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1. Carbon aerogels with atomic dispersion of binary iron–cobalt sites as effective oxygen catalysts for flexible zinc–air batteries

   https://doi.org/10.1039/d0ta04633g  

   Chen, Yang ; Hu, Shengqiang ; Nichols, Forrest ; Bridges, Frank ; Kan, Shuting ; He, Ting ; Zhang, Yi ; Chen, Shaowei ( June 2020 , Journal of Materials Chemistry A)

   null (Ed.)

   Iron single atom catalysts have emerged as one of the most active electrocatalysts towards the oxygen reduction reaction (ORR), but the unsatisfactory durability and limited activity for the oxygen evolution reaction (OER) has hampered their commercial applications in rechargeable metal–air batteries. By contrast, cobalt-based catalysts are known to afford excellent ORR stability and OER activity, due to the weak Fenton reaction and low OER Gibbs free energy. Herein, a bimetal hydrogel template is used to prepare carbon aerogels containing Fe–Co bimetal sites (NCAG/Fe–Co) as bifunctional electrocatalysts towards both ORR and OER, with enhanced activity and stability, as compared to the monometal counterparts. High-resolution transmission electron microscopy, elemental mapping and X-ray photoelectron spectroscopy measurements demonstrate homogeneous distributions of the metal centers within defected carbon lattices by coordination to nitrogen dopants. X-ray absorption spectroscopic measurements, in combination with other results, suggest the formation of FeN 3 and CoN 3 moieties on mutually orthogonal planes with a direct Fe–Co bonding interaction. Electrochemical measurements show that NCAG/Fe–Co delivers a small ORR/OER potential gap of only 0.64 V at the current density of 10 mA cm −2 , 60 mV lower than that (0.70 V) with commercial Pt/C and RuO 2 catalysts. When applied in a flexible Zn–air battery, the dual-metal NCAG/Fe–Co catalyst also shows a remarkable performance, with a high open-circuit voltage of 1.47 V, a maximum power density of 117 mW cm −2 , as well as good rechargeability and flexibility. Results from this study may offer an ingenious protocol in the design and engineering of highly efficient and durable bifunctional electrocatalysts based on dual metal-doped carbons. 

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2. Iron Active Center Coordination Reconstruction in Iron Carbide Modified on Porous Carbon for Superior Overall Water Splitting

   https://doi.org/10.1002/advs.202401455  

   Guo, Wenxin ; Li, Jinlong ; Chai, Dong‐Feng ; Guo, Dongxuan ; Sui, Guozhe ; Li, Yue ; Luo, Dan ; Tan, Lichao ( April 2024 , Advanced Science)

   In this work, a novel liquid nitrogen quenching strategy is engineered to fulfill iron active center coordination reconstruction within iron carbide (Fe₃C) modified on biomass‐derived nitrogen‐doped porous carbon (NC) for initiating rapid hydrogen and oxygen evolution, where the chrysanthemum tea (elm seeds, corn leaves, and shaddock peel, etc.) is treated as biomass carbon source within Fe₃C and NC. Moreover, the original thermodynamic stability is changed through the corresponding force generated by liquid nitrogen quenching and the phase transformation is induced with rich carbon vacancies with the increasing instantaneous temperature drop amplitude. Noteworthy, the optimizing intermediate absorption/desorption is achieved by new phases, Fe coordination, and carbon vacancies. The Fe₃C/NC‐550 (550 refers to quenching temperature) demonstrates outstanding overpotential for hydrogen evolution reaction (26.3 mV at −10 mA cm⁻²) and oxygen evolution reaction (281.4 mV at 10 mA cm⁻²), favorable overall water splitting activity (1.57 V at 10 mA cm⁻²). Density functional theory (DFT) calculations further confirm that liquid nitrogen quenching treatment can enhance the intrinsic electrocatalytic activity efficiently by optimizing the adsorption free energy of reaction intermediates. Overall, the above results authenticate that liquid nitrogen quenching strategy open up new possibilities for obtaining highly active electrocatalysts for the new generation of green energy conversion systems.

    

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3. Highly selective oxygen reduction to hydrogen peroxide on transition metal single atom coordination

   https://doi.org/10.1038/s41467-019-11992-2  

   Jiang, Kun ; Back, Seoin ; Akey, Austin J. ; Xia, Chuan ; Hu, Yongfeng ; Liang, Wentao ; Schaak, Diane ; Stavitski, Eli ; Nørskov, Jens K. ; Siahrostami, Samira ; et al ( September 2019 , Nature Communications)

   Shifting electrochemical oxygen reduction towards 2e^–pathway to hydrogen peroxide (H₂O₂), instead of the traditional 4e^–to water, becomes increasingly important as a green method for H₂O₂generation. Here, through a flexible control of oxygen reduction pathways on different transition metal single atom coordination in carbon nanotube, we discovered Fe-C-O as an efficient H₂O₂catalyst, with an unprecedented onset of 0.822 V versus reversible hydrogen electrode in 0.1 M KOH to deliver 0.1 mA cm⁻²H₂O₂current, and a high H₂O₂selectivity of above 95% in both alkaline and neutral pH. A wide range tuning of 2e^–/4e^–ORR pathways was achieved via different metal centers or neighboring metalloid coordination. Density functional theory calculations indicate that the Fe-C-O motifs, in a sharp contrast to the well-known Fe-C-N for 4e^–, are responsible for the H₂O₂pathway. This iron single atom catalyst demonstrated an effective water disinfection as a representative application.

    

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4. MitoBK Ca channel is functionally associated with its regulatory β1 subunit in cardiac mitochondria

   https://doi.org/10.1113/JP277769  

   Balderas, Enrique ; Torres, Natalia S. ; Rosa‐Garrido, Manuel ; Chaudhuri, Dipayan ; Toro, Ligia ; Stefani, Enrico ; Olcese, Riccardo ( July 2019 , The Journal of Physiology)

   Association of plasma membrane BK_Cachannels with BK‐β subunits shapes their biophysical properties and physiological roles; however, functional modulation of the mitochondrial BK_Cachannel (mitoBK_Ca) by BK‐β subunits is not established.

   MitoBK_Ca‐α and the regulatory BK‐β1 subunit associate in mouse cardiac mitochondria.

   A large fraction of mitoBK_Cadisplay properties similar to that of plasma membrane BK_Cawhen associated with BK‐β1 (left‐shifted voltage dependence of activation,V_1/2 = −55 mV, 12 µmmatrix Ca²⁺).

   In BK‐β1 knockout mice, cardiac mitoBK_Cadisplayed a lowP_oand a depolarizedV_1/2of activation (+47 mV at 12 µmmatrix Ca²⁺)

   Co‐expression of BK_Cawith the BK‐β1 subunit in HeLa cells doubled the density of BK_Cain mitochondria.

   The present study supports the view that the cardiac mitoBK_Cachannel is functionally modulated by the BK‐β1 subunit; proper targeting and activation of mitoBK_Cashapes mitochondrial Ca²⁺handling.

   Association of the plasma membrane BK_Cachannel with auxiliary BK‐β1–4 subunits profoundly affects the regulatory mechanisms and physiological processes in which this channel participates. However, functional association of mitochondrial BK (mitoBK_Ca) with regulatory subunits is unknown. We report that mitoBK_Cafunctionally associates with its regulatory subunit BK‐β1 in adult rodent cardiomyocytes. Cardiac mitoBK_Cais a calcium‐ and voltage‐activated channel that is sensitive to paxilline with a large conductance for K⁺of 300 pS. Additionally, mitoBK_Cadisplays a high open probability (P_o) and voltage half‐activation (V_1/2 = −55 mV,n = 7) resembling that of plasma membrane BK_Cawhen associated with its regulatory BK‐β1 subunit. Immunochemistry assays demonstrated an interaction between mitochondrial BK_Ca‐α and its BK‐β1 subunit. Mitochondria from the BK‐β1 knockout (KO) mice showed sparse mitoBK_Cacurrents (five patches with mitoBK_Caactivity out of 28 total patches fromn = 5 different hearts), displaying a depolarizedV_1/2of activation (+47 mV in 12 µmmatrix Ca²⁺). The reduced activity of mitoBK_Cawas accompanied by a high expression of BK_Catranscript in the BK‐β1 KO, suggesting a lower abundance of mitoBK_Cachannels in this genotype. Accordingly, BK‐β1subunit increased the localization of BKDEC (i.e. the splice variant of BK_Cathat specifically targets mitochondria) into mitochondria by two‐fold. Importantly, both paxilline‐treated and BK‐β1 KO mitochondria displayed a more rapid Ca²⁺overload, featuring an early opening of the mitochondrial transition pore. We provide strong evidence that mitoBK_Caassociates with its regulatory BK‐β1 subunit in cardiac mitochondria, ensuring proper targeting and activation of the mitoBK_Cachannel that helps to maintain mitochondrial Ca²⁺homeostasis.

    

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5. Facile Functionalization of Graphene to Tune Response of Printed Electrochemical Sensors to Neurotransmitters

   https://doi.org/10.1149/MA2023-01532651mtgabs  

   Kammarchedu, Vinay ; Butler, Derrick ; Khamsi, Pouya Soltan ; Ebrahimi, Aida ( August 2023 , ECS Meeting Abstracts)

   Neurotransmitters are small molecules involved in neuronal signaling and can also serve as stress biomarkers.¹Their abnormal levels have been also proposed to be indicative of several neurological diseases such as Alzheimer’s disease, Parkinson’s disease, Huntington disease, among others. Hence, measuring their levels is highly important for early diagnosis, therapy, and disease prognosis. In this work, we investigate facile functionalization methods to tune and enhance sensitivity of printed graphene sensors to neurotransmitters. Sensors based on direct laser scribing and screen-printed graphene ink are studied. These printing methods offer ease of prototyping and scalable fabrication at low cost.

   The effect of functionalization of laser induced graphene (LIG) by electrodeposition and solution-based deposition of TMDs (molybdenum disulfide²and tungsten disulfide) and metal nanoparticles is studied. For different processing methods, electrochemical characteristics (such as electrochemically active surface area: ECSA and heterogenous electron transfer rate: k⁰) are extracted and correlated to surface chemistry and defect density obtained respectively using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. These functionalization methods are observed to directly impact the sensitivity and limit of detection (LOD) of the graphene sensors for the studied neurotransmitters. For example, as compared to bare LIG, it is observed that electrodeposition of MoS₂on LIG improves ECSA by 3 times and k⁰by 1.5 times.³Electrodeposition of MoS₂also significantly reduces LOD of serotonin and dopamine in saliva, enabling detection of their physiologically relevant concentrations (in pM-nM range). In addition, chemical treatment of LIG sensors is carried out in the form of acetic acid treatment. Acetic acid treatment has been shown previously to improve C-C bonds improving the conductivity of LIG sensors.⁴In our work, in particular, acetic acid treatment leads to larger improvement of LOD of norepinephrine compared to MoS₂electrodeposition.

   In addition, we investigate the effect of plasma treatment to tune the sensor response by modifying the defect density and chemistry. For example, we find that oxygen plasma treatment of screen-printed graphene ink greatly improves LOD of norepinephrine up to three orders of magnitude, which may be attributed to the increased defects and oxygen functional groups on the surface as evident by XPS measurements. Defects are known to play a key role in enhancing the sensitivity of 2D materials to surface interactions, and have been explored in tuning/enhancing the sensor sensitivity.⁵Building on our previous work,³we apply a custom machine learning-based data processing method to further improve that sensitivity and LOD, and also to automatically benchmark different molecule-material pairs.

   Future work includes expanding the plasma chemistry and conditions, studying the effect of precursor mixture in laser-induced solution-based functionalization, and understanding the interplay between molecule-material system. Work is also underway to improve the machine learning model by using nonlinear learning models such as neural networks to improve the sensor sensitivity, selectivity, and robustness.

   References

   A. J. Steckl, P. Ray, (2018), doi:10.1021/acssensors.8b00726.

   Y. Lei, D. Butler, M. C. Lucking, F. Zhang, T. Xia, K. Fujisawa, T. Granzier-Nakajima, R. Cruz-Silva, M. Endo, H. Terrones, M. Terrones, A. Ebrahimi,Sci. Adv.6, 4250–4257 (2020).

   V. Kammarchedu, D. Butler, A. Ebrahimi,Anal. Chim. Acta.1232, 340447 (2022).

   H. Yoon, J. Nah, H. Kim, S. Ko, M. Sharifuzzaman, S. C. Barman, X. Xuan, J. Kim, J. Y. Park,Sensors Actuators B Chem.311, 127866 (2020).

   T. Wu, A. Alharbi, R. Kiani, D. Shahrjerdi,Adv. Mater.31, 1–12 (2019).

    

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