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.

Highly Efficient Oxygen Reduction Reaction Electro-catalyzed by Ultra-small Pt@Mn Core-shell Nanoparticles

Electro-catalyzed oxygen reduction reaction (ORR), as the positive electrode reaction, is significant to the performance of fuel cells and metal-air batteries. Toward ORR, ultra-small Pt@Mn core-shell nanoparticles catalysts supported on Ketjen black are synthesized by a simple one-pot hydrothermal method. TEM results show that the Pt@Mn/C nanoparticles with an average size of 3~4 nm are uniformly distributed on the carbon surface. ORR performance of the electrocatalysts show that Pt@Mn/C exhibits better oxygen reduction activity than Pt/C (20 wt%) in a KOH solution. Methanol tolerance ability as well as the durability of the Pt@Mn/C is also superior to the performance of Pt/C, suggesting an enhanced ORR activity upon the introduction of Mn.

Supported Mn3O4 Nanosystems for Hydrogen Production through Ethanol Photoreforming

Photoreforming promoted by metal oxide nanophotocatalysts is an attractive route for clean and sustainable hydrogen generation. In the present work, we propose for the first time the use of supported Mn₃O₄ nanosystems, both pure and functionalized with Au nanoparticles (NPs), for hydrogen generation by photoreforming. The target oxide systems, prepared by chemical vapor deposition (CVD) and decorated with gold NPs by radio frequency (RF) sputtering, were subjected to a thorough chemico-physical characterization and utilized for a proof-of-concept H₂ generation in aqueous ethanolic solutions under simulated solar illumination. Pure Mn₃O₄ nanosystems yielded a constant hydrogen production rate of 10 mmol h^-1 m^-2 even for irradiation times up to 20 h. The introduction of Au NPs yielded a significant enhancement in photocatalytic activity, which decreased as a function of irradiation time. The main phenomena causing the Au-containing photocatalyst deactivation have been investigated by morphological and compositional analysis, providing important insights for the design of Mn₃O₄-based photocatalysts with improved performances.

Synthesis of TiO2/rGO composites with different morphologies and their electrocatalysis for the oxygen reduction reaction

An octahedral TiO₂/rGO composite shows the best catalytic activity for the ORR.