Multi-Level Architecture Optimization of MOF-Templated Co-Based Nanoparticles Embedded in Hollow N-Doped Carbon Polyhedra for Efficient OER and ORR

Abstract

Emerging clean energy technologies such as regenerative fuel cells and rechargeable metal–air batteries have attracted increasing global interest because of their high efficiency and environmental benignity, but the lack of highly active bifunctional electrocatalysts at low cost for both oxygen reduction and evolution reactions (ORR and OER) greatly hinders their commercial applications. Here, we report the multilevel architecture optimization of Co-based nanoparticles (NPs) embedded in hollow N-doped carbon polyhedra for boosting the ORR and OER, which are fabricated by a two-step pyrolysis–oxidation strategy with a Co-based MOF (ZIF-67) as precursor. The key for this strategy lies in the precise and effective control of the oxidation processes of Co NPs, which enables the synthesis of a series of Co–Co3O4-based nanoarchitectures that are embedded in hollow nitrogen-doped carbon polyhedra (HNCP), including core–shell Co/Co3O4, yolk@shell Co@Co3O4, and hollow Co3O4 NPs. Benefiting from its abundant oxygen vacancies and tetrahedral Co2+ and the potential synergies of CoO x species and nitrogen-doped carbon as well as the efficient mass transfer of hollow and yolk–shell structures, the optimal yolk@shell Co3O4/HNCP-40 exhibits high activity for the OER with a low overpotential of 333 mV at 10 mA cm–2 and a small Tafel slope of 69 mV dec–1, which is better than those of commercial IrO2 (its overpotential and Tafel slope are 409 mV at 10 mA cm–2 and 104 mV dec–1, respectively). Meanwhile, the catalyst also exhibits comparable ORR catalytic activity with a half-wave potential of 0.834 V but better stability and methanol tolerance relative to commercial Pt/C (20 wt %), making it a potential bifunctional electrocatalyst for both the OER and ORR. This MOF-templated strategy for multilevel nanostructures provides insights into the development of highly efficient and low-cost bifunctional electrocatalysts for the OER/ORR.

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

“…The MOF‐derived porous carbon supported TM nanoparticles have been reported with highly efficient ORR activity endowed by the following advantages: 1) high surface area and abundant hierarchical pores to increase the exposure of the active sites and facilitate the mass transfer; 2) well‐dispersed nanoparticles with high electrochemical activity and structural stability, which is in situ reduced from the metal species in the MOF structure; 3) enough heteroatom dopants from the ligand precursor to act as the complementary ORR active sites; and 4) porous graphitic carbon from the organic ligand for enhanced conductivity and accelerated electron transfer. For example, a multilevel architecture optimization of hollow N‐doped carbon polyhedral structure supported Co nanoparticles (Co/HNCP) has been proposed with ZIF‐67 as precursor as shown in Figure 2 a 60. The resultant Co/HNCP retained the rhombic dodecahedral morphology of ZIF‐67 well but with a hollow structure with even distribution of the C, N, Co, and O elements as shown in Figure 2b–d, which was caused by the fast pyrolysis of the ligand and consumption of carbon.…”

“…Various sites of the catalysts have been verified active in the reaction of the ORR process, including metal–sulfur bonding, metal–oxygen bonding, oxygen vacancy, and so on 60,137…”

Isostructural NiII Metal–Organic Frameworks (MOFs) for Efficient Electrocatalysis of Oxygen Evolution Reaction and for Gas Sorption Properties

“…[3] Therefore, there is high demandf or an efficient electrocatalyst which can increase the rate of OER at lower overpotential. [8][9][10][11] Amongt he TMOs, cobalt-based spinel oxides have been shown as outstanding OER electrocatalysts. [4,5] However,t heir scarcity,i nferior durability and excessive cost, limit their use in large-scale industrial applications.…”

Cobalt‐Embedded N‐Doped Carbon Arrays Derived In Situ as Trifunctional Catalyst Toward Hydrogen and Oxygen Evolution, and Oxygen Reduction

“…Figure b shows the Raman spectra of Co/MMCs and Co/CNWs. The G‐band located at 1586 cm −1 corresponds to the E 2g mode vibration of graphitic carbon, whereas the D‐band at 1347 cm −1 is associated with the defect mode . The ratio of I D /I G of Co/MMCs is 1.06, whereas which is 1.00 for Co/CNWs.…”