Initial Performance Research Articles

Haptic feedback during virtual reality training significantly improves First-Year orthopedic resident performance at tibia drilling: a randomized trial

Background: Few studies have investigated whether haptic feedback improves the effectiveness of virtual reality (VR) simulation. This study aimed to determine whether new orthopedic surgery residents trained on haptic feedback-enabled VR performed basic drilling better than residents who had trained on VR without haptic feedback. Methods: Fourteen first-year orthopedic surgery residents were enrolled and randomized into “haptic” or “non-haptic” groups and blinded to study goals and randomization. Residents participated in a VR tibia drilling simulation with haptic feedback either turned on or off and then performed a plastic resin tibia model drilling session where overdrill depth was measured by two raters blinded to study groups. Questionnaires were completed before and after the hands-on sessions with responses on a five-point Likert scale. Results: There were no significant differences in demographics between groups. Overdrill depth during the first trial was significantly less in the haptic group than the non-haptic group (3.9 mm vs. 6.0 mm, P=0.005). Subsequent trials showed no significant difference in mean overdrill depth between groups (P>0.05). Haptic group participants reported higher confidence in the safe use of surgical tools (4 vs. 3, P<0.01) and more simulation realism (4 vs. 3, P<0.01). Conclusion: VR training with haptic feedback significantly improves initial performance during use of a surgical drill through a tibia model compared to VR training without haptic feedback in first year orthopedic residents. The addition of haptic feedback also increases the perceived value, realism, and enjoyment of VR simulation. Level of Evidence: Level II.

Older Age at First Screening Colonoscopy is Associated With an Increased Risk of Colorectal Adenomas and Cancer.

The goal of colorectal cancer (CRC) screening is to detect precancerous polyps before cancer development or identification of cancer at an early stage. Guidelines have recommended screening colonoscopy to start at age 45. Our aim was to determine the impact of delays in performing the first screening colonoscopy on the risk of adenoma or CRC detection. We analyzed colonoscopy and histopathology data of average CRC risk patients who had their first screening colonoscopy between 2010 and 2017. Univariate and multivariable logistic regression was performed to determine the association between demographic variables and the risk of adenomas or CRC. A total of 1155 average risk patients underwent their initial screening colonoscopy during the study period. Median age was 54 years (range of 45-87) and 58.2% were females. In multivariable analysis, older age at first screening colonoscopy was significantly associated with the detection of adenomatous polyps (odds ratio 1.05, 95% confidence interval 1.04-1.07, P<0.001) and CRC (odds ratio 1.11, 95% confidence interval 1.06-1.16, P<0.001). The association between age and risk of adenomatous polyps (F-test 35.43, P=0.0019) and CRC (F-test 36.94, P=0.0017) fit an exponential growth model. It was estimated that the detection rate doubled every 14.20 years and 4.75 years for adenomas and CRC, respectively. We found that older age at the initial performance of a screening colonoscopy was associated with increased detection of adenomatous polyps and CRC. This work highlights the need for guideline adherence for the prevention of CRC development.

Muconic acid production from algae hydrolysate as a high-value co-product of an algae biorefinery

Muconic acid is an attractive bio-derived product because it can be easily converted to adipic acid, a high-value and high-volume monomer used in the production of nylon and other valuable consumer plastics. As such, production of muconic acid from algae hydrolysate was explored to expand the suite of products available from algal biomass. We have established initial performance parameters and have shown that the range of substrates present in algae hydrolysate that are consumed by Pseudomonas putida includes at least glucose, mannose, glycerol, acetic acid, and lactic acid. We achieved complete utilization of these major carbon sources found in Scenedesmus acutus hydrolysate with a maximum muconic acid productivity of 0.25 g/L h. Final titer was 13.0 g/L (27 % molar process yield) at approximately 50 h. In addition, algae hydrolysate does not require any additional nutrients to achieve these performance metrics. Techno-economic analysis showed the potential to support up to 150 algal biorefineries at this yield with significant greenhouse gas reductions.

Investigating the Skill Development of Medical Students in Focused Assessment With Sonography for Trauma (FAST) Ultrasound: A Comparative Analysis Across Different Stages of Medical Training.

Focused assessment with sonography for trauma (FAST) ultrasound (US) is a valuable medical examination used in trauma settings, particularly for rapid responses to events such as natural disasters. Although the efficacy and benefits of FAST in patient care have been extensively studied, there is limited research on training medical students in FAST. Previous studies have found that medical students can proficiently perform a FAST US after two days of training. However, these studies exclusively included first-year medical students without considering variations in their medical knowledge. Particularly, the advantage of medical students having US experience before undergoing FAST training has not been previously examined. Assess the performance and knowledge acquisition of medical students with and without prior US experience after completing a FAST training course. The study included a total of 71 students, consisting of 33 males and 38 females, who were between the ages of 18 and 31, with an average age of 24.6 and a standard deviation of 2.4. The inclusion criteria targeted first- and second-year medical school students who participated on a volunteer basis. Students were divided into two groups: group A, consisting of those without prior USexperience, and group B, made up of those who had previous US experience. All students completed a pre-training survey to share their comfort and confidence in US use and knowledge. A baseline FAST exam was conducted to establish initial performance. A comprehensive three-hour training session was then provided. Post-training, students performed another FAST exam to assess improvement, followed by a post-training survey to evaluate comfort and confidence. Medical students who had prior experience in the US (group B) performed significantly better (p<0.01) in both the pre- and post-training FAST exams when compared to students without previous US experience. Specifically, in locating the liver, right kidney, hepatorenal recess, and left kidney, as well as detecting fluid accumulation when in a supine position. Additionally, medical students with prior US experience (group B) exhibited higher baseline confidence (p<0.005-p<0.01) in their ability to perform a FAST exam, as indicated by the results of the pre-testing survey. Previous experience with USsignificantly boosted confidence and knowledge gains following FAST training. This emphasizes the value of including US training in medical school programs after earlier exposure, offering evident benefits. The study reveals the unexplored benefit of having prior US experience for medical students undergoing FAST training, thus addressing a previously unexplored area in current research. The conclusions stress the necessity of integrating US training into medical school curricula after initial exposure. This understanding can direct medical educators in refining the education process, enabling students to be better equipped for real-world medical situations involving FAST.

Direct-Fed Ethanol Metal-Supported Solid Oxide Fuel Cell System with Regeneration Process by Air Pulsing

Metal-Supported-SOFC (MS-SOFC) can handle rapid start-up and cool-down without cracking, making it more suitable for mobile applications than a conventional cermet-based SOFC, which is more susceptible to cracking when experiencing thermal shock due to its ceramic component. Despite having more robust mechanical properties, the MS-SOFC still relies on Ni as its anode catalyst, where it can be deactivated due to coking formation if the cell is operated under liquid logistics or hydrocarbon fuels. One of the most effective solutions is introducing a micro-reforming catalyst layer on the anode layer. The micro-reforming catalyst will reform the fuel into H2 and CO mixture called syngas, and then the anode will use the reformatted syngas to run the electrochemical reaction to produce electricity. This method will effectively improve the cell power output, stability, and coking resistance.In this work, we integrated the MS-SOFC with a reforming catalyst through the precursor infiltration method. We infiltrated a non-noble metal-based catalyst with a ceria-zirconia (CZ) into the MS-SOFC. The cell is then operated under direct ethanol fuel at 700 °C with the S/C ratio of 2. The non-noble metal catalyst is less expensive than noble but it also has lower catalytic activity and coking resistance during the cell operation in ethanol. Therefore, a regeneration cycle is necessary to maintain the cell performance and the catalytic activity of the cell. The regeneration cycle is performed by air pulsing directly into the cell’s anode surface to burn off the coking generated during the cell operation. The regeneration process involves a redox cycle that is only possible for a mechanically stable structure like MS-SOFC.Our experimental data showed that the MS-SOFC with infiltrated micro-reforming catalyst was gradually deactivated during the operation under ethanol fuel, indicated by the cell voltage drops due to coking. After the regeneration procedure with air pulsing, the cell voltage was recovered to its original performance. At the same time, the gas chromatograph detects a significant CO2 signal from the effluent gas, suggesting that the carbon removal process was successfully performed. Additionally, we observed an improvement in the cell’s performance under H2 and ethanol fuel. After a long-term constant current stability test, the cell shows up to ~20% and ~25% maximum current density drops under H2 and ethanol fuel, respectively, compared to its initial performance. Upon the cell regeneration with air pulse, the cell’s maximum current density was recovered to its initial performance and showed an improvement up to ~21 and 13% under H2 and ethanol, respectively, compared to its initial performance before the long-term test. This result suggests that some of the carbons might remain within the cell’s functional layer and help improve its conductivity and electrochemical performances. These data clearly show that the air pulsing regeneration process in the MS-SOFC can improve the cell’s lifetime by removing the coking deposit within the anode and enhancing its electrochemical and catalytic activity.-------Figure Caption: Fig 1.(A) The IV pot of the MS-SOFC with reforming catalyst under H2 and (B) ethanol solution (S/C=2) at 700 °C of the MS-SOFC. The IV measurements were taken during its initial screening, after both constant current stability tests, and after both regeneration procedures. (C) Long-term stability test of the cell in ethanol solution under the constant current density of 125 mA/cm2. Figure 1

The Reduction Step and Mechanism Analysis of the NiO-8YSZ Anode Affected by the Hydrogen Concentration

The reduction of the NiO-YSZ anode has a direct bearing on the performance of the solid oxide fuel cell, and the hydrogen concentration is a significant condition during the reduction process. Hydrogen at different concentrations were used to reduce the NiO-YSZ anode and the initial performances of the solid oxide fuel cells were tested to reveal the influence of the hydrogen concentration on the reduction of the NiO-YSZ anode. The experimental results suggested that four stages of the open circuit voltage exist during the reduction of the NiO-YSZ anode, namely rapid increase period, temporary stasis period, slow increase period and final stable period successively. The rates of the rapid increase period and the slow growth period showed significant positive correlations with the hydrogen concentration of the reduction while there was a negative correlation between the duration of the temporary stasis period and the hydrogen concentration of the reduction. The values of the temporary stasis period were 0.83V approximately, which were irrelevant to the hydrogen concentration of the reduction. During the final stable period, the variation of the open circuit voltage is less than 1mV/h, which were close to the theoretical open circuit voltage. After the reduction of the NiO-YSZ anode, the ohmic resistance of the solid oxide fuel cell was about 0.31Ω /cm2 and did not reveal a clear correlation with the hydrogen concentration of the reduction. The polarization resistance showed significant negative correlation with the hydrogen concentration of the reduction on open circuit. But under the on-load condition, the same phenomenon only occurred in low hydrogen concentration of the reduction and then the polarization resistance remained largely the same with the increasing hydrogen concentration of the reduction. There was a direct correlation between the initial performances of the solid oxide fuel cell and the polarization resistance under the on-load condition that the initial performances can be improved with the increasing hydrogen concentration during the reduction process of the NiO-YSZ anode when the hydrogen concentration was low and then the initial performances remained constant basically with the continuing increasing hydrogen concentration. The abovementioned phenomena demonstrate that the resistance on open circuit represent nothing to the performances of the solid oxide fuel cell under the on-load condition. Previous researches about the NiO reduction by hydrogen, especially the shrinking core model can be used to explain the abovementioned phenomena. The reduction of the NiO is a volume reduction process. The reaction interface of the Ni/NiO moves inwards during the reduction, forming an unreacted NiO core surrounded by a rim of metallic Ni with much porous structures finally. The H2O produced in the reduction is absorbed onto the surface of the unreacted NiO core, improving the apparent activation energy and limiting diffusion of the Ni atoms to appropriate nucleation centers. Thus, the reduction process is retarded, forming the temporary stasis period. The absorbed H2O removes out through the porous structures of the rim of the metallic Ni. Meanwhile the H2 penetrates deeper and continues to reduce the unreacted NiO core, which is the mechanism of the slow increase period. According to the shrinking core model, higher hydrogen concentration can make the unreacted NiO core smaller, lessening the H2O absorbed onto the surface. Thus, the time needed for the absorbed H2O removal is shorten, leading the duration of the temporary stasis period showed significant negative correlation with the hydrogen concentration. The previous researches attribute the activation of the solid oxide fuel cell to the coarsening of the Ni particle or the further reduction of the unreacted NiO core. In this experiment, the performance of the solid oxide fuel cell with the NiO-YSZ anode reduced by 5% hydrogen concentration was lowest, and thus its potential of the activation was highest. In the first 20 hours of the operation, its performance kept improving and achieved that of the solid oxide fuel cells with the NiO-YSZ anodes reduced by higher hydrogen concentration. But the performance of the solid oxide fuel cells with the NiO-YSZ anodes reduced by higher hydrogen concentration did not significantly improve in the first 20 hours of the operation. The comparison showed that the cause of the activation of the solid oxide fuel cell is quite possible the further reduction of the unreacted NiO core.

Alkaline Water-Assisted Polyol Synthesis of Pt/Vulcan PEMFC Cathode Electrocatalysts

Sluggish oxygen reduction reaction (ORR) kinetics motivates great focus on PEMFC cathode electrocatalyst development.1 Electrocatalysts based on Pt are often prepared via the so-called polyol process, a solvothermal process that allows controlling of the structure, morphology, and chemical nature of various metal nanoparticles.2 Several parameters have been well-studied and thoroughly discussed in literature over the years, varying from surfactant removal or water addition to pH or NaOH/Pt molar ratio effect on Pt particle size. 3,4 Here, we present a slight modification of the well-established surfactant-free alkaline one-pot polyol synthesis of Pt-nanoparticles on Vulcan XC 72R carbon support and the subsequent PEMFC characterization tests with respect to initial electrochemical performance and standardized accelerated stress tests (AST). In this approach, the solvent composition is systematically changed by the substitution of ethylene glycol to water and by increasing the Pt precursor concentration per mass of solvent to ultimately minimize the amount of ethylene glycol used.The so-synthesized electrocatalyst powders, with Pt particle sizes ranging from 2 to 6 nm, were physico-chemically analyzed by powder X-ray diffraction, thermogravimetric analysis, and transmission/scanning electron microscopy. The initial electrochemical performance as well as the stability were evaluated by implementing membrane electrode assemblies (MEAs), prepared from a series of synthesized electrocatalysts in a differential flow single cell setup (12 cm2). The electrochemical performance of the prepared MEAs was evaluated and compared to a commercial reference catalyst coated membrane (CCM), as well as to an internal reference CCM, that was prepared using a cathode Pt/C catalyst synthesized via pure ethylene glycol-based polyol route.Beginning-of-life MEA data indicate the possibility of reducing the required ethylene glycol amount per mass of synthesized catalyst by up to 98%. Taking catalyst durability as an additional optimization criterion into account, a Pt/C electrocatalyst synthesized with 45 vol% H2O at a Pt precursor concentration of 32 mM, ultimately leading to an ethylene glycol reduction of 90%, showed a decent initial electrochemical performance (716 mV at 1 A cm-2), as well as an AST stability similar to the internal reference (Pt/C synthesized using pure EG and Pt precursor concentration of 16 mM).In summary, we conclude that water content and Pt precursor concentration have a crucial impact on the characteristics of Pt/C electrocatalysts in the modified polyol route. At optimum parameter values, catalysts with optimized electrochemical performance in PEMFC applications can be synthesized, with substantially lowered synthesis cost due to solvent substitution.

Long-Term Sulfur Tolerance of Solid Oxide Fuel Cells with Alternative Titanate-Based Fuel Electrodes

The future renewable energy system relies on devices capable of energy conversion and storage. Solid oxide fuel cells (SOFCs) convert the chemical energy of a fuel into electricity and heat with high electrical efficiency. The fuel flexibility of SOFCs allows for the use of not only hydrogen, but also C-containing fuels, including biogas and green fuels from power-to-X. Such fuels contain trace amounts of sulfur, either being present from the original source or added for safety reasons as odorant, which causes loss of performance in state-of-the-art (SoA) SOCFs with Ni-based cermet fuel electrodes, due to sulfur adsorption on the Ni. An upstream desulfurization unit mitigates this problem in commercial SOFC-systems, increasing CAPEX and system complexity.Hence, alternative S-tolerant fuel electrode materials are highly desirable. All-ceramic doped strontium titanates perovskite compounds (ABO3) are interesting candidates due to their high electronic conductivity and chemical stability. Among these, La0.4Sr0.4Fe0.03Ni0.03Ti0.94O3 (LSFNT), is particularly interesting, due to its B-site exsolution of electrocatalytically active Fe and Ni nanoparticles under reducing conditions. However, the electrochemical activity from the exsoluted catalyst is not sufficient and integration of additional electrocatalyst by infiltration ensures electrochemical performance comparable to SoA.In this study, the electrochemical performance and sulfur tolerance of three different, electrolyte supported cells are examined: Cell 1 contains a standard Ni/CGO cermet fuel electrode, Cell 2 contains a LSFNT electrode backbone with Ni:CGO electrocatalyst and Cell 3 contains LSFNT electrode backbone with Fe-Ni:CGO electrocatalyst.. Fe is added to the Ni:CGO to investigate if alloy formation on the nanoscale can improve the sulfur tolerance. All the cells contain LSM-YSZ oxygen electrodes. The cells were integrated in a short, 5-cell stack and tested at HEXIS AG. The fuel was a natural gas directly supplied from the grid, pre-reformed in a catalytic partial oxidation (CPOx) unit, where a desulfurization unit was connected or by-passed for determining the sulfur tolerance. The electrochemical performance was investigated for each cell in the stack individually by iV-curves and electrochemical impedance spectroscopy (EIS) with and without the use of an upstream desulfurization unit. This was followed by a durability test for ca. 400 hours with sulfur exposure. While the initial performances with short term exposure to sulfur indicate reversible degradation on both types of infiltrated LSFNT fuel electrodes, Cell 1 with the Ni/CGO cermet fuel electrode experiences loss of performance related to an increase in the Ohmic resistance. Cell 1 together with Cell 2 (LSFNT infiltrated with Ni:CGO) are both stable over several hundred hours of operation in sulfur, whereas accelerated degradation of cell voltage is observed on Cell 3 where Fe is present in the infiltrate. Details on electrochemical behavior during the durability test and origins of degradation will be presented together with a microstructural analysis. Figure 1

Metal-Supported Solid Oxide Cells for Energy Conversion, Electrolysis, and Chemical Synthesis

This talk will provide an overview and update of performance, durability, and applications of metal-supported solid oxide fuel cell (MS-SOFC) and electrolysis cell (MS-SOEC) technology developed at Lawrence Berkeley National Laboratory (LBNL). The unique LBNL symmetric cell architecture design, with thin zirconia ceramic backbones and electrolyte sandwiched between porous metal supports, offers a number of advantages over conventional all-ceramic cells, including low-cost structural materials (e.g. stainless steel), mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. These features enable a wide variety of applications including vehicle range extenders, electrolysis for intermittent renewables, personal power generators, and distributed generation.With infiltrated catalysts, the catalyst compositions can be easily tailored to a variety of reactions, without re-optimizing the entire cell. Recent efforts have developed catalysts for internal reforming of natural gas and ethanol, steam electrolysis to produce hydrogen, oxidative coupling of methane to synthesize ethylene, and oxygen generation from air. A recent focus is 1000+ hour continuous operation with detailed post-mortem analysis. Progress on cell performance and durability for each of these applications will be discussed.Infiltrated catalysts, however, present a tradeoff between initial performance and long-term stability. Extremely high surface area promotes high electrochemical reaction rates, but also provides high surface energy leading to coarsening and facilitates Cr deposition. Recent approaches to mitigating catalyst coarsening and Cr deposition within the cathode include coatings to prevent Cr evaporation from the stainless steel components, and optimization of infiltrated catalyst processing to stabilize the microstructure during operation. The metal support structure has also been optimized for improved mass transport.

Analysis of Degradation Phenomena of SOC Stacks Operated in Reversible SOFC / SOEC Cycling Mode

The reversible SOFC/SOEC operation of solid oxide cell (SOC) stacks promise high overall electricity-to-electricity round-trip efficiencies and low storage costs. Although in recent years the degradation rates of SOFC and SOEC stacks in single mode long-term operation have been steadily decreased, the understanding of degradation mechanisms during reversible SOFC/SOEC operation remains an important and challenging issue. Therefore, the Korean-German project “Solid Oxide Reversible Fuel Cell / Electrolysis Stack” (SORFES) focuses on the development of the core component technology for a 1 kW reversible SOC stack in order to enhance the hydrogen productivity and its utilization. The primary goals are the improvement of the performance and the durability of SOC stacks during reversible SOFC/SOEC operation and the quantification and the qualification of the relevant degradation effects.The paper presents and compares the performance and degradation results of two SOC stacks which were operated mainly in galvanostatic steady-state SOFC mode and in reversible SOFC/SOEC cycling mode. The stacks with ASC cells of Elcogen (Estonia) were fabricated by the industrial project partner E&KOA (Daejeon, Korea). The reversible cycles consist of day/night switches between SOEC and SOFC, thus covering intermittent renewable electricity supply (e.g. of photovoltaics). The stacks were electrochemically characterized by jV-curves and electrochemical impedance spectroscopy (EIS).The first SOC stack with 10 cells was operated during 500 h in SOFC at constant current density followed by 500 h of operation under reversible SOFC/SOEC cycling conditions. The initial performance and homogeneity along the repeat units (RUs) of the stack in SOFC and SOEC at the beginning of operation are presented. In order to better understand the stack degradation, the results between reversible SOFC/SOEC cycling and galvanostatic steady-state SOFC operation are compared. The degradation, especially of the OCV, the power density and the area specific resistance (ASR) of the different RUs are analyzed and discussed. Moreover, the progression of the individual resistances, specifically of the ohmic-, the electrode polarization- and the gas concentration resistances of the RUs are evaluated and presented. The influence of temperature gradients and thermo-mechanical stresses during reversible exothermic (SOFC) and endothermic (SOEC) cycling are outlined and discussed.The results of the first stack test were used to improve the stack components and setup, e.g. the contacting and sealing of the cells in the stack and the protective coating on the interconnects. Moreover, the operating conditions during reversible SOFC/SOEC cycling were optimized. The second improved stack with 6 RUs was operated for 2800 h in galvanostatic steady-state SOFC mode and reversible SOFC/SOEC cycling mode with low degradation rate.The results of the present paper help to understand and improve the long-term stability of SOC stacks during reversible SOFC/SOEC cycling, thus promoting the SOC technology for renewable energy storage applications.

Performance and Degradation of Electrolyte Supported SOECs with Advanced GDC Thin-film Layers in Long-term Stack Test

Solid oxide electrolyser (SOE) based on electrolyte-supported cell (ESC) architecture is proven to be highly efficient and reliable technology for green hydrogen production via high temperature electrolysis. Operating under industrial conditions, the performance, lifetime and robustness of the cells and stacks belong to the most important factors for an up-scaled penetration of the SOE technology into energy and chemistry sectors. A typical ESC consists of scandia- or yttria-stabilized zirconia electrolyte, Ni-cermet fuel electrode, lanthanum strontium cobalt ferrite (LSCF) oxygen electrode and either one or two Gd-doped ceria (GDC) layers with a thickness of 5-7 µm between electrolyte and electrodes. At the oxygen electrode side, the GDC layer prevents interdiffusion (mainly of Sr), whereas at the fuel electrode side, the GDC layer may improve the electrode adherence to electrolyte and reduce the interfacial resistance. State-of-the-art fabrication route of the GDC layers is screen-printing followed by partially sintering at high temperature between 1200 °C to 1300 °C. This fabrication process usually results in porous structure in the GDC layers and residual stresses which reduce the mechanical strength of the cells.Aiming to improve the mechanical strength of ESCs and the properties (e.g. porosity and electrical conductivity) of GDC layers, the conventional screen-printed GDC layers either only at the oxygen electrode or at both electrodes were replaced by 0.5 µm thick thin-film GDC layers fabricated by electron-beam physical evaporation deposition (EB-PVD) method at 600 °C. These EB-PVD-fabricated thin-film GDC layers were electrochemically characterized in a so-called “rainbow” stack with 30 repeat units (RUs), including 4 RUs with EB-PVD GDC layers at the oxygen electrode and screen-printed GDC at fuel electrode, 3 RUs with EB-PVD GDC layers at both electrodes and 23 RUs with state-of-the-art screen-printed GDC layers at both electrodes. The stack was operated for over 5000 h in SOEC mode under a current density of -410 mA cm−2 and 75 % steam conversion, with a feed gas composition of 80 % steam + 10 % H2 + 10 % N2 on the fuel electrode and air on oxygen electrode.In this paper, the investigation focuses on the electrochemical characteristics of RUs containing the EB-PVD thin-film GDC layers during the SOEC stack testing. The performance and degradation behavior of the stack and representative RUs were investigated and compared by means of current-voltage curves and electrochemical impedance spectroscopy (EIS). The initial performance and the degradation of the voltage and resistances of the stack and the RUs with EB-PVD GDC thin-film layers were determined and discussed in order to evaluate the effectiveness of the modifications in the scenario of long-term SOEC stack testing.The German Federal Ministry for Education and Research (BMBF) is acknowledged for the financial supports within the project H2GiGa-HTEL (grant no. 03HY124E).

Micro Tubular Solid Oxide Reversible Cell Using LaGaO3 Electrolyte Film Prepared on Channel Size Controlled NiO-YSZ Substrate

Reversible operation of SOFC is now important subjects from energy storage of renewable electric power from solar or wind power. At present, planer type cell design is widely used for this purpose, however, because of tight gas sealing, tubular type cell design is more suitable. In this study, micro tubular solid oxide cell using La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) thin electrolyte film was prepared by dip-coating and co-sintering process.NiO-YSZ porous substrate with 10 mm diameter and 30 mm length was used for preparation of the cell. LaGaO3 based oxide film was deposited with dip coating method. Two kinds of NiO and YSZ particles with different particle size (0.91 and 0.65 mm for NiO and 0.62 and 0.25 mm for YSZ) were mixed and extruded for tubular substrate. 4 types of NiO-YSZ anode porous substrate were Average porosity of each 4 tubular substrate was ca. 70% after reduction. However, from SEM observation, channel size in NiO-YSZ substrate was changed and NiO-YSZ using larger NiO and YSZ particles shows larger channel diameter.Power generation property of 4 tubular cell using different NiO and YSZ particle size for substrate. It was found that the cell deposited on NiO-YSZ using larger particles shows lager power density, in particular, the cell using both NiO and YSZ larger particles shows the largest power density (0.37 W/cm2 at 873 K), which is reasonably large power density. On the other hand, in case of electrolysis, channel size is also strongly influenced on the electrolysis current. As similar manner with fuel cell operation, the LSGM cell prepared on larger particles size of NiO and YSZ shows larger steam electrolysis current. Impedance analysis suggests that the effects of particle size of NiO and YSZ was explained by small concentration overpotential, and so larger channel size is effective for improving the initial performance of the SORC performance. Long term stability of the steam electrolysis was performed and it was found that the LSGM tubular cell prepared on NiO-YSZ with larger particles shows the reasonable stable electrolysis performance in long term stability (-4%/1000h average degradation rate). The main reason for degradation was assigned to the increased IR loss however overpotential was hardly changed over 600 h and so it seems most likely that the reoxidation of NiO or aggregation of NiO is the main reason for degradation of the cell.This study reveals that the control of channel size in NiO-YSZ porous substrate is highly important for initial performance and long-term stability of SORC.

Stabilization of Platinum Catalyst Surface-Treated by Atomic Layer Deposition of Cobalt for Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) are attracting attention as next-generation energy-conversion devices because they are environmentally friendly and have high energy-conversion efficiencies. A membrane electrode assembly (MEA), composed of an anode, membrane, and cathode, is the most important part of a PEMFC where electrochemical reactions occur. A Pt/C catalyst, wherein Pt is supported on a carbon, is used as the catalyst layer for the anode and cathode. However, as Pt is a precious metal, current research is focused on reducing its loading and improving durability of PEMFCs. This study focused on improving the durability of catalysts by suppressing agglomeration, one of the degradation mechanisms of Pt catalysts. A protective layer of Co metal was deposited using the atomic layer deposition (ALD) process to improve the durability of catalysts. The ALD process is a type of chemical vapor deposition (CVD) process. This process is suitable for the PT/C catalyst as it allows for the deposition of a uniform thin film even on the porous catalyst layer. If the protective layer is thick, it may block the active site of the catalyst, resulting in decreased activity and reduced performance. However, ALD can form a thin protective layer because it can be controlled at the atomic level by adjusting the number of cycles. After fabricating a single cell using ALD Co-Pt/C as a catalyst for the cathode, The U.S. Department of Energy's electrocatalyst durability protocol was used for an accelerated degradation test (ADT). After Co-ALD was used as a cathode for 10 and 20 cycles, the active area of the Pt catalyst particles was reduced owing to the metal Co protective layer. The initial performance and electrochemical surface area (ECSA) of Co-ALD 10, 20 cycles decreased compared to the case of using Co-ALD 0 cycle. However, after ADT, the performance and ECSA reduction rate rather decreased, confirming that the co-protective layer through the plasma-enhanced atomic layer deposition (PEALD) process can improve the durability of the Pt/C catalyst. To identify the cause of the durability improvement, the cathode catalyst particles before and after ADT were compared through high resolution transmission electron microscopy (HR-TEM) analysis. As a result, in the HR-TEM images after ADT, the Pt catalyst particles were relatively uniformly distributed on the carbon support in the Co-Pt/C catalyst compared to Co-ALD 0 cycle. In addition, it was confirmed that the size of the Pt catalyst particles of Co-Pt/C was smaller than that of bare Pt/C (Co-ALD 0 cycle). It was concluded that when the Co protective layer was deposited on the Pt/C cathode, the protective layer suppressed the agglomeration of Pt catalyst particles, therefore, the increase in Pt particle size improved compared to the Co-ALD 0 cycle, and it was revealed that durability improved by suppressing catalyst degradation.

Numerical Simulation of the Carbon Deposition Mechanism of Solid Oxide Fuel Cells Based on Total Harmonic Distortion Analysis

Identifying the corresponding degradation mechanisms at the early stage of operation is important for the long-term stable operation of solid oxide fuel cells (SOFCs). This paper uses total harmonic distortion analysis (THDA) to identify the anode carbon deposition mechanism in the early stage of SOFC operation with carbon-containing fuels. An accelerated calculation model for the electrochemical impedance spectrum (EIS) and a total harmonic distortion calculation model were constructed to study the carbon deposition mechanism and carbon removal strategy of SOFC anodes based on a one-dimensional transient elementary reaction kinetic model of an SOFC fueled by a CH4/H2O mixture. It is shown that the THDA calculation model can identify the primary stages of carbon deposition on SOFC anodes at specific frequencies. The THDA profiles at frequencies greater than 2 kHz contain essentially the same key information as at lower frequencies, suggesting that THDA can significantly reduce the test time for identifying performance degradation in the early stages of SOFC operation compared to EIS. Using a mixture of hydrogen and water vapor to remove the solid carbon generated by the cell anode and restore it to its initial performance, the THDA computational model can successfully respond to this process.

(Digital Presentation) Finding the Optimum Loading of Fe & Au in NiO/GDC, for the Reversible Operation of Solid Oxide Cells

Reversible solid oxide cells (rSOCs) are ideal candidates for renewable energy storage and usage, due to their ability to work under electrolysis mode for H2 production or fuel cell mode for power generation, both by the same unit. Operation of SOCs at high-temperatures enables high energy efficiency, increases reaction rates, and allows the use of low-cost catalysts compared to low temperature technologies. The state-of-the-art (SoA) fuel electrodes: Ni/YSZ and Ni/GDC, despite their advantages, are prone to various degradation phenomena, such as Ni coarsening, agglomeration, and depletion/migration. One way to mitigate these issues is by dispersing small amounts of transition metal additives, either non-noble or noble elements, into the Ni-based electrode [1, 2, 3].Recent studies [1] on how Fe interacts with Ni in Ni/GDC showed that the enhancing effect of Fe on the electrochemical performance under electrolysis conditions is constrained by its wt.% concentration, whereas even if the electrode exhibited high activity, it was prone to fast degradation. In our latest work, we presented a first attempt on co-depositing Fe and Au, with the primary objective being the stabilization of the enhancing effect of Fe on Ni/GDC. Thus, an electrode consisted of the, by that time, best performing loadings was synthesized, namely 0.5 wt.% Fe and 3 wt.% Au, showcasing the enhancing effect of this modification on both the activity and stability, under rSOC operation. The superiority of this electrode is primarily ascribed to the induced changes by the Fe-Au-modification on the intrinsic electrochemical characteristics, as indicated by the ohmic and polarization resistance values. These are far lower to those of Ni/GDC and of the optimum Au-Mo-modified electrode [3], particularly under SOE operation. Another remark is the rSOC stability of both electrochemical characteristics, but especially of the Rpol .The presented study focuses on how each of the Au and Fe modifiers affects the physicochemical and electrochemical characteristics of the electrode. In this respect, several electrocatalysts were synthesized, consisted of different Au and Fe loadings, and then evaluated under r-SOC operation. By reducing the Au concentration to 1 wt.%, the performance of the electrode increased, which is attributed mainly to the lower Rohm values, and less to these of Rpol that remain practically constant. On the other hand, by increasing the Fe loading to 2 wt.% and by keeping the Au loading to 3 wt.%, the electrode had the same initial performance, but after three rSOC cycles the performance slightly dropped, due to the increase of both Rohm and Rpol values. In parallel to the electrochemical measurements, physicochemical characterization is performed for further elucidation of the electrodes/powders properties.

Atomically Dispersed Single Mn Site-Rich Carbon for PtCo Intermetallic Catalysts with Promoted Performance and Durability for Heavy-Duty Fuel Cells

Promoting the activity and durability of the Pt-based catalysts with a reduced platinum group metal (PGM) loading holds significance to the deployment of proton-exchange membrane fuel cells (PEMFCs) in the transportation market. In this work, synergistic catalysts, which integrate ultrafine Pt-based nanoparticles with ORR-active single atom catalysts (SACs), were studied to meet the activity and stability milestones for Pt-based catalysts. The synergistic effect between different SACs and ultrafine Pt nanoparticles were firstly elucidated via DFT calculations. It indicates that MnSA-NC catalyst with high surface area and abundant single atoms sites can improve the activity and stability of Pt catalyst via a strong electronic interaction. Ultrafine Pt and L12 Pt3Co intermetallic nanoparticles were uniformly anchored in the MnSA-NC via a facile strategy. The structures of the Pt@MnSA-NC and Pt3Co@MnSA-NC were comprehensively studied by multiple transmission microscopy and X-ray absorption spectroscopy. It reveals that ultrafine Pt and L12 Pt3Co intermetallic nanoparticles are anchored amongst the atomically dispersed MnNx sites. The Pt@MnSA-NC catalyst achieved a mass activity (MA) of 0.698 A mgPt −1 (@0.9ViR-free) and maintained 86 % of its initial performance after 30,000 cycles of accelerated stress test (AST, 0.6 and 0.95 V), exceeding the DOE target for 2025. By intercalating Co into the Pt nanoparticles, the L12 Pt3Co@MnSA-NC catalyst achieved significantly improved activity, achieving a MA of 0.905 A mgPt −1 and 1.631 A cm−2 (@0.7 V, H2-air fuel cell) at 150 kPaabs with 0.10 mgPt cm−2 in the cathode. The loss in the performance at 0.7 V is only 27.2 %, manifesting its high intrinsic stability. Furthermore, the performance of L12 Pt3Co@MnSA-NC catalyst (20 wt.% Pt) was studied under the heavy-duty vehicle (HDV) conditions with a higher Pt loading (0.20 mgPt cm−2) and higher backpressure (250 kPaabs). Encouragingly, the current densities at 0.67 and 0.7 V are 2.12 and 1.80 A cm−2, respectively. After 30,000 cycles of AST, the loss in MA is only 17.4 %, 87.0 % of performance were retained at 0.67 and 0.7 V. The compelling performance holds a great potential to meet the DOE target set for HDVs (>1.07 A cm−2 at 0.7 V after 250,000 hours equivalent operations). The synergistic effect revealed in this work shed light on the design of highly efficient catalysts for PEMFCs.

Experimental Analysis of the Effect of Cathodic CO2 Supply to Industrial Solid Oxide Fuel Cells

The integration of Solid Oxide Fuel Cells (SOFCs) in hybrid power generation systems offers the opportunity to achieve higher electric efficiencies. In the SOS-CO2 cycle [1], a newly developed cycle for blue power production (i.e., power generated starting from natural gas while capturing CO2), the SOFC cathode is supplied with mixtures of CO2 and O2, up to 79% CO2 molar fraction, while the anode is supplied with a reformate feed, containing H2, CH4, CO, CO2, and water vapour. Aim of this work is to experimentally evaluate the performance and the durability of industrial 5x5 cm2 Ni-YSZ anode-supported SOFCs under the SOS-CO2 cycle conditions, focusing on the effects of the CO2-rich cathodic atmosphere. The cells mounted a LSCF-based (La0.6Sr0.4Co0.2Fe0.8O3) single phase cathode, coated by a current collection layer of LSC (La0.6Sr0.4CoO3). Laboratory tests were performed at 700°C, acquiring polarization (I/V) curves and EIS spectra by means of a Horiba – FuelCon C50 Evaluator test station. Initial investigations with 7% humidified H2 and 21/79 O2/CO2 cathodic mixture revealed 25% power loss compared to the base case with cathodic air. The test showed not only that the loss of performance was stable in time, but also that the power reduction was reversible since the initial performance in air was recovered. The EIS spectra showed an increase of the polarization resistance and of the ohmic resistance upon feeding CO2. This latter observation suggested a reduction of the electronic conductivity of the cathode, compatible with the formation of Sr carbonates on the perovskite surface [2–4]. To assess the performance of the SOFC under the operating conditions of the SOS-CO2 cycle, the anode was supplied with reformate. Compared to the base case with humidified hydrogen and air, the current density at 0.7 V decreased by 37% (490 mA/cm2). When supplying the 21/79 O2/CO2 mixture at the cathode, the current density stabilized at 420 mA/cm2 (Figure 1). Durability tests (over 300 h) at 700°C with reformate and 21/79 O2/CO2 mixture highlighted a moderate decrease of the current density at 0.7 V. After these tests, the cathode was characterized post-mortem with XRD, SEM and Raman to analyse the consequences of the prolonged exposure to CO2. To further quantify the effect of CO2 on the cathode, symmetric button cells were also characterized with EIS, measuring ohmic and polarization resistances. The results suggested that the adsorption of CO2 is reversible and indicated a better suitability of LSCF- compared to LSC-based cathodes for operations with CO2-rich mixtures. Experiments performed between 550 and 700°C at varying CO2 and O2 partial pressures allowed to describe the kinetics of the oxygen reduction reaction and extract its activation energy. Overall, the results provided key elements for the integration of SOFCs in the SOS-CO2 blue power technology.

Dialing in the Voltage Window: Reconciling Interfacial Degradation and Cycling Performance Decay with Cation-Disordered Rocksalt Cathodes

Lithium-excess, cation-disordered rocksalt (DRX) materials have received considerable interest as cathode materials for Li-ion batteries, owing to their high specific capacity and compositional flexibility. Despite these advantages, high interfacial reactivity of DRX materials causes extensive oxidative electrolyte degradation at the cathode-electrolyte interface. In addition to consuming electrolyte, this interfacial degradation is likely to lead to a cascade of deleterious effects throughout the cell, as reactive degradation products drive secondary degradation processes like dissolution of transition metals and decomposition of passivating interfacial species. While in-situ gas evolution measurements conducted by differential electrochemical mass spectrometry (DEMS) allow for the observation and quantification of the degradation processes occurring at the DRX surface, the customized cell configuration with which the technique is conducted is not well suited for capturing the performance decay driven by the interfacial degradation. In particular, a large excess of electrolyte and a large Li metal counter-electrode, both of which are necessary features of DEMS cells, serve to mask the deleterious effects of the interfacial degradation on electrochemical performance. In this work, we reconcile the degradation observed by DEMS with performance decay measured by extended cycling experiments in electrolyte-lean full cells. By comparing DRX outgassing and cycling performance in different voltage windows, we demonstrate a positive correlation between the extent of outgassing and the rate of DRX performance decay during cycling. This result provides a crucial link between the degradation measured by techniques like DEMS and the performance decay measured by cycling experiments, and it allows for the fine-tuning of a cycling voltage window which optimizes the tradeoff between initial performance and long-term stability. Furthermore, this work emphasizes the importance of cell design features, like electrolyte volume and counter-electrode material, and their impact on different electrochemical experiments.

Electrochemical Performance According to High-Capacity Silicon Active Materials in Lithium Ion Batteries

Carbon has been used as stable anode material for lithium-ion secondary batteries. However, instead of graphite with a low capacity, a new material with a high capacity that can increase the energy density per volume or mass of a lithium ion secondary battery is required. Among the various candidates, silicon has a high capacity of about 4000 mAh/g, making it a major research subject. Graphite is a combination of 6 carbon atoms and 1 lithium ion, but silicon accepts 4.4 lithium ions per atom, resulting in high volume expansion. In this way, excessive volume expansion causes cracks in the electrode and electrochemical disconnection, which eventually leads to a decrease in battery capacity. The large volume change and low electrical conductivity of silicon limits its application to anodes. Potential silicon-based materials include silicon oxide-based (SiOx), carbon-silicon composite (SiC), and pure silicon (pure Si). Silicon-based oxides have the advantages of high capacity and stable battery life, but have the limitations of low initial efficiency and low electrical conductivity. Carbon-composite silicon has high initial efficiency, high ionic conductivity, high capacity, and can be applied in the same slurry system as existing graphite electrodes. Selection of a stable binder and conductive material is important for active use of silicon-based materials. Promising binders include polyvinyl alcohol (PVA), polyacrylic acid (PAA), and polyacrylamide (PAM), and conductive materials include single-walled carbon nano tube (SWCNT), multi-walled carbon nano tube (MWCNT), and carbon-based conductive materials. In this study, we applied poly(vinyl alcohol-co-acrylic acid) random copolymer polymer as a binder and analyzed the characteristics of silicon-based batteries with various conductive materials. Slurry analyzes such as slurry dispersibility, phase stability, and rheology were performed. The initial efficiencies and cycle performances of different types of silicon-based materials were compared. It was confirmed that the type of silicon-based negative electrode material and the type of conductive material affect battery performance.

Degradation Behavior of MK35x Stacks with Chromium-Based Interconnects in Steam Electrolysis Operation

The currently ongoing commercialization of high-temperature solid oxide electrolysis (SOEL) requires the understanding of the underlying dominant degradation mechanisms to enable continuous progress in reducing stack degradation rates.In the present study, the degradation behavior of stacks with chromium-based interconnects (MK35x) and electrolyte-supported cells (ESC) developed at Fraunhofer IKTS is investigated. For this purpose, the initial electrochemical performance of 10-layer stacks was extensively characterized in various operating conditions in both fuel cell and electrolysis mode by electrochemical impedance spectroscopy (EIS). Degradation was evaluated during galvanostatic steady-state steam electrolysis operation over >3000 h in the temperature range of 800-825°C at a current density of -0.6 A cm-2, corresponding to a steam conversion rate of 75%. EIS analysis was used to separate the different loss contributions in the stack and showed that the ohmic resistance increase was the dominating performance degradation phenomenon. Moreover, electrochemical degradation rates in steady-state SOEL mode are compared to the ones in reversible mode with a daily cycling between electrolysis and fuel cell operation.Post-mortem analysis was carried out with scanning electron microscopy (SEM) to correlate the observed degradation phenomena with microstructural and morphological changes. The observed low degradation rates demonstrate that MK35x are ready for scale-up, and the present work gives guidance for operation strategies and stack design to extend their lifetime even further.