The ex vivo application of enzymes in various processes, especially via enzyme immobilization techniques, has been extensively studied in recent years in order to enhance the recyclability of enzymes, to minimize enzyme contamination in the product, and to explore novel horizons for enzymes in biomedical applications. Possessing remarkable amenability in structural design of the frameworks as well as almost unparalelled surface tunability, Metal-Organic Frameworks (MOFs) have been gaining popularity as candidates for enzyme immobilization platforms. Many MOF-enzyme composites have achieved unprecedented results, far outperforming free enzymes in many aspects. This review summarizes recent developments of MOF-enzyme composites with special emphasis on preparative techniques and the synergistic effects of enzymes and MOFs. The applications of MOF-enzyme composites, primarily in transferation, catalysis and sensing, are presented as well. The enhancement of enzymatic activity of the composites over free enzymes in biologically incompatible conditions is emphasized in many cases.

Aqueous zinc-ion batteries (ZIBs) have been intensively investigated as potential energy storage devices on account of their low cost, environmental benignity, and intrinsically safe merits. With the exploitation of highperformance cathode materials, electrolyte systems, and in-depth mechanism investigation, the electrochemical performances of ZIBs have been greatly enhanced. However, there are still some challenges that need to be overcome before its commercialization. Among them, the obstinate dendrites, corrosion, and hydrogen evolution reaction (HER) on Zn anodes are critical issues that severely limit the practical applications of ZIBs. To address these issues, various strategies have been proposed, and tremendous progress has been achieved in the past few years. In this article, we analyze the origins and effects of the dendrites, corrosion, and HER on Zn anodes in neutral and mildly acid aqueous solutions at first. And then, a scientific understanding of the fundamental design principles and strategies to suppress these problems are emphasized. Apart from these, this article also puts forward some requirements for the practical applications of Zn anodes as well as several cost-effectivemodifying strategies. Finally, perspectives on the future development of Zn anodes in aqueous solutions are also briefly anticipated. This article provides pertinent insights into the challenges on anodes for the development of highperformance ZIBs, which will greatly contribute to their practical applications. K E Y W O R D S corrosion, hydrogen evolution reaction, Zn anode, Zn dendrites 1 | INTRODUCTION As a result of the ongoing crisis in the depletion of conventional fossil fuels, renewable clean energy sources, such as solar energy, wind energy, hydropower, geothermal, and nuclear energy, are rapidly developing. 1,2 Nevertheless, it remains an extreme challenge to efficiently store the energy generated by those renewable

Mixtures of copper and iron oxides are used as industrial catalysts for the water-gas shift (WGS, CO + H 2 O f H 2 + CO 2 ). In-situ time-resolved X-ray diffraction, X-ray absorption fine structure, and atomic pair distribution function analysis were used to study the reduction of CuFe 2 O 4 with CO and the behavior of CuFe 2 O 4 and Cu/Fe 2 O 3 catalysts under WGS reaction conditions. MetalToxygenTmetal interactions enhance the stability of Cu 2+ and Fe 3+ in the CuFe 2 O 4 lattice, and the mixed-metal oxide is much more difficult to reduce than CuO or Fe 2 O 3 . Furthermore, after heating mixtures of CuFe 2 O 4 /CuO in the presence of CO or CO/H 2 O, the cations of CuO migrate into octahedral sites of the CuFe 2 O 4 lattice at temperatures (200-250 °C) in which CuO is not stable. Above 250 °C, copper leaves the oxide, the occupancy of the octahedral sites in CuFe 2 O 4 decreases, and diffraction lines for metallic Cu appear. From 350 to 450 °C, there is a massive reduction of CuFe 2 O 4 with the formation of metallic Cu and Fe 3 O 4 . At this point, the sample becomes catalytically active for the production of H 2 from the reaction of H 2 O with CO. Neutral Cu 0 (i.e., no Cu 1+ or Cu 2+ cations) is the active species in the catalysts, but interactions with the oxide support cannot be neglected. These studies illustrate the importance of in situ characterization when dealing with mixed-metal oxide WGS catalysts.