Successfully predicted electrical conductivity and energy level according to the relative fusion ratio.
Synthesized high-performance dual-phase electrochemical catalyst, which layered a 6:4 ratio nickel-silver (Ag0.6Ni0.4) on a three-dimensional cobalt-niobium oxide (CoNb2O6) nanocube structure 1.4 times the charging capacity of existing Zn-Air (metal-air) secondary batteries and 3.8 times the stability
Published in the latest issue of ‘Applied Catalysis B: Environmental,’ the top international journal in the field of energy and environment

Demand continues to rise as the application fields for secondary batteries, such as mobile electronic gadgets and electric vehicles, expand. While traditional lithium-ion-based secondary batteries have such problems as the risk of explosion and limited charge capacity, Zn-Air (metal-air) batteries have several advantages, such as relatively high energy density, low cost, and high stability, and are regarded as superior secondary batteries when compared to existing lithium-ion batteries.

However, a new highly active catalyst was developed because the carbon cathode employed for the air contact surface lacks an efficient electrochemical OER-ORR (oxygen generation-oxygen reduction reaction). As a result, because silver and nickel metals have outstanding electrochemical catalytic capabilities, research was needed to simultaneously improve battery performance and stability by maximizing their physical qualities by manufacturing them into a multi-metal alloy.

A research team led by the Dongguk University Department of Energy and Materials Engineering Research Professor Bala (first author) and Professor Kwon Soon-cheol (corresponding author) successfully developed a new dual-phase cathode material catalyst material by layering multi-metal alloy nanoparticles (AgNi, nickel silver) alloyed in a specific ratio on a unique three-dimensional metal oxide nanocube structure (CoNb2O6, cobalt-niobium oxide).

Professor Kwon's research team focused on the fact that the relative fusion ratio of AgNi multi-metal alloy catalysts can significantly contribute to electrical conductivity and energy level management and applied "Virtual Crystal Approximation" (VCA) based on density functional theory. As a result, when the relative fusion ratio of silver and nickel is 6:4, the maximum electrical conductivity (σ) is anticipated to reach ~2 x 107 S cm-1 and the work function -5.4 eV.
 

Based on this knowledge, a three-dimensional nano cube structure (cobalt niobium oxide, CoNb2O6) capable of serving as an OER was hydrothermally synthesized. Through successive hydrothermal synthesis, nickel-silver metal multi-alloy nanoparticles in a 6:4 ratio that may play the role of ORR were uniformly stacked on top of this three-dimensional structure. Consequently, the research team could create a novel high-performance two-phase catalyst material.
 

The two-phase catalyst material developed in this manner, in particular, is absorbed into the pores of the existing carbon cathode material, increasing the reaction surface area and facilitating electron, ion, and mass transfer, resulting in higher catalytic activity and Zn-Air (metal-air) battery performance when compared to the existing carbon electrode. The charging capacity of the Zn-Air battery using the two-phase catalyst material was 806.8 mAhg-1, which is more than 1.4 times greater than the 576.6 mAhg-1 of the Zn-Air battery using a single metal oxide catalyst. Furthermore, the charge/discharge performance of the two-phase catalyst Zn-Air battery was 587 hours, 3.8 times that of a single catalyst battery, due to an efficient and balanced OER-ORR reaction (156 hours).

"Through this research, we have completed a technology that can maximize and stabilize the electrical and physical characteristics of the metal multi-alloy electrochemical catalyst based on the relative fusion ratio," said Professor Kwon Soon-cheol, " We were able to develop a new high-performance two-phase electrochemical catalyst material using this technology, which is absorbed on the existing carbon electrode to enable efficient/balanced OER-ORR (oxygen generation-oxygen reduction reaction) with a larger surface area, which is significant in realizing an ultra-high performance/stability next-generation Zn-Air secondary battery," and expected, "Because the developed carbon electrode, which includes the two-phase catalyst, operates consistently for 160 hours even in a pouch cell type, we will be able to move a step closer to commercialization of next-generation thin-film or flexible secondary batteries."
 

This research was funded through the National Research Foundation of Korea's senior researcher support project and innovative and challenging research support project. The findings were published online on March 14, 2023, in Applied Catalysis B: Environmental (IF=24.319), the top international journal in the field of energy and environment, under the title <High-performance rechargeable metal-air batteries enabled by efficient charge transport in multielement random alloy electrocatalyst >.

<Prediction of energy level and electrical conductivity according to the fusion ratio of AgNi (nickel silver) multi-metal alloy catalyst using “Virtual Crystal Approximation (VCA)”>
(a) Prediction of crystal structure change depending on the relative fusion ratio of Ag and Ni
(b), (c), (d) Prediction of changes in work function, electrical conductivity, and magnetic movement depending on the relative fusion ratio of Ag and Ni.

* For inquiries regarding this material, please contact Dongguk University Professor Kwon Soon-cheol (02-2260-3678, kwansc12@dongguk.edu).