Showing papers by "Rodney S. Ruoff published in 2023"
13 citations
TL;DR: In this paper , a redox-active quinone-based porous organic polymer (rPOP) was synthesized and studied and found ultralong cycle life: it is a promising organic cathode for aqueous zinc-ion batteries.
Abstract: We synthesized and studied a redox-active quinone-based porous organic polymer (rPOP) and found ultralong cycle life: it is a promising organic cathode for aqueous zinc-ion batteries (ZIBs). It has high physicochemical stability and enhanced intrinsic conductivity from its fused-aromatic conjugated skeleton. rPOP’s high porosity allows for efficient Zn2+ infiltration through the pores during charging–discharging cycles and contributes to the efficient utilization of redox-active quinone units. It delivers a specific capacity of 120 mAh g–1 at a current density of 0.1 A g–1 with a flat and long discharge plateau, which is critically important to provide a stable voltage output. It provides ultralong cycle life at a current density of 1.0 A g–1 for 1000 and at 2.0 A g–1 for 30 000 cycles, with initial capacity retention of 95 and 66%, respectively. The co-insertion (Zn2+ and H+) charge storage mechanism was investigated using various electrochemical measurements and ex/in situ structural characterization techniques, and is explained herein. These findings contribute to a better understanding of the structure–property relationship for rPOP and open a new avenue for new organic cathode materials for high-performance next-generation aqueous batteries.
TL;DR: In this article , a density functional theory-based molecular dynamics (DFT-MD) was used to examine the mechanism of single-crystal diamond growth on various low-index crystallographic diamond surfaces (100, (110), and (111) in liquid Ga with CH4.
Abstract: Ruoff and co-workers recently demonstrated low-temperature (1193 K) homoepitaxial diamond growth from liquid gallium solvent. To develop an atomistic mechanism for diamond growth underlying this remarkable demonstration, we carried out density functional theory-based molecular dynamics (DFT-MD) simulations to examine the mechanism of single-crystal diamond growth on various low-index crystallographic diamond surfaces (100), (110), and (111) in liquid Ga with CH4. We find that carbon linear chains form in liquid Ga and then react with the growing diamond surface, leading first to the formation of carbon rings on the surface and then initiation of diamond growth. Our simulations find faster growth on the (110) surface than on the (100) or (111) surfaces, suggesting the (110) surface as a plausible growth surface in liquid Ga. For (110) surface growth, we predict the optimum growth temperature to be ∼1300 K, arising from a balance between the kinetics of forming carbon chains dissolved in Ga and the stability of carbon rings on the growing surface. We find that the rate-determining step for diamond growth is dehydrogenation of the growing hydrogenated (110) surface of diamond. Inspired by the recent experimental studies by Ruoff and co-workers demonstrating that Si accelerates diamond growth in Ga, we show that addition of Si into liquid Ga significantly increases the rate of dehydrogenating the growing surface. Extrapolating from the DFT-MD predicted rates at 2800 to 3500 K, we predict the growth rate at the experimental growth temperature of 1193 K, leading to rates in reasonable agreement with the experiment. These fundamental mechanisms should provide guidance in optimizing low-temperature diamond growth.