Abstract
The development of electrocatalysts for energy conversion and storage devices is of paramount importance to promote sustainable development. Among the different families of materials, catalysts based on transition metals supported on a nitrogen-containing carbon matrix have been found to be effective catalysts toward oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) with high potential to replace conventional precious metal-based catalysts. In this work, we developed a facile synthesis strategy to obtain a Fe-N-C bifunctional ORR/HER catalysts, involving wet impregnation and pyrolysis steps. Iron (II) acetate and imidazole were used as iron and nitrogen sources, respectively, and functionalized carbon black pearls were used as conductive support. The bifunctional performance of the Fe-N-C catalyst toward ORR and HER was investigated by cyclic voltammetry, rotating ring disk electrode experiments, and electrochemical impedance spectroscopy in alkaline environment. ORR onset potential and half-wave potential were 0.95 V and 0.86 V, respectively, indicating a competitive performance in comparison with the commercial platinum-based catalyst. In addition, Fe-N-C had also a good HER activity, with an overpotential of 478 mV @10 mAcm−2 and Tafel slope of 133 mVdec−1, demonstrating its activity as bifunctional catalyst in energy conversion and storage devices, such as alkaline microbial fuel cell and microbial electrolysis cells.
Highlights
The TG curve of the carbon support indicates that Black pearls 2000 (BP) exhibits a main first mass loss in the 30–115 ◦ C temperature range due to the vaporization of adsorbed water molecules; mass losses above 120 ◦ C were due to the decomposition of oxygenated functionalities in carbon black pearls [21]
The TG curve of the Fe-N-C precursor is different as compared to the pristine compounds, imidazole, iron acetate, and BP, in which the main mass loss from 138 to 316 ◦ C (Table 1) indicates a higher contribution of imidazole carbonization, as can be evidenced by comparison of TG curves profiles for imidazole and iron acetate at this temperature range
A three-electrode electrochemical cell was used for the electrochemical experiments: the working electrode (WE) was either a rotating ring disk electrode (RRDE-AFE6R2GCPT, Disk OD = 5.5 mm; Ring OD = 8.50 mm; Ring ID = 6.50 mm) or a glassy carbon disk (AFE1XFP030GCR, 3 mm disk diameter, 0.071 cm2, for Oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) experiments, respectively, both purchased by Pine Research Instrumentation (Durham, NC, US)
Summary
The environment pollution generated by use of fossil fuels combined with their depletion demands urgent development of renewable and clean energy technology. In this scenario, fuel cells and electrolyzers offer a good strategy for electrochemical energy storage and conversion; in particular microbial fuel cells are able to generate electricity by the oxidation of organic matter at the anode side promoted by the action of microorganisms [1,2,3]. Oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are the most crucial cathodic reactions of fuel cell and electrolyzers, respectively. The development of bifunctional electrocatalyst materials plays a key role in the rapid advancement of these hydrogen-based renewable energy strategies [4]
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