DFT calculation of vibrational frequency of hydrogen atoms on Pt electrodes: Analysis of the electric field dependence of the Pt–H stretching frequency

The Roles of Surface Hydrogen and Hydroxyl in Alkaline Hydrogen Oxidation on Ni-Based Electrocatalysts

One important target for anion exchange membrane fuel cells (AEMFCs) is to enable the application of anode non-precious metal hydrogen oxidation reaction (HOR) catalyst. Nickel presents a promising candidate for alkaline HOR; yet, its practical application is hampered by the intrinsically sluggish activity and poor stability. Herein, a series of Ni-based metals (Ni5Mo, Ni25Co, Ni14W and Ni) are electrodeposited as model catalysts to systematically explore the alkaline HOR by considering the role of adsorbed hydroxyl (OHad). Spectroscopic studies together with density functional theory calculations shed light on the beneficial effect of transition metal M (M=Mo, Co, W) alloying/doping on HOR by introducing the charge transfer from M to Ni and down shifting Ni 3d band center. The HOR specific activities on Ni-based catalysts reveal a volcano-type relationship with the hydrogen binding energy (HBE). The strongly adsorbed OHad is proven to induce deactivation for Ni active sites, and the deactivation potential is OHad binding energy (OHBE) dependent. This study adds new insight into the HOR mechanism and stability of Ni-based electrocatalysts, providing a new avenue for the rational design of highly efficient and robust alkaline HOR catalysts.

Selective hydrogenolysis of the Csp2-O bond in the furan ring using hydride-proton pairs derived from hydrogen spillover

Selective hydrogenolysis of biomass-derived furanic compounds is a promising approach for synthesizing aliphatic polyols by opening the furan ring. However, there remains a significant need for highly efficient catalysts that selectively target the Csp2-O bond in the furan ring, as well as for a deeper understanding of the fundamental atomistic mechanisms behind these reactions. In this study, we present the use of Pt-Fe bimetallic catalysts supported on layered double hydroxides [PtFe x /LDH] for the hydrogenolysis of furanic compounds into aliphatic alcohols, achieving over 90% selectivity toward diols and triols. Our findings reveal that the synergy between Pt nanoparticles, atomically dispersed Pt sites and the support facilitates the formation of hydride-proton pair at the Pt δ+⋯O2- Lewis acid-base unit of PtFe x /LDH through hydrogen spillover. The hydride specifically targets the Csp2-O bond in the furan ring, initiating an SN2 reaction and ring cleavage. Moreover, the presence of Fe improves the yield of desired alcohols by inhibiting the adsorption of vinyl groups, thereby suppressing the hydrogenation of the furan ring.

Ab Initio Investigation of the Hydrogen Interaction on Two Dimensional Silicon Carbide

A series of density functional theory calculations were performed to understand the bonding and interaction of hydrogen adsorption on two-dimensional silicon carbide obtained from molecular dynamics simulation. The converged energy results pointed out that the H atom can sufficiently bond to 2D SiC at the top sites (atop Si and C), of which the most stable adsorption site is TSi. The vibrational properties along with the zero-point energy were incorporated into the energy calculations to further understand the phonon effect of the adsorbed H. Most of the 2D SiC structure deformations caused by the H atoms were found at the adsorbent atom along the vertical axis. For the first time, five SiC defect formations, including the quadrilateral-octagon linear defect (8-4), the silicon interstitial defect, the divacancy (4-10-4) defect, the divacancy (8-4-4-8) defect, and the divacancy (4-8-8-4) defect, were investigated and compared with previous 2D defect studies. The linear defect (8-4) has the lowest formation energy and is most likely to be formed for SiC materials. Furthermore, hydrogen atoms adsorb more readily on the defect surface than on the pristine SiC surface.

Simultaneous Detection of Mixed-Gas Components by Ionic-Gel Sensors with Multiple Electrodes

The sensing of gas components in a mixed gas is required for breath-based health monitoring and diagnosis. In this work, we report the simultaneous detection of mixed-gas components using a sensor consisting of [EMIM][BF₄]-based ionic gel with four electrodes made of Au, Pt, Rh, and Cr. The voltage between any given pair of electrodes depends on the gas molecules absorbed in the ionic gel and the elements the electrodes are made of. When the voltage signals between all pairs of electrodes were used, H₂, NH₃, and C₂H₅OH concentrations were simultaneously estimated by a neural-network-based inference. From molecular dynamics simulations, the origin of the voltage signal was attributed to the catalytically generated adsorbates on the electrodes.

Spectroscopic Verification of Adsorbed Hydroxy Intermediates in the Bifunctional Mechanism of the Hydrogen Oxidation Reaction

Elucidating hydrogen oxidation reaction (HOR) mechanisms in alkaline conditions is vital for understanding and improving the efficiency of anion-exchange-membrane fuel cells. However, uncertainty remains around the alkaline HOR mechanism owing to a lack of direct in situ evidence of intermediates. In this study, in situ electrochemical surface-enhanced Raman spectroscopy (SERS) and DFT were used to study HOR processes on PtNi alloy and Pt surfaces, respectively. Spectroscopic evidence indicates that adsorbed hydroxy species (OH_ad ) were directly involved in HOR processes in alkaline conditions on the PtNi alloy surface. However, OH_ad species were not observed on the Pt surface during the HOR. We show that Ni doping promoted hydroxy adsorption on the platinum-alloy catalytic surface, improving the HOR activity. DFT calculations also suggest that the free energy was decreased by hydroxy adsorption. Consequently, tuning OH adsorption by designing bifunctional catalysts is an efficient method for promoting HOR activity.

Activation Energy of Hydrogen Adsorption on Pt(111) in Alkaline Media: An Impedance Spectroscopy Study at Variable Temperatures

The hydrogen evolution reaction is one of the most studied processes in electrochemistry, and platinum is by far the best catalyst for this reaction. Despite the importance of this reaction on platinum, detailed and accurate kinetic measurements of the steps that lead to the main reaction are still lacking, particularly because of the fast rate of the reaction. Hydrogen adsorption on Pt(111) has been taken as a benchmark system in a large number of computational studies, but reliable experimental data to compare with the computational studies is very scarce. To gain further knowledge on this matter, a temperature study of the hydrogen adsorption reaction has been carried out to obtain kinetic information for this process on Pt(111) in alkaline solution. This was achieved by measuring electrochemical impedance spectra and cyclic voltammograms in the range of 278 ≤ T ≤ 318 (K) to obtain the corresponding surface coverage by adsorbed species and the faradaic charge transfer resistance. From this data, the standard rate constant has been extracted with a kinetic model assuming a Frumkin-type isotherm, resulting in values of 2.60 × 10^-7 ≤ k⁰ ≤ 1.68 × 10^-6 (s^-1). The Arrehnius plot gives an activation energy of 32 kJ mol^-1. Comparisons are made with values calculated by computational methods and reported values for the overall HER, giving a reference frame to support future studies on hydrogen catalysis.

Hydrogen adsorption on two-dimensional germanene and its structural defects: an ab initio investigation

Herein, the adsorption of hydrogen on pristine germanene was studied using ab initio calculations. By performing a converged density functional theory calculation, we have found the nearly degenerate nature of hydrogen at the top sites HT1 and HT2, among which HT1 is the most stable site. The adsorption of a hydrogen atom on germanene led to local structural changes in germanene. To the best of our knowledge, this is the first study on the investigation of the localized surface curvature and zero-point energy of hydrogen for 2D germanene. Moreover, we demonstrated the properties of germanene defects via the four obtained defects: the Stone-Wales (55-77), divacancy (77-555-6), divacancy (555-7), and pentagon-heptagon linear (5-7) defect. The lowest formation energy of the pentagon-heptagon linear defect is shown for the first time in this study.

Insight into the mechanism of methanol assistance with syngas conversion over partially hydroxylated γ-Al2O3(110D) surface in slurry bed

Despite numerous studies devoted to the various properties of γ-Al2O3, the explorations of its catalytic activity remain scarce. In this study, density functional theory calculations are performed to study the elementary adsorption and reaction mechanisms for syngas conversion on partially hydroxylated γ-Al2O3(110D) surface in liquid paraffin. It is found that the partially hydroxylated γ-Al2O3(110D) surface with the hydroxyl coverage of 8.9 OH nm-2 is formed by two dissociative adsorptions of H2O on the dry γ-Al2O3(110D) surface. The hydroxyl coverage conditions play a key role in determining the dominant reaction mechanism on account of the existence of strong hydrogen bonds. The preferential pathway for syngas conversion with assistance of methanol over the partially hydroxylated γ-Al2O3(110D) surface in liquid paraffin has been proven to be CH3OH → CH3O + H → CH3 + OH, CH3 + CO → CH3CO. C2H5OH is then formed by successive hydrogenation via the pathway CH3CO + 3H → CH3CHO + 2H → CH3CH2O + H → C2H5OH. Here, CH3CHO formation by CH3CO hydrogenation is not inhibited. Actually, with the assistance of partially hydroxylated γ-Al2O3, CH3CHO has been synthesized with high selectivity in our previous experiment by the reaction of methanol and syngas, which provides favorable evidence for our results. The rate-limiting step is the formation of CH3O from CH3OH dehydrogenation with an activation barrier of 122.2 kJ mol-1. Moreover, the reaction barrier of CO insertion into the adsorbed CH3 group is at least 89.4 kJ mol-1, lower than those of CH4, C2H6, and CH3OCH3 formations. ADCH charge and ESP analyses indicate that the typical (Al, O) Lewis acid-base pair may have a significant effect upon the initial C-C chain formation. Thus, the present study provides a new approach for the rational tailoring and designing of new catalysts with superior reactivity involved in syngas conversion.

DME synthesis from methanol over hydrated γ-Al2O3(110) surface in slurry bed using continuum and atomistic models

The possible paths of dimethyl ether (DME) synthesis from methanol over hydrated [Formula: see text]-Al2O3(110) in vacuum and liquid paraffin have been investigated by using density functional theory (DFT). Over hydrated [Formula: see text]-Al2O3(110), the three possible paths of methanol dehydration to DME have been investigated by the DFT method in vacuum and liquid paraffin. DME synthesis from methanol is carried out along the same pathway 2CH3OH(g) [Formula: see text] 2* [Formula: see text] 2CH3OH* [Formula: see text] 2CH3O* [Formula: see text] 2H* [Formula: see text] CH3OCH3* [Formula: see text] H2O* in vacuum and liquid paraffin, and the step of highest energy barrier is the reaction of 2CH3O* [Formula: see text] CH3OCH3* [Formula: see text] O*. The energy barrier of the step in liquid paraffin is higher than that in vacuum by 0.33[Formula: see text]eV. The surface acid strength in liquid paraffin decreases over [Formula: see text]-Al2O3(110) surface comparing with vacuum, showing that stronger surface acid strength benefits to DME synthesis. Our result is in consistent with the experiment results.