Ultrahigh Photocatalytic Rate at a Single‐Metal‐Atom‐Oxide

Metal oxides, as one of the mostly abundant and widely utilized materials, are extensively investigated and applied in environmental remediation and protection, and in energy conversion and storage. Most of these diverse applications are the result of a large diversity of the electronic states of metal oxides. Noticeably, however, many metal oxides present obstacles for applications in catalysis, mainly due to the lack of efficient active sites with desired electronic states. Here, the fabrication of single‐tungsten‐atom‐oxide (STAO) is demonstrated, in which the metal oxide's volume reaches its minimum as a unit cell. The catalytic mechanism in the STAO is determined by a new single‐site physics mechanism, named as quasi‐atom physics. The photogenerated electron transfer process is enabled by an electron in the spin‐up channel excited from the highest occupied molecular orbital to the lowest unoccupied molecular orbital +1 state, which can only occur in STAO with W⁵⁺. STAO results in a record‐high and stable sunlight photocatalytic degradation rate of 0.24 s^?1, which exceeds the rates of available photocatalysts by two orders of magnitude. The fabrication of STAO and its unique quasi‐atom photocatalytic mechanism lays new ground for achieving novel physical and chemical properties using single‐metal‐atom oxides (SMAO).     

Noble‐Metal‐Free Electrocatalysts for Oxygen Evolution

Oxygen evolution reaction (OER) plays a vital role in many energy conversion and storage processes including electrochemical water splitting for the production of hydrogen and carbon dioxide reduction to value‐added chemicals. IrO₂ and RuO₂, known as the state‐of‐the‐art OER electrocatalysts, are severely limited by the high cost and low earth abundance of these noble metals. Developing noble‐metal‐free OER electrocatalysts with high performance has been in great demand. In this review, recent advances in the design and synthesis of noble‐metal‐free OER electrocatalysts including Ni, Co, Fe, Mn‐based hydroxides/oxyhydroxides, oxides, chalcogenides, nitrides, phosphides, and metal‐free compounds in alkaline, neutral as well as acidic electrolytes are summarized. Perspectives are also provided on the fabrication, evaluation of OER electrocatalysts and correlations between the structures of the electrocatalysts and their OER activities.     

Metal‐Free Click Chemistry Reactions on Surfaces

In the last decade, interest in the functionalization of surfaces and materials has increased dramatically. In this regard, click chemistry deserves a central focus because of its mild reaction conditions, high efficiency, and easy post‐treatment. Among such novel click reactions, those that do not require any metal catalyst are of special interest, as metals may have undesirable effects in many fields. In this Review, the backgrounds and application of such metal‐free click reactions for the modification of surfaces are highlighted.     

A Liquid‐Metal‐Enabled Versatile Organic Alkali‐Ion Battery

Despite the high specific capacity and low redox potential of alkali metals, their practical application as anodes is still limited by the inherent dendrite‐growth problem. The fusible sodium–potassium (Na–K) liquid metal alloy is an alternative that detours this drawback, but the fundamental understanding of charge transport in this binary electroactive alloy anode remains elusive. Here, comprehensive characterization, accompanied with density function theory (DFT) calculations, jointly expound the Na–K anode‐based battery working mechanism. With the organic cathode sodium rhodizonate dibasic (SR) that has negligible selectivity toward cations, the charge carrier is screened by electrolytes due to the selective ionic pathways in the solid electrolyte interphase (SEI). Stable cycling for this Na–K/SR battery is achieved with capacity retention per cycle to be 99.88% as a sodium‐ion battery (SIB) and 99.70% as a potassium‐ion battery (PIB) for over 100 cycles. Benefitting from the flexibility of the liquid metal and the specially designed carbon nanofiber (CNF)/SR layer‐by‐layer cathode, a flexible dendrite‐free alkali‐ion battery is achieved with an ultrahigh areal capacity of 2.1 mAh cm^?2. Computation‐guided materials selection, characterization‐supported mechanistic understanding, and self‐validating battery performance collectively promise the prospect of a high‐performance, dendrite‐free, and versatile organic‐based liquid metal battery.     

All‐Solution‐Processed Metal‐Oxide‐Free Flexible Organic Solar Cells with Over 10% Efficiency

All‐solution‐processing at low temperatures is important and desirable for making printed photovoltaic devices and also offers the possibility of a safe and cost‐effective fabrication environment for the devices. Herein, an all‐solution‐processed flexible organic solar cell (OSC) using poly(3,4‐ethylenedioxythiophene):poly‐(styrenesulfonate) electrodes is reported. The all‐solution‐processed flexible devices yield the highest power conversion efficiency of 10.12% with high fill factor of over 70%, which is the highest value for metal‐oxide‐free flexible OSCs reported so far. The enhanced performance is attributed to the newly developed gentle acid treatment at room temperature that enables a high‐performance PEDOT:PSS/plastic underlying substrate with a matched work function (≈4.91 eV), and the interface engineering that endows the devices with better interface contacts and improved hole mobility. Furthermore, the flexible devices exhibit an excellent mechanical flexibility, as indicated by a high retention (≈94%) of the initial efficiency after 1000 bending cycles. This work provides a simple route to fabricate high‐performance all‐solution‐processed flexible OSCs, which is important for the development of printing, blading, and roll‐to‐roll technologies.     

Alkali‐Metal‐Intercalated Percolation Network Regulates Self‐Assembled Electronic Aromatic Molecules

In the continuously growing field of correlated electronic molecular crystals, there is significant interest in addressing alkali‐metal‐intercalated aromatic hydrocarbons, in which the possibility of high‐temperature superconductivity emerges. However, searching for superconducting aromatic molecular crystals remains elusive due to their small shielding fraction volume. To exploit this potential, a design principle for percolation networks of technologically important film geometry is indispensable. Here the effect of potassium‐intercalation is shown on the percolation network in self‐assembled aromatic molecular crystals. It is demonstrated that one‐dimensional (1D) dipole pairs, induced by dipole interaction, regulate the conductivity, as well as the electronic and optical transitions, in alkali‐metal‐intercalated molecular electronic crystals. A solid‐solution growth methodology of aromatic molecular films with a broad range of stability is developed to uncover electronic and optical transitions of technological importance. The light‐induced electron interactions enhance the charge‐carrier itinerancy, leading to a switchable metal‐to‐insulator transition. This discovery opens a route for the development of aromatic molecular electronic solids and long‐term modulation of electronic efficacy in nanotechnologically important thin films.     

MOFBOTS: Metal–Organic‐Framework‐Based Biomedical Microrobots

Motile metal?organic frameworks (MOFs) are potential candidates to serve as small‐scale robotic platforms for applications in environmental remediation, targeted drug delivery, or nanosurgery. Here, magnetic helical microstructures coated with a kind of zinc‐based MOF, zeolitic imidazole framework‐8 (ZIF‐8), with biocompatibility characteristics and pH‐responsive features, are successfully fabricated. Moreover, it is shown that this highly integrated multifunctional device can swim along predesigned tracks under the control of weak rotational magnetic fields. The proposed systems can achieve single‐cell targeting in a cell culture media and a controlled delivery of cargo payloads inside a complex microfluidic channel network. This new approach toward the fabrication of integrated multifunctional systems will open new avenues in soft microrobotics beyond current applications.     

Efficient Metal‐Free Electrocatalysts from N‐Doped Carbon Nanomaterials: Mono‐Doping and Co‐Doping

N‐doped carbon nanomaterials have rapidly grown as the most important metal‐free catalysts in a wide range of chemical and electrochemical reactions. This current report summarizes the latest advances in N‐doped carbon electrocatalysts prepared by N mono‐doping and co‐doping with other heteroatoms. The structure–performance relationship of these materials is subsequently rationalized and perspectives on developing more efficient and sustainable electrocatalysts from carbon nanomaterials are also suggested.     

Chemical Approaches to Carbon‐Based Metal‐Free Catalysts

Highly active and durable catalysts play a key role in clean energy technologies. However, the high cost, low reserves, and poor stability of noble‐metal‐based catalysts have hindered the large‐scale development of renewable energy. Owing to their low cost, earth abundance, high activity, and excellent stability, carbon‐based metal‐free catalysts (CMFCs) are promising alternatives to precious‐metal‐based catalysts. Although many synthetic methods based on solution, surface/interface, solid state, and noncovalent chemistries have been developed for producing numerous CMFCs with diverse structures and functionalities, there is still a lack of effective approaches to precisely control the structures of active sites. Therefore, novel chemical approaches are needed for the development of highly active and durable CMFCs that are capable of replacing precious‐metal catalysts for large‐scale applications. Herein, a comprehensive and critical review on chemical approaches to CMFCs is given by summarizing important advancements, current challenges, and future perspectives in this emerging field. Through such a critical review, our understanding of CMFCs and the associated synthetic processes will be significantly increased.     

Recent Advances in Carbon‐Based Metal‐Free Electrocatalysts

Precious noble metals (such as Pt, Ir) and nonprecious transition metals (e.g., Fe, Co), including their compounds (e.g., oxides, nitrides), have been widely investigated as efficient catalysts for energy conversion, energy storage, important chemical productions, and many industrial processes. However, they often suffer from high cost, low selectivity, poor durability, and susceptibility to gas poisoning with adverse environmental issues. As a low‐cost alternative, the first carbon‐based metal‐free catalyst (C‐MFC based on N‐doped carbon nanotubes) was discovered in 2009. Since then, various C‐MFCs have been demonstrated to show similar or even better catalytic performance than their metal‐based counterparts, attractive energy conversion and storage (e.g., fuel cells, metal–air batteries, water splitting), environmental remediation, and chemical production. Enormous progress has been achieved while the number of publications still rapidly increases every year. Herein, a critical overview of the very recent advances in this rapidly developing field during the last couple of years is presented.     

Metal‐containing Polymers via Electropolymerization

Electropolymerization represents a suitable and well‐established approach for the assembly of polymer structures, in particular with regard to the formation of thin, insoluble films. Utilization of monomers that are functionalized with metal complex units allows the combination of structural and functional benefits of polymers and metal moieties. Since a broad range of both electropolymerizable monomers and metal complexes are available, various structures and, thus, applications are possible. Recent developments in the field of synthesis and potential applications of metal‐functionalized polymers obtained via electropolymerization are presented, highlighting the significant advances in this field of research.