Revealing Nanoscale Solid-Solid Interfacial Phenomena for Long-Life and High-Energy All-Solid-State Batteries.

Enabling long cyclability of high-voltage oxide cathodes is a persistent challenge for all-solid-state batteries, largely because of their poor interfacial stabilities against sulfide solid electrolytes. While protective oxide coating layers such as LiNbO3 (LNO) have been proposed, its precise working mechanisms are still not fully understood. Existing literature attributes reductions in interfacial impedance growth to the coating's ability to prevent interfacial reactions. However, its true nature is more complex, with cathode interfacial reactions and electrolyte electrochemical decomposition occurring simultaneously, making it difficult to decouple each effect. Herein, we utilized various advanced characterization tools and first-principles calculations to probe the interfacial phenomenon between solid electrolyte Li6PS5Cl (LPSCl) and high-voltage cathode LiNi0.85Co0.1Al0.05O2 (NCA). We segregated the effects of spontaneous reaction between LPSCl and NCA at the interface and quantified the intrinsic electrochemical decomposition of LPSCl during cell cycling. Both experimental and computational results demonstrated improved thermodynamic stability between NCA and LPSCl after incorporation of the LNO coating. Additionally, we revealed the in situ passivation effect of LPSCl electrochemical decomposition. When combined, both these phenomena occurring at the first charge cycle result in a stabilized interface, enabling long cyclability of all-solid-state batteries

Alkene Hydrosilylation on Oxide-supported Pt-ligand Single-site Catalysts

Heterogeneous single-site catalysts (SSCs), widely regarded as promising next-generation catalysts, blend the easy recovery of traditional heterogeneous catalysts with desired features of homogeneous catalysts: high fraction of active sites and uniform metal centers. We previously reported the synthesis of Pt-ligand SSCs through a novel metal-ligand self-assembly method on MgO, CeO$_2$, and Al$_2$O$_3$ supports (J. Catal. 2018, 365, 303-312). Here, we present their applications in the industrially-relevant alkene hydrosilylation reaction, with 95% yield achieved under mild conditions. As expected, they exhibit better metal utilization efficiency than traditional heterogeneous Pt catalysts. The comparison with commercial catalysts (Karstedt and Speier) reveals several advantages of these SSCs: higher selectivity, less colloidal Pt formation, less alkene isomerization/hydrogenation, and better tolerance towards functional groups in substrates. Despite some leaching, our catalysts exhibit satisfactory recyclability and the singlesite structure remains intact on oxide supports after reaction. Pt single-sites were proved to be the main active sites rather than colloidal Pt formed during the reaction. An induction period is observed in which Pt sites are activated by Cl detachment and replacement by reactant alkenes. The most active species likely involves temporary detachment of Pt from ligand or support. Catalytic performance of Pt SSCs is sensitive to the ligand and support choices, enabling fine tuning of Pt sites. This work highlights the application of heterogeneous SSCs created by the novel metal-ligand self-assembly strategy in an industrially-relevant reaction. It also offers a potential catalyst for future industrial hydrosilylation applications with several improvements over current commercial catalysts

Effect of Redox-Inactive Metal Ion–Nickel(III) Interactions on the Redox Properties and Proton-Coupled Electron Transfer Reactivity

Mononuclear nickel(II) and nickel(III) complexes of a bisamidate-bisalkoxide ligand, (NMe$_4$)$_2$[NiII(HMPAB)] (1) and (NMe$_4$)[NiIII(HMPAB)] (2), respectively, have been synthesized and characterized by various spectroscopic techniques including X-ray crystallography. The reaction of redox-inactive metal ions (M$^{n+}$ = Ca$^{2+}$, Mg$^{2+}$, Zn$^{2+}$, Y$^{3+}$, and Sc$^{3+}$) with 2 resulted in 2-M$^{n+}$ adducts, which was assessed by an array of spectroscopic techniques including X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR), and reactivity studies. The X-ray structure of Ca$^{2+}$ coordinated to Ni(III) complexes, 2-Ca$^{2+}$T, was determined and exhibited an average Ni–Ca distance of 3.1253 Å, close to the metal ions’ covalent radius. XAS analysis of 2-Ca$^{2+}$ and 2-Y$^{3+}$ in solution further revealed an additional coordination to Ca and Y in the 2-M$^{n+}$ adducts with shortened Ni–M distances of 2.15 and 2.11 Å, respectively, implying direct bonding interactions between Ni and Lewis acids (LAs). Such a short interatomic distance between Ni(III) and M is unprecedented and was not observed before. EPR analysis of 2 and 2-M$^{n+}$ species, moreover, displayed rhombic signals with gav > 2.12 for all complexes, supporting the +III oxidation state of Ni. The NiIII/NiII redox potential of 2 and 2-M$^{n+}$ species was determined, and a plot of E$_{1/2}$ of 2-M$^{n+}$ versus pK$_a$ of [M(H$_2$O)$_n$]$^{m+}$ exhibited a linear relationship, implying that the Ni$^{III}$/Ni$^{II}$ potential of 2 can be tuned with different redox-inactive metal ions. Reactivity studies of 2 and 2-Mn+ with different 4-X-2,6-ditert-butylphenol (4-X-DTBP) and other phenol derivatives were performed, and based on kinetic studies, we propose the involvement of a proton-coupled electron transfer (PCET) pathway. Analysis of the reaction products after the reaction of 2 with 4-OMe-DTBP showed the formation of a Ni(II) complex (1a) where one of the alkoxide arms of the ligand is protonated. A pKa value of 24.2 was estimated for 1a. The reaction of 2-M$^{n+}$ species was examined with 4-OMe-DTBP, and it was observed that the k2 values of 2-M$^{n+}$ species increase by increasing the Lewis acidity of redox-inactive metal ions. However, the obtained k$_2$ values for 2-M$^{n+}$ species are much lower compared to the k2 value for 2. Such a variation of PCET reactivity between 2 and 2-M$^{n+}$ species may be attributed to the interactions between Ni(III) and LAs. Our findings show the significance of the secondary coordination sphere effect on the PCET reactivity of Ni(III) complexes and furnish important insights into the reaction mechanism involving high-valent nickel species, which are frequently invoked as key intermediates in Ni-mediated enzymatic reactions, solar-fuel catalysis, and biomimetic/synthetic transformation reactions

Alkene Hydrosilylation on Oxide‐Supported Pt‐Ligand Single‐Site Catalysts

Heterogeneous single-site catalysts (SSCs), widely regarded as promising next-generation catalysts, blend the easy recovery of traditional heterogeneous catalysts with desired features of homogeneous catalysts: high fraction of active sites and uniform metal centers. We previously reported the synthesis of Pt-ligand SSCs through a novel metal-ligand self-assembly method on MgO, CeO$_2$, and Al$_2$O$_3$ supports (J. Catal. 2018, 365, 303-312). Here, we present their applications in the industrially-relevant alkene hydrosilylation reaction, with 95% yield achieved under mild conditions. As expected, they exhibit better metal utilization efficiency than traditional heterogeneous Pt catalysts. The comparison with commercial catalysts (Karstedt and Speier) reveals several advantages of these SSCs: higher selectivity, less colloidal Pt formation, less alkene isomerization/hydrogenation, and better tolerance towards functional groups in substrates. Despite some leaching, our catalysts exhibit satisfactory recyclability and the singlesite structure remains intact on oxide supports after reaction. Pt single-sites were proved to be the main active sites rather than colloidal Pt formed during the reaction. An induction period is observed in which Pt sites are activated by Cl detachment and replacement by reactant alkenes. The most active species likely involves temporary detachment of Pt from ligand or support. Catalytic performance of Pt SSCs is sensitive to the ligand and support choices, enabling fine tuning of Pt sites. This work highlights the application of heterogeneous SSCs created by the novel metal-ligand self-assembly strategy in an industrially-relevant reaction. It also offers a potential catalyst for future industrial hydrosilylation applications with several improvements over current commercial catalysts

Kinetic and Mechanistic Evaluation of Inorganic Arsenic Species Adsorption onto Humic Acid Grafted Magnetite Nanoparticles

Humic acid coated magnetic iron oxide nanoparticles (HA-MNPs) were synthesized, characterized, and studied for the removal of toxic inorganic arsenic species from aqueous media. The adsorption of As­(III) and As­(V) followed pseudo-second-order kinetics, and the observed data were accurately modeled employing the Freundlich adsorption isotherm. Application of the Weber and Morris intraparticle diffusion model to the observed kinetic data suggests that the adsorption occurs in three distinct stages, fast, intermediate, and slow steps. We propose the initial stage is governed by surface association, followed by intraparticle diffusion of arsenic through the HA matrix and, finally, chemical reaction or bonding between the arsenic species and HA functionality. The HA-MNP nanoadsorbent absorbs >95% of the inorganic arsenic species with an absorption capacity of 12.2–12.6 mg/g from aqueous media and is effective under a variety of conditions. Post arsenic adsorption characterization of the nanoparticles suggests that As­(III) binds with the carboxylate group of HA through a proposed ester type linkage, while electrophilic reactions can occur between the nucleophilic functional groups present in HA and the electrophilic arsenic atom in As­(V). The results obtained demonstrated that HA-MNPs are robust and have promise for effective As­(III) and As­(V) remediation