Oxygen Reduction Reaction Catalyzed by Noble Metal Clusters

Abstract

Highly-efficient catalysts for the oxygen reduction reaction (ORR) have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs). The state-ofthe-art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. Engineering ultra-small noble metal clusters with high surface-to-volume ratios and robust stabilities for ORR represents a new avenue. After a simple introduction regarding the significance of ORR and the recent development of noble metal clusters, the general ORR mechanism in both acidic and basic media is firstly discussed. Subsequently, we will summarize the recent efforts employing Pt, Au, Ag, Pd and Ru clusters, as well as the alloyed bi-metallic clusters for acquiring highly efficient catalysts to enhance both the activity and stability of ORR. Molecular noble metal clusters with definitive composition to reveal the relevant ORR mechanism will be particularly highlighted. Finally, the current challenges, the future outlook, as well as the perspectives in this booming field will be proposed, featuring the great opportunities and potentials to engineering noble metal clusters as highly-efficient and durable cathodic catalysts for fuel cell applications.

Metal Nanoclusters: New Paradigm in Catalysis for Water Splitting, Solar and Chemical Energy Conversion

“…Similar reactions also take place in metal–air batteries and water splitting devices, which has triggered considerable attention for renewable energy technology. The cathodic ORR, opposite to OER, is a crucial and challenging electrochemical reaction demanding high cathodic potentials of at least 1.23 V . Pt and its alloys are among the leading catalysts to accelerate the ORR at low overpotentials.…”

“…Therefore, better electrode materials that address the sluggish and slow kinetics of ORR have been extensively searched for . In this regard, nanostructured materials such as MNCs are among the emerging and promising materials, for which the selectivity of the electrode material can be improved towards the challenging reactions . The catalytic properties of MNCs are very sensitive to the change of the core atoms and surface chemistry.…”

“…Electronsm ove through the external circuit whereas protons move through am embrane towards the cathode, where they combine with electrons for the production of water.T he cathodic reaction to produce water is the reductiono ft he O 2 molecule. Similar reactions also take place in metal-airb atteries and water splitting devices, which has triggered considerable attention for renewable energy technology.T he cathodic ORR, opposite to OER, is ac rucial and challenging electrochemical reaction demanding high cathodicp otentials of at least 1.23 V. [213,214] Pt and its alloys are among the leadingc atalysts to accelerate the ORR at low overpotentials. However,t he main problem associated with ORR catalysts is the irreversible attachment of oxygen species to the electrode material, which can not only deactivate the active sites butalso decreaselong-term stability of the catalyst.…”

“…[215] In this regard, nanostructured materials such as MNCs are among the emerging and promising materials, for which the selectivity of the electrode material can be improved towards the challenging reactions. [213] The catalytic properties of MNCs are very sensitive to the change of the core atoms and surfacec hemistry.T he exciting aspecto fM NCs, which can play ap ivotal role in the ORR, is the fluctuationo fe lectronic densities on the surface of clusters by changing the number and nature of ligands that can tune the optimum adsorption of O 2 molecules. In this regard, as eries of Au NCs (11-140 core atoms) were reported for ORR by Chen andC hen.…”

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. [2,3] The state-of-the-art fuel cells still rely on the scarce and precious platinum (Pt)-based electrocatalysts to catalyset he ORR, which seriously hinders the large-scale implementation 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.…”