High-Entropy Oxide Derived from Metal–Organic Framework as a Bifunctional Electrocatalyst for Efficient Urea Oxidation and Oxygen Evolution Reactions

Abstract

High-entropy oxides (HEOs) offer unique features through a combination of incompatible metal cations to a single crystalline lattice. Owing to their special characteristics such as abundant cation compositions, high entropy stabilization, chemical and thermal stability, and lattice distortion effect, they have drawn ever-increasing attention for various applications. However, very few studies have been reported for catalytic application, and developing HEOs with large surface areas for efficient catalytic application is still in infancy. Herein, we design nanostructured HEO of (FeNiCoCrCu) 3 O 4 using metal−organic frameworks (MOFs) as sacrificial templates to achieve a large surface area, high density of exposed active sites, and more oxygen vacancies. Single-crystalline phase HEOs with surface area as large as 206 m 2 g −1 are produced and further applied as bifunctional electrocatalysts for the urea oxidation reaction (UOR) and oxygen evolution reaction (OER). Benefiting from enhanced oxygen vacancies and a large surface area with abundant exposed active sites, the optimized HEO exhibited excellent electrocatalytic activity toward UOR with a very low potential of 1.35 V at the current density of 10 mA cm −2 and showed long-term stability for 36 h operation, making a significant catalytic performance over previously reported HEOs. Moreover, the HEO demonstrated an efficient catalytic performance toward OER with a low overpotential of 270 mV at 10 mA cm −2 and low Tafel slope of 49 mV dec −1 . The excellent catalytic activity is ascribed to the starting MOF precursor and favorable high-entropy effect.

Phase Purity Regulated by Mechano-Chemical Synthesis of Metal–Organic Frameworks for the Electrocatalytic Oxygen Evolution Reaction

“…However, the efficiency of OER is often hindered at conventional electrodes due to the slow kinetics and high overpotential. , Noble metals oxides such as RuO 2 and IrO 2 have been recognized as effective electrocatalysts toward OER but their widespread uses are hampered by their scarcity, high cost, and poor selectivity. , Hence, non-noble metal-based OER electrocatalyst with low cost and high activity are essential. Transition metal oxides, hydroxides, MOFs, and carbon-based materials have been employed as OER electrocatalysts. , Among them, MOF-based electrocatalysts have received considerable interest in energy conversion and storage systems. − However, majority of MOFs showed intrinsically poor electrocatalytic activity and thus various strategies , have been attempted to enhance the catalytic activity of these MOFs. As per our knowledge, the direct use of mechanochemically synthesized bare MOF as an efficient electrocatalyst toward OER is extremely rare.…”

Multicomponent 3d-Metal Nanoparticles in Amorphous Carbon Sponge for Electrocatalysis Water Splitting

“…Accommodation of several different metal ions and organic linkers into a single framework has been realized in the multivariate MOFs, leading to complicated sequences and modulated properties . MOFs have also been proven to be useful precursors and templates to prepare various derivatives through postsynthetic structure transformation under either physical or chemical treatments. , These derivatives include a large family of nanosized electrocatalysts as complex chemical systems, showing a great potential to promote efficient energy conversion. − …”

Three-Dimensional Cadmium–Organic Framework with Dual Functions of Oxygen Evolution in Water Splitting and Fenton-like Photocatalytic Removal of Organic Pollutants

“…This has prompted intense research efforts leading to the development of a series of cheap electrocatalysts with appreciable catalytic performance for OER, such as metal oxides, metal hydroxides, alloys, and carbon-based materials. − Among the various candidates, transition metals (TMs) have triggered significant interest as an alternative to promote the OER process. , In particular, materials based on metal–organic frameworks (MOFs) stand out for their highly porous structures with rich active metal sites and structure tunability by varying the metal centers and ligands. − However, unsatisfying electrical conductivity and catalytic activities are achieved; therefore, the design of MOFs with the optimal conductivity, mass transfer, and active site density is essential to realize their practical applications …”