Publications

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2024
Krishnamoorthy, V, Bangolla HK, Chen C-Y, Huang Y-T, Cheng C-M, Ulaganathan RK, Sankar R, Lee K-Y, Du H-Y, Chen L-C, Chen K-H, Chen R-S.  2024.  Efficient Hydrogen Evolution Reaction in 2H-MoS2 Basal Planes Enhanced by Surface Electron Accumulation, 2024. Catalysts. 14(1) Abstract

An innovative strategy has been developed to activate the basal planes in molybdenum disulfide (MoS2) to improve their electrocatalytic activity by controlling surface electron accumulation (SEA) through aging, annealing, and nitrogen-plasma treatments. The optimal hydrogen evolution reaction (HER) performance was obtained on the surface treated with nitrogen-plasma for 120 s. An overpotential of 0.20 V and a Tafel slope of 120 mV dec−1 were achieved for the optimized condition. The angle-resolved photoemission spectroscopy measurement confirmed the HER efficiency enhanced by the SEA conjugated with the sulfur vacancy active sites in the MoS2 basal planes. This study provides new insight into optimizing MoS2 catalysts for energy applications.

2022
Bayikadi, KS, Imam S, Ubaid M, Aziz A, Chen K-H, Sankar R.  2022.  Effect of aliovalent substituted highly disordered GeTe compound's thermoelectric performance, 2022. 922:166221. AbstractWebsite

As a lead-free high-performance thermoelectric material, germanium telluride (GeTe) has recently been extensively studied for mid-temperature (500–800 K) applications. The carrier concentration and the thermal conductivity are reduced for vacancy-controlled GeTe compounds compared with pristine GeTe. We explored and optimized the Ge0.9−xSb0.1PxTe (x = 0.01–0.05) material's highest thermoelectric performance at elevated temperatures. Intrinsic Ge vacancy control and manipulation of Ge (+2) with Sb/P (+3) increased the charge contribution to power factor improvement to ∼42 µWcm−1 K−2 while minimizing the lattice thermal contribution to ∼0.4 W/mK. This resulted in an increase in thermoelectric performance of ∼2.4 @ 773 K for the Ge0.88Sb0.1P0.02Te sample. The inclusion of atomically disordered Sb/P ions considerably increases the scattering effects caused by the point defect, whereas stretched grain boundaries reveal the decreased lattice thermal contribution. The current work demonstrates the effectiveness of phosphorus as a co-dopant in increasing the average thermoelectric performance (ZTavg) value over the GeTe operating temperature range.

2021
Samireddi, S, Aishwarya V, Shown I, Muthusamy S, Unni SM, Wong K-T, Chen K-H, Chen L-C.  2021.  Synergistic Dual-Atom Molecular Catalyst Derived from Low-Temperature Pyrolyzed Heterobimetallic Macrocycle-N4 Corrole Complex for Oxygen Reduction. Small. 17:2103823., Number 46 AbstractWebsite

Abstract A heterobimetallic corrole complex, comprising oxygen reduction reaction (ORR) active non-precious metals Co and Fe with a corrole-N4 center (PhFCC), is successfully synthesized and used to prepare a dual-atom molecular catalyst (DAMC) through subsequent low-temperature pyrolysis. This low-temperature pyrolyzed electrocatalyst exhibited impressive ORR performance, with onset potentials of 0.86 and 0.94 V, and half-wave potentials of 0.75 and 0.85 V, under acidic and basic conditions, respectively. During potential cycling, this DAMC displayed half-wave potential losses of only 25 and 5 mV under acidic and alkaline conditions after 3000 cycles, respectively, demonstrating its excellent stability. Single-cell Nafion-based proton exchange membrane fuel cell performance using this DAMC as the cathode catalyst showed a maximum power density of 225 mW cm−2, almost close to that of most metal–N4 macrocycle-based catalysts. The present study showed that preservation of the defined CoN4 structure along with the cocatalytic Fe–Cx site synergistically acted as a dual ORR active center to boost overall ORR performance. The development of DAMC from a heterobimetallic CoN4-macrocyclic system using low-temperature pyrolysis is also advantageous for practical applications.

2019
Pathak, A, Shen J-W, Usman M, Wei L-F, Mendiratta S, Chang Y-S, Sainbileg B, Ngue C-M, Chen R-S, Hayashi M, Luo T-T, Chen F-R, Chen K-H, Tseng T-W, Chen L-C, Lu K-L.  2019.  Integration of a (–Cu–S–)n plane in a metal–organic framework affords high electrical conductivity, 2019. 10(1):1721. AbstractWebsite

Designing highly conducting metal–organic frameworks (MOFs) is currently a subject of great interest for their potential applications in diverse areas encompassing energy storage and generation. Herein, a strategic design in which a metal–sulfur plane is integrated within a MOF to achieve high electrical conductivity, is successfully demonstrated. The MOF {[Cu2(6-Hmna)(6-mn)]·NH4}n (1, 6-Hmna = 6-mercaptonicotinic acid, 6-mn = 6-mercaptonicotinate), consisting of a two dimensional (–Cu–S–)n plane, is synthesized from the reaction of Cu(NO3)2, and 6,6′-dithiodinicotinic acid via the in situ cleavage of an S–S bond under hydrothermal conditions. A single crystal of the MOF is found to have a low activation energy (6 meV), small bandgap (1.34 eV) and a highest electrical conductivity (10.96 S cm−1) among MOFs for single crystal measurements. This approach provides an ideal roadmap for producing highly conductive MOFs with great potential for applications in batteries, thermoelectric, supercapacitors and related areas.

2017
Pathak, A, Chiou GR, Gade NR, Usman M, Mendiratta S, Luo T-T, Tseng TW, Chen J-W, Chen F-R, Chen K-H, Chen L-C, Lu K-L.  2017.  High-κ Samarium-Based Metal–Organic Framework for Gate Dielectric Applications. ACS Appl. Mater. Interfaces. 9(26):21872–21878.