Multicomponent Gas Diffusion in Porous Electrodes

Multicomponent gas transport is investigated with unprecedented precision by AC impedance analysis of porous YSZ anode-supported solid oxide fuel cells. A fuel gas mixture of H2-H2O-N2 is fed to the anode, and impedance data are measured across the range of hydrogen partial pressure (10-100%) for open circuit conditions at three temperatures (800C, 850C and 900C) and for 300mA applied current at 800C. For the first time, analytical formulae for the diffusion resistance (Rb) of three standard models of multicomponent gas transport (Fick, Stefan-Maxwell, and Dusty Gas) are derived and tested against the impedance data. The tortuosity is the only fitting parameter since all the diffusion coefficients are known. Only the Dusty Gas model leads to a remarkable data collapse for over twenty experimental conditions, using a constant tortuosity consistent with permeability measurements and the Bruggeman relation. These results establish the accuracy of the Dusty Gas model for multicomponent gas diffusion in porous media and confirm the efficacy of electrochemical impedance analysis to precisely determine transport mechanisms

Role of 18F-MD-PSMA PET/CT in initial stage of intermediate and high risk prostate cancer

Objective·To evaluate the role of 18F-MD-PSMA PET/CT in the initial stage of patients with moderate and high risk prostate cancer (PCa).Methods·A total of 67 patients with moderate and high risk PCa who were treated in Xinhua Hospital, Shanghai Jiao Tong University School of Medicine from September 2017 to June 2022 were initially staged by 18F-MD-PSMA PET/CT. Conventional imaging (CI), including multi-parameter magnetic resonance imaging (mp-MRI) and bone scintigraphy (BS), were performed within two weeks before 18F-MD-PSMA PET/CT. Twenty-five patients underwent 18F-FDG PET/CT at the same time. The sensitivity (SEN), specificity (SPEC), positive predictive value (PPV), negative predictive value (NPV) and accuracy (ACU) of 18F-MD-PSMA PET/CT in the initial stage were evaluated, and the results were compared with those of 18F-FDG PET/CT, mp-MRI and BS. The consistency of 18F-MD-PSMA PET/CT and CI in terms of primary lesion, regional lymph node metastasis and bone metastasis was evaluated by Kappa consistency test refering to the postoperative pathological T and N staging results and bone metastasis results of clinical follow-up. Kappa coefficient was calculated and compared.Results·Of the 67 patients with PCa, 38 patients underwent radical prostatectomy and had completed pathological data, with 27 patients undergoing regional lymphadenectomy and 1 patient undergoing expanded pelvic lymphadenectomy at the same time. The pathological results were obtained as gold standard. The detection rates of mp-MRI and 18F-MD-PSMA PET/CT in diagnosing intrathecal lesions were both 100%. The SENs in diagnosing bilateral intralobular lesions were 26.3% and 63.2%, respctively; the SPECs were both 75.0%.The Kappa consistency test showed that the consistency of 18F-MD-PSMA PET/CT in diagnosis of extracapsular extension (EPE), seminal vesicle invasion (SVI), and bladder neck invasion (BNI) was higher than that of mp-MRI. Fisher′s exact test showed that there were no statistically significant differences in SEN (P=0.226, P=0.491) and SPEC (P=1.000, P=0.342) between the two methods for diagnosing EPE and SVI, as well as SEN (P=1.000) for diagnosing BNI. In terms of diagnosis of lymph node metastasis, based on the analysis of lymph node numbers, the consistency between 18F-MD-PSMA PET/CT and pathological results was higher than that of mp-MRI (Kappa coefficients of 0.555 and 0.137, respectively). Fisher′s exact test showed that there were no statistically significant differences in SEN and SPEC between the two examination methods (P=0.562, P=0.829). Based on the patients, the consistency between 18F-MD-PSMA PET/CT and pathological results was higher than that of mp-MRI (Kappa coefficients of 0.850 and 0.313, respectively). There was no statistically significant difference in SEN between the two methods (P=1.000). In terms of diagnosis of bone metastasis, based on the analysis of bone lesion numbers, the consistency between 18F-MD-PSMA PET/CT and clinical follow-up results was higher than that of BS (Kappa coefficients of 0.500 and 0.299, respectively). Fisher′s exact test showed that there was no statistically significant difference in SEN between the two methods (P=0.219). Based on the patients, the consistency between 18F-MD-PSMA PET/CT and clinical follow-up results was higher than that of BS (Kappa coefficients of 0.953 and 0.766, respectively). There was no statistically significant difference in SEN between the two methods (P=1.000). The risks of 21 patients (31.3%) were increased after 18F-MD-PSMA PET/CT detection, with 1 patient (1.5%) decreasing. The initial stage of 32 cases (47.8%) were changed after 18F-MD-PSMA PET/CT detection, with 27 cases (40.3%) upstaged and 5 cases (7.5%) downstaged.Conclusion·18F-MD-PSMA PET/CT is superior to CI in the diagnosis of bilateral intralobular lesions, EPE, SVI, regional lymph node metastasis and bone metastasis in intermediate and high risk PCa, and on this basis, the diagnosis of clinical stage and metastatic status of some patients has been changed

Diffuse charge and Faradaic reactions in porous electrodes

Porous electrodes instead of flat electrodes are widely used in electrochemical systems to boost storage capacities for ions and electrons, to improve the transport of mass and charge, and to enhance reaction rates. Existing porous electrode theories make a number of simplifying assumptions: (i) The charge-transfer rate is assumed to depend only on the local electrostatic potential difference between the electrode matrix and the pore solution, without considering the structure of the double layer (DL) formed in between; (ii) the charge-transfer rate is generally equated with the salt-transfer rate not only at the nanoscale of the matrix-pore interface, but also at the macroscopic scale of transport through the electrode pores. In this paper, we extend porous electrode theory by including the generalized Frumkin-Butler-Volmer model of Faradaic reaction kinetics, which postulates charge transfer across the molecular Stern layer located in between the electron-conducting matrix phase and the plane of closest approach for the ions in the diffuse part of the DL. This is an elegant and purely local description of the charge-transfer rate, which self-consistently determines the surface charge and does not require consideration of reference electrodes or comparison with a global equilibrium. For the description of the DLs, we consider the two natural limits: (i) the classical Gouy-Chapman-Stern model for thin DLs compared to the macroscopic pore dimensions, e.g., for high-porosity metallic foams (macropores >50 nm) and (ii) a modified Donnan model for strongly overlapping DLs, e.g., for porous activated carbon particles (micropores <2 nm). Our theory is valid for electrolytes where both ions are mobile, and it accounts for voltage and concentration differences not only on the macroscopic scale of the full electrode, but also on the local scale of the DL. The model is simple enough to allow us to derive analytical approximations for the steady-state and early transients. We also present numerical solutions to validate the analysis and to illustrate the evolution of ion densities, pore potential, surface charge, and reaction rates in response to an applied voltage

Theoretical and experimental study of solid oxide fuel cell (SOFC) using impedance spectra

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, September 2014.Cataloged from PDF version of thesis. "June 2014."Includes bibliographical references (pages 100-107).Solid oxide fuel cell (SOFC) is a promising alternative energy source, with its advantages of high operating efficiency, fuel flexibility, low emissions and relatively low cost. However, there are several challenges concerning the SOFC research. Little is known about the complex interfacial electrochemistry and thermochemistry, and it is also difficult to diagnose problems and optimize cell performance. Therefore, physics-based models are needed to better understand the underlying mechanisms of SOFCs. This research work addressed two important aspects of the numerical modeling of SOFCs: the multicomponent gas diffusion in porous electrode at the anode and the heterogeneous electrocatalysis of oxygen reduction reaction (ORR) at the cathode. First, anode was diagnosed to be mainly controlled by multicomponent gas diffusion inside the anode bulk (supporting) layer, and the Dusty Gas model is identified as an appropriate model to describe the gas diffusion resistance extracted from no bias AC impedance. Anode-supported SOFCs with Ni-yttria-stabilized zirconia (YSZ) anode were used to study the multicomponent gas transport in porous electrodes. A fuel gas mixture of H₂-H₂O-N₂ was fed to the anode and AC impedance data were measured at 800°C by varying hydrogen partial pressure at both no bias and a current of 300 mA. Impedance data were also collected at no bias at three different temperatures (800°C, 850°C and 900°C). For the first time, three models were used to analytically derive the diffusion resistance (Rb), which was then compared to the values extracted from experimental impedance data. The Dusty Gas model yields the best predictions and the tortuosity values derived from Dusty Gas model are found to be independent of feeding gas composition, operating current and temperatures, which is consistent with the fundamental or underlying physics. Moreover, with the anode porosity known to be approximately 46%, the tortuosity derived from the Dusty Gas model is 2.3~3.3, which matches both theoretical expectations and experimental measurements. This gas diffusion resistance analysis using AC impedance greatly improves the way to study the multicomponent gas diffusion within porous electrodes. Secondly, electrocatalysis at the SOFC cathode was studied using symmetric cathode cells, whose no bias AC impedance was investigated and modeled using a physics-based electrocatalysis model, describing the coupled dissociative adsorption of oxygen molecules onto the catalytic lanthanum strontium manganite (LSM) particles and surface diffusion of adsorbed species, assuming the charge transfer reaction is relatively fast and at equilibrium. A Gerischer type impedance response with a reflecting boundary condition was theoretically derived assuming the oxygen adsorption follows Langmuir type kinetics. This cathode electrocatalysis model not only captures the frequency dependence of the no bias AC impedance, it also well represents the oxygen partial pressure (pO₂) dependence. Four different impedance curves at pO₂ 2 of 21%, 15%, 10% and 5% were fitted at the same time, and the model was able to well describe them using one set of physically meaningful fitting parameters. Microstructure of the cathode functional layer (CFL) was also studied using this electrocatalysis model. It was found that the diffusion length Ls, is a critical parameter, whose ratio with respect to the characteristic boundary layer length l[delta], (the Thiele modulus) critically controls the effectiveness of the catalytic activity of the cathode functional layer. These understandings of the anode gas diffusion and cathode electrocatalytic process was used to propose an equivalent circuit for the full solid oxide fuel cell, which captures all important resistances in the SOFC, but is still as simple as possible, in order to minimize the number of fitting parameters. This full cell model greatly helps to break down the AC impedance which has overlapped responses from several processes. The analysis identified the rate limiting step of the full Saint-Gobain button cell to be the cathode electrocatalytic process, which indicates that in order to improve the cell performance, research should be focused on improving the cathode functional layer, by either improving the surface catalytic activity of the LSM particles, or changing the microstructure of the cathode functional layer.by Yeqing Fu.Ph. D

Diffuse charge and Faradaic reactions in porous electrodes,&quot; Physical Review E,

Porous electrodes instead of flat electrodes are widely used in electrochemical systems to boost storage capacities for ions and electrons, to improve the transport of mass and charge, and to enhance reaction rates. Existing porous electrode theories make a number of simplifying assumptions: (i) The charge-transfer rate is assumed to depend only on the local electrostatic potential difference between the electrode matrix and the pore solution, without considering the structure of the double layer (DL) formed in between; (ii) the charge-transfer rate is generally equated with the salt-transfer rate not only at the nanoscale of the matrix-pore interface, but also at the macroscopic scale of transport through the electrode pores. In this paper, we extend porous electrode theory by including the generalized Frumkin-Butler-Volmer model of Faradaic reaction kinetics, which postulates charge transfer across the molecular Stern layer located in between the electron-conducting matrix phase and the plane of closest approach for the ions in the diffuse part of the DL. This is an elegant and purely local description of the charge-transfer rate, which self-consistently determines the surface charge and does not require consideration of reference electrodes or comparison with a global equilibrium. For the description of the DLs, we consider the two natural limits: (i) the classical Gouy-Chapman-Stern model for thin DLs compared to the macroscopic pore dimensions, e.g., for high-porosity metallic foams (macropores &gt;50 nm) and (ii) a modified Donnan model for strongly overlapping DLs, e.g., for porous activated carbon particles (micropores &lt;2 nm). Our theory is valid for electrolytes where both ions are mobile, and it accounts for voltage and concentration differences not only on the macroscopic scale of the full electrode, but also on the local scale of the DL. The model is simple enough to allow us to derive analytical approximations for the steady-state and early transients. We also present numerical solutions to validate the analysis and to illustrate the evolution of ion densities, pore potential, surface charge, and reaction rates in response to an applied voltage

MLAOS: A Multi-Point Linear Array of Optical Sensors for Coniferous Foliage Clumping Index Measurement

The canopy foliage clumping effect is primarily caused by the non-random distribution of canopy foliage. Currently, measurements of clumping index (CI) by handheld instruments is typically time- and labor-intensive. We propose a low-cost and low-power automatic measurement system called Multi-point Linear Array of Optical Sensors (MLAOS), which consists of three above-canopy and nine below-canopy optical sensors that capture plant transmittance at different times of the day. Data communication between the MLAOS node is facilitated by using a ZigBee network, and the data are transmitted from the field MLAOS to a remote data server using the Internet. The choice of the electronic element and design of the MLAOS software is aimed at reducing costs and power consumption. A power consumption test showed that, when a 4000 mAH Li-ion battery is used, a maximum of 8–10 months of work can be achieved. A field experiment on a coniferous forest revealed that the CI of MLAOS may reveal a clumping effect that occurs within the canopy. In further work, measurement of the multi-scale clumping effect can be achieved by utilizing a greater number of MLAOS devices to capture the heterogeneity of the plant canopy

CAR-based cell therapy: evaluation with bibliometrics and patent analysis

Chimeric antigen receptors-based cell therapies have shown impressive preclinical and clinical success and revolutionized biomedicine. However, the link between science and invention, the impact of international cooperation, and the influence and prestige of CARs research have not been explored. This study analyzed the landscape of peer-reviewed articles and patents related to CARs. A total of 5,681 publications were analyzed using bibliometrics and machine learning-based text mining to assess publication metrics, subject areas, and research hotspots. 5,010 Inpadoc families were also analyzed for patent filing trends, priority countries, and applicant and inventor rankings. The results show that CARs research has the following distinctive features: high research prestige among research community; strong global geographical bias in both academic output and patenting patterns; strong links between science and invention, but significant differences among countries; and an inverse relationship between country size and international collaboration rates

Different composites inhibit Cd accumulation in grains under the rice-oilseed rape rotation mode of karst area: A field study

Ensuring the safe production of food and oil crops in soils with elevated cadmium (Cd) content in karst regions is crucial. We tested a field experiment to examine the long-term remediation effects of compound microorganisms (CM), strong anion exchange adsorbent (SAX), processed oyster shell (POS), and composite humic acids (CHA) on Cd contamination in paddy fields under a rice-oilseed rape rotation system. In comparison to the control group (CK), the application of amendments significantly increased soil pH, cation exchange capacity (CEC), and soil organic matter (SOM) content while markedly decreasing the content of available Cd (ACd). During the rice cultivation season, Cd was predominantly concentrated in the roots. Relative to the control (CK), the Cd content in each organ was significantly reduced. The Cd content in brown rice decreased by 19.18–85.45%. The Cd content in brown rice following different treatments exhibited the order of CM > POS > CHA > SAX, which was lower than the Chinese Food Safety Standard (GB 2762–2017) (0.20 mg/kg). Intriguingly, during the oilseed rape cultivation season, we discovered that oilseed rape possesses potential phytoremediation capabilities, with Cd mainly accumulating in roots and stems. Notably, CHA treatment alone significantly decreased the Cd content in oilseed rape grains to 0.156 mg/kg. CHA treatment also maintained soil pH and SOM content, consistently reduced soil ACd content, and stabilized Cd content in RSF within the rice-oilseed rape rotation system. Importantly, CHA treatment not only enhances crop production but also has a low total cost (1255.230 US$/hm2). Our research demonstrated that CHA provides a consistent and stable remediation effect on Cd-contaminated rice fields within the crop rotation system, as evidenced by the analysis of Cd reduction efficiency, crop yield, soil environmental change, and total cost. These findings offer valuable guidance for sustainable soil utilization and safe production of grain and oil crops in the context of high Cd concentrations in karst mountainous regions