Materials Futures

Metallic glasses or amorphous alloys are an important engineering material that has a history of research of about 80-90 years. While different fast cooling methods were developed for multi-component metallic glasses between 1960s and 1980s, 1990s witnessed a surge of research interest in the development of bulk metallic glasses. Since then, one central theme of research in the metallic-glass community has been compositional design that aims to search for metallic glasses with a better glass forming ability, a larger size and/or more interesting properties, which can hence meet the demands from more important applications. In this review article, we focus on the recent development of chemically complex metallic glasses, such as high entropy metallic glasses, with new tools that were not available or mature yet until recently, such as the state-of-the-art additive manufacturing technologies, high throughput materials design techniques and the methods for big data analyses (e.g. machine learning and artificial intelligence). We also discuss the recent use of metallic glasses in a variety of novel and important applications, from personal healthcare, electric energy transfer to nuclear energy that plays a pivotal role in the battle against global warming.

Conjugated polymers (CPs), organic macromolecules with linear backbone of alternating C–C and C=C bonds, possess unique semiconductive properties, providing new opportunities for organic electronics, photonics, information, and energy devices. Seeking the metallic or metallic-like, even superconducting properties beyond semiconductivity in CPs is always one of the ultimate goals in polymer science and condensed matter. Only two metallic and semi-metallic transport cases – aniline-derived polyaniline (PANI) and thiophene-derived poly(3,4-ethylenedioxythiophene) (PEDOT) – have been reported since the development of CPs for four decades. Controllable synthesis is a key challenge in discovering more cases. Here we report the metallic-like transport behavior of another CP, polypyrrole (PPy). We observe that the transport behavior of PPy changes from semiconductor to insulator-metal transition, and gradually realizes metallic-like performance when the crystalline degree increases. Using a generalized Einstein relation model, we rationalized the mechanism behind the observation. The metallic-like transport in PPy demonstrates electron strong correlation and phonon-electron interaction in soft condensation matter, and may find practical applications of CPs in electrics and spintronics.

Biomimetic scaffolds with extracellular matrix (ECM)-mimicking structure have been widely investigated in wound healing applications, while insufficient mechanical strength and limited biological activity remain major challenges. Here, we present a microfluidic 3D printing biomimetic polyhydroxyalkanoates-based scaffold with excellent mechanical properties and hierarchical porous structures for enhanced wound healing. This scaffold is composed of poly(3-hydroxybutyrate-4-hydroxybutyrate) (P34HB) and polycaprolactone (PCL), endowing it with excellent tensile strength (2.99 MPa) and degradability (80% of weight loss within 7 days). The ECM-mimicking hierarchical porous structure allows bone marrow mesenchymal stem cells (BMSCs) and human umbilical vein endothelial cells (HUVECs) to proliferate and adhere on the scaffolds. Besides, anisotropic composite scaffolds loaded with BMSCs and HUVECs can significantly promote re-epithelization, collagen deposition and capillary formation in rat wound defects, indicating their satisfactory in vivo tissue regenerative activity. These results indicate the feasibility of polyhydroxyalkanoates-based biomimetic scaffolds for skin repair and regeneration, which also provide a promising therapeutic strategy in diverse tissue engineering applications.

The ion hybrid capacitor is expected to combine the high specific energy of battery-type materials and the superior specific power of capacitor-type materials, being considered as a promising energy storage technique. Particularly, the aqueous zinc-ion capacitors (ZIC) possessing merits of high safety, cost-efficiency and eco-friendliness, have been widely explored with various electrode materials and electrolytes to obtain excellent electrochemical performance. In this review, we first summarized the research progress on enhancing the specific capacitance of capacitor-type materials and reviewed the research on improving the cycling capability of battery-type materials under high current densities. Then, we looked back on the effects of electrolyte engineering on the electrochemical performance of ZIC. Finally, the research challenges and development directions of ZIC have been proposed. This review provides a guidance for the design and construction of the high-performance ZIC.

In the crucial area of sustainable energy storage, solid-state batteries (SSBs) with nonflammable solid electrolytes stand out due to their potential benefits of enhanced safety, energy density, and cycle life. However, the complexity within the composite cathode determines that fabricating an ideal electrode needs to link chemistry (atomic scale), materials (microscopic/mesoscopic scale), and electrode system (macroscopic scale). Therefore, understiang solid-state composite cathodes covering multiple scales is of vital importance for the development of practical SSBs. In this review, the challenges and basic knowledge of composite cathodes from the atomic scale to the macroscopic scale in SSBs are outlined with a special focus on the interfacial structure, charge transport, and mechanical degradation. Based on these dilemmas, emerging strategies to design a high-performance composite cathode and advanced characterization techniques are summarized. Moreover, future perspectives toward composite cathodes are discussed, aiming to facilitate the develop energy-dense solid-state batteries.