A Universal Method to Engineer Metal Oxide–Metal–Carbon Interface for Highly Efficient Oxygen Reduction

Abstract

Oxygen is the most abundant element in the Earth's crust. The oxygen reduction reaction (ORR) is also the most important reaction in life processes and energy converting/storage systems. Developing techniques toward high-efficiency ORR remains highly desired and a challenge. Here, we report a N-doped carbon (NC) encapsulated CeO/Co interfacial hollow structure (CeO-Co-NC) via a generalized strategy for largely increased oxygen species adsorption and improved ORR activities. First, the metallic Co nanoparticles not only provide high conductivity but also serve as electron donors to largely create oxygen vacancies in CeO. Second, the outer carbon layer can effectively protect cobalt from oxidation and dissociation in alkaline media and as well imparts its higher ORR activity. In the meanwhile, the electronic interactions between CeO and Co in the CeO/Co interface are unveiled theoretically by density functional theory calculations to justify the increased oxygen absorption for ORR activity improvement. The reported CeO-Co-NC hollow nanospheres not only exhibit decent ORR performance with a high onset potential (922 mV vs RHE), half-wave potential (797 mV vs RHE), and small Tafel slope (60 mV dec) comparable to those of the state-of-the-art Pt/C catalysts but also possess long-term stability with a negative shift of only 7 mV of the half-wave potential after 2000 cycles and strong tolerance against methanol. This work represents a solid step toward high-efficient oxygen reduction.

Gadolinium‐Induced Valence Structure Engineering for Enhanced Oxygen Electrocatalysis

“…This speculation can be supported by the previous reported CeO x /M (M = Pt and Co etc.) studies 42,67,68. For example, DFT calculations by Kim et al, demonstrated that CeO 2 can perturbe the electronic structure of Co species and further optimize the binding energy of intermediate oxygenated adsorbates 69.…”

Efficient Oxygen Reduction Catalysts of Porous Carbon Nanostructures Decorated with Transition Metal Species

“…The oxygen vacancy/defect has been studied in the ORR process and verified as the most active adsorption sites 19,138. The high‐resolution Ce 3d spectrum in a metal oxide–metal–carbon interface nanostructure (CeO 2 ‐Co‐NC) showed the existence of Ce 2+ and Ce 3+ ( Figure 8 a),19 in which Ce 3+ led to the charge imbalance and created oxygen vacancies 19. The DFT simulation method136 can be applied to clarify the ORR mechanism and the role of the oxygen vacancy as shown in Figure 8b–e, revealing that the charge redistribution between CeO 2 and metallic Co has led to an electron‐rich region on CeO 2 and a hole‐rich region on the Co, corresponding to the new Ce 3+ peak in the partial density of states around the Fermi level.…”

“…The adsorption of the oxygen molecule at the initial step is believed one of the rate‐determining steps in the ORR process as shown in Equations and , which is especially of vital importance for the metal oxide catalysts. The oxygen vacancy/defect has been studied in the ORR process and verified as the most active adsorption sites 19,138. The high‐resolution Ce 3d spectrum in a metal oxide–metal–carbon interface nanostructure (CeO 2 ‐Co‐NC) showed the existence of Ce 2+ and Ce 3+ ( Figure 8 a),19 in which Ce 3+ led to the charge imbalance and created oxygen vacancies 19.…”

“…e) Total density of states curves of CeO 2 (111) (top) and CeO 2 (111)/Co(111) (bottom). Reproduced with permission 19. Copyright 2018, ACS.…”

Fabricating Nitrogen‐Rich Fe−N/C Electrocatalysts through CeO2‐Assisted Pyrolysis for Enhanced Oxygen Reduction Reaction

“…Especially, CeO 2 is possible to stabilize more nitrogen sources during catalyst synthesis process . Furthermore, it is worth mentioning that there also exists an electronic interaction between CeO 2 and metal in the co‐synthesized catalyst, which may enhance the oxygen absorption on the catalyst for improved ORR activity . Besides, CeO 2 can effectively catalyze the decomposition of H 2 O 2 , which is very favorable for the retention of active sites in ORR catalysts, thereby improving the long‐term stability .…”