High demand of energy, environmental problems, and energy crisis have brought great attentions in renewable and environment-friendly energy resources(1). Among various candidate energy sources, electrochemistry based energy storage and harvesting devices such as rechargeable batteries, supercapacitors, utilized regenerative fuel cells(URFCs), and solar cells have received great interests (1, 2). Particularly, URFCs which include fuel cells and water electrolyzers are getting a big spotlight in the renewable energy fields due to their high efficiency and clean properties(3, 4).

The key technology for URFCs is to develop the cost-effective, durable, and high catalytic active catalysts for oxygen reduction(ORR) and evolution reactions(OER) in order to decrease the overpotential and improve efficiency of cells (5). Ideal bifunctional ORR and OER catalysts are Pt, RuO, and IrO for URFCs(6-8). However, precious metal-based catalysts are inadequate in terms of price competitiveness and limited durability to commercialize the URFCs(9).

Recently, modification of cobalt oxides nanostructures with various dopants have reported to reduce the overpotential with high OER and ORR performances (10). Furthermore, nitrogen-doped graphene oxide is used to further enhance the electronic conductivity with durable mechanical property, because nitrogen sites can function as electrochemical active sites(11). In this work, several short-length N-doped carbon nanofibers(N-CNF) are introduced to maximize electrochemical active sites of catalysts. The shortened N-CNF catalysts are synthesized by the hydrothermal method.

The physicochemical properties of the N-CNF-supported cobalt oxides nanostructures are investigated by various tools such as X-ray diffraction, scanning electron microscope, Brunauer Emmett Teller, and transmission electron microscope. To analyze electrochemical activities, rotating ring disk electrode system is used with an Hg/HgO, a platinum wire, and a 0.1M KOH solution for reference, counter, and electrolyte respectively. The electrochemical characteristics are measured by linear sweep voltammetry at a scan rate of 5 mVs^-1 for OER (1.2V–1.7V) and ORR (0.2V–1.2V). To analyze the long-term stability for OER and ORR, the accelerated degradation tests are performed at a scan rate of 200 mVs^-1.

References

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