Designing an efficient oxygen evolution reaction (OER) electrocatalysts based on single-atom catalysts is a highly promising option for cost-effective alkaline water electrolyzers. However, the instability of the OOH* intermediate and...

Noble-metal-oxide support catalysts have been demonstrated to be unique for electrocatalytic water oxidation in acidic media. Highly porous three-dimensional oxide supported can serve as an ideal platform to confine ultrasmall metal catalysts on specific sites and modulate their reactivity, resulting in the reduction of noble metal content in the catalyst by boosting the mass activity. However, due to poor control over the support morphology, geometricdriven shifts in mass activity of metal-oxide support catalysts for the oxygen evolution reaction in acidic media have not been realized. Herein, a nanoscale Kirkendall effect is exploited to produce and control a structural evolution yielding an oxygen-evolving catalyst that is highly efficient and robust in acidic medium. By selective reaction−diffusion under oxidizing conditions, the starting solid CoIr NC is directly transformed into an unprecedented Ir−Co 3 O 4 @Co 3 O 4 porous-core@shell hollow nanospheres (ICO PCSHS), in which an ultrasmall Ir catalyst is spatially isolated within a porous Co 3 O 4 -backbone core, encapsulated by a hollow Co 3 O 4 outer shell. With a low Ir content of 14 wt %, the iridium mass activity exhibited by ICO PCSHS-400 catalyst is 24 times higher than that of benchmark RuO 2 , substantially exceeding the known oxide-supported metal catalysts. More importantly, the electrocatalyst shows high stability during 8 h of continuous testing in acidic medium.

We performed a band modulation of the phase-selectively disordered rutile P25 TiO2 and disordered anatase P25 TiO2 and their band structures were confirmed by transient absorption spectroscopy.

The role of countercations that do not bind to core nanocrystals (NCs) but rather ensure charge balance on ligand-exchanged NC surfaces has been rarely studied and even neglected. Such a scenario is unfortunate, as an understanding of surface chemistry has emerged as a key factor in overcoming colloidal NC limitations as catalysts. In this work, we report on the unprecedented role of countercations in ligand exchange for a colloidal transition metal dichalcogenide (TMD), WSe2, to tune the d-band center toward the Fermi level for enhanced hydrogen desorption. Conventional long-chain organic ligands, oleylamine, of WSe2 NCs are exchanged with short atomic S2– ligands having countercations to preserve the charge balance (WSe2/S2–/M+, M = Li, Na, K). Upon exchange with S2– ligands, the charge-balancing countercations are intercalated between WSe2 layers, thereby serving a unique function as an electrochemical hydrogen evolution reaction (HER) catalyst. The HER activity of ligand-exchanged colloidal WSe2 NCs shows a decrease in overpotential by down-shift of d-band center to induce more electron-filling in antibonding orbital and an increase in the electrochemical active surface area (ECSA). Exchanging surface functionalities with S2– anionic ligands enhances HER kinetics, while the existence of intercalated countercations improves charge transfer with the electrolyte. The obtained results suggest that both anionic ligands and countercationic species in ligand exchange must be considered to enhance the overall catalytic activity of colloidal TMDs.

Assembled amyloid beta (Aβ) peptides have been considered pathological assemblies involved in human brain diseases, and the electron transfer or electron transport characteristics of Aβ are important for the formation of structured assemblies. Here, we report the electrical characteristics of surface-assembled Aβ peptides similar to those observed in Alzheimer’s patients. These characteristics correlate to their electron transfer characteristics. Electrical current–voltage plots of Aβ vertical junction devices show the Aβ sequence dependence of the current densities at both Aβ monomers (mono-Aβs) and Aβ oligomers (oli-Aβs), while Aβ sequence dependence is not clearly observed in the electrical characteristics of Aβ planar field effect transistors (FETs). In particular, surface oligomerization of Aβ peptides drastically decreases the activity of electron transfer, which presents a change in the electron transport pathway in the Aβ vertical junctions. Electron transport at oli-Aβ junctions is symmetric (tunneling/tunneling) due to the weak and voltage-independent coupling of the less redox-reactive oli-Aβ to the contacts, while that at mono-Aβ junctions is asymmetric (hopping/tunneling) due to redox levels of mono-Aβ voltage-dependently coupled with contact electrodes. Consequently, through vertical junctions, the sequence- and conformation-dependent electrical characteristics of Aβs can reveal their electron transfer activities.

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Epoxidation of dicyclopentadiene (DCPD) is studied on a series of TiO2 catalysts using hydrogen peroxide as an oxidant. DCPD derivatives have applications in several areas including polymer, pharmaceutical and pesticide...

The steric effects of the ligands unveil the charged chalcogen sites which are induced by the ligand adsorption, thus promoting the anisotropic growth of two-dimensional transition metal chalcogenides (TMCs).