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Synergistic interaction of perovskite oxides and N-doped graphene in versatile electrocatalyst
Bu, Yunfei,Jang, Haeseong,Gwon, Ohhun,Kim, Su Hwan,Joo, Se Hun,Nam, Gyutae,Kim, Seona,Qin, Yong,Zhong, Qin,Kwak, Sang Kyu,Cho, Jaephil,Kim, Guntae The Royal Society of Chemistry 2019 Journal of Materials Chemistry A Vol.7 No.5
<P>Multifunctional electrocatalysts with high catalytic activity and durability are needed for environmentally clean energy technologies such as water-splitting devices and metal-air batteries. Herein, we investigate a new catalyst, P-3G, consisting of a cation-ordered perovskite (PrBa0.5Sr0.5)0.95Co1.5Fe0.5O5+δ (PBSCF) and 3D porous N-doped graphene (3DNG). This new type of composite electrocatalyst simultaneously exhibited outstanding multifunctional catalytic activities and excellent stabilities for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). A possible mechanism for the synergistic effects between perovskite oxides and 3DNG on ORR, OER and HER was firstly proposed by DFT calculations. The electrocatalytic activity of P-3G appeared to have great potential for a rechargeable Zn-air battery system. The operating voltage differences between the charge and discharge (Δ<I>η</I>) of P-3G and Pt/C-IrO2 after 110 cycles were 0.63 V and 0.87 V, respectively, indicating the substantial durability of P-3G. Moreover, a water-splitting device using P-3G efficiently produced H2 and O2 gases at rates of 0.859 μL s<SUP>−1</SUP> and 0.417 μL s<SUP>−1</SUP>, respectively. This study highlights extended applications of coupled perovskite oxides/carbon materials as versatile electrocatalysts for ORR, OER, and HER and unveils the cause of synergistic interactions between oxide and carbon by DFT calculation.</P>
Wang, Shuai,Nam, Gyutae,Li, Ping,Jang, Haeseong,Wang, Jia,Kim, Min Gyu,Wu, Zexing,Liu, Xien,Cho, Jaephil The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.33
<P>Developing highly efficient non-noble metal electrocatalysts for oxygen electrode reactions is highly desirable for industrial scale application in energy related devices. Herein, two new kinds of Ni (POxN3−x)2/NPC and Co (POxN3−x)2/NPC (NPC: N, P-co-doped carbon) are synthesized through a facile post-treatment of nickel- or cobalt-phytic acid xerogel, followed by an annealing procedure under an argon and ammonia atmosphere at 800 °C. The as-prepared catalysts exhibit outstanding catalytic activities for both the oxygen reduction and evolution reactions, which are comparable to those of Pt/C and IrO2. Furthermore, the primary zinc-air batteries assembled with Ni (POxN3−x)2/NPC and Co (POxN3−x)2/NPC as the cathodes show gravimetric energy densities of 894 and 836 W h kgZn<SUP>−1</SUP>, which are superior to that of Pt/C (793 W h kgZn<SUP>−1</SUP>). In addition, the rechargeable zinc-air battery assembled with Ni (POxN3−x)2/NPC exhibits an excellent round-trip efficiency, which is shown by a slight increase in the sum of the overpotentials for discharge-charge cycling at a current density of 20 mA cm<SUP>−2</SUP>, even after experiencing 33 h of testing. To the best of our knowledge, there are few reports on metaphosphate salts where oxygen is partially replaced by nitrogen as bifunctional oxygen electrode catalysts for zinc-air batteries. This work provides an easy, low-cost and scalable avenue to develop new kinds of catalyst for application in energy devices.</P>
Park, Minjoon,Jeon, In-Yup,Ryu, Jaechan,Jang, Haeseong,Back, Jong-Beom,Cho, Jaephil Elsevier 2016 Nano energy Vol.26 No.-
<P><B>Abstract</B></P> <P>The catalytic activity of V<SUP>2+</SUP>/V<SUP>3+</SUP> and VO<SUP>2+</SUP>/VO<SUB>2</SUB> <SUP>+</SUP> redox couples on the halogen-doped graphene nanoplatelets (F-, Cl-, and Br-GNPs) is studied by ball-milling graphite flakes with fluorine (F<SUB>2</SUB>), chlorine (Cl<SUB>2</SUB>), and bromine (Br<SUB>2</SUB>) molecules, respectively. Using the edge-selectively halogenated graphene materials with different edge exfoliation degrees, the vanadium redox reactions can be significantly facilitated by having abundant edge defects with large surface area in the order: Br-GNP>Cl-GNP>F-GNP. The influence of halogen functionalization on graphene nanoplatelets towards vanadium redox couples is further confirmed by stack-type vanadium redox flow batteries that demonstrates better cell performance than graphene nanoplatelets without dopant at the edges. Notably, the Br-GNP showed unique electrochemical performance of increased initial charge/discharge capacity and improved rate capability, respectively. It was found that halogen doping on graphene-based materials can promote vanadium redox reactions by creating effective active sites, and the electrocatalytic activity is dependent on edge exfoliation degree and well-preserved basal planes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Edge-halogenated graphene nanoplatelets for vanadium redox reactions was studied. </LI> <LI> Halogen doping on graphene-based materials can promote vanadium redox reactions. </LI> <LI> A large degree of edge exfoliation by Br facilitates mass transport of vanadium ions. </LI> <LI> Br-GNP catalyst leads to decrease of cell overpotentials in VRFBs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Bu, Yunfei,Gwon, Ohhun,Nam, Gyutae,Jang, Haeseong,Kim, Seona,Zhong, Qin,Cho, Jaephil,Kim, Guntae American Chemical Society 2017 ACS NANO Vol.11 No.11
<P>Of the various catalysts that have been developed to date for high performance and low cost, perovskite oxides have attracted attention due to their inherent catalytic activity as well as structural flexibility. In particular, high amounts of Pr substitution of the cation ordered perovskite oxide originating from the state-of-the-art Ba<SUB>0.5</SUB>Sr<SUB>0.5</SUB>Co<SUB>0.8</SUB>Fe<SUB>0.2</SUB>O<SUB>3−δ</SUB> (BSCF) electrode could be a good electrode or catalyst because of its high oxygen kinetics, electrical conductivity, oxygen capacity, and structural stability. However, even though it has many favorable intrinsic properties, the conventional high-temperature treatment for perovskite synthesis, such as solid-state reaction and combustion process, leads to the particle size increase which gives rise to the decrease in surface area and the mass activity. Therefore, we prepared mesoporous nanofibers of various cation-ordered PrBa<SUB>0.5</SUB>Sr<SUB>0.5</SUB>Co<SUB>2–<I>x</I></SUB>Fe<SUB><I>x</I></SUB>O<SUB>5+δ</SUB> (<I>x</I> = 0, 0.5, 1, 1.5, and 2) perovskites <I>via</I> electrospinning. The well-controlled B-site metal ratio and large surface area (∼20 m<SUP>2</SUP> g<SUP>–1</SUP>) of mesoporous nanofiber result in high performance of the oxygen reduction reaction and oxygen evolution reaction and stability in zinc-air battery.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2017/ancac3.2017.11.issue-11/acsnano.7b06595/production/images/medium/nn-2017-06595y_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn7b06595'>ACS Electronic Supporting Info</A></P>