Bifunctional NiCo2O4 porous nanotubes electrocatalyst for overall water-splitting

Sulfidation of CoCuOx Supported on Nickel Foam to Form a Heterostructure and Oxygen Vacancies for a High-Performance Anion-Exchange Membrane Water Electrolyzer

Anion-exchange membrane water electrolyzer (AEMWE) is attracting attention for hydrogen production owing to its ability to employ nonprecious metal catalysts and high energy conversion efficiency. Spinel-structured transition metal oxides exhibit excellent potential in oxygen evolution reaction (OERs). Nevertheless, the research on highly active and durable spinel-structured electrodes for the anodic OER of AEMWE is deficient. Herein, a self-supported S-CoCu oxide/nickel foam (S-CoCuOx/NF) anode was synthesized through a two-step method (electrodeposition and sulfidation). The formation of abundant oxygen vacancies and heterostructure collaboratively enhances the electron and mass transfer, resulting in an overpotential of 313 mV at 100 mA cm-2 for OER. For the lab-scale AEMWE system with the S-CoCuOx/NF anode, a current density of 1 A cm-2 was obtained at 1.87 V (cell voltage) with high durability for 110 h (1 A cm-2) at 60 °C. The results will provide insights into developing the spinel structure-derived anode for high-performance AEMWE.

Recent Progress on Bimetallic-Based Spinels as Electrocatalysts for the Oxygen Evolution Reaction

Electrocatalytic water splitting is a promising and viable technology to produce clean, sustainable, and storable hydrogen as an energy carrier. However, to meet the ever-increasing global energy demand, it is imperative to develop high-performance non-precious metal-based electrocatalysts for the oxygen evolution reaction (OER), as the OER is considered the bottleneck for electrocatalytic water splitting. Spinels, in particular, are considered promising OER electrocatalysts due to their unique properties, precise structures, and compositions. Herein, the recent progress on the application of bimetallic-based spinels (AFe₂ O₄ , ACo₂ O₄ , and AMn₂ O₄ ; where A = Ni, Co, Cu, Mn, and Zn) as electrocatalysts for the OER is presented. The fundamental concepts of the OER are highlighted after which the family of spinels, their general formula, and classifications are introduced. This is followed by an overview of the various classifications of bimetallic-based spinels and their recent developments and applications as OER electrocatalysts, with special emphasis on enhancing strategies that have been formulated to improve the OER performance of these spinels. In conclusion, this review summarizes all studies mentioned therein and provides the challenges and future perspectives for bimetallic-based spinel OER electrocatalysts.

Mesoporous K-doped NiCo2O4 derived from a Prussian blue analog: high-yielding synthesis and assessment as oxygen evolution reaction catalyst

The conversion and storage of clean renewable energy can be achieved using water splitting. However, water splitting exhibits sluggish kinetics because of the high overpotentials of the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) and should therefore be promoted by OER and/or HER electrocatalysts. As the kinetic barrier of the former reaction exceeds that of the latter, high-performance OER catalysts are highly sought after. Herein, K-doped NiCo₂O₄ (HK-NCO) was hydrothermally prepared from a Prussian blue analog with a metal–organic framework structure and assessed as an OER catalyst. Extensive K doping increased the number of active oxygen vacancies and changed their intrinsic properties (e.g., binding energy), thus increasing conductivity. As a result, HK-NCO exhibited a Tafel slope of 49.9 mV dec⁻¹ and a low overpotential of 292 mV at 10 mA cm⁻², outperforming a commercial OER catalyst (Ir) and thus holding great promise as a component of high-performance electrode materials for metal-oxide batteries and supercapacitors.

OER characteristics of K-doped NiCo₂O₄ catalyst and K doping control through simple hydrothermal synthesis.

Fabrication of Magnetic Superstructure NiFe2O4@MOF-74 and Its Derivative for Electrocatalytic Hydrogen Evolution with AC Magnetic Field

As an ideal hydrogen production route, electrolyzed water still faces the challenges of high cost of noble-metal electrocatalysts and low performance of non-noble-metal catalysts in scalable applications. Recently, introduction of external fields (such as magnetic fields, light fields, etc.) to improve the electrocatalytic water splitting performance of non-noble-metal catalysts has attracted great attention due to their simplicity. Here, a simple method for preparing magnetic superstructure (NiFe₂O₄@MOF-74) is described, and the hydrogen evolution reaction (HER) behavior of its carbonized derivative, a ferromagnetic superstructure, is revealed in a wide range of applied voltage under an AC magnetic field. The overpotential (@10 mA cm^-2) required for the HER of the obtained ferromagnetic superstructure in 1 M KOH was reduced by 31 mV (7.7%) when a much small AC magnetic field (only 2.3 mT) is applied. Surprisingly, the promotion effect of the AC magnetic field is not monotonically increasing with the increase of the applied voltage or the strength of AC magnetic field, but increasing first, then weakening. This unusual behavior is believed to be mainly caused by the enhanced induced electromotive force and the additional energy by the applied AC magnetic field. This discovery provides a new idea for adjusting the performance of electrocatalytic reactions.