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1. Kinetically Stable Oxide Overlayers on Mo ₃ P Nanoparticles Enabling Lithium–Air Batteries with Low Overpotentials and Long Cycle Life

   https://doi.org/10.1002/adma.202004028  

   Kondori, Alireza; Jiang, Zhen; Esmaeilirad, Mohammadreza; Tamadoni_Saray, Mahmoud; Kakekhani, Arvin; Kucuk, Kamil; Navarro_Munoz_Delgado, Pablo; Maghsoudipour, Sadaf; Hayes, John; Johnson, Christopher_S; et al (November 2020, Advanced Materials)

   Abstract The main drawbacks of today's state‐of‐the‐art lithium–air (Li–air) batteries are their low energy efficiency and limited cycle life due to the lack of earth‐abundant cathode catalysts that can drive both oxygen reduction and evolution reactions (ORR and OER) at high rates at thermodynamic potentials. Here, inexpensive trimolybdenum phosphide (Mo₃P) nanoparticles with an exceptional activity—ORR and OER current densities of 7.21 and 6.85 mA cm⁻²at 2.0 and 4.2 V versus Li/Li⁺, respectively—in an oxygen‐saturated non‐aqueous electrolyte are reported. The Tafel plots indicate remarkably low charge transfer resistance—Tafel slopes of 35 and 38 mV dec⁻¹for ORR and OER, respectively—resulting in the lowest ORR overpotential of 4.0 mV and OER overpotential of 5.1 mV reported to date. Using this catalyst, a Li–air battery cell with low discharge and charge overpotentials of 80 and 270 mV, respectively, and high energy efficiency of 90.2% in the first cycle is demonstrated. A long cycle life of 1200 is also achieved for this cell. Density functional theory calculations of ORR and OER on Mo₃P (110) reveal that an oxide overlayer formed on the surface gives rise to the observed high ORR and OER electrocatalytic activity and small discharge/charge overpotentials. 

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2. Unexpected effect of an axial ligand mutation in the type 1 copper center in small laccase: structure-based analyses and engineering to increase reduction potential and activity

   https://doi.org/10.1039/D5SC02177D  

   Wang, Jing-Xiang; Vilbert, Avery C; Williams, Lucas H; Mirts, Evan N; Cui, Chang; Lu, Yi (January 2025, Chemical Science)

   Type 1 copper (T1Cu) centers are crucial in biological electron transfer (ET) processes, exhibiting a wide range of reduction potentials (E°′T1Cu) to match their redox partners and optimize ET rates. While tuning E°′T1Cu in mononuclear T1Cu proteins like azurin has been successful, it is more difficult for multicopper oxidases. Specifically, while replacing axial methionine to leucine in azurin increased its E°′T1Cu by ~100 mV, the corresponding M298L mutation in small laccase from Streptomyces coelicolor (SLAC) unexpectedly decreased its E°′T1Cu by 12 mV. X-ray crystallography revealed two axial water molecules in M298L-SLAC, leading to the decrease of E°′T1Cu due to decreased hydrophobicity. Structural alignment and molecular dynamics simulation indicated a key difference in T1Cu axial loop position, leading to the different outcome upon methionine to leucine mutation. Based on structural analyses, we introduced additional F195L and I200F mutations, leading to partial removal of axial waters, a 122-mV increase in E°′T1Cu, and a 7-fold increase in kcat/KM from M298L-SLAC. These findings highlight the complexity of tuning E°′T1Cu in multicopper oxidases and provide valuable insights into how structure-based protein engineering can contribute to the broader understanding of T1Cu center, E°′T1Cu and reactivity tuning for applications in solar energy transfer, fuel cells, and bioremediation. 

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3. Sulfur incorporation into NiFe oxygen evolution electrocatalysts for improved high current density operation

   https://doi.org/10.1039/d2ma00902a  

   Wang, Jiaying; Barforoush, Joseph M.; Leonard, Kevin C. (January 2023, Materials Advances)

   The efficient production of green hydrogen via electrochemical water splitting is important for improving the sustainability and enabling the electrification of the chemical industry. One of the major goals of water electrolysis is to utilize non-precious metal catalysts, which can be accomplished with alkaline electrolyzer technologies. However, there is a continuing need for designing catalysts that can operate in alkaline environments with high efficiencies under high current densities. Here we describe a simple, aqueous-based synthesis method to incorporate sulfur into NiFe-based electrocatalysts for the oxygen evolution reaction (OER). Sulfur incorporation was able to reduce the overpotential for the OER from ca. 350 mV on a NiFe catalyst to ca. 290 mV on the NiFeS catalyst at 100 mA cm −2 on a flat supporting electrode. Electrochemical impedance spectroscopy data showed a small decrease in the charge transfer resistance of the NiFeS catalysts, showing that sulfur incorporation may improve the electronic conductivity. Surface-interrogation scanning electrochemical microscopy (SI-SECM) studies combined with Tafel slope analysis suggested that the NiFeS catalyst was able to have vacant surface sites available under OER conditions and was able to maintain a Tafel slope of 39 mV dec −1 . This is in contrast to the NiFe catalyst, for which the SI-SECM studies showed a saturated surface under OER conditions with the Tafel slope transitioning from 39 mV dec −1 to 118 mV dec −1 . The low Tafel slope enabled the NiFeS catalyst to maintain low overpotentials under high current densities, which we attribute to the ability of the NiFeS catalyst to maintain vacant sites during the OER. 

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4. Resonance Raman spectra and excited state properties of methyl viologen and its radical cation from time‐dependent density functional theory

   https://doi.org/10.1002/jcc.27207  

   Ozuguzel, Umut; Aquino, Adelia J. A.; Nieman, Reed; Minteer, Shelley D.; Korzeniewski, Carol (August 2023, Journal of Computational Chemistry)

   Abstract Time‐dependent density functional theory (TDDFT) was applied to gain insights into the electronic and vibrational spectroscopic properties of an important electron transport mediator, methyl viologen (MV²⁺). An organic dication, MV²⁺has numerous applications in electrochemistry that include energy conversion and storage, environmental remediation, and chemical sensing and electrosynthesis. MV²⁺is easily reduced by a single electron transfer to form a radical cation species (MV^•+), which has an intense UV–visible absorption near 600 nm. The redox properties of the MV²⁺/MV^•+couple and light‐sensitivity of MV^•+have made the system appealing for photo‐electrochemical energy conversion (e.g., solar hydrogen generation from water) and the study of photo‐induced charge transfer processes through electronic absorption and resonance Raman spectroscopic measurements. The reported work applies leading TDDFT approaches to investigate the electronic and vibrational spectroscopic properties of MV²⁺and MV^•+. Using a conventional hybrid exchange functional (B3‐LYP) and a long‐range corrected hybrid exchange functional (ωB97X‐D3), including with a conductor‐like polarizable continuum model to account for solvation, the electronic absorption and resonance Raman spectra predicted are in good agreement with experiment. Also analyzed are the charge transfer character and natural transition orbitals derived from the TDDFT vertical excitations calculated. The findings and models developed further the understanding of the electronic properties of viologens and related organic redox mediators important in renewable energy applications and serve as a reference for guiding the interpretation of electronic absorption and Raman spectra of the ions. 

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5. Energy transfer and thermoelectricity in molecular junctions in non-equilibrated solvents

   https://doi.org/10.1063/5.0086319  

   Kirchberg, Henning; Nitzan, Abraham (March 2022, The Journal of Chemical Physics)

   We consider a molecular junction immersed in a solvent where the electron transfer is dominated by Marcus-type steps. However, the successive nature of the charge transfer through the junction does not imply that the solvent reaches thermal equilibrium throughout the transport. In our previous work [Kirchberg et al., J. Phys. Chem. Lett. 11, 1729 (2020)], we have determined the nonequilibrium distribution of the solvent where its dynamics, expressed by a friction, is considered in two limiting regimes of fast and slow solvent relaxation. In dependence of the nonequilibrium solvent dynamics, we investigate now the electrical, thermal, and thermoelectric properties of the molecular junction. We show that by suitable tuning of the friction, we can reduce the heat dissipation into the solvent and enhance the heat transfer between the electrodes. Interestingly, we find that the Seebeck coefficient grows significantly by adapting the solvent friction in both regimes. 

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