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The formation of complex hierarchical nanostructures has attracted a lot of attention from both the fundamental science and potential applications point of view. Spherulite structures with radial fibrillar branches have been found in various solids; however, their growth mechanisms remain poorly understood. Here, we report real time imaging of the formation of two-dimensional (2D) iron oxide spherulite nanostructures in a liquid cell using transmission electron microscopy (TEM). By tracking the growth trajectories, we show the characteristics of the reaction front and growth kinetics. Our observations reveal that the tip of a growing branch splits as the width exceeds certain sizes (5.5–8.5 nm). The radius of a spherulite nanostructure increases linearly with time at the early stage, transitioning to nonlinear growth at the later stage. Furthermore, a thin layer of solid is accumulated at the tip and nanoparticles from secondary nucleation also appear at the growing front which later develop into fibrillar branches. The spherulite nanostructure is polycrystalline with the co-existence of ferrihydrite and Fe3O4 through-out the growth. A growth model is further established, which provides rational explanations on the linear growth at the early stage and the nonlinearity at the later stage of growth. [Figure not available: see fulltext.].

Selective nitrogen-doping of graphene oxide with a high pyridinic N ratio (51%; L-GO) was achieved by laser irradiation of graphene oxide with ammonia. The resulting L-GO exhibited enhanced electrocatalytic properties; specifically, the overpotential of the hydrogen evolution reaction (HER) was improved by over 400 mV at 10 mA cm-2 compared to the pristine graphene oxide.

The electrochemical reduction of carbon monoxide is a promising approach for the renewable production of carbon-based fuels and chemicals. Copper shows activity toward multi-carbon products from CO reduction, with reaction selectivity favoring two-carbon products; however, efficient conversion of CO to higher carbon products such as n-propanol, a liquid fuel, has yet to be achieved. We hypothesize that copper adparticles, possessing a high density of under-coordinated atoms, could serve as preferential sites for n-propanol formation. Density functional theory calculations suggest that copper adparticles increase CO binding energy and stabilize two-carbon intermediates, facilitating coupling between adsorbed *CO and two-carbon intermediates to form three-carbon products. We form adparticle-covered catalysts in-situ by mediating catalyst growth with strong CO chemisorption. The new catalysts exhibit an n-propanol Faradaic efficiency of 23% from CO reduction at an n-propanol partial current density of 11 mA cm-2.

Electrochemical reduction of carbon dioxide (CO2RR) to formate provides an avenue to the synthesis of value-added carbon-based fuels and feedstocks powered using renewable electricity. Here, we hypothesized that the presence of sulfur atoms in the catalyst surface could promote undercoordinated sites, and thereby improve the electrochemical reduction of CO2 to formate. We explored, using density functional theory, how the incorporation of sulfur into tin may favor formate generation. We used atomic layer deposition of SnSx followed by a reduction process to synthesize sulfur-modulated tin (Sn(S)) catalysts. X-ray absorption near-edge structure (XANES) studies reveal higher oxidation states in Sn(S) compared with that of tin in Sn nanoparticles. Sn(S)/Au accelerates CO2RR at geometric current densities of 55 mA cm−2 at −0.75 V versus reversible hydrogen electrode with a Faradaic efficiency of 93%. Furthermore, Sn(S) catalysts show excellent stability without deactivation (

An understanding of bimetallic alloy oxidation is key to the design of hollow-structured binary oxides and the optimization of their catalytic performance. However, one roadblock encountered in studying these binary oxide systems is the difficulty in describing the heterogeneities that occur in both structure and chemistry as a function of reaction coordinate. This is due to the complexity of the three-dimensional mosaic patterns that occur in these heterogeneous binary systems. By combining real-time imaging and chemical-sensitive electron tomography, we show that it is possible to characterize these systems with simultaneous nanoscale and chemical detail. We find that there is oxidation-induced chemical segregation occurring on both external and internal surfaces. Additionally, there is another layer of complexity that occurs during the oxidation, namely that the morphology of the initial oxide surface can change the oxidation modality. This work characterizes the pathways that can control the morphology in binary oxide materials.

Alloying is regarded as one of the most promising strategies for boosting performance of catalysts for hydrogen evolution reaction (HER) due to the adjustable electronic structure and intermediate adsorption. However, there is no theory (including d‐band center theory) can accurately guide the preparation and design of alloy catalysts, and thus resulting all the reported alloy catalysts are obtained by time‐consuming and laborious experimental exploration. Herein, we proposed a mean d‐band center (εas) as a new accurate descriptor for alloy activity prediction. Theoretical simulation and experiment results revealed that this descriptor exhibits a strong scaling relation with H adsorption energy. Besides, the obtained Cu–Ag alloy displays an optimal overpotential of 223 mV at 10 mA/cm2 in 0.5 mol/L H2SO4, which is more than 300 mV lower than those of pristine Cu (530 mV) and Ag (569 mV) powder. Our work provides a new idea toward designing highly efficient HER catalysts and broadens the applicability of d‐band theory to activity prediction of alloys. [ABSTRACT FROM AUTHOR]

Highly active, durable, and cost‐effective electrodes for hydrogen evolution reaction (HER) at ultrahigh current densities (≥1 A cm−2) are extremely demanded for industrial high‐rate hydrogen production, but challenging. Here, a robust strongly coupled Ag(S)@NiO/nickel foam (NF) electrode is reported. Taking advantage of millisecond laser direct writing in liquid nitrogen technique, lattice‐matched and coherent interfaces are formed between Ag nanoparticles with stacking faults (denoted by Ag(S)) and NiO nanosheets, leading to strong interfacial electronic coupling, not only promoting H2O adsorption and dissociation on Ni2+ but also enhancing H* adsorption on intrinsically inactive but most electrically conductive Ag. Strong chemical bonding is established at NiO/NF interface, guaranteeing rapid electron transfer and excellent mechanical durability under high‐rate hydrogen evolution. The physicochemically stable electrode achieves record‐low alkaline HER overpotential of 167 and 180 mV at 1 and 1.5 A cm−2, respectively, along with negligible activity decay after 120 h test at ≈1.5 A cm−2, surpassing reported non‐platinum group metal electrocatalysts. [ABSTRACT FROM AUTHOR]

Sunlight‐driven photoreduction of the environmentally mobile uranyl (VI) to less soluble tetravalent uranium is of considerable value to environmental sustainability, yet the pursuit for high‐performance semiconductors is plagued by the current disadvantages of inferior charge separation/migration. This study reports that a nickel single atom isolated on a sulfur‐functionalized graphitic carbon nitride/reduced graphene oxide 2D heterostructure enables exceptional uranyl photoreduction. Under only 11 min of visible light irradiation, the single atom anchored semiconductor yields a high removal rate of 99.8% and a record‐high extraction capacity of 4144 mg g−1 in uranyl‐containing wastewater and seawater. Theoretical calculations confirm that the remarkable uranyl photoreduction originates from the synergetic effect of Ni single atoms and intimate heterojunction establishment that can not only promote the separation/migration of photoexcited carriers, but also greatly reduce the energy barrier of uranyl reduction. This study showcases the exciting potential of single atom semiconductors for efficient uranyl removal from uranium‐contaminated aqueous environments. [ABSTRACT FROM AUTHOR]

Large‐scale application of alkaline water electrolysis for high‐rate hydrogen production is severely hindered by high electricity cost, mainly due to difficulties to acquire cost‐effective catalytic electrodes with both extremely low overpotential and long‐term durability at ultrahigh current densities (≥1 A cm−2). Here it is demonstrated that by adopting a synthetic method of laser direct writing in liquid nitrogen via a commercial laser welding machine, a remarkably efficient and durable electrode with large area and low platinum content is obtained, where PtNi nanocatalysts with dislocation network are firmly welded on a nickel foam (NF). The dense dislocation network not only improves intrinsic activity of a majority of surface‐active sites induced by coupled compressive‐tensile strains synergistically promoting both Volmer and Tafel steps of alkaline hydrogen evolution reaction (HER), but also well stabilizes surface dislocations for HER at ultrahigh current densities. Such a robust electrode achieves record‐low overpotentials of 5 and 63 mV at 10 and 1000 mA cm−2 in alkaline medium, respectively, exhibiting negligible activity decay after 300 h chronoamperometric test at 1 A cm−2. It displays a high Pt mass activity 16 times higher than 20 wt% Pt/C loaded on NF, surpassing most of the recently reported efficient Pt‐based catalysts. [ABSTRACT FROM AUTHOR]