Efficient visible-light-driven hydrogen evolution over ternary MoS2/PtTiO2 photocatalysts with low overpotential

By surface-decorating PtTiO₂ hybrid catalyst with MoS₂ nanosheets, we prepared a new MoS₂/PtTiO₂ ternary system as high-performance photocatalysts. The ternary MoS₂/PtTiO₂ outperforms both the binary MoS₂TiO₂ and PtTiO₂ systems in photocatalytic hydrogen evolution with an AQY (apparent quantum yield) value of 12.54% at 420 nm, owing to the unique ternary design that creates more efficient electron transport path and electron-hole separation mechanism. Electrochemical characterization showed that the MoS₂/PtTiO₂ ternary electrode afford an efficient pathway of photo-excited electrons from TiO₂ to surface-decorated Pt nanoparticles using MoS₂ and internal Pt nanoparticles as bridges, thus significantly promoting electron transfer, reducing the system overpotential and leading to the activation of more reactive sites. This internal electron transfer pathway (TiO₂ → Pt (internal) → MoS₂ → Pt (surface)) eliminates the need of other metal cocatalysts because the Pt nanoparticles play two roles of storing the conduction band electrons of TiO₂ and acting as co-catalyst for reduction of protons to hydrogen. This unique ternary metal-semiconductor heterojunction for efficient photocatalytic hydrogen evolution provides a meaningful reference for reasonable design of other hybrid photocatalysts.     

One-pot synthesis of ultrasmall PtAg nanoparticles decorated on graphene as a high-performance catalyst toward methanol oxidation

A one-pot synthesis method is utilized for the fabrication of ultrasmall platinum-silver nanoparticles decorated on graphene (PtAg/G) catalyst. This method has several advantages such as inexpensiveness, simplicity, low temperature, surfactant free, reductant free, being environmentally friendly and greenness. In this work, graphene and silver formate were dispersed in ultrapure water in an ultrasonic bath at 25 °C followed by through a galvanic displacement reaction; to prepare PtAg/G, PtCl₂ was added to the suspension under mild stirring condition. The morphology, crystal structure and chemical compositions of the as-fabricated PtAg/G and Pt/C catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Energy dispersive X-ray spectroscopy (EDS) techniques. Electrochemical techniques, including cyclic voltammetry (CV) and chronoamperometry (CA) measurements were used to analyze the electrochemical activity of the PtAg/G and Pt/C catalysts. The TEM images illustrate the uniform distribution of ultrasmall PtAg nanoparticles with the average size of 2–3 nm on the graphene nanosheets. The PtAg/G promoted the current density 2.46 times as much as Pt/C with a negative shift in onset oxidation potential and peak potential for oxidation reaction of methanol. Besides, the novel PtAg/G catalyst shows large electrochemically active surface area, lower apparent activation energy, and higher levels of durability in comparison to the Pt/C catalyst for the oxidation of methanol. The PtAg/G catalyst depicts extraordinary catalytic performance and stability to those of the Pt/C catalyst toward methanol oxidation in alkaline media.     

Mesocrystalline Ta2O5 nanosheets supported PdPt nanoparticles for efficient photocatalytic hydrogen production

We successfully synthesized mesocrystalline Ta₂O₅ nanosheets supported bimetallic PdPt nanoparticles by the photo-reduction method. The as-prepared mesocrystalline Ta₂O₅ nanosheets in this work showed amazing visible-light absorption, mainly because of the formation of oxygen vacancy defects. And the as-prepared bimetallic PdPt/mesocrystalline Ta₂O₅ nanaosheets also showed highly enhanced UV–Vis light absorption and highly improved photocatalytic activity for hydrogen production in comparison to that of commercial Ta₂O₅, mesocrystalline Ta₂O₅ nanosheets, Pd/mesocrystalline Ta₂O₅ nanosheets and Pt/mesocrystalline Ta₂O₅ nanosheets. The highest photocatalytic hydrogen production rate of PdPt/mesocrystalline Ta₂O₅ nanaosheets was 21529.52 g^?1 h^?1, which was about 21.2 times of commercial Ta₂O₅, and the apparent quantum efficiency of PdPt/mesocrystalline Ta₂O₅ nanaosheets for hydrogen production was about 16.5% at 254 nm. The highly enhanced photocatalytic activity was mainly because of the significant roles of PdPt nanoparticles for accelerating the charge separation and transport upon illumination. The as-prepared PdPt/mesocrystalline Ta₂O₅ nanaosheets in this work could serve as an efficient photocatalyst for green energy production.     

Effective excitons separation on graphene supported ZrO2TiO2 heterojunction for enhanced H2 production under solar light

A novel photocatalyst comprises of ZrO₂TiO₂ immobilized on reduced graphene oxide (rGO) – a ternary heterojunction (ZrO₂TiO₂/rGO) was synthesized by using facile chemical method. The nanocomposite was prepared with a strategy to achieve better utilization of excitons for catalytic reactions by channelizing from metal oxide surfaces to rGO support. TEM and XRD analysis results revealed the heterojunction formed between ZrO₂ and single crystalline anatase TiO₂. The mesoporous structure of ZrO₂TiO₂ was confirmed using BET analysis. The red shift in absorption edge position of ZrO₂TiO₂/rGO photocatalyst was characterized by using diffuse reflectance UV–Visible spectra. ZrO₂TiO₂/rGO showed greater interfacial charge transfer efficiency than ZrO₂TiO₂, which was evidenced by well suppressed PL intensity and high photocurrent of ZrO₂TiO₂/rGO. The suitable band gap of 1.0 wt% ZrO₂TiO₂/rGO facilitated the utilization of solar light in a wide range by responding to the light of energy equal to as well as greater than 2.95 eV by the additional formation of excited high-energy electrons (HEEs). ZrO₂TiO₂/rGO showed the enhanced H₂ production than TiO₂/rGO, which revealed the role of ZrO₂ for the effective charge separation at the heterojunction and the solar light response. The optimum loading of 1.0 wt% of ZrO₂ and rGO on TiO₂ showed the highest photocatalytic performance (7773 μmolh^?1$g_{cat}^{?1}$) for hydrogen (H₂) production under direct solar light irradiation.     

Hydrogen-iodide decomposition over PdCeO2 nanocatalyst for hydrogen production in sulfur-iodine thermochemical cycle

A highly active and stable catalyst for hydrogen-iodide decomposition reaction in sulfur-iodine (SI) cycle has been prepared in the form of PdCeO₂ nanocatalyst by sol-gel method with different calcination temperatures (300 °C, 500 °C, and 700 °C). XRD and TEM confirmed a size around 6–8 nm for PdCeO₂ particles calcined at 300 °C. Raman study revealed large number oxygen vacancies in PdCeO₂-300 when compared to PdCeO₂-500 and PdCeO₂-700. With increase in calcination temperature, the average particle size increased whereas the specific surface area and number of oxygen vacancies decreased. Hydrogen-iodide catalytic-decomposition was carried out in the temperature range of 400°C–550 °C in a quartz-tube, vertical, fixed-bed reactor with 55 wt % aqueous hydrogen-iodide feed over PdCeO₂ catalyst using nitrogen as a carrier gas. PdCeO₂-300 showed hydrogen-iodide conversion of 23.3%, which is close to the theoretical equilibrium conversion of 24%, at 550 °C. It also showed a reasonable stability with a time-on-stream of 5 h.     

AuCu alloys deposited on titanium dioxide nanosheets for efficient photocatalytic hydrogen evolution

This work first reports AuCu alloys deposited on the surface of TiO₂ nanosheets (TiNs) to form heterojunction. A simple deposition-precipitation method was used to construct a new type of AuCu/TiNs heterostructures through gradually depositing Au and Cu nanoparticles on TiNs. Such structures served the dual advantage of constructing a heterostructure which can improve visible light absorption, and the formation of a Schottky barrier between AuCu alloys (lower Fermi level) and TiNs (higher Fermi level) which can suppress the recombination of photo-generated charge carriers to improve the overall photocatalytic activity. The mass ratio of Au and Cu in the AuCu/TiNs heterostructures and the sequence and method of their deposition are found to be the important factors which affect the photocatalytic performance. When the mass ratio of Au to Cu was determined to be 1: 1, the AuCu/TiNs heterostructure exhibited the best photocatalytic performance for hydrogen production from water splitting (over 9 times than TiNs, 1.47 times than Au/TiNs, and 1.75 times than Cu/TiNs).     

PtPd nanoparticles supported on sulfonated nitrogen sulfur co-doped graphene for methanol electro-oxidation

In this paper, sulfonated nitrogen sulfur co-doped graphene (S-NS-GR) nanocomposite, i.e., nitrogen sulfur co-doped graphene functionalized with SO₃H group as a novel catalyst support material was prepared. PtPd nanoparticles (PtPd NPs) were deposited on the surface of S-NS-GR by a facile electrochemical approach. The morphology and structure of Pd-PtNPs/S-NS-GR were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and electrochemical impedance spectroscopy (EIS), respectively. In addition, the electrocatalytic performance of catalyst for methanol oxidation reaction (MOR) was systematically studied by cyclic voltammetry and chronoamperometry in alkaline media. Compared with PtPd NPs supported on nitrogen sulfur co-doped graphene (Pt-PdNPs/NS-GR), the excellent performance of Pd-PtNPs/S-NS-GR is mainly ascribed to the embedding of abundant functional groups (SO₃H) into the NS-GR layers, which not only facilitate the homogeneous distribution of metal NPs, but also strengthen the interaction between metals and support material, thus improve the stability of catalyst in MOR.     

PtCo@NCNTs cathode catalyst using ZIF-67 for proton exchange membrane fuel cell

Zeolitic Imidazolate Frameworks (ZIF) is one of the potential candidates as highly conducting networks with large surface area with a possibility to be used as catalyst support for low temperature fuel cells. In the present study, highly active state-of-the-art PtCo@NCNTs (Nitrogen Doped Carbon Nanotube) catalyst was synthesized by pyrolyzing ZIF-67 along with Pt precursor under flowing ArH₂ atmosphere. The multi-walled NCNTs were densely grown on the surface of ZIF particles after pyrolysis. The high resolution TEM examination was employed to examine the nature of the PtCo particles as well as multi-walled NCNTs. Rotating disk electrode study was used for measuring oxygen reduction reaction performance for PtCo@NCNTs in 0.1 M HClO₄ and compared with commercial Pt/C catalyst. Fuel cell performance with PtCo@NCNT and commercial Pt/C catalysts was evaluated at 70 °C using Nafion-212 electrolyte using H₂ and O₂ gases (100% RH) and the observed peak power density of 630 and 560 mW cm^?2, respectively.     

Highly efficient hydrogen evolution catalysis based on MoS2/CdS/TiO2 porous composites

Efficient production of hydrogen through visible-light-driven water splitting mechanism using semiconductor-based composites has been identified as a promising strategy for converting light into clean H₂ fuel. However, researchers are facing lots of challenges such as light absorption and electron-hole pair recombination and so on. Here, new sheet-shaped MoS₂ and pyramid-shaped CdS in-situ co-grown on porous TiO₂ photocatalysts (MoS₂CdSTiO₂) are successfully obtained via mild sulfuration of MoO₃ and CdO coexisted inside porous TiO₂ monolith by a hydrothermal route. The scanning electron microscopy and transmission electron microscopy results exhibit that the MoS₂CdSTiO₂ composites have average pore size about 500 nm. The 3%MoS₂10%CdSTiO₂ demonstrated excellent photocatalytic activity and high stability for a hydrogen production with a high H₂-generation rate of 4146 μmol h^?1 g^?1 under visible light irradiation even without noble-metal co-catalysts. The super photocatalytic performance of the visible-light-driven hydrogen evolution is predominantly attributed to the synergistic effect. The conduction band of MoS₂ facilitates in transporting excited electrons from visible-light on CdS to the porous TiO₂ for catalytic hydrogen production, and holes to MoS₂ for inhibiting the photocorrosion of CdS, respectively, leading to enhancing the efficient separation of electrons and holes.     

Mechanistic insights into tandem amine-borane dehydrogenation and alkene hydrogenation catalyzed by [Pd(NHC)(PCy3)]

The mechanism of tandem dimethylamine-borane (NHMe₂BH₃, DMAB) dehydrogenation and alkene hydrogenation catalyzed by [Pd(NHC)(PMe₃)] are investigated by density functional theory (DFT) calculations [NHC = N,N′-bis(2,6-diisopropylphenyl) imidazole-2-ylidene]. Four possible DMAB dehydrogenation mechanisms have been carefully investigated involving concerted BH/NH activation, sequential BH/NH activation, sequential NH/BH activation, and proton transfer mechanism. DFT studies show that the NH proton transfers to ligated carbene carbon and sequential CH/BH activation is the most kinetically favorable pathway with the lowest activation barrier of 23.8 kcal/mol. For hydrogenation, it was found that a trans-dihydride Pd(II) complex, [Pd(H)₂(NHC)(PMe₃)], formed in the dehydrogenation process, serves as an effective catalyst for reduction of trans-stilbene.     

Noble metal-free FeN-CNFs as an efficient electrocatalyst for oxygen reduction reaction

Carbonaceous materials containing non-precious metal atoms and doped with nitrogen have enthralled stunning attention in the field of electrochemical energy conversion systems. Herein, we demonstrated a facile method to fabricate iron and nitrogen doped carbon nanofiber (FeN-CNFs) catalyst material from ferric chloride and interfacial synthesized polyaniline (PANI) nanofibers, by carbonization process in an inert atmosphere at 800 °C. Further, synthesized material was characterized by elemental analysis and X-ray photoelectron spectroscopy (XPS) that confirms the presence of FeN bonds. The structural and morphological features are studied using various microscopy and spectroscopy techniques. The oxygen reduction reaction (ORR) activity of synthesized catalyst materials was examined by rotating disk electrode experiments in 0.1 M KOH. Among all these synthesized materials FeN-CNFs material showed enhanced ORR activity regarding current density and onset potential. Also, FeN-CNFs catalyst exhibited tolerance to methanol and durability in comparison to commercial Pt/C catalyst. The superior performance of FeN-CNFs may be attributed due to the introduction of Fe and formation of FeN bond in catalyst material.     

Bimetallic Pt-M electrocatalysts supported on single-wall carbon nanotubes for hydrogen and methanol electrooxidation in fuel cells applications

A series of PtRu and PtMo bimetallic catalysts were prepared via a chemical reduction method by bubbling CO to form carbonyl compounds as metal precursors. In both cases the PtRu and PtMo bimetallic electrocatalysts achieved the maximum activity when the amount of Ru and Mo in the material was 50%wt. The physicochemical characterization of the electrocatalytic materials through X-ray diffraction (XRD) and transmission electron microscopy (TEM) has determined the presence of bimetallic structures. The electrochemical characterization using cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and polarization curves in Proton Exchange Membrane Fuel Cells (PEMFC) and Direct Methanol Fuel Cell (DMFC) allowed to systematically investigate the electrocatalytic activity of the synthesized materials for the electrooxidation of hydrogen and methanol. The PtRu/SWCNT electrocatalysts showed a higher current density at least 7-fold and 3-fold compared with Pt/SWCNT and PtMo/SWCNT electrocatalysts, respectively. Besides, the Pt50%–Ru50%/SWCNT exhibited a shifting to negative values in the onset potential reaction for the electrooxidation of methanol of 200 mV in comparison with Pt100%/SWCNT and Pt50%–Mo50%/SWCNT electrocatalysts. The experimental and simulated polarization curves obtained from DMFC show that PtRu/SWCNT and PtMo/SWCNT electrocatalysts exhibited higher power and current densities values compared with the Pt/SWCNT electrocatalyst. The membrane-electrode assembly (MEA) with Nafion^® and the PtRu/SWCNT electrocatalysts showed an open-circuit voltage value of 0.730 V, significantly higher than that the values for the MEAs with Pt/SWCNT (0.663 V) and PtMo/SWCNT (0.633 V), respectively.     

CeO2 overlapped with nitrogen-doped carbon layer anchoring Pt nanoparticles as an efficient electrocatalyst towards oxygen reduction reaction

To engineering high-efficient, sustainable and novel Pt-based composite system, a newly “Pt-oxide” based composites electrocatalyst of “CeO₂ overlapped with nitrogen-doped carbon layer anchoring Pt nanoparticles” (PtCeO₂@CN) has been fabricated. In comparison with Pt/C, the results exhibit that PtCeO₂@CN possesses a preferable methanol tolerance ability, superior stability (30000 s degradation: 35% for PtCeO₂@CN vs. 50% for Pt/C), and more positively the onset potential (16 mV) as well as half-wave potential (29 mV) towards oxygen reduction reaction. Further, the investigation shows that PtCeO₂@CN has a certain selectivity with quasi-four electron pathway (n = 3.2–3.3 e^?). This is attributed to the establishment of “nitrogen-doped carbon layer” structure, which heightens the conductivity of CeO₂, further promotes electron transfer between Pt and CeO₂, as well as strengthens the anchoring effect for Pt nanoparticles. Overall, this study would shed bright light to develop some effective Pt-oxide based composite electrocatalysts.     

Synergic effect of vanadium trichloride on the reversible hydrogen storage performance of the MgMgH2 system

Vanadium trichloride (VCl₃) is one of the best catalysts for the hydrogenation-dehydrogenation MgMgH₂ system. X-ray photoelectron spectroscopy (XPS) has shown that VCl₃ reduced to metallic vanadium during ball milling along with MgH₂. The in-situ-formed metallic vanadium doped over the MgH₂ surface which has shown an excellent catalytic effect on hydrogenation-dehydrogenation of the MgMgH₂ system. The catalyzed surface reduced the activation energies of hydrogenation-dehydrogenation reactions and correspondingly on-set hydrogenation-dehydrogenation temperatures. The microstructural analysis has also shown an excellent grain refinement property of VCl₃ which reduced the crystallite size of MgH₂. The decreased crystallite size decreases the diffusion path length of hydrogen and increases the active surface area which eventually enhances the hydrogenation-dehydrogenation kinetics of MgMgH₂.     

Rare earth metal Gd influenced defect sites in N doped TiO2: Defect mediated improved charge transfer for enhanced photocatalytic hydrogen production

In this experimental studies, we report the synthesis of TiO₂ co-doped by both cationic and anionic sites by simple sol-gel based method. All the prepared samples exhibit the anatase crystalline morphology however, showed lattice distortion caused by the displacement of Ti⁴⁺ sites by Gd³⁺. The improved visible absorption is witnessed by the Gd and N co-doping with an assured redshift in the absorption edge. The N and Gd displacement inside TiO₂ lattice accompanied by the creation of OTiN and GdOTi bonds are characterized by the X-ray photoelectron spectra. The strong resonance signal by Gd4f electrons in the electron paramagnetic resonance spectroscopy further substantiate the displacement of lattice cites of TiO₂ by Gd³⁺ ions. The longevity of the photo produced charges observed in fluorescence spectra of Gd and N co-doped TiO₂ is because of the effective transfer of charges to the defect sites. The aforementioned catalysts are tested for their capacity for the H₂ production from water splitting. The 2 wt% gadolinium and nitrogen co-doped TiO₂ has shown 10764 μmol g^?1 H₂ production which is 26 times higher than the commercial Degussa P-25 catalyst. The enhanced activity for hydrogen production can be attributed to factors such as increased absorptivity under visible light and effective charge carrier separation.     

Fabrication of CdS/NiFe LDH heterostructure for improved photocatalytic hydrogen evolution from aqueous methanol solution

2D CdS/NiFe LDH (short for layered double hydroxide) heterostructures were designed and fabricated by following a facile in-situ growth method. The CdS nanoparticles are well dispersed on the surface of NiFe LDH to form nanoscale heterojunctions, as suggested from the TEM and elemental mapping images. The composites with optimum CdS amount (15 wt%) take on notably higher hydrogen evolution activity (469 μmol h^?1 g^?1) than the independent CdS and NiFe LDH from aqueous methanol solution under xenon lamp irradiation. The nano-heterojunction notably promotes the H₂ evolution kinetics and greatly suppresses the recombination of photo-induced electrons and holes, which is responsible for the enhanced photocatalytic activity of the composites, as demonstrated by the reducing onset potential and increasing photocurrent of the composites in the photoelectrochemical experiments. The possible photocatalytic mechanism is proposed on the basis of the defined position of energy band edges.     

NiPt sinter as a promising electrode for methanol electrocatalytic oxidation

Methanol is one of the chemical compounds utilized in fuel cells. The direct methanol fuel cell (DMFC) can be applied in many devices such as light electric vehicles and field equipment. Such a fuel cell is characterized by its high fuel energy density and low pollution. Despite many advantages of DMFCs, they are not commercially available, as the most efficient catalyst, which can be used in this process, has not been developed yet. Traditionally, it was platinum that was used in these fuel cells which is expensive and susceptible to CO poisoning. The solution to this is the use of bimetallic catalysts such as a NiPt system. In this study, we used a sintered NiPt electrode as the anode for the electrocatalytic oxidation of methanol. Based on our results, the sintered NiPt electrodes exhibited much higher activity in the oxidation of methanol, when compared with some conventional anodes.     

Bismuth doped TiO2 as an excellent photocathode catalyst to enhance the performance of microbial fuel cell

Bismuth impregnation on pure TiO₂ (BiTiO₂) was carried out and tested in microbial fuel cell (MFC) as photocathode catalyst. UV–Visible spectral observation confirmed higher catalytic activity of BiTiO₂ under visible light irradiation with reduced band gap of 2.80 eV as compared to pure TiO₂ (3.26 eV). Electrochemical impedance spectroscopy also showed two times higher exchange current density with lower charge transfer resistance for BiTiO₂ (1.90 Ω) than pure TiO₂ (3.95 Ω), thus confirming it as superior oxygen reduction reaction catalyst. MFC operated with BiTiO₂ could generate a maximum power density of 224 mW m^?2, which was higher than MFC with Pt as cathode catalyst (194 mW m^?2) and much higher than MFCs with TiO₂ catalyzed cathode (68 mW m^?2) and without any cathode catalyst (60 mW m^?2). The results thus promote Bi doped TiO₂ as a superior low-cost alternative to the costly Pt catalyst to take this MFC technology forward for field application.     

AuNi alloy nanoparticles supported on reduced graphene oxide as highly efficient electrocatalysts for hydrogen evolution and oxygen reduction reactions

Bimetallic nanoparticles of Au and Ni in the form of alloy nanostructures with varying Ni content are synthesized on reduced graphene oxide (rGO) sheets via a simple solution chemistry route and tested as electrocatalysts towards the hydrogen evolution (HE) and oxygen reduction (OR) reactions using polarization and impedance studies. The AuNi alloy NPs/rGO nanocomposites display excellent electrocatalytic activity which is found to improve with increasing Ni content in the AuNi/rGO alloy nanocomposites. For HER, the best AuNi alloy NPs/rGO electrocatalyst, the one with the highest Ni content, exhibits high activity with an onset overpotential approaching zero versus the reversible hydrogen electrode and an overpotential of only 37 mV at 10 mA cm^?2. Additionally, a low Tafel slope of 33 mV dec^?1 and a high exchange current density of 0.6 mA cm^?2 are measured which are very close to those of commercial Pt/C catalyst. Also, in the ORR tests, this electrocatalyst displays comparable activity to Pt/C. The Koutecky–Levich plots referred to a 4-electron mechanism for the reduction of dissolved O₂ on the AuNi alloy NPs/rGO catalyst. The electrocatalyst thus demonstrates excellent activity towards HER and ORR. Additionally, it exhibits outstanding operational durability and activation after 10,000^th cycles assuring its practical applicability.     

Achieving the dehydriding reversibility and elevating the equilibrium pressure of YFe2 alloy by partial Y substitution with Zr

To overcome the hydrogen-induced amorphization and phase disproportionation in the fast de-/hydrogenation of YFe₂, the alloying of partial substituting Y with Zr was carried out to obtain Y_1?xZr_xFe₂ (x = 0.1, 0.2, 0.3, 0.5) alloys. All YZrFe alloys remained single C15 Laves phase structure at states of as-annealed, hydrogenated and dehydrogenated. With the increasing of Zr content, the YZrFe alloys showed the decrease in the lattice constants and hydrogenation capacity, but the increase in the dehydrogenation capacity and dehydriding equilibrium pressure. The alloy Y_0.9Zr_0.1Fe₂ showed maximum initial hydrogenation capacity of 1.87 wt% H, while the alloy Y_0.5Zr_0.5Fe₂ showed highest desorption capacity of 1.26 wt% with obvious dehydriding plateau. Based on experiment analysis and first principle calculation of binding energy, the great improvement in the dehydriding thermodynamics for YZrFe alloys is attributed to the change in the unit cell volume, electron concentration and stability of hydrides due to the Zr substitution.