Haihong Zhong

Electrocatalytic Cobalt Nanoparticles Interacting with Nitrogen-Doped Carbon Nanotube in Situ Generated from a Metal–Organic Framework for the Oxygen Reduction Reaction

A metal organic framework (MOF), synthesized from cobalt salt, melamine (mela), and 1,4-dicarboxybezene (BDC), was used as precursor to prepare Co/CoNx/N-CNT/C electrocatalyst via heat treatment at different temperature (700-900 °C) under nitrogen atmosphere. Crystallites size and microstrain in the 800 °C heat-treated sample (MOFs-800) were the lowest, whereas the stacking fault value was the highest among the rest of the homemade samples, as attested to by the Williamson-Hall analysis, hence assessing that the structural or/and surface modification of Co nanoparticles (NPs), found in MOFs-800, was different from that in other samples. CNTs in MOFs-800, interacting with Co NPs, were formed on the surface of the support, keeping the hexagonal shape of the initial MOF. Among the three homemade samples, the MOF-800 sample, with the best electrocatalytic performance toward oxygen reduction reaction (ORR) in 0.1 M KOH solution, showed the highest density of CNTs skin on the support, the lowest ID/IG ratio, and the largest N atomic content in form of pyridinic-N, CoNx, pyrrolic-N, graphitic-N, and oxidized-N species. Based on the binding energy shift toward lower energies, a strong interaction between the active site and the support was identified for MOFs-800 sample. The number of electron transfer was 3.8 on MOFs-800, close to the value of 4.0 determined on the Pt/C benchmark, thus implying a fast and efficient multielectron reduction of molecular oxygen on CoNx active sites. In addition, the chronoamperometric response within 24 000 s showed a more stable current density at 0.69 V/RHE on MOFs-800 as compared with that of Pt/C.

Design and Synthesis of Cobalt-Based Electrocatalysts for Oxygen Reduction Reaction

Oxygen reduction reaction (ORR) is the crucial step of various renewable energy conversion and storage technologies such as fuel cells and air-batteries. Cobalt-based electrocatalysts including oxides/chalcogenides and Co-Nx /C, one kind of non-precious metal electrocatalysts with competitive activity, enhanced durability, and acceptable cost, have been proposed as the potentially interesting alternatives to Pt-based electrocatalysts. In this account, we summarized the synthesis methods and the corresponding main impact factors including ligand effect, particle size effect, crystal structure, nanostructure, defects and active centers related to the ORR performance on both of oxides/chalcogenides and Co-Nx /C. Some special points have been discussed on design and synthesis of low-cost and high-performance cobalt-based electrocatalysts with enhanced electrocatalytic activity. Also, the current challenges and future trends are proposed for improving the performance of Co-involving electrocatalysts.