Theoretical study of solvent effects on the decomposition of formic acid over a Co(111) surface

Solvent effects on the decomposition of formic acid over a Co(111) surface were studied via density functional theory calculations combined with a continuum implicit solvation model. The solvents used here were water, methanol, and acetone. The adsorption energies of key intermediates, the activation barriers and the rate and equilibrium constants of various elementary reactions in vacuum and in the solvents were obtained. Solvent presences decrease the adsorption energies of species. Formic acid decomposition on the surface goes through HCOO rather than COOH both in vacuum and in the solvents. The most favorable decomposition pathways in vacuum and in acetone are HCOOH → HCOO → HCO → CO. The corresponding rate determining steps are HCOO deoxidation to HCO with activation barriers of 0.78 and 0.76 eV, respectively. In the presences of water and methanol, the preferred pathways are shifted to HCOOH → HCOO → HCOO-m → CO₂ below 750–800 K. Above those temperatures, the path of HCOOH → HCOO → HCO → CO becomes dominant again.     

First-principles GGA + U calculation investigating the hydriding and diffusion properties of hydrogen in PuH2+x, 0 ≤x≤ 1

The hydrogen (H) diffusion process is a crucial issue related to storage of plutonium safely. In this work, first-principles GGA + U calculation is performed to elucidate the hydriding and diffusion behaviors of an additional H atom (H_i) in “perfect” PuH_2+x (0 $\le x\le$ 1) matrixes. It finds the value of incorporation energy increases with increasing x. The interaction energies show that an extra H_i atom interacts much further with surrounding host atoms in PuH₃ than in other Pu hydride matrixes. The minimum migration paths of a H_i atom in PuH_2+x are characterized by the image nudged elastic band (CINEB) method. The H_i atom diffuses in PuH₂, PuH_2.25, and PuH₅ matrixes through directly migrating from an octahedral interstice to its nearest octahedral site with energy barriers of 1.36 eV, 1.15 eV, and 1.59 eV, respectively. Oppositely, the metastable I_H-site plays a dominant role for the H_i migration into the O-site in PuH_2.75. The diffusion path of the H_i atom in PuH₃ is I_Pu $\to$ I_H0160 $\to$ I_PU path with the lowest migration energy of 0.72 eV, which concludes the H_i has relatively higher mobility in PuH₃. These findings provide detailed insight into how the H atom corrodes the Pu metal by connecting H atom diffusion in PuH₂, PuH₃, and intermediate compositions, which can be great interest for assisting the development of the new nuclear fuel for next generation reactors.     

Crystal structure,electrical and electrochemical properties of Cu co-doped Pr1.3Sr0.7NiO4+δ mixed ionic-electronic conductors (MIECs)

Room temperature crystal structure, electrical properties and electrochemical properties in the temperature range 25–700 °C of Cu co-doped Pr_1.3Sr_0.7NiO_4+δ prepared by acetate combustion is investigated from intermediate temperature solid oxide fuel cell cathode viewpoint. The Pr_1.3Sr_0.7Ni_1?xCu_xO_4+δ (PSNCO) solid solutions have a tetragonal I4/mmm K₂NiF₄-type structure which consists of a (Pr_1.3Sr_0.7) (Ni_1.xCu_x)O₃ perovskite unit and a (Pr_1.3Sr_0.7)O rock salt unit in the whole compositional range 0 ≤ x ≤ 0.4. A reduction in bond-length of Ni/Cu-O resulting from PSNCO lattice contraction eases hop of small polaron from Ni³⁺ to Ni²⁺/Cu²⁺ in (Ni_1?xCu_x)-O layer with low activation energy, which increases electron conductivity. The maximum electronic conductivity (σ = Ω cm^?1) with minimum activation energy (E_a = eV) is observed at x = 0.3. Lattice expansion along c-direction owing to Cu²⁺ doping facilitates hop of O^2? from its occupied interstitial site (O₃) to nearby equivalent site assisted by anisotropic thermal motion of apical oxygen O2 resulting in increase in ionic conductivity. The minimum polarization resistance value (R_p = 0.13 (2) Ω cm²) and activation energy (E_a = 1.321 (5) eV) at x = 0.3 is attributed to high electronic and ionic conductivities compared to other compositions. Complex impedance spectroscopy studies suggest that the ORR is co-limited by O^2? diffusion and O₂ surface exchange.     

A study on lithium/air secondary batteries—Stability of NASICON-type glass ceramics in acid solutions

The stability of a NASICON-type lithium ion conducting solid electrolyte, Li_1+x+yTi_2−xAl_xP_3−ySi_yO₁₂ (LTAP), in acetic acid and formic acid solutions was examined. XRD patterns of the LTAP powders immersed in 100% acetic acid and formic acid at 50 °C for 4 months showed no change as compared to the pristine LTAP. However, the electrical conductivity of LTAP drastically decreased. On the other hand, no significant electrical conductivity change of LTAP immersed in lithium formate saturated formic acid-water solution was observed, and the electrical conductivity of LTAP immersed in lithium acetate saturated acetic acid-water increased. Cyclic voltammogram tests suggested that acetic acid was stable up to a high potential, but formic acid decomposed under the decomposition potential of water. The acetic acid solution was considered to be a candidate for the active material in the air electrode of lithium-air rechargeable batteries. The cell reaction was considered as 2Li + 2 CH₃COOH + 1/2O₂ = 2CH₃COOLi + H₂O. The energy density of this lithium-air system is calculated to be 1477 Wh kg⁻¹ from the weights of Li and CH₃COOH, and an observed open-circuit voltage of 3.69 V.     

Selective substitution of Ni by Ti in LaNiO3 perovskites: A parameter governing the oxy-carbon dioxide reforming of methane

A series of LaNi_1?xTi_xO₃ perovskite catalysts varying titanium (x = 0.0, 0.2, 0.4, 0.5, 0.6 and 1.0) are synthesized and investigated using BET, XRD, TPR, TEM, FT-IR and XPS. The catalysts were evaluated for oxy-carbon dioxide reforming of methane at 800 °C under atmospheric pressure maintaining CO₂/CH₄/O₂ ratio 0.8/1.0/0.2. LaNi_0.5Ti_0.5O₃ is showing typical stability with gradual H₂ consumption in TPR. The stability of these catalysts is supported by O 1s binding energies wherein it is clearly evident that incorporation of Ti stabilized LaNiO₃ generating suitable catalysts in the range of x = 0.4–0.6 with high performance.     

Water splitting for hydrogen generation over lanthanum-calcium-iron perovskite-type membrane driven by reducing atmosphere

Here, we systematically investigated the behavior of water splitting in a La_0.9Ca_0.1FeO_3?δ (LCF-91) perovskite-type oxygen-transport membrane (OTM) reactor driven by different reducing atmospheres (i.e., CO, H₂/CO and CH₄). The LCF-91 membrane showed favorable oxygen permeability and hydrogen production rates toward different reducing atmospheres (0.0617, 0.0523 and 0.0390 μmol s^?1 cm^?2 for CO, H₂/CO and CH₄ reducing gases, respectively). The activation of CO is easier than that of CH₄ over the surface of LCF-91, which promotes the surface oxygen diffusion and following oxygen permeation rate. Further crystallization of the membrane materials is observed during the water splitting test, which is much more serious for the side exposing in the oxidation atmosphere (steam side) compared with the reducing atmospheres. Grain growth of materials in both reduction and oxidation sides of membrane is associated with the reducing atmospheres, and the growth rate follows a rank order of CH₄ > H₂/CO > CO. This crystallization of LCF-9 membrane materials is beneficial for improving the stability of the reactor for successive generation of hydrogen. The LCF-91 membrane reveals a favorable stability during the CH₄-driven water splitting test.     

Characterization of defects in titanium created by hydrogen charging

In the present work positron annihilation spectroscopy was employed for investigation of defects created in titanium by hydrogen loading. Pure titanium samples were firstly annealed to remove dislocations introduced by cutting and polishing. Subsequently the samples were loaded with hydrogen up to various hydrogen concentrations. Ti samples with different microstructures were compared: (i) conventional coarse grained sample, (ii) ultra fine grained material with microstructure refined by severe plastic deformation. Hydrogen gas loading of coarse grained and ultra fine grained samples was performed at hydrogen gas pressure of 103 bar and temperature of 150 °C. This resulted in formation of δ-TiH_x phase in Ti matrix. The hydrogen content absorbed in the samples was determined by thermogravimetric analysis. The phase composition of hydrogen-loaded samples was characterized by X-ray diffraction. Hydrogen loading introduced vacancies which agglomerated in the sample into small vacancy clusters. In addition to vacancies, dislocations were created by α-Ti → δ-TiH_x phase transition. Differential thermal analysis revealed that hydrogen is trapped at several kinds of traps characterized by different binding energies. The release of hydrogen from these traps precedes the decomposition of the δ-TiH_x phase.     

Hydrogen desorption kinetics of the destabilized LiBH4AlH3 composites

LiBH₄ can be destabilized by AlH₃ addition. In this work, the hydrogen desorption kinetics of the destabilized LiBH₄AlH₃ composites were investigated. Isothermal hydrogen desorption studies show that the LiBH₄ + 0.5AlH₃ composite releases about 11.0 wt% of hydrogen at 450 °C for 6 h and behaves better kinetic properties than either the pure LiBH₄ or the LiBH₄ + 0.5Al composite. The apparent activation energy for the LiBH₄ decomposition in the LiBH₄ + 0.5AlH₃ composite estimated by Kissinger's method is remarkably lowered to 122.0 kJ mol^?1 compared with the pure LiBH₄ (169.8 kJ mol^?1). Besides, AlH₃ also improves the reversibility of LiBH₄ in the LiBH₄ + 0.5AlH₃ composite. For the LiBH₄ + xAlH₃ (x = 0.5, 1.0, 2.0) composites, the decomposition kinetics of LiBH₄ are enhanced as the AlH₃ content increases. The sample LiBH₄ + 2.0AlH₃ can release 82% of the hydrogen capacity of LiBH₄ in 29 min at 450 °C, while only 67% is obtained for the LiBH₄ + 0.5AlH₃ composite in 110 min. Johnson?Mehl?Avrami (JMA) kinetic studies indicate that the reaction LiBH₄ + Al → ‘LiAlB’ + AlB₂ + H₂ is controlled by the precipitation and subsequently growth of AlB₂ and LiAlB compounds with an increasing nucleation rate.     

Co-deficient PrBaCo2−xO6−δ perovskites as cathode materials for intermediate-temperature solid oxide fuel cells: Enhanced electrochemical performance and oxygen reduction kinetics

Co-deficient PrBaCo_2?xO_6?δ perovskites (x = 0, 0.02, 0.06 and 0.1) are synthesized by a solid-state reaction, and the effects of Co-deficiency on the crystal structure, oxygen nonstoichiometry and electrochemical properties are investigated. The PrBaCo_2?xO_6?δ samples have an orthorhombic layered perovskite structure with double c axis. The degree of oxygen nonstoichiometry increases with decreasing Co content (0 ≤ x ≤ 0.06) and then slightly decreases at x = 0.1. All the samples exhibit the electrical conductivity values of >300 S cm^?1 in the temperature range of 100–800 °C in air, which match well the requirement of cathode. With significantly enhanced electrochemical performance and good chemical compatibility between PrBaCo_2?xO_6?δ and CGO, this system of Co-deficient perovskite is promising cathode material for IT-SOFCs. Among all these components, PrBaCo_1.94O_6?δ gives lowest polarization resistance of 0.059 Ω cm² at 700 °C in air. When tested as cathode in fuel cell, the anode-supported Ni-YSZ|YSZ|CGO|PrBaCo_1.94O_6?δ cell delivers a maximum peak power density of 889 mW cm^?2 at 650 °C, which is higher than that of PrBaCoO_6?δ cathode-based cell (764 mW cm^?2). The oxygen reduction kinetics at the PrBaCo_1.94O_6?δ cathode interface is also explored, and the rate-limiting steps for oxygen reduction reaction are determined.     

Efficient catalytic properties of SO42−/MxOy (M = Cu,Co, Fe) catalysts for hydrogen generation by methanolysis of sodium borohydride

The SO₄^2?/M_xO_y (M = Cu, Co, Fe) catalysts were prepared and applied to hydrogen production from methanolysis of sodium borohydride for the first time. The morphologies and properties of the as-prepared catalysts were characterized by XRD, BET, FT-IR, TEM and SEM-EDX techniques. Under our experimental conditions, SO₄^2?/CuO exhibits much higher catalytic activity than those of SO₄^2?/CoO and SO₄^2?/Fe₂O₃ catalysts and follows the order of SO₄^2?/CuO > SO₄^2?/CoO > SO₄^2?/Fe₂O₃, which is opposite to order of BET surface area, implying that the methanolysis of sodium borohydride is not a structure-sensitive reaction. It can be inferred that both acidic and metallic sites are responsible for the high catalytic performance of the SO₄^2?/M_xO_y catalysts towards NaBH₄ methanolysis. In addition, the effects of the concentrations of NaBH₄ and methanol, catalyst dosage, and reaction temperature on the hydrogen generation rate have been investigated using SO₄^2?/CuO as catalyst. The SO₄^2?/CuO-catalyzed methanolysis reaction follows a power law, i.e. r = A·exp (?13135/RT)·[NaBH₄]^1.01·[CH₃OH]^1.60·[Catalyst]^0.52. The apparent activation energy was calculated to be 13.13 kJ/mol.     

Effect of Ti substitution on electrochemical properties of ZrNi alloy electrode for use in nickel-metal hydride batteries

Crystal structure and electrochemical properties of the Zr_1?xTi_xNi (0.05 ≤ x ≤ 0.5) alloys were investigated. X-ray diffraction spectra showed that the primary phase of all Zr_1?xTi_xNi alloys had the B33-type orthorhombic crystal structure, which was characteristic of ZrNi, and the unit cell volume of the primary phase linearly decreased with an increase in the x value. In the charge–discharge tests with the Zr_1?xTi_xNi alloy negative electrodes, the initial discharge curves for the alloys with x ≥ 0.3 had two plateaus. Both plateau potentials negatively shifted with an increase in the x value. The initial discharge capacity for the Zr_0.6Ti_0.4Ni alloy negative electrode was 349 mAh g^?1 at 25 mA g^?1 and 333 K, which was the highest in this study. The high-rate dischargeability and cycle performance were also improved by the partial replacement of Zr by Ti.     

FexCo1−x-doped titanium oxide nanotubes as effective photocatalysts for hydrogen extraction from ammonium phosphate

Theoretically, tri-ammonium phosphate (NH₄)₃PO₄ embeds considerable amount of hydrogen. Typically, the expected hydrogen release from this cheap and stable material is 73.83 mmol/g_salt if a proper catalyst is exploited in the hydrolysis reaction. In this study Fe_xCo_1?x-doped titanium oxide nanotubes are introduced as an efficient photocatalyst under solar radiation. The introduced modified titanium oxide nanotubes have been prepared in two successive steps. First, Na-doped TiO₂ nanotubes were synthesized by hydrothermal treatment in presence of 10 N NaOH solution at 160 °C for 16 h. Then, doping by the proposed metals was carried out by ion exchange process in a microwave oven. X-ray photoelectron microscopy (XPS) and transmission electron microscopy (TEM) confirmed the success of the doping process and the nanotubular morphology, respectively. Study the photo characteristics indicated that the proposed metal doping shifted the band gap from UV to the visible light region as the estimated band gap energies for the as-prepared and doped nanotubes were 3.4 and 2.1 eV, respectively. Moreover, distinct enhancement for the visible light absorption capacity was observed. Accordingly, a distinguished improvement in the photocatalytic activity toward tri-ammonium phosphate hydrolysis was observed. However, the two metals content has a strong influence on the amount of the obtained hydrogen per gram of tri-ammonium phosphate salt. Numerically, the maximum obtained hydrogen was 4.0, 11.2, 11.2, 11.6, 13.4, 16.5, 17.4, 13.4 and 9.8 mmol/g_salt for the pristine TiO₂, and Fe_xCo_1?x-doped TiO₂ with x = 1, 0.8, 0.6, 0.5, 0.4, 0.3, 0.2, and 0.0, respectively.     

Dehydrogenation mechanisms of Ca(NH2BH3)2: The less the charge transfer,the lower the barrier

Our first-principles study of Ca(NH₂BH₃)₂ reveals that the gas phase energy barrier for the first H₂ release is 1.90 eV via a Ca?H transition state and 1.71 eV via an N–H?B transition state for the second H₂ release. In the dimer, the barrier for H₂ release from the bridging [NH₂BH₃]⁻ species is 1.60 eV via an N–H?B transition state, and 0.94 eV via an N–H?B transition state for the non-bridging [NH₂BH₃]⁻ species. Analysis of the atomic charge distribution shows that the mechanism of dehydrogenation is determined by the charge transfer between the transition state and the initial state: the less the charge transfer, the lower the barrier to dehydrogenation.     

The electrocatalysis of oxygen evolution reaction on La1−xCaxFeO3−δ perovskites in alkaline solution

The electrocatalytic oxygen evolution reaction (OER) on iron based perovskites with composition La_1?xCa_xFeO_3?δ (0.0 ≤ x ≤ 1.0) in alkaline solution has been investigated. The perovskite samples were synthesized by combustion method. Energy dispersive spectroscopy and X-ray photoelectron spectroscopy were used to determine the bulk and the surface composition, respectively. The X-ray diffraction and iodometric titration method were employed to examine the phases and the oxidation state, respectively. It was observed that incorporation of calcium (Ca²⁺) ions in the lattice of LaFeO₃ decreases the lattice parameters and the cell volume systematically as evaluated by Rietveld method. Furthermore, increase in the degree of Ca²⁺ substitution from 0.0 to 1.0, increases the average oxidation state of iron from Fe³⁺ to Fe⁴⁺ in addition to creating oxygen vacancies. The evaluation of OER kinetics on a rotating disk electrode setup suggests that incorporation of Ca²⁺ decreases the activity initially (0.0 ≤ x ≤ 0.4), but further substitution increases the activity. The maximum activity was observed for x = 1.0. This change in the OER activity suggests an interplay between the bond lengths and angles, oxygen vacancy and the average oxidation state of Fe.     

Dehydrogenation and rehydrogenation of a 0.62LiBH4-0.38NaBH4 mixture with nano-sized Ni

The dehydrogenation reaction pathway of a 0.91 (0.62LiBH₄-0.38NaBH₄)-0.09Ni mixture in the temperature range of 25–650 °C in flowing Ar and the cycling stability in H₂ are presented. No H₂ is released immediately after melting at 225 °C. The major dehydrogenation occurs above 350 °C. Adding nano-sized Ni reduces the dehydrogenation peak temperatures by 20–25 °C, leading to three decomposition steps where Ni₄B₃ and Li_1.2Ni_2.5B₂ are found in the major dehydrogenation products for the 1^st and the 3^rd step; whilst the Ni-free mixture decomposes through a two-step decomposition pathway. A total of 8.1 wt% of hydrogen release from the 0.91 (0.62LiBH₄-0.38NaBH₄)-0.09Ni mixture is achieved at 650 °C in Ar. This mixture has a poor hydrogen cycling stability as its reversible hydrogen content decreases from 5.1 wt% to 1.1 wt% and 0.6 wt% during three complete desorption-absorption-cycles. However, the addition of nano-sized Ni facilitates the reformation of LiBH₄.     

Study of the decomposition of a 0.62LiBH4–0.38NaBH4 mixture

This work highlights the dehydrogenation mechanisms of a 0.62LiBH₄–0.38NaBH₄ mixture in the range of 25–650 °C in flowing Ar. The dehydrogenation starts from 287 °C followed by two decomposition steps at 488 °C and 540 °C. These peak temperatures are in the range of 470 °C (for pure LiBH₄)–580 °C (for pure NaBH₄) due to different Pauling electronegativity values for Li⁺ (0.98) and Na⁺ (0.93) that affects the stability and decomposition temperatures. The 1^st step of dehydrogenation is accompanied with precipitation of LiH, Li₂B₁₂H₁₂ and B in between 287 and 520 °C; whilst the 2^nd step of dehydrogenation is mainly accompanied by the precipitation of Na and B when temperature is higher than 520 °C. The total amount of H₂ released is 10.8 wt.% that exceeds the estimated amount (8.9 wt.%), indicating less metal dodecaborate (than that for pure LiBH₄) is formed during the decomposition.     

Towards activation of amorphous MoSx via Cobalt doping for enhanced electrocatalytic hydrogen evolution reaction

Amorphous molybdenum sulfide (a-MoS_x) has been shown as one of the most promising catalysts in acidic electrolytes towards hydrogen evolution reaction (HER). Its intrinsic electrocatalytic activity can be further enhanced via doping and cropping the electronic structure.In this study, one-step electro-deposition was employed to fabricate MoS_xCo_y/TNAs hybrid electrodes using TiO₂ nanotube arrays as support. The microstructure and chemical composition of the samples were characterized via X-ray diffraction (XRD), scanning electron microscope (SEM), tunneling electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS). The electrochemical properties of the samples were investigated through linear sweep voltammetry (LSV), cyclic voltammetry (CV), Tafel curves, and electrochemical impedance spectroscopy (EIS). According to experimental results, MoSCo structure was formed after Co²⁺ was incorporated into MoS_x, resulting in increases in both unsaturated Mo and S atoms acting as the active sites that lead to enhancement of intrinsic electrocatalytic activity. The pseudo-capacitance of MoS_xCo_y/TNAs (x = 1.70, y = 0.25) reached 46 mF cm^?2, a 31.4% improvement over 35 mF cm^?2 of MoS_x/TNAs. The onset hydrogen evolution potential, overpotentials at current densities of ?10 mA cm^?2 and –20 mA cm^?2 were recorded at ?92 mV, ?173 mV, and ?209 mV, respectively, reduction of 30 mV, 24 mV, and 28 mV than ?112 mV, ?197 mV, and ?237 mV of MoS_x/TNAs, respectively. This electrode was subjected to 1000-cycle testing and demonstrated stable electrochemical activity, illustrating excellent stability.     

Bio-oil catalytic reforming without steam addition: Application to hydrogen production and studies on its mechanism

A novel process for hydrogen production via bio-oil catalytic reforming without steam addition was proposed. The liquid feedstock was a distillation fraction from crude bio-oil molecular distillation. The fraction obtained was enriched with the low-molecular-weight organics (acids, aldehydes, and ketones), and contained nearly all of the water from crude bio-oil. The highest catalytic performance, with a carbon conversion of 95% and a H₂ yield of 135 mg g⁻¹ organics, was obtained by processing the distillate over Ni/Al₂O₃ catalyst at 700 °C. The steam involved in the reforming reaction was derived entirely from the water in the crude bio-oil. The fresh and spent catalysts were characterized by N₂-physisorption, thermogravimetric analysis, and high-resolution transmission electron microscopy. To further understand the reaction mechanisms, symmetric density functional theory calculations for decomposition were performed on four model compounds in bio-oil (acetic acid, hydroxyacetone, furfural, and phenol) over the Ni(111) surface. In addition, the decomposition of H₂O∗ to OH∗ and O∗ and their subsequent steam reforming reactions with carbon precursors (CH∗ and CH₃C∗) were also examined.     

Ethylene glycol as an alternative solvent approach for very efficient hydrogen production from sodium borohydride with phosphoric acid and acetic acid catalysts

For the first time, phosphoric acid (H₃PO₄) and acetic acid (CH₃COOH) catalysts were used for efficient hydrogen (H₂) production from sodium borohydride (NaBH₄) ethylene glycolysis reaction. In this experimental study, the effects of ethylene glycol/water ratio, ethylene glycol/acid ratio, NaBH₄ concentration, acid concentration, and temperature were investigated. These ethylene glycol/water ratio experiments showed that the use of water alongside ethylene glycol negatively affects H₂ production. The hydrogen generation rate (HGR) values obtained for this ethylene glycolysis reaction with 1 M H₃PO₄ and 1 M CH₃COOH catalysts are 5800 and 4542 mLmin^-1, respectively. Also, the completion times of ethylene glycolysis reactions with these acids are 8 and 10 s, respectively. The n value obtained for ethylene glycolysis reactions according to the power-law kinetic model was 0.50. The activation energies obtained with H₃PO₄ and CH₃COOH catalysts were 24.45 kJ mol^?1and 33.23 kJ mol^?1, respectively.     

Synthesis and characterization of mixed sodium and lithium fullerides for hydrogen storage

We herein report on the synthesis of mixed alkali cluster intercalated fullerides Na_xLi_y?xC₆₀ (y = 12; x = 1–6) by a two-steps mechanochemical reaction of fullerene with sodium and lithium. These compounds crystallize in the cubic lattice of C₆₀ displaying a contracted lattice parameter with respect to the Na₆C₆₀ parent structure. The analysis of the hydrogen sorption behaviour shows a slight decrease in the dehydrogenation enthalpy for y = 12 with respect to the sodium free member. Raman spectroscopy highlighted a partial electron transfer from alkali metals to C₆₀, suggesting the presence of charged sodium/lithium clusters. Finally, we applied muon spectroscopy to understand the different hydrogenation mechanisms in Na_xLi_6?xC₆₀ and Na_xLi_12?xC₆₀ and explain their different performance.