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The kinetics of electrode reactions including mass transfer and surface reaction is essential in electrocatalysis, as it strongly determines the apparent reaction rates, especially on nanostructured electrocatalysts. However, important challenges still remain in optimizing the kinetics of given catalysts with suitable constituents, morphology, and crystalline design to maximize the electrocatalytic performances. We propose a comprehensive kinetic model coupling mass transfer and surface reaction on the nanocatalyst-modified electrode surface to explore and shed light on the kinetic optimization in electrocatalysis. Moreover, a theory-guided microchemical engineering (MCE) strategy has been demonstrated to rationally redesign the catalysts with optimized kinetics. Experimental measurements for methanol oxidation reaction in a 3D ordered channel with tunable channel sizes confirm the calculation prediction. Under the optimized channel size, mass transfer and surface reaction in the channeled microreactor are both well regulated. This MCE strategy will bring about a significant leap forward in structured catalyst design and kinetic modulation.

Designing high-efficiency catalyst is at the heart of a transition to future renewable energy systems. Great achievements have been made to optimize thermodynamics to reduce energetic barriers of the catalytic reactions. However, little attention has been paid to design catalysts to improve kinetics to enrich the local concentration of reactant molecules surrounding electrocatalysts. Here, we find that well-designed nanocatalysts with periodic structures can optimize kinetics to accelerate mass-transport from bulk electrolyte to the catalyst surface, leading to the enhanced catalytic performance. This achievement stems from regulation of the surface reactant flux due to the gradient of the microelectric field directing uniformly to the nearest catalyst on ordered pattern, so that all of the reactant molecules are utilized sufficiently for reactions, enabling the boost of the electrocatalytic performance. This novel concept is further confirmed in various catalytic systems and nanoassemblies, such as nanoparticles, nanorods, and nanoflakes.

Two-dimensional (2D) nanomaterials are attracting increasing research interest because of their unique properties and promising applications. Here, we report a facile method to manipulate the assembly of nanoparticles (NPs) to fabricate free-standing 2D quasi-nanosheets. The as-generated 2D products are composed of few-layer NPs; that is, their thicknesses are only tens of nanometers but lateral dimensions could be up to several micrometers. Therefore, the novel structure was denoted as 2D “quasi-nanosheets (QNS)”. Specifically, several types of building blocks could be assembled into 2D unary, binary, ternary, and even quaternary QNS by a universal procedure. The entire assembly process is carried out in solution and mediated simply by tuning the concentration of ligands surrounding the NPs. In contrast to traditional assembly techniques, even without any substrate or template, these QNS showed exceptionally high stability. They can remain intact for several days without any disassembly regardless of the solvent environment (e.g., water, ethanol, methanol, and hexane). In general, our method has effectively tackled several limitations associated with traditional assembly techniques and allows more freedom in manipulating assembly of NPs, which may hold great potential for future fabrication of 2D devices with rich functionalities.

Axially, epitaxially organizing nano-objects of distinct compositions and structures into superlattice nanowires enables full utilization of sunlight, readily engineered band structures, and tunable geometric parameters to fit carrier transport, thus holding great promise for optoelectronics and solar-to-fuel conversion. To maximize their efficiency, the general and high-precision synthesis of colloidal axial superlattice nanowires (ASLNWs) with programmable compositions and structures is the prerequisite; however, it remains challenging. Here, we report an axial encoding methodology toward the ASLNW library with precise control over their compositions, dimensions, crystal phases, interfaces, and periodicity. Using a predesigned, editable nanoparticle framework that offers the synthetic selectivity, we are able to chemically decouple adjacent sub-objects in ASLNWs and thus craft them in a controlled approach, yielding a library of distinct ASLNWs. We integrate therein plasmonic, metallic, or near-infrared-active chalcogenides, which hold great potential in solar energy conversion. Such synthetic capability enables a performance boost in target applications, as we report order-of-magnitude enhanced photocatalytic hydrogen production rates using optimized ASLNWs compared to corresponding solo objects. Furthermore, it is expected that such unique superlattice nanowires could bring out new phenomena.

Ion migration has been recognized as a critical step in determining the performance of numerous devices in chemistry, biology, and material science. However, direct visualization and quantitative investigation of solid-phase ion migration among anisotropic nanostructures have been a challenging task. Here, we report an in-situ ChemTEM method to quantitatively investigate the solid-phase ion migration process among coassembled nanowires (NWs). This complicated process was tracked within a NW and between NWs with an obvious nanogap, which was revealed by both phase field simulation and ab initio modeling theoretical evaluation. A migration "bridge" between neighboring NWs was observed. Furthermore, these new observations could be applied to migration of other metal ions on semiconductor NWs. These findings provide critical insights into the solid-phase ion migration kinetics occurring in nanoscale systems with generality and offer an efficient tool to explore other ion migration processes, which will facilitate fabrication of customized and new heteronanostructures in the future.

The development of facile methods for screening organic functional molecules through C-H bond activation is a revolutionary trend in materials research. The prediction of mechanochromism as well as mechanochromic trends of luminogens is an appealing yet challenging puzzle. Here, we present a strategy for the design of mechanochromic luminogens based on the dipole moment of donor-acceptor molecules. For this purpose, a highly efficient route to 2,7-diaryl-[1,2,4]triazolo[1,5-a]pyrimidines (2,7-diaryl-TAPs) has been established through programmed C-H arylation, which unlocks a great opportunity to rapidly assemble a library of fluorophores for the discovery of mechanochromic regularity. Molecular dipole moment can be employed to explain and further predict the mechanochromic trends. The 2,7-diaryl-TAPs with electron-donating groups on the 2-aryl and electron-withdrawing groups on the 7-aryl possess a relatively small dipole moment and exhibit a red-shifted mechanochromism. When the two aryls are interchanged, the resulting luminogens have a relatively large dipole moment and display a blue-shifted mechanochromism. Seven pairs of isomers with opposite mechanochromic trends are presented as illustrative examples. The aryl-interchanged congeners with a bidirectional emission shift are structurally similar, which provides an avenue for understanding in-depth the mechanochromic mechanism.

The electrochemical reduction of oxides to metals has been studied for decades. Earlier work produced polycrystalline bulk metals. Here, we report that pre-electrodeposited epitaxial face-centered cubic magnetite thin films can be electrochemically reduced to epitaxial body-centered cubic iron thin films in aqueous solution on single-crystalline gold substrates at room temperature. This technique opens new possibilities to produce special epitaxial metal/metal oxide heterojunctions and a wide range of epitaxial metallic alloy films from the corresponding mixed metal oxides.

Defect-chemistry magnetite superlattices and compositional superlattices in the magnetite/zinc ferrite system are electrodeposited as epitaxial films onto single-crystal Au(111). The defect-chemistry superlattices have alternating nanolayers with different Fe(III)/Fe(II) ratios, whereas the compositional superlattices have alternating nanolayers with different Zn/Fe ratios. The electrochemical/chemical (EC) nature of the electrodeposition reaction is exploited to deposit the superlattices by pulsing the applied potential during deposition. The defect-chemistry superlattices show low-to-high and high-to-low resistance switching that may be applicable to the fabrication of resistive random access memory (RRAM).