Rational Dispersion of Co₂P₂O₇ Fine Particles on N,P-Codoped Reduced Graphene Oxide Aerogels Leading to Enhanced Reversible Oxygen Reduction Ability for Zn–Air Batteries

Abstract

Developing low-cost and highly efficient non-precious-metal-based bifunctional electrocatalysts for both oxygen reduction and evolution reactions concerns the key steps for the fabrication of rechargeable metal–air batteries. Herein, a rationally designed strategy is developed to join the merits of metal phosphate and carbonaceous materials for the fabrication of novel hybrid electrocatalysts. Through the self-polymerization of organophosphonic acid and cobalt salts on graphene oxide (GO) under a hydrothermal process to form cobalt phosphonate, and subsequently high-temperature pyrolysis, the N,P-codoped three-dimensional (3D) reduced-graphene-oxide-aerogel-supported (rGOA-supported) Co2P2O7 (CoPi) fine particles (CoPi/NPGA) are obtained. The pyrolysis of cobalt phosphonate introduces abundant heteroatom defects and the in situ formed CoPi particles on rGOA, wherein the rGOA permits enhanced electric conductivity and corrosion resistance. Thereby, these two aspects possess different abilities, and together endow the obtained hybrid material with enhanced electrocatalytic performance. In 0.1 M KOH, CoPi/NPGA affords a positive onset and half-wave potentials in catalyzing oxygen reduction, close to that of the Pt/C benchmark, along with impressive durability. In addition, it also exhibits considerable oxygen evolution electrochemical performance, and renders a potential of 1.57 V to achieve a current density of 10 mA cm–2 in 1.0 M KOH. Impressively, employed as the air cathode of the assembled Zn–air battery, this synthesized bifunctional catalyst enables high open-circuit potential, large powder density, and impressive cycling durability, holding great potential in practical rechargeable batteries.

Mn3+ Active Surface Site Enriched Manganese Phosphate Nano‐polyhedrons for Enhanced Bifunctional Oxygen Electrocatalyst

“…Figure d shows the high‐resolution TEM image having a group of nano‐polyhedrons and Figure e shows the image of one single MnP nano‐polyhedron (length 1944 nm and width of 540 nm) confirming the SEM observation. Figure f, i shows the selective area electron diffraction (SAED) pattern obtained from TEM analysis reveals that the prepared MnP possesses a high crystalline nature which will be supportive for operational stability during electrocatalysis activity . Figure g, h shows the HR‐TEM images at different magnification.…”

Design Strategies of Transition‐Metal Phosphate and Phosphonate Electrocatalysts for Energy‐Related Reactions

“…Various transition‐metal phosphates have been worked as efficient electrocatalysts for the ORR. Moreover, a much higher ORR activity can be obtained through combining with conducting carbon materials such as graphene nanosheets, carbon nanotubes or N‐doped carbons [75,118–120] . The carbon materials can improve the conductivity and prevent the aggregation tendency of metal phosphate nanoparticles, thus promoting the ORR activity.…”

“…Moreover, a much higher ORR activity can be obtained through combining with conducting carbon materials such as graphene nanosheets, carbon nanotubes or N-doped carbons. [75,[118][119][120] The carbon materials can improve the conductivity and prevent the aggregation tendency of metal phosphate nanoparticles, thus promoting the ORR activity. Particularly, the carbon deriving from N-containing polymer or phosphonate-based MOF via high-temperature thermal treatment can lead to the in situformed N-doped graphitic carbons, which is found can be coupling with metal phosphates to synergistically catalyze the ORR.…”

Insights into Transition Metal Phosphate Materials for Efficient Electrocatalysis

“…For instance, the composite of transition metal phosphates and graphene oxide aerogels have been employed as the air cathode of Zn-air battery, exhibiting great potential in practical rechargeable batteries. [13] Additionally, transition metal phosphates are a highly promising candidate to supercapacitors because their open structures with large channels and cavities allow high charge/ion conductivity and charge storage capacity. [14] Hence, it has been reported the superior electrochemical capacitance behavior of transition metal phosphates with a high specific capacitances and robust stability after numerous cycles.…”