The elementary steps of the reactions of hypophosphite ions with Cu, Ni, and Pd were calculated theoretically using Density Functional Theory (DFT) to demonstrate the reaction mechanism and gain insight at the molecular level. The elementary steps of these reactions are adsorption, dehydrogenation, and oxidation (hydroxyl base attack). In the adsorption step, hypophosphite ions adsorb onto each surface spontaneously with stabilities in the order of Ni (111) > Pd (111) > Cu (111). In the dehydrogenation step, hypophosphite ions dehydrogenate on Ni (111) and Pd (111) with small reaction barriers, whereas they react on Cu (111) with a large reaction barrier. The large reaction barrier on Cu (111) is not compensated for by the adsorption energy on the surface. In the oxidation step, dehydrogenated anions on each metal surface react spontaneously with the hydroxyl base. The reaction barriers on each metal surface in this step are not so significant compared to the adsorption energies on each surface, suggesting that a reaction barrier of hypophosphite ion oxidation should exist in the dehydrogenation step and only be observed for Cu (111). This proposition elucidates the experimental catalytic behaviors of metal surfaces in the electroless deposition process using hypophosphite ions.
Self‐stability in light‐emitting electrochemical cells (LECs) based on Ir(III) ionic transition metal complexes (Ir‐iTMC) has been long overlooked. Herein, it is demonstrated that the nature of the active layer blending an archetype Ir‐iTMC as emitter and ionic electrolytes—ionic liquid (IL) or ionic polyelectrolyte (IP)—is paramount for the storage and mechanical stability of rigid/flexible LECs. Strikingly, devices with ionic polyelectrolytes (IPs) stand out compared to those with traditional configurations with or without ILs. They exhibit i) superior brightness and efficiencies in rigid/flexible devices due to the higher photoluminescence quantum yield, ii) the best performance at pulsed current driving mode under inert/ambient operation conditions due to a slower growth of the doped regions, iii) enhanced device stabilities upon ambient/inert storage, resulting in <10% performance loss after 1 month of aging, and iv) the smallest performance loss (<10%) upon bending stress, since IPs prevent mechanically induced damage, preserving morphological and spectroscopic features. These findings are supported by steady‐state and time‐resolved emission spectroscopy, electrochemical impedance spectroscopy, microscopic and mechanical assays, along with the analysis of fresh and aged devices driven at different modes under inert/ambient conditions. Overall, this work highlights the need of revisiting new emitter:electrolyte combinations toward realizing highly self‐stable LECs.
In order to elucidate the reactivity difference of hypophosphite ions used as reducing agents for electroless deposition on different metal surfaces, such as Pd and Cu, electronic structures of the activation states of hypophosphite ion oxidation on these surfaces were intensively analyzed by using Density Functional Theory (DFT). In the calculation, we focused on the dehydrogenation reaction which should be a rate-determining step in the elementary reaction steps. From the calculation results, a particular orbital interaction between the hypophosphite ion and the metal surface was observed. On Pd (111), the s-orbital of H in the hypophosphite ion interacts singly with the d-or p-orbital of Pd (111). This interaction induces an anti-bonding interaction between H and P in the hypophosphite ion, which is responsible for P-H cleavage. On the other hand, on Cu (111), the s-orbital of H and the s-orbital of P in a hypophosphite ion interact simultaneously with the p-orbital of Cu (111). This interaction barely induces an antibonding interaction between H and P in the hypophosphite ion. Such a difference in orbital interaction structures should be related to P-H cleavage activity and the reactivity difference of hypophosphite ion on each metal surface.Electroless deposition has attracted considerable attention owing to a progress in the field of nanotechnology. 1-3 In order to obtain fundamental knowledge about a reaction mechanism for greater precise control in this process, we have analyzed the reaction behavior of species in the process by applying a theoretical calculation methodology 4,5 to propose several reaction models. 6 We are now focusing on the reactivities of a hypophosphite ion on metal surfaces; a hypophosphite ion is widely used as a reducing agent in electroless nickel deposition. 2,3,7 Although a hypophosphite ion exhibits high oxidation reactivity, the catalytic activities of the deposited metal surfaces affect the reactivity; the hypophosphite ion oxidizes on the surface of Ni or Pd, whereas it does not oxidize on the surface of Cu. 8 Comprehension of the factors determining the reactivity enables us to obtain one of the most important guidelines for the design of more sophisticated and controlled reaction processes.In our previous study, we analyzed the reaction mechanisms of the hypophosphite ion, and we estimated the reaction barriers of its oxidation reaction on metal surfaces. 9 The reaction was divided into three steps, namely, adsorption, dehydrogenation, and oxidation. [10][11][12] The results indicated that the reaction barrier of dehydrogenation on the Cu surface ($100 kJ/mol) could not be overcome by the adsorption energy on the surface ($À 50 kJ/mol), whereas the reaction barrier on the Ni surface ($ 50 kJ/mol) could be compensated for by the adsorption energy on the surface ($ 250 kJ/mol). Moreover, a reaction barrier was not expected to exist on the surface of Pd. Oxidation of the dehydrogenated residue by OH À attack proceeds spontaneously on metal surfaces with a low reaction barrier...
Zn is a promising anode material for next-generation large-scale energy storage devices. However, irregular shape evolution on its surface during cycling causes electrode degradation. The shapes and crystal structures of the deposits naturally originate from the initial behaviors of the depositions. At the initial stage of deposition, a micro-protrusion initiates on the Zn electrode, leading to an irregular shape evolution. This study focuses on the initial steps of Zn deposition using a multiscale simulation comprising density functional theory (DFT) calculations and kinetic Monte Carlo (KMC) simulations. This simulation allows analyses of phenomena from the picometer to the nanometer scale to yield mechanistic insight into the shape evolution of the deposits with respect to the electronic state of a particular species. The DFT calculations indicate that the Zn adatom exhibits specific behavior during surface diffusion: faster flat surface diffusion on the (0001) surface and slower interlayer diffusion. The KMC simulations show an irregular shape evolution based on the surface diffusion behavior of Zn as follows: (i) a two-dimensional (2D) hexagonal nucleation of the (0001) surface occurs on the substrate; (ii) the adatoms accumulate on the first layer to form layer-by-layer structures; (iii) the layer-by-layer structure forms the mountain structure, where the top layer exhibits a small area; and (iv) the top layer results in the protrusion. Therefore, the (0001) surface and interlayer diffusion rates are significant in the irregular shape evolution.
Elementary steps in the electrochemical reduction process of SiCl 4 in trimethyl-n-hexylammonium bis(trifluoromethylsulfonyl) imide (TMHATFSI) was investigated, focusing on molecular level behavior of the reactants at solid-liquid interface. Electrochemical measurements using an electrochemical quartz crystal microbalance (EQCM) identified a reduction peak corresponding to Si electrodeposition and several elementary steps with stable intermediates forming prior to the deposition. For detailed analysis, X-ray reflectivity (XRR) measurements with synchrotron radiation were applied in situ. The change in reflectivity of the electrode surface during the deposition was found to be due to the formation of a polymer-like Si such as Si 2 Cl 6 , which is an intermediate layer during the deposition process. These results were theoretically supported by density functional theory (DFT) calculations: after an electron transfers from the electrode, the Si in SiCl 4 forms the bond with another SiCl 4 , rather than the Si of the substrate, resulting in the formation of the intermediate structure. These data suggest an elementary step in the SiCl 4 reduction process which can be described as follows; when SiCl 4 is reduced, a polymer-like Si form such as Si 2 Cl 6 is generated. This intermediate species further reacts with other Si reactants after receiving additional electrons, which then finally deposits as Si on the substrate.
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