Various Mesoporous Structured-Bifunctional Catalyst for Oxygen Reduction Reaction and Oxygen Evolution Reaction
Authors: Lee Sungwon , Kim Nam-In , Park Jun-Young 
Published: February 2020

Nowadays, energy sources of power mainly come from fossil fuels. However, fossil fuels will be eventually depleted and also cause severe pollutions with global climate change. Thus, we need clean and alternative energy sources for our next generation in the near future.[1] For the candidate energy sources, recently, the electrochemical devices have received great attentions such as fuel cells, redox fuels, supercapacitors, and rechargeable batteries. Particularly, utilized regenerative fuel cells (URFCs) which include fuel cells and water electrolyzers are getting spotlight in the renewable energy fields due to their high efficiency and environment-friendly property. Meanwhile, Pt as the water splitting catalyst is nearly an ideal catalyst for oxygen reduction reaction (ORR) and RuO and IrO have emerged as the most promising catalyst for oxygen evolution reaction (OER) for URFCs[2]. However, making commercialization of URFCs with precious metal-based catalysts as bifunctional catalysts is inappropriate for its price competitiveness and limited durability.[3] Consequently, much efforts are needed to develop cost-effective, earth-abundant, and non-precious metal based catalysts with outstanding performance and long-term stability.[4,5] Up to now, in order to substitute precious metal-based catalysts, nanostructured cobalt oxide with various dopants have investigated.[6,7] Recently, perovskite oxide-based bifunctional catalysts have shown reliable electrocatalytic properties for electrochemical energy conversion and storage devices. However, in order to use perovskite oxide practically as bifunctional catalysts, extra active sites should make as many as possible to improve electrochemical properties.[8,9] To maximize electrochemical active sites of catalysts, in this work, ordered mesoporous structure is introduced. Mesoporous structure is a combination of large specific surface area and periodic pore structure. As a candidate material for the bifunctional catalyst, Lanthanoid nickelate (LnNiO3) is considered due to high electrical conductivity with durable mechanical property. The ordered mesoporous structured LnNiO3 catalysts are synthesized by the nanocasting method with various mesoporous templates and also a variety of dopants at A- and B-site in ABO3 perovskite structure. The physicochemical properties of the final samples are investigated by various tools such as X-ray diffraction (XRD), small angle X-ray scattering (SAXS), Brunauer-Emmett- Teller (BET), scanning electron microscope (SEM), and transmission electron microscope (TEM). To analyze electrochemical activities, rotating ring electrode (RDE) 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 (LSV) 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 200mVs-1.

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