Niobium pentoxides are promising acid catalysts for the conversion of biomass into fuels and chemicals. Developing new synthesis routes is essential for designing niobium pentoxide catalysts with improved activity for specific practical processes. Here we show a synthesis approach in acetophenone, which produces nanostructured niobium pentoxides with varying structure and acidity that act as efficient acid catalysts. The oxides have orthorhombic structures with different extents of distortions and coordinatively unsaturated metal atoms. A strong dependence is observed between the type and strength of the acid sites and specific structural motifs. Ultrasmall niobium pentoxide nanoparticles, which have strong Brønsted acidity, as well as Lewis acidity, give product yields of 96% (3 h, 140 °C, 100% conversion), 85% (3 h, 140 °C, 86% conversion), and 100% (3 h, 110 °C, 100% conversion) in the reactions of furfuryl alcohol, 5-(hydroxymethyl)furfural, and α-angelica lactone with ethanol, respectively.

Defect‐engineering is a viable strategy to improve the activity of nanocatalysts for the oxygen evolution reaction (OER), whose slow kinetics still strongly limits the broad market penetration of electrochemical water splitting as a sustainable technology for large‐scale hydrogen production. High‐entropy spinel oxides (HESOs) are in focus due to their great potential as low‐cost OER electrocatalysts. In this work, electrospun HESO nanofibers (NFs), based on (Cr,Mn,Fe,Co,Ni), (Cr,Mn,Fe,Co,Zn) and (Cr,Mn,Fe,Ni,Zn) combinations, with granular architecture and oxygen‐deficient surface are produced by calcination at low temperature (600 or 500 °C), characterized by a combination of benchtop analytical techniques and evaluated as electrocatalysts for OER in alkaline medium. The variation of HESO composition and calcination temperature produces complex and interdependent changes in the morphology of the fibers, crystallinity and inversion degree of the spinel oxide, concentration of the oxygen‐vacancies, cation distribution in the lattice, which mirror on different electrochemical properties of the fibers. The best electrocatalytic performance (overpotential and Tafel slope at 10 mA cm⁻²: 360 mV and 41 mV dec⁻¹, respectively) pertains to (Cr_1/5Mn_1/5Fe_1/5Co_1/5Ni_1/5)₃O₄ NFs calcined at 500 °C and results from the lower outer 3d‐electron number, e_g filling closer to its optimal value and higher occupation of 16d sites by the most redox‐active species.

High‐entropy oxides (HEOs) have emerged as promising anode materials for next‐generation lithium‐ion batteries (LIBs). Among them, spinel HEOs with vacant lattice sites allowing for lithium insertion and diffusion seem particularly attractive. In this work, electrospun oxygen‐deficient (Mn,Fe,Co,Ni,Zn) HEO nanofibers are produced under environmentally friendly calcination conditions and evaluated as anode active material in LIBs. A thorough investigation of the material properties and Li⁺ storage mechanism is carried out by several analytical techniques, including ex situ synchrotron X‐ray absorption spectroscopy. The lithiation process is elucidated in terms of lithium insertion, cation migration, and metal‐forming conversion reaction. The process is not fully reversible and the reduction of cations to the metallic form is not complete. In particular, iron, cobalt, and nickel, initially present mainly as Fe³⁺, Co³⁺/Co²⁺, and Ni²⁺, undergo reduction to Fe⁰, Co⁰, and Ni⁰ to different extent (Fe < Co < Ni). Manganese undergoes partial reduction to Mn³⁺/Mn²⁺ and, upon re‐oxidation, does not revert to the pristine oxidation state (+4). Zn²⁺ cations do not electrochemically participate in the conversion reaction, but migrating from tetrahedral to octahedral positions, they facilitate Li‐ion transport within lattice channels opened by their migration. Partially reversible crystal phase transitions are observed.

Entropy‐stabilized oxides (ESOs), such as (Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)O, have recently gained significant interest as novel anodes for lithium‐ion batteries (LIBs) due to their stable crystal structure and robust lithium‐storage properties. In this work, (Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)O oxides with different morphologies are prepared by electrospinning and solvothermal method and are applied as anode active materials for LIBs. It is found that different morphologies possess different characteristics, namely particle size, particle size range, and defect density, which have a significant effect on the electrochemical behavior. The most active (Mg, Co, Ni, Cu, Zn) ESO shows outstanding electrochemical properties in terms of high reversible capacity (480 mAh g^–1 at 20 mA g^–1), superior rate capability (206 mAh g^–1 at 2 A g^–1), and excellent cycling stability (390 mAh g^–1 at 500 mA g^–1 after 300 cycles). The strategy demonstrates the importance of engineering microstructures in tailoring the electrochemical performance.