Non‐Pt Nanostructured Catalysts for Oxygen Reduction Reaction: Synthesis, Catalytic Activity and its Key Factors

Abstract

caused by electrochemical polarization, Ohmic polarization and mass transport polarization. [ 4 ] The electrochemical reaction occurring on the cathode is oxygen reduction reaction (ORR). It is kinetically much more sluggish as compared to anode reaction, thereby calling for effi cient ORR catalysts. [ 1 ] Basically for ORR catalysis there are two main pathways, i.e., direct 4e pathway (O 2 + 4H + + 4e − → 2H 2 O) and 2 by 2e pathway (O 2 + 2H + + 2e → H 2 O 2 , H 2 O 2 + 2H + + 2e → 2H 2 O), the latter of which ends up with H 2 O 2 generation in 2-electron pathway or H 2 O generation in 4-electron pathway, making the 4-electron pathway more efficient and desirable. [ 1,5 ] In the past few decades, Pt catalysts have been considered to be the best catalysts; however, typical problems facing Pt, including unsatisfactory long-term durability due to dissolution, methanol crossover and CO poisoning, are hindrances to mass application of PEMFC and make it a nontrivial issue to develop some novel cathode electrocatalysts. [ 6,7 ] Moreover, around half of the cost of PEMFC power system is the fuel cell stack cost, a large proportion of which stems from expensive Pt catalysts; unlike other stack components, Pt catalyst cost seems to be less affected by economies of sale due to the scarcity and increasing demand of Pt. [ 8 ] Many strategies have therefore been proposed to address these challenges. They can reasonably be classifi ed into two types, i.e., lowering the Pt concentration by mixing Pt with other metals to form Pt-based alloys [ 7,9 ] or Pt-skin/skeleton surface structures, [ 10,11 ] and developing non-Pt catalysts [ 12 ] or even metalfree catalysts. [ 13 ] Recently, a wide variety of non-Pt ORR catalysts have been intensively studied as substitutes for state-ofthe-art Pt or Pt-based catalysts. Monometallic catalysts such as Au, Ag with tunable particle size, morphology and preferential surface orientation have attracted growing attention due to their enhanced activities; in particular, monometallic catalysts supported on graphene or its derivatives are shown to have extraordinary catalytic performance and long-term durability since graphene, with its sp 2 -hybridized honeycomb structure, enhances mass transport and electron transfer, and the synergetic coupling between monometallic catalysts and graphene supports prevents the occurrence of particle dissolution and aggregation. [ 6,14 ] Similarly, metal chalcogenides grown on (heteroatom-doped) graphenes have noticeably higher ORR activities relative to unsupported counterparts due to the Pt-based electrocatalysts for the oxygen reduction reaction (ORR) are the topic of extensive and intensive research since a few decades. Nevertheless, the scarcity of these Pt-based electrocatalysts, their high cost and unsatisfactory durability are the primary hindrances to their further commercialization. In recent years, non-Pt electrocatalysts have garnered considerable interest as alternatives to Pt-based catalysts for the ORR. This review highlights the synthesis, catalyti...

3D Space-Confined Pyrolysis of Double-Network Aerogels Containing In-Fe Cyanogel and Polyaniline: A New Approach to Hierarchically Porous Carbon with Exclusive Fe-N x Active Sites for Oxygen Reduction Catalysis

“…The oxygen reduction reaction (ORR) is a basic and indispensable reaction for renewable energy storage and conversion devices, such as metal–air batteries and fuel cells . Platinum (Pt)‐based materials are usually considered as the most efficient ORR catalysts, but their large‐scale application is still hindered by the scarcity and prohibitive cost . This has stimulated the researchers to explore more efficient nonprecious metal catalysts (NPMCs) for ORR to replace the state‐of‐the‐art Pt/C catalyst.…”

Towards High‐Performance Electrocatalysts for Oxygen Reduction: Inducing Atomic‐Level Reconstruction of Fe‐Nx Site for Atomically Dispersed Fe/N‐Doped Hierarchically Porous Carbon

“…[1] The oxygen reduction reaction (ORR) at the cathode, which is inherently six orders of magnitude more sluggish compared with the anodic hydrogeno xidation reaction, is the bottleneck for improving the energyt ransfere fficiency of fuel cells. [4] Great efforts have been devotedt ot he development of lowcost and high-performance non-precious metal electrocatalysts (NPMCs) for ORR, including transition metal-nitrogen co-doped carbon (TM-N-C, TM:F e, Co, Cu, Ni,e tc. [4] Great efforts have been devotedt ot he development of lowcost and high-performance non-precious metal electrocatalysts (NPMCs) for ORR, including transition metal-nitrogen co-doped carbon (TM-N-C, TM:F e, Co, Cu, Ni,e tc.…”

A new 3D crosslinked polymer strategy for highly efficient oxygen reduction Fe–Nx/C catalysts

“…23 Herein, the suitable mesoporous structure and high conductivity properties are of signicance for their high performance Fe-based catalysts. 24 Besides, the mesoporous structure is also helpful to increase the specic surface area of the catalyst and make the active sites accessible to reactants.…”