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Abstract Developing efficient and stable earth-abundant electrocatalysts for acidic oxygen evolution reaction is the bottleneck for water splitting using proton exchange membrane electrolyzers. Here, we show that nanocrystalline CeO 2 in a Co 3 O 4 /CeO 2 nanocomposite can modify the redox properties of Co 3 O 4 and enhances its intrinsic oxygen evolution reaction activity, and combine electrochemical and structural characterizations including kinetic isotope effect, pH- and temperature-dependence, in situ Raman and ex situ X-ray absorption spectroscopy analyses to understand the origin. The local bonding environment of Co 3 O 4 can be modified after the introduction of nanocrystalline CeO 2 , which allows the Co III species to be easily oxidized into catalytically active Co IV species, bypassing the potential-determining surface reconstruction process. Co 3 O 4 /CeO 2 displays a comparable stability to Co 3 O 4 thus breaks the activity/stability tradeoff. This work not only establishes an efficient earth-abundant catalysts for acidic oxygen evolution reaction, but also provides strategies for designing more active catalysts for other reactions.

Although catenanes comprising two ring-shaped components can be made in large quantities by templation, the preparation of three-dimensional (3D) catenanes with cage-shaped components is still in its infancy. Here, we report the design and syntheses of two 3D catenanes by a sequence of S N 2 reactions in one pot. The resulting triply mechanically interlocked molecules were fully characterized in both the solution and solid states. Mechanistic studies have revealed that a suit[3]ane, which contains a threefold symmetric cage component as the suit and a tribromide component as the body, is formed at elevated temperatures. This suit[3]ane was identified as the key reactive intermediate for the selective formation of the two 3D catenanes which do not represent thermodynamic minima. We foresee a future in which this particular synthetic strategy guides the rational design and production of mechanically interlocked molecules under kinetic control.

Since anions are vital for many chemical, biological and environmental processes, their recognition and separation continue to attract attention from chemists, materials scientists and engineers. Employing exo-binding of artificial macrocycles to recognize selectively anions remains a challenge in supramolecular chemistry. Herein, we report the instantaneous co-crystallization and concomitant co-precipitation between hexachloroplatinate dianions and cucurbit[6]uril, a phenomenon which relies on the selective recognition of these dianions through the noncovalent bonding interactions on the outer surface of cucurbit[6]uril. The selective hexachloroplatinate dianion recognition is driven by the weak [Pt-Cl···H-C] hydrogen bonding and [Pt-Cl···C=O] ion-dipole interactions. The synthetic protocol is highly selective. It is not observed in combinations between cucurbit[6]uril and other Pt- and Pd- or Rh-based chloride anions. We have also demonstrated that cucurbit[6]uril is able to separate selectively hexachloroplatinate dianions from mixtures of hexachloroplatinate, tetrachloropalladate, and hexachlororhodate anions. This highly selective and fast co-crystallization process, in principle, could be exploited to recover platinum from the spent vehicular three-way catalytic converters and other platinum-bearing metal waste.

Electrochemical synthesis of hydrogen peroxide (H 2 O 2 ) in acidic solution can enable the electro-Fenton process for decentralized environmental remediation, but robust and inexpensive electrocatalysts for the selective two-electron oxygen reduction reaction (2e − ORR) are lacking. Here, we present a joint computational/experimental study that shows both structural polymorphs of earth-abundant cobalt diselenide (orthorhombic o -CoSe 2 and cubic c -CoSe 2 ) are stable against surface oxidation and catalyst leaching due to the weak O* binding to Se sites, are highly active and selective for the 2e − ORR, and deliver higher kinetic current densities for H 2 O 2 production than the state-of-the-art noble metal or single-atom catalysts in acidic solution. o -CoSe 2 nanowires directly grown on carbon paper electrodes allow for the steady bulk electrosynthesis of H 2 O 2 in 0.05 M H 2 SO 4 with a practically useful accumulated concentration of 547 ppm, the highest among the reported 2e − ORR catalysts in acidic solution. Such efficient and stable H 2 O 2 electrogeneration further enables the effective electro-Fenton process for model organic pollutant degradation.