High‐Entropy Oxides: Fundamental Aspects and Electrochemical Properties

Abstract

High‐entropy materials, especially high‐entropy alloys and oxides, have gained significant interest over the years due to their unique structural characteristics and correlated possibilities for tailoring of functional properties. The developments in the area of high‐entropy oxides are highlighted here, with emphasis placed on their fundamental understanding, including entropy‐dominated phase‐stabilization effects and prospective applications, e.g., in the field of electrochemical energy storage. Critical comments on the different classes of high‐entropy oxides are made and the underlying principles for the observed properties are summarized. The diversity of materials design, provided by the entropy‐mediated phase‐stabilization concept, allows engineering of new oxide candidates for practical applications, warranting further studies in this emerging field of materials science.

Gassing Behavior of High‐Entropy Oxide Anode and Oxyfluoride Cathode Probed Using Differential Electrochemical Mass Spectrometry

“…HEO was prepared by the NSP method . Mg(NO 3 ) 2 ⋅ 6H 2 O (Sigma Aldrich, 99.9 %), Zn(NO 3 ) 2 ⋅ 6H 2 O (Alfa Aesar, 99.9 %), Cu(NO 3 ) 2 ⋅ 2.5H 2 O (Sigma Aldrich, 99.9 %), Ni(NO 3 ) 2 ⋅ 6H 2 O (Sigma Aldrich, 99.9 %) and Co(NO 3 ) 2 ⋅ 6H 2 O (Sigma Aldrich, 99.9 %) served as precursors in the synthesis, with the final material forming in the gas phase of a hot‐wall reactor at 1150 °C and subsequent sintering at 1000 °C for 1 h …”

“…Synthesis HEO was prepared by the NSP method. [19] Mg(NO 3 ) 2 · 6H 2 O (Sigma Aldrich, 99.9 %), Zn(NO 3 ) 2 · 6H 2 O (Alfa Aesar, 99.9 %), Cu (NO 3 ) 2 · 2.5H 2 O (Sigma Aldrich, 99.9 %), Ni(NO 3 ) 2 · 6H 2 O (Sigma Aldrich, 99.9 %) and Co(NO 3 ) 2 · 6H 2 O (Sigma Aldrich, 99.9 %) served as precursors in the synthesis, with the final material forming in the gas phase of a hot-wall reactor at 1150°C and subsequent sintering at 1000°C for 1 h. [14][15][16] Li(HEO)F was prepared by high-energy planetary ball-milling of a 1 : 1 molar mixture of LiF (Alfa Aesar, 99.99 %) and HEO at 500 rpm for 24 h under an Ar atmosphere. [17] To this end, 50 ml WC vials and WC balls of 4 mm diameter were used, with the ball-to-powder ratio being 40 : 1 by weight.…”

“…Very recently, a new class of multicomponent electrode materials has been reported, which seems promising for the development of next‐generation LIBs . These materials exhibit tailorable properties and good cycling performance and belong to the so‐called high‐entropy oxides (HEOs).…”

“…Very recently, a new class of multicomponent electrode materials has been reported, which seems promising for the development of next-generation LIBs. [14][15][16][17] These materials exhibit tailorable properties and good cycling performance and belong to the so-called high-entropy oxides (HEOs). HEOs are a class of materials where a large number of different (incorporated) elements increases the configurational entropy, leading to entropy stabilization.…”

Nanoporous Al‐Ni‐Co‐Ir‐Mo High‐Entropy Alloy for Record‐High Water Splitting Activity in Acidic Environments

“…Mo, Nb, and Cu have very different physiochemical properties in terms of melting point, electronegativity, redox potential, etc. The fact that the addition of the three quite different metal species forming three different np‐HEAs can all enhance the cycling stability suggests that the high‐entropy stabilization effect based on ∆ G mix = ∆ H mix − T ∆ S mix , distorted lattice effect and/or the sluggish diffusion effect may be responsible for the enhanced stability compared with binary or ternary alloys. After the durability test, the microstructure and element distribution of the np‐AlNiCoIrMo were investigated by STEM‐EDS (Figure S5, Supporting Information).…”