Jaechan Ryu

Corn protein-derived nitrogen-doped carbon materials with oxygen-rich functional groups: a highly efficient electrocatalyst for all-vanadium redox flow batteries

Recent studies on all-vanadium redox flow batteries (VRFBs) have focused on carbon-based materials for cost-effective electrocatalysts to commercialize them in grid-scale energy storage markets. We report an environmentally friendly and safe method to produce carbon-based catalysts by corn protein self-assembly. This new method allows carbon black (CB) nanoparticles to be coated with nitrogen-doped graphitic layers with oxygen-rich functionalities (N-CB). We observed increased catalytic activity of this catalyst toward both V2+/V3+ and VO2+/VO2+ ions, showing a 24% increased mass transfer process and ca. 50 mV higher reduction onset potential compared to CB catalyst. It is believed that the abundant oxygen active sites and nitrogen defects in the N-CB catalyst are beneficial to the vanadium redox reaction by improving the electron transfer rate and giving faster vanadium ion transfer kinetics.

Nanostructured Electrocatalysts for All-Vanadium Redox Flow Batteries.

Vanadium redox reactions have been considered as a key factor affecting the energy efficiency of the all-vanadium redox flow batteries (VRFBs). This redox reaction determines the reaction kinetics of whole cells. However, poor kinetic reversibility and catalytic activity towards the V(2+)/V(3+) and VO(2+)/VO2(+) redox couples on the commonly used carbon substrate limit broader applications of VRFBs. Consequently, modified carbon substrates have been extensively investigated to improve vanadium redox reactions. In this Focus Review, recent progress on metal- and carbon-based nanomaterials as an electrocatalyst for VRFBs is discussed in detail, without the intention to provide a comprehensive review on the whole components of the system. Instead, the focus is mainly placed on the redox chemistry of vanadium ions at a surface of various metals, different dimensional carbons, nitrogen-doped carbon nanostructures, and metal-carbon composites.

Organic-Catholyte-Containing Flexible Rechargeable Lithium Batteries

Organic-catholyte-containing flexible rechargeable lithium batteries are developed using fused cyclic quinone derivatives. The structural dependence of the quinone isomers in the liquid catholyte is studied using a combined experimental and theoretical approach. Stable electrochemical performance even under severe bending/stretching deformations is successfully demonstrated by prototype batteries containing liquid catholytes.

Material selection and optimization for highly stable composite bipolar plates in vanadium redox flow batteries

The design of a graphite-based polymer composite bipolar plate is systematically studied for the vanadium redox flow battery system by the compression molding method with different major and minor filler contents. The optimized composite bipolar plate (denoted as the f-GKB-80) composed of flake-type natural graphite (<80 μm) and ketjenblack nanoparticles (<50 nm) exhibits excellent electrical conductivity of 114 S cm−1 and flexural strength of 26 MPa at a total filler loading of 85 wt%. This result can be attributed to the well-developed conducting pathways between the natural graphite flakes that are effectively filled with the ketjenblack minor fillers. Furthermore, this sample is substantially stable even when in storage in highly oxidative V5+ electrolyte solution at 80 °C for a week. We believe this excellent stability is due to the well-established packing structures, which protect it from concentrated acid-based electrolytes. Significantly, the f-GKB-80 demonstrates enhanced rate capability stable cycling performance, including only a 0.87% decay in energy efficiency for 50 cycles compared with commercial graphite plates (2.5% decay in energy efficiency).

Seed-mediated atomic-scale reconstruction of silver manganate nanoplates for oxygen reduction towards high-energy aluminum-air flow batteries

Aluminum–air batteries are promising candidates for next-generation high-energy-density storage, but the inherent limitations hinder their practical use. Here, we show that silver nanoparticle-mediated silver manganate nanoplates are a highly active and chemically stable catalyst for oxygen reduction in alkaline media. By means of atomic-resolved transmission electron microscopy, we find that the formation of stripe patterns on the surface of a silver manganate nanoplate originates from the zigzag atomic arrangement of silver and manganese, creating a high concentration of dislocations in the crystal lattice. This structure can provide high electrical conductivity with low electrode resistance and abundant active sites for ion adsorption. The catalyst exhibits outstanding performance in a flow-based aluminum–air battery, demonstrating high gravimetric and volumetric energy densities of ~2552 Wh kgAl−1 and ~6890 Wh lAl−1 at 100 mA cm−2, as well as high stability during a mechanical recharging process.Aluminum-air batteries are lightweight and cost effective, but performance is limited by corrosion and solid by-products. Here the authors catalyze oxygen reduction with silver manganate nanoplates and develop an aluminum-air flow battery that delivers high energy density and alleviates side reactions.

Nonaqueous arylated quinone catholytes for lithium–organic flow batteries

Chemically modified organic redox couples have the advantages of tunable redox properties, high solubility, environmental benignity, and cost effectiveness. Inspired by nature, a series of quinone derivatives bearing electron-donating methoxy or electron-withdrawing trifluoromethyl groups are synthesized in moderate to high yields by Pd-catalyzed Suzuki cross-coupling reactions. This study utilizes the synthetic quinones as redox-active organic molecules for nonaqueous lithium–organic flow batteries. The aryl moiety incorporated quinone scaffolds show enhanced electrochemical stability and rate capability. The nonaqueous catholyte, 2-phenyl-1,4-naphthoquinone, reaches a cell voltage of ∼2.6 V and a specific capacity of 196 mA h g−1, while the discharge capacity is retained at ∼92% for 150 cycles. Moreover, the tubular lithium–organic flow battery system features stable cycle performance under a continuous circulation without clogging-associated intermittency flow.

A Ternary Ni46Co40Fe14 Nanoalloy-Based Oxygen Electrocatalyst for Highly Efficient Rechargeable Zinc-Air Batteries

Replacing noble-metal-based oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts is the key to developing efficient Zn-air batteries (ZABs). Here, a homogeneous ternary Ni46 Co40 Fe14 nanoalloy with a size distribution of 30-60 nm dispersed in a carbon matrix (denoted as C@NCF-900) as a highly efficient bifunctional electrocatalyst produced via supercritical reaction and subsequent heat treatment at 900 °C is reported. Among all the transition-metal-based electrocatalysts, the C@NCF-900 exhibits the highest ORR performance in terms of half-wave potential (0.93 V) in 0.1 m KOH. Moreover, C@NCF-900 exhibits negligible activity decay after 10 000 voltage cycles with minor reduction (0.006 V). In ZABs, C@NCF-900 outperforms the mixture of Pt/C 20 wt% and IrO2 , cycled over 100 h under 58% depth of discharge condition. Furthermore, density functional theory (DFT) calculations and in situ X-ray absorption spectroscopy strongly support the active sites and site-selective reaction as a plausible ORR/OER mechanism of C@NCF-900.