It
is highly desirable but remains challenging to develop efficient bifunctional
electrocatalysts for both the oxygen reduction and oxygen evolution
reactions (ORR/OER) in rechargeable metal–air batteries and
unitized regenerative fuel cells. Herein, we developed a facile and
cost-effective strategy to prepare a cobalt and nitrogen codoped three-dimensional
(3D) graphene catalyst through inserting carbon nanospheres into the
interlayers of graphene sheets. The catalyst exhibited not only excellent
ORR performance but also excellent OER performance, and both were
greatly enhanced by the insertion of carbon nanospheres. Its activities
for the ORR/OER ranked among the best for doped carbon catalysts thus
far reported. Its overall oxygen electrode activity parameter (ΔE) was as low as 0.807 V, which was much lower than that
of Pt/C, and made it comparable with the best nonprecious metal based
catalysts to date. Furthermore, the catalyst exhibited excellent stability
toward ORR and OER, making it a new noble-metal-free bifunctional
catalyst for future applications in the fields of alternative energy
conversion and storage systems.
Proton exchange membrane fuel cells (PEMFCs) are a highly efficient hydrogen energy conversion technology, which shows great potential in mitigating carbon emissions and the energy crisis. Currently, to accelerate the kinetics of the oxygen reduction reaction (ORR) required for PEMFCs, extensive utilization of expensive and rare platinum‐based catalysts are required at the cathodic side, impeding their large‐scale commercialization. In response to this issue, atomically dispersed metal–nitrogen–carbon (M–N–C) catalysts with cost‐effectiveness, encouraging activity, and unique advantages (e.g., homogeneous activity sites, high atom efficiency, and intrinsic activity) have been widely investigated. Considerable progress in this domain has been witnessed in the past decade. Herein, a comprehensive summary of recent development in atomically dispersed M–N–C catalysts for the ORR under acidic conditions and of their application in the membrane electrode assembly (MEA) of PEM fuel cells, are presented. The ORR mechanisms, composition, and operating principles of PEMFCs are introduced. Thereafter, atomically dispersed M–N–C catalysts towards improved acidic ORR and MEA performance is summarized in detail, and improvement strategies for MEA performance and stability are systematically analyzed. Finally, remaining challenges and significant research directions for design and development of high‐performance atomically dispersed M–N–C catalysts and MEA are discussed.
A P, N dual doped reduced graphene oxide (PN-rGO) catalyst with high surface area (376.20 m 2 ·g −1 ), relatively high P-doping level (1.02 at. %) and a trace amount of N (0.35 at. %) was successfully prepared using a one-step method by directly pyrolyzing a homogenous mixture of graphite oxide (GO) and diammonium hydrogen phosphate ((NH4)2HPO4) in an argon atmosphere, during which the thermal expansion, deoxidization of GO and P, N co-doping were realized simultaneously. The catalyst exhibited enhanced catalytic performances for oxygen reduction reaction (ORR) via a dominated four-electron reduction pathway, as well as superior long-term stability, better tolerance to methanol crossover than that of commercial Pt/C catalyst in an alkaline solution.
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