Boosting Bifunctional Oxygen Electrocatalysis with 3D Graphene Aerogel‐Supported Ni/MnO Particles

Abstract

Electrocatalysts for oxygen-reduction and oxygen-evolution reactions (ORR and OER) are crucial for metal-air batteries, where more costly Pt- and Ir/Ru-based materials are the benchmark catalysts for ORR and OER, respectively. Herein, for the first time Ni is combined with MnO species, and a 3D porous graphene aerogel-supported Ni/MnO (Ni-MnO/rGO aerogel) bifunctional catalyst is prepared via a facile and scalable hydrogel route. The synthetic strategy depends on the formation of a graphene oxide (GO) crosslinked poly(vinyl alcohol) hydrogel that allows for the efficient capture of highly active Ni/MnO particles after pyrolysis. Remarkably, the resulting Ni-MnO/rGO aerogels exhibit superior bifunctional catalytic performance for both ORR and OER in an alkaline electrolyte, which can compete with the previously reported bifunctional electrocatalysts. The MnO mainly contributes to the high activity for the ORR, while metallic Ni is responsible for the excellent OER activity. Moreover, such bifunctional catalyst can endow the homemade Zn-air battery with better power density, specific capacity, and cycling stability than mixed Pt/C + RuO catalysts, demonstrating its potential feasibility in practical application of rechargeable metal-air batteries.

Gadolinium‐Induced Valence Structure Engineering for Enhanced Oxygen Electrocatalysis

“…The sol–gel formation is ascribed to hydrogen bonding between PVA chains and oxygen‐containing groups of GO 46. GO with a lone electron pair can also bind metal ions (M n+ ) efficiently through coordination and electrostatic interaction,47,48 which allows reduced GO to effectively anchor Gd 2 O 3 –Co heterostructures. The freeze‐drying was proved to be useful to get three‐dimensional (3D) porous carbon because that sublimation of the formed ice by freeze‐drying avoids formation of a liquid/vapor interface 49,50.…”

Versatile Aerogels for Sensors

“…Moreover, because of the high degree of graphitization, the CNT and graphene aerogels possess superior thermal and chemical stability, and electrical properties than common carbon aerogels and can be used in many fields . As a supporting material, carbon aerogel can supply a 3D porous and electrically conductive network for fast mass transport and electron transfer, and large surface area for the depositing and avoiding the ripening and aggregation of active particles . Besides, the carbon aerogels themselves can be used as functional materials through the defect design and heteroatom doping …”

Hydrogels for Medical and Environmental Applications

“…Their large surface area structures provide ample space to accommodate foreign particles which could impart different functionalities and make them viable for a wide range of “smart” applications, making them a very hot topic of research . When water from the hydrogels is replaced with air by maintaining the 3D structure, we obtain aerogels, which find diverse applications too . Both aerogels and hydrogels, with their very high surface area to volume ratio, find a lot of applications in energy applications like metal–air batteries, supercapacitors, batteries, which require a lot of ions to be intercalated for the charge‐storage mechanisms .…”

“…When water from the hydrogels is replaced with air by maintaining the 3D structure, we obtain aerogels, which find diverse applications too . Both aerogels and hydrogels, with their very high surface area to volume ratio, find a lot of applications in energy applications like metal–air batteries, supercapacitors, batteries, which require a lot of ions to be intercalated for the charge‐storage mechanisms . With their porous structure and absence of solvents like water, they are also used as dielectric materials, catalysts and even for nuclear waste storage, etc …”