L10-FeCoPt nanoparticles to enhance the electrocatalytic performance

The L10-FeCoPt nanoparticles with ultra-small size, highly ordered structure, and various Co contents have been successfully obtained by annealing the wet-chemical synthesized nanoparticles. The addition of third-element Co into L10-FePt nanoparticles would increase the grain size, facilitate the disorder-order transition, and enhance the saturation magnetization and coercivity. The better permanent magnet properties and maximum electrocatalytic HER activity of L10-FeCoPt nanoparticles were achieved when added the moderate Co content (4.5 % and 8.5 %). The hydrogen evolution reaction (HER) kinetics and density functional theory revealed that the Co atom would promote the hybridization of Fe-3d and Pt-5d orbitals and increase the hydrogen adsorption free energy to closer to 0. Optimization of Co content to a suitable range would generate higher permanent magnetic properties and suitable surface energy, which facilitated the proton transformation and lowered the Tafel slope to follow the Volmer-Tafel process in HER. This work illustrates that optimizing third-element content in Pt-based magnetic intermetallic is a feasible strategy to operate the electrocatalytic reaction pathway and enhance the electrocatalytic performance.

Interfacial carbon dots introduced distribution-structure modulation of Pt loading on graphene towards enhanced electrocatalytic hydrogen evolution reaction

To easily load Pt on smoothy graphene synthesized by cathodic exfoliation method and achieve adjacent plane distribution of Pt, carbon dots (CDs) are used to construct anchoring points to load highly dispersed Pt species due to strong interaction between CDs and Pt species. The composite of Pt-CDs/graphene is synthesized via a continuous process of cathodic exfoliation-hydrothermal-impregnation-reduction. Characterization results indicate the distribution configuration of Pt varies from coated structure of CDs@Pt to dispersed configuration of CDs&Pt or Pt&CDs, then to wrapping configuration of Pt@CDs with increased amount of CDs. It’s found that suitable introduction of CDs promotes the adjacent plane distribution of Pt species. The obtained best Pt-4CDs/G shows the low overpotential of 36 mV (10 mA⋅cm−2) and high mass activity of 3747.8 mA mg−1 at −40 mV towards electrocatalytic hydrogen evolution reaction (HER), 9.2 times more active than that of Pt/C (406.2 mA mg−1). The superior HER performance of Pt-4CDs/G is attributed to its relatively adjacent plane distribution of Pt, which supports high electrochemically active surface area and more adjacent Pt sites for H* adsorption. Benefitting from that, the HER process for Pt-4CDs/G favorably follows the Tafel pathway, resulting in low hydrogen adsorption free energy and excellent HER activity.

Light-driven assembly of Pt clusters on Mo-NiOx nanosheets to achieve Pt/Mo-NiOx hybrid with dense heterointerfaces and optimized charge redistribution for alkaline hydrogen evolution

Designing cost-effective alkaline hydrogen evolution reaction (HER) catalysts with high water dissociation ability, enhanced hydroxyl transfer rate and optimized hydrogen adsorption free energy (ΔGH*) by a time and energy efficient strategy is pivotal, but still challenging for alkaline water electrolysis. Herein, Pt/Mo-NiOx hybrid consisting of Pt clusters assembled on Mo-doped NiOx nanosheet arrays is prepared on the surface of raw NiMo foam (NMF) by a light-driven strategy to address this challenge. Benefitting from the electronic interaction between Mo-NiOx and Pt, the Pt/Mo-NiOx composite owns optimized ΔGH* and is beneficial for accelerating water dissociation and hydroxyl transfer. As a result, the optimized Pt/Mo-NiOx/NMF electrode displays an exceptional alkaline HER activity with a low overpotential of 62 mV to obtain 100 mA cm−2 and a high Pt mass activity (13.2 times as high as that of commercial 20 wt% Pt/C). Furthermore, the assembled two-electrode cell of Pt/Mo-NiOx/NMF||NiFe-LDH/NF requires a voltage of only 1.549 V to deliver 100 mA cm−2, along with negligible activity decay after 70 h stability test. The present study provides a promising strategy for exploiting high-performance electrocatalysts towards alkaline HER.

Interfacial electronic engineering of heterostructured Co2P-MoNiP/NF nano-sea-urchin catalysts for efficient and stable hydrogen evolution via water/seawater splitting

Using hydrogen as a fuel is an effective way to combat the energy crisis, at the same time, reduce greenhouse gas emissions. Designing high-performance and low-cost catalysts for the hydrogen evolution reaction (HER) is critical for commercial seawater electrolysis. Here, we designed a heterostructured Co2P-MoNiP/NF nano-sea-urchin catalyst that only showed an overpotential of 46 mV for 10 mA cm−2 to actuate HER in alkaline electrolytes along with superior stability. Theoretical calculations demonstrate that the constructed heterogeneous interfaces effectively promote the redistribution of the charge density and optimize the adsorbed hydrogen intermediates, lowering the hydrogen adsorption free energy barrier and promoting H2 desorption, thus boosting the HER activity. Moreover, the assembled two-electrode electrolyzer only required ultra-low voltages of 1.51 and 1.66 V to deliver current densities of 10 and 100 mA cm−2, respectively. The solar-driven water electrolysis system achieves a high and stable solar-to-hydrogen (STH) conversion efficiency of 19.68 %.

Electronic optimization of heterostructured MoS2/Ni3S2 by P doping as bifunctional electrocatalysts for water splitting

MoS2 is an excellent catalyst for hydrogen evolution reaction (HER) because of its close proximity to the optimum hydrogen adsorption free energy (ΔGH*). However, poor oxygen evolution reaction (OER) intrinsic activity, insufficient active sites, and poor conductivity hinder its application as a bifunctional electrocatalyst. Here, Ni3S2 is combined with MoS2 forming MoS2/Ni3S2 heterostructure due to its intrinsic OER activity and P is chosen as an anion dopant to optimize ΔGH* due to its near-thermoneutral H adsorption to explore the bifunctional performance of MoS2 based nanocomposites. The electronic configurations of Mo, Ni, and S on the interface are modulated by P doping, which optimizes their adsorption/desorption ability of intermediates. The synergistic effect of anion doping and heterostructure induces excellent catalytic activity in P40-MoS2/Ni3S2–5 (Mo to S molar ratio of 1:5 and 40 mg P dopants) with overpotentials of 142 mV for HER and 278 mV for OER at 100 mA cm−2 in 1.0 M KOH solution. The voltage of overall water splitting is 1.76 V using P40-MoS2/Ni3S2–5 as the anode and cathode. This work elucidates a method of optimizing the electronic structure by doping P anion in heterointerface, providing an avenue to boost the catalytic activity of non-noble metal-based catalysts.

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.

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.

Constructing heterostructure of WP/WP2 to enhance catalytic activity and stability toward hydrogen generation

Transition metal phosphides (TMPs) have been identified as potential electrocatalysts for the hydrogen evolution reaction (HER) due to their unique structural and electronic properties. However, TMPs have not yet achieved the desired HER performance, and further improvements are required. Herein, we fabricate heterostructured tungsten phosphide/tungsten diphosphide (WP/WP2) composite microrods grown on carbon cloth (WP/WP2/CC) as an efficient self-supported electrocatalyst, which is proven to be highly efficient and stable for the HER. Various experimental results and density functional theory calculations reveal that the formation of WP/WP2 heterostructures can regulate the electronic structure of active sites and optimize hydrogen adsorption free energy on active sites, which accelerates the electron transfer and boosts the HER performance to WP/WP2/CC. By tuning the phosphidation temperatures, the optimized WP/WP2/CC electrocatalyst shows a superior HER performance with low overpotentials of 92 mV and 146 mV at 10 mA cm−2 in 0.5 M H2SO4 and 1.0 M KOH solutions. Meanwhile, it maintains a stable activity at 100 and 150 mV for at least 12 h in 0.5 M H2SO4 and 1.0 M KOH media, respectively. This study demonstrates that the construction of heterostructures can serve as an efficient strategy to improve the electrocatalytic performance of metal phosphide-based electrocatalysts.

Confined tuning of the charge distribution of Pt electrocatalyst for reinforcing anti-poisoning ability: Toward efficient separation of hydrogen from gases containing ammonia

The development of catalysts for hydrogen oxidation reaction (HOR) with enhanced resistance to ammonia poisoning is an important factor in the practical application of hydrogen electrochemical purification devices (HEPDs). This paper reports on the creation of a highly active and anti-ammonia HOR catalyst developed by tuning the charge distribution of the support material through nitrogen-doping of carbon. The nitrogen-doped carbon-supported platinum catalyst (Pt-N2/KB, 2.03 wt% Pt) achieves a high mass activity and exchange current density of 2788 mA mgpt-1 and 1020 mA mgpt-1, respectively, which are 5.4 and 4.7 times higher than that of the comm. 20% Pt/C. The Pt-N2/KB catalyst also displays a lower percentage of current decay and enhanced electrochemical stability, indicating superior anti-ammonia toxicity in the tests with HEPD. Density functional theory (DFT) calculations reveal that the hydrogen adsorption free energy (ΔGH*) on the surface of Pt-N2/KB is close to zero and has a lower ammonia adsorption energy, thus accounting for its superior HOR activity and anti- ammonia poisoning ability. Consequently, this work facilitates the implementation of HOR catalysts for anti-ammonia poisoning in the HEPDs, thus accelerating the advancement of ammonia cracking for hydrogen production.

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.

Phase-dependent growth of Pt on MoS2 for highly efficient H2 evolution.

Crystal phase is a key factor determining the properties, and hence functions, of two-dimensional transition-metal dichalcogenides (TMDs)1,2. The TMDmaterials, explored for diverse applications3-8, commonly serve as templates for constructing nanomaterials3,9 and supported metal catalysts4,6-8. However, how the TMD crystal phase affects the growth of the secondary material is poorly understood, although relevant, particularly for catalyst development. In the case of Pt nanoparticles on two-dimensional MoS2 nanosheets used as electrocatalysts for the hydrogen evolution reaction7, only about two thirds of Pt nanoparticles were epitaxially grown on the MoS2 template composed of the metallic/semimetallic 1T/1T' phase but with thermodynamically stable and poorly conducting 2H phase mixed in. Here we report the production of MoS2 nanosheets with high phase purity and show that the 2H-phase templates facilitate the epitaxial growth of Pt nanoparticles, whereas the 1T'phase supports single-atomically dispersed Pt (s-Pt)atoms with Ptloading up to 10 wt%. We find that the Pt atoms in this s-Pt/1T'-MoS2 system occupy three distinct sites, with density functional theory calculations indicating for Pt atoms located atop of Mo atoms a hydrogen adsorption free energy of close to zero. This probably contributes to efficient electrocatalyticH2 evolution in acidic media, where we measure for s-Pt/1T'-MoS2 a mass activity of 85 ± 23 A [Formula: see text] at the overpotential of -50 mV and a mass-normalized exchange current density of 127 A [Formula: see text] and we see stable performance in an H-type cell and prototype proton exchange membrane electrolyser operated at room temperature. Although phase stability limitations prevent operation at high temperatures, we anticipate that 1T'-TMDs will also be effective supports for other catalysts targeting other important reactions.

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.

Machine Learning for the Expedited Screening of Hydrogen Evolution Catalysts for Transition Metal-Doped Transition Metal Dichalcogenides

Two-dimensional transition metal dichalcogenides (TMDs) have gained attention as potent catalysts for the hydrogen evolution reaction (HER). The traditional trial-and-error methodology for catalyst development has proven inefficient due to its costly and time-intensive nature. To accelerate the catalyst development process, the Gibbs free energy of hydrogen adsorption ( Δ G H ∗ ), computed using the density functional theory (DFT), is widely used as the paramount descriptor for evaluating and predicting HER catalyst performance. However, DFT calculations for Δ G H ∗ are time-consuming and thus pose a challenge for high-throughput screening. Herein, we devise a predictive model for Δ G H ∗ within transition metal-doped TMD systems using a machine learning (ML) framework. We calculate DFT Δ G H ∗ values for 150 TM-doped MX2 (CrS2, MoS2, WS2, MoSe2, and MoTe2) and apply various ML algorithms. We validate the universality of our model by constructing 15 new external test sets. The prediction results show a high correlation coefficient of R 2 = 0.92 . Based on feature analysis, the three most important parameters are the number of valence electrons of the doped transition metal, the distance of the valence electrons of the doped transition metal, and the electronegativity of the doped transition metal. Our DFT-based ML model provides a useful guideline for the material development process through Δ G H ∗ prediction and facilitates the efficient design of transition metal dichalcogenide catalysts that exhibit superior HER activity.

Probing Active Sites on Pristine and Defective MnPX3 (X: S and Se) Monolayers for Electrocatalytic Water Splitting.

The state-of-the-art density functional theory approach was used to study the structural and electronic properties of pristine and defective MnPX3 monolayers as well as their activity toward water and hydrogen evolution reaction (HER) catalytic performance. The adsorption behavior of H2O on a pristine MnPX3 structure is of physisorption nature, whereas the adsorption energy is significantly increased for the defective structures. At the same time, the water dissociation process is more energetically favorable, and the reactivity of MnPX3 is determined by the vacancy configuration. Following Nørskov's approach, the HER catalytic performance is evaluated by calculating the hydrogen adsorption free energy on the respective MnPX3 surface. Our calculation results demonstrate that defective 2D MnPX3 with low coordinated P shows significantly higher HER performance compared to the pristine counterpart.

Novel two-dimensional square-AlAs: Direct semiconductor coupled with high electron-hole mobility ratio toward sunlight-driven water-splitting

The design of new monolayered atomic motifs always attracts enormous attention due to their interesting properties induced by unique crystal phases and promising catalytic applications in low dimensional devices. Herein, we propose a novel square-AlAs monolayer based on ab initio density functional theory calculations, whose good stability is confirmed from the perspectives of energy, dynamics, thermodynamics, and mechanics. Electronic structure calculations reveal that the newly predicted square-AlAs monolayer is a direct-gap semiconductor with a bandgap of 1.39 eV, which is sensitive to in-plane strain, meanwhile the strain induced changes in bandgap allow advantageous modulations of optical absorption in visible-light region. Unfortunately, the unfavorable hydrogen evolution reaction (HER) band edge levels make square-AlAs not suitable for photocatalytic water-splitting in spite of the appropriate bandgap, high electron-hole mobility ratio and strong visible light absorption. However, a favorable effect caused by strain engineering is revealed by the fact that the square-AlAs can meet the requirement of photocatalytic water-splitting under the suitable biaxial loading. Particularly, compared to pure AlAs, the Gibbs free energy of hydrogen adsorption indicate that Boron-doping can effectively decrease the HER overpotential. Moreover, the external potential provided by photoexcited electrons for oxygen evolution reaction (OER) is quite positive, which can serve as a free and pollution-free driving force to drive OER to proceed spontaneously for pure AlAs or reduce the OER overpotential to a very low value (0.15 V) for Boron-doped AlAs, overmatching widely used IrO2 catalyst.

Turing structuring with multiple nanotwins to engineer efficient and stable catalysts for hydrogen evolution reaction

Low-dimensional nanocrystals with controllable defects or strain modifications are newly emerging active electrocatalysts for hydrogen-energy conversion and utilization; however, a crucial challenge remains in insufficient stability due to spontaneous structural degradation and strain relaxation. Here we report a Turing structuring strategy to activate and stabilize superthin metal nanosheets by incorporating high-density nanotwins. Turing configuration, realized by constrained orientation attachment of nanograins, yields intrinsically stable nanotwin network and straining effects, which synergistically reduce the energy barrier of water dissociation and optimize the hydrogen adsorption free energy for hydrogen evolution reaction. Turing PtNiNb nanocatalyst achieves 23.5 and 3.1 times increase in mass activity and stability index, respectively, compared against commercial 20% Pt/C. The Turing PtNiNb-based anion-exchange-membrane water electrolyser with a low Pt mass loading of 0.05 mg cm−2 demonstrates at least 500 h stability at 1000 mA cm−2, disclosing the stable catalysis. Besides, this new paradigm can be extended to Ir/Pd/Ag-based nanocatalysts, illustrating the universality of Turing-type catalysts.