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Item Atomic Structure Evolution of Pt–Co Binary Catalysts: Single Metal Sites versus Intermetallic Nanocrystals(Wiley, 2021-12) Li, Xing; He, Yanghua; Cheng, Shaobo; Li, Boyang; Zeng, Yachao; Xie, Zhenhua; Meng, Qingping; Qingping, Lu; Kisslinger, Kim; Tong, Xiao; Hwang, Sooyeon; Yao, Siyu; Li, Chenzhao; Qiao, Zhi; Shan, Chongxin; Zhu, Yimei; Xie, Jian; Wang, Guofeng; Wu, Gang; Su, Dong; Mechanical and Energy Engineering, School of Engineering and TechnologyDue to their exceptional catalytic properties for the oxygen reduction reaction (ORR) and other crucial electrochemical reactions, PtCo intermetallic nanoparticle (NP) and single atomic (SA) Pt metal site catalysts have received considerable attention. However, their formation mechanisms at the atomic level during high-temperature annealing processes remain elusive. Here, the thermally driven structure evolution of Pt–Co binary catalyst systems is investigated using advanced in situ electron microscopy, including PtCo intermetallic alloys and single Pt/Co metal sites. The pre-doping of CoN4 sites in carbon supports and the initial Pt NP sizes play essential roles in forming either Pt3Co intermetallics or single Pt/Co metal sites. Importantly, the initial Pt NP loadings against the carbon support are critical to whether alloying to L12-ordered Pt3Co NPs or atomizing to SA Pt sites at high temperatures. High Pt NP loadings (e.g., 20%) tend to lead to the formation of highly ordered Pt3Co intermetallic NPs with excellent activity and enhanced stability toward the ORR. In contrast, at a relatively low Pt loading (<6 wt%), the formation of single Pt sites in the form of PtC3N is thermodynamically favorable, in which a synergy between the PtC3N and the CoN4 sites could enhance the catalytic activity for the ORR, but showing insufficient stability.Item Atomically dispersed iron sites with a nitrogen–carbon coating as highly active and durable oxygen reduction catalysts for fuel cells(Springer Nature, 2022) Liu, Shengwen; Li, Chenzhao; Zachman, Michael J.; Zeng, Yachao; Yu, Haoran; Li, Boyang; Wang, Maoyu; Braaten, Jonathan; Liu, Jiawei; Meyer, Harry M., III; Lucero, Marcos; Kropf, A. Jeremy; Alp, Esen E.; Gong, Qing; Shi, Qiurong; Feng, Zhenxing; Xu, Hui; Wang, Guofeng; Myers, Deborah J.; Xie, Jian; Cullen, David A.; Litster, Shawn; Wu, Gang; Mechanical and Energy Engineering, School of Engineering and TechnologyNitrogen-coordinated single atom iron sites (FeN4) embedded in carbon (Fe–N–C) are the most active platinum group metal-free oxygen reduction catalysts for proton-exchange membrane fuel cells. However, current Fe–N–C catalysts lack sufficient long-term durability and are not yet viable for practical applications. Here we report a highly durable and active Fe–N–C catalyst synthesized using heat treatment with ammonia chloride followed by high-temperature deposition of a thin layer of nitrogen-doped carbon on the catalyst surface. We propose that catalyst stability is improved by converting defect-rich pyrrolic N-coordinated FeN4 sites into highly stable pyridinic N-coordinated FeN4 sites. The stability enhancement is demonstrated in membrane electrode assemblies using accelerated stress testing and a long-term steady-state test (>300 h at 0.67 V), approaching a typical Pt/C cathode (0.1 mgPt cm−2). The encouraging stability improvement represents a critical step in developing viable Fe–N–C catalysts to overcome the cost barriers of hydrogen fuel cells for numerous applications.Item Atomically dispersed single iron sites for promoting Pt and Pt3Co fuel cell catalysts: performance and durability improvements(RSC, 2021-09) Qiao, Zhi; Wang, Chenyu; Li, Chenzhao; Zeng, Yachao; Hwang, Sooyeon; Li, Boyang; Karakalos, Stavros; Park, Jaehyung; Kropf, A. Jeremy; Wegener, Evan C.; Gong, Qing; Xu, Hui; Wang, Guofeng; Myers, Deborah J.; Xie, Jian; Spendelow, Jacob S.; Wu, Gang; Mechanical and Energy Engineering, School of Engineering and TechnologySignificantly reducing platinum group metal (PGM) loading while improving catalytic performance and durability is critical to accelerating proton-exchange membrane fuel cells (PEMFCs) for transportation. Here we report an effective strategy to boost PGM catalysts through integrating PGM-free atomically-dispersed single metal active sites in the carbon support toward the cathode oxygen reduction reaction (ORR). We achieved uniform and fine Pt nanoparticle (NP) (∼2 nm) dispersion on an already highly ORR-active FeN4 site-rich carbon (FeN4–C). Furthermore, we developed an effective approach to preparing a well-dispersed and highly ordered L12 Pt3Co intermetallic nanoparticle catalyst on the FeN4–C support. DFT calculations predicted a synergistic interaction between Pt clusters and surrounding FeN4 sites through weakening O2 adsorption by 0.15 eV on Pt sites and reducing activation energy to break O–O bonds, thereby enhancing the intrinsic activity of Pt. Experimentally, we verified the synergistic effect between Pt or Pt3Co NPs and FeN4 sites, leading to significantly enhanced ORR activity and stability. Especially in a membrane electrode assembly (MEA) with a low cathode Pt loading (0.1 mgPt cm−2), the Pt/FeN4–C catalyst achieved a mass activity of 0.451 A mgPt−1 and retained 80% of the initial values after 30 000 voltage cycles (0.60 to 0.95 V), exceeding DOE 2020 targets. Furthermore, the Pt3Co/FeN4 catalyst achieved significantly enhanced performance and durability concerning initial mass activity (0.72 A mgPt−1), power density (824 mW cm−2 at 0.67 V), and stability (23 mV loss at 1.0 A cm−2). The approach to exploring the synergy between PGM and PGM-free Fe–N–C catalysts provides a new direction to design advanced catalysts for hydrogen fuel cells and various electrocatalysis processes.Item Effects of Stepwise Denervation of the Stellate Ganglion: Novel Insights from an Acute Canine Study(Elsevier, 2016-07) Wu, Gang; DeSimone, Christopher V.; Suddendorf, Scott H.; Asirvatham, Roshini S.; Asirvatham, Samuel J.; Huang, Congxin; Chen, Peng-Sheng; Cha, Yong-Mei; Department of Medicine, IU School of MedicineBackground The stellate ganglion (SG) is important for cardiac autonomic control. SG modification is an option for treating refractory ventricular tachyarrhythmias. The optimal extent of left- and right-sided SG denervation necessary for antiarrhythmic effect, however, remains to be learned. Objective The purpose of this study was to evaluate the effects of stepwise SG denervation on hemodynamic and electrophysiological parameters in dogs. Methods After sequential left and right thoracotomy in 8 healthy dogs, the SG was exposed by dissection. Two pacing wires were placed in the upper SG to deliver high-frequency stimulation. The lower SG, ansae subclaviae, and upper SG were removed in a stepwise manner. The same protocol was performed on the right side. Blood pressure (BP), heart rate, and electrophysiological parameters were recorded at baseline and after 5 minutes of stimulation. Results Systolic and diastolic BP significantly increased during stimulation of the upper left SG. The mean increase in systolic BP from baseline was 49.4 ± 26.6 mm Hg (P = .007), 25.5 ± 14.1 mm Hg after the lower SG was removed (P = .02), and 8.6 ± 3.4 mm Hg after resection of the ipsilateral ansae subclaviae (P = .048). Heart rate and other electrophysiological parameters did not change significantly. After the complete removal of the left SG, systolic BP increased by 34.0 ± 17.6 mm Hg (P = .005) after stimulation of the right SG. Conclusion Sympathetic output remains after the lower SG is removed, and sympathetic output from the right SG remains after the complete resection of the left SG and ansae subclaviae. Thus, some patients who undergo left SG denervation can still have significant sympathetic response via right SG regulation.Item Naphthoquinones Oxidize H2S to Polysulfides and Thiosulfate, Implications for Therapeutic Applications(MDPI, 2022-10-31) Olson, Kenneth R.; Clear, Kasey J.; Derry, Paul J.; Gao, Yan; Ma, Zhilin; Cieplik, Nathaniel M.; Fiume, Alyssa; Gaziano, Dominic J.; Kasko, Stephen M.; Narloch, Kathleen; Velander, Cecilia L.; Nwebube, Ifeyinwa; Pallissery, Collin J.; Pfaff, Ella; Villa, Brian P.; Kent, Thomas A.; Wu, Gang; Straub, Karl D.; Chemistry and Chemical Biology, School of Science1,4-Napththoquinones (NQs) are clinically relevant therapeutics that affect cell function through production of reactive oxygen species (ROS) and formation of adducts with regulatory protein thiols. Reactive sulfur species (RSS) are chemically and biologically similar to ROS and here we examine RSS production by NQ oxidation of hydrogen sulfide (H2S) using RSS-specific fluorophores, liquid chromatography-mass spectrometry, UV-Vis absorption spectrometry, oxygen-sensitive optodes, thiosulfate-specific nanoparticles, HPLC-monobromobimane derivatization, and ion chromatographic assays. We show that NQs, catalytically oxidize H2S to per- and polysulfides (H2Sn, n = 2−6), thiosulfate, sulfite and sulfate in reactions that consume oxygen and are accelerated by superoxide dismutase (SOD) and inhibited by catalase. The approximate efficacy of NQs (in decreasing order) is, 1,4-NQ ≈ juglone ≈ plumbagin > 2-methoxy-1,4-NQ ≈ menadione >> phylloquinone ≈ anthraquinone ≈ menaquinone ≈ lawsone. We propose that the most probable reactions are an initial two-electron oxidation of H2S to S0 and reduction of NQ to NQH2. S0 may react with H2S or elongate H2Sn in variety of reactions. Reoxidation of NQH2 likely involves a semiquinone radical (NQ·−) intermediate via several mechanisms involving oxygen and comproportionation to produce NQ and superoxide. Dismutation of the latter forms hydrogen peroxide which then further oxidizes RSS to sulfoxides. These findings provide the chemical background for novel sulfur-based approaches to naphthoquinone-directed therapies.Item Redox and Nucleophilic Reactions of Naphthoquinones with Small Thiols and Their Effects on Oxidization of H2S to Inorganic and Organic Hydropolysulfides and Thiosulfate(MDPI, 2023-04-19) Olson, Kenneth R.; Clear, Kasey J.; Gao, Yan; Ma, Zhilin; Cieplik, Nathaniel M.; Fiume, Alyssa R.; Gaziano, Dominic J.; Kasko, Stephen M.; Luu, Jennifer; Pfaff, Ella; Travlos, Anthony; Velander, Cecilia; Wilson, Katherine J.; Edwards, Elizabeth D.; Straub, Karl D.; Wu, Gang; Cellular and Integrative Physiology, School of MedicineNaphthoquinone (1,4-NQ) and its derivatives (NQs, juglone, plumbagin, 2-methoxy-1,4-NQ, and menadione) have a variety of therapeutic applications, many of which are attributed to redox cycling and the production of reactive oxygen species (ROS). We previously demonstrated that NQs also oxidize hydrogen sulfide (H2S) to reactive sulfur species (RSS), potentially conveying identical benefits. Here we use RSS-specific fluorophores, mass spectroscopy, EPR and UV-Vis spectrometry, and oxygen-sensitive optodes to examine the effects of thiols and thiol-NQ adducts on H2S-NQ reactions. In the presence of glutathione (GSH) and cysteine (Cys), 1,4-NQ oxidizes H2S to both inorganic and organic hydroper-/hydropolysulfides (R2Sn, R=H, Cys, GSH; n = 2-4) and organic sulfoxides (GSnOH, n = 1, 2). These reactions reduce NQs and consume oxygen via a semiquinone intermediate. NQs are also reduced as they form adducts with GSH, Cys, protein thiols, and amines. Thiol, but not amine, adducts may increase or decrease H2S oxidation in reactions that are both NQ- and thiol-specific. Amine adducts also inhibit the formation of thiol adducts. These results suggest that NQs may react with endogenous thiols, including GSH, Cys, and protein Cys, and that these adducts may affect both thiol reactions as well as RSS production from H2S.Item Simultaneous noninvasive recording of skin sympathetic nerve activity and electrocardiogram(Elsevier, 2017-01) Doytchinova, Anisiia; Hassel, Jonathan L.; Yuan, Yuan; Lin, Hongbo; Yin, Dechun; Adams, David; Straka, Susan; Wright, Keith; Smith, Kimberly; Wagner, David; Shen, Changyu; Salanova, Vicenta; Meshberger, Chad; Chen, Lan S.; Kincaid, John C.; Coffey, Arthur; Wu, Gang; Li, Yan; Kovacs, Richard J.; Everett, Thomas H., IV; Victor, Ronald; Cha, Yong-Mei; Lin, Shien-Fong; Chen, Peng-Sheng; Medicine, School of MedicineBACKGROUND: Sympathetic nerve activity is important to cardiac arrhythmogenesis. OBJECTIVE: The purpose of this study was to develop a method for simultaneous noninvasive recording of skin sympathetic nerve activity (SKNA) and electrocardiogram (ECG) using conventional ECG electrodes. This method (neuECG) can be used to adequately estimate sympathetic tone. METHODS: We recorded neuECG signals from the skin of 56 human subjects. The signals were low-pass filtered to show the ECG and high-pass filtered to show nerve activity. Protocol 1 included 12 healthy volunteers who underwent cold water pressor test and Valsalva maneuver. Protocol 2 included 19 inpatients with epilepsy but without known heart diseases monitored for 24 hours. Protocol 3 included 22 patients admitted with electrical storm and monitored for 39.0 ± 28.2 hours. Protocol 4 included 3 patients who underwent bilateral stellate ganglion blockade with lidocaine injection. RESULTS: In patients without heart diseases, spontaneous nerve discharges were frequently observed at baseline and were associated with heart rate acceleration. SKNA recorded from chest leads (V1-V6) during cold water pressor test and Valsalva maneuver (protocol 1) was invariably higher than during baseline and recovery periods (P < .001). In protocol 2, the average SKNA correlated with heart rate acceleration (r = 0.73 ± 0.14, P < .05) and shortening of QT interval (P < .001). Among 146 spontaneous ventricular tachycardia episodes recorded in 9 patients of protocol 3, 106 episodes (73%) were preceded by SKNA within 30 seconds of onset. Protocol 4 showed that bilateral stellate ganglia blockade by lidocaine inhibited SKNA. CONCLUSION: SKNA is detectable using conventional ECG electrodes in humans and may be useful in estimating sympathetic tone.