No abstract

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-N /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-N /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.

A facile two-step chemical route using cobalt ions coordinated with EDTA (Co II /EDTA chelate complex supported on glucose mixture), followed by the in situ pyrolysis process, from 500 to 900°C, was developed to prepare Co embedded in N-doped porous carbon hybrids (Co@CÀ T). The EDTA chelating agent served as both the N source and pore former. The physicochemical characterization results revealed that the pore structure, graphitization degree, and relative content of active centers, e. g., cobalt-based components and nitrogen species, for Co@CÀ T electrocatalysts, were tailored by controlling the temperature of pyrolysis. The optimized material generated at 600°C (Co@C-600), showed an excellent oxygen reduction reaction activity with an onset potential of 0.91 V vs. RHE, and a half-wave potential of 0.80 V vs. RHE.

Converting carboxylic acids into value-added products by electrochemical processes is of great interest. In this work, the electrochemical conversion of valeric acid (VA) on carbon materials including glassy-carbon (GC) electrodes and carbon-paper (CP) electrodes was studied. Owing to the porous structure, CP electrodes showed superior performance relative to GC electrodes. The surface properties of CP electrodes were modified via electro-oxidation processes. The structures of the CP electrodes were characterized by scanning electron microscopy, X-ray diffraction pattern, X-ray photoelectron spectroscopy spectra, and Raman spectra. It was found that the electrochemical activation process had more pronounced effects on electro-oxidation of VA than H 2 O. The onset potential of VA oxidation on electrochemically activated CP electrodes was negatively shifted and the current density was significantly improved. The products of VA oxidation by CP electrodes were determined by gas chromatography-mass spectra. VA was mainly transformed into 2-butanol, butyl valerate, and pentanoic acid 1-methylpropyl ester. The conversion of VA, Faraday efficiency, and product selectivity were determined. The optimal CP electrode exhibited the largest values of product selectivity (85.0%) and VA conversion (13.0%). In-situ Raman spectra were recorded to study the mechanism of VA oxidation on the CP electrodes. The oxidation of VA by CP electrodes follows the non-Kolbe route and the corresponding pathway was proposed.