Background Surgery is a main event in an individual's life. The full surgical episode is known as perioperative interval. Perioperative process in general includes three stages: preoperative, intraoperative, and postoperative. The first stage (preoperative) includes giving of nursing care to the patients who are planned to undergo surgery. It was evident that through this stage, evaluation and education of the patient are the main responsibility of health service providers to have better results of the patients. Objective The purpose of the study was to assess the methods of performing preoperative fitness assessment for noncardiac patients in Assiut University Hospital for Children, to compare these methods with the standard methods, to confirm what is necessary and bypass needless investigations, and to provide a reference framework for the preoperative evaluation of children. Patients and methods The study was conducted at Assiut University Children Hospital. Data of children who attended the outpatient fitness assessment clinic during a 6-month period were collected and analyzed, and their management was compared with the standard management guidelines. All patients attended the outpatient fitness clinic during 6 months from 1 November 2017 to 30 April 2017. The authors collected all cases that attended the outpatient fitness clinic for surgery except cardiac surgeries. Conclusion It was concluded that preoperative blood tests are unnecessary in American Society of Anesthesiologists grade-1 patients undergoing minor/moderate surgery. A main cause of overtesting is the belief between junior staff that consultants wanted them or simply by habit. When compared with surgeon-ordered testing, anesthesiologist-ordered testing was more focused and less costly. There is a requirement to have guidelines for indicated tests in different groups of diseases and procedures to be ordered by the physicians to prevent unnecessary loss of time, money, and resources and to bypass overburdening laboratory staff.

The purpose of this study is to compare the degradation phenomena in high-temperature polymer electrolyte fuel cells (HT-PEFCs) under various operating conditions and investigate the degradation mechanism by using accelerated stress tests. Five stressors (i.e., high temperature, thermal cycling, open circuit voltage, high load cycling, and low load cycling) are applied to identical HT-PEFCs and compared to the standard operating condition. Extensive characterizations of the aged HT-PEFCs are then performed using techniques that include focused ion beam/scanning electron microscopy, inductively coupled plasma-mass spectrometry, energy dispersive X-ray mapping/line-scan analysis, polarization curves, electrochemical impedance spectroscopy and cyclic voltammetry. The results present a negligible amount of phosphoric acid leaching and notable degradation of the Pt/C catalyst. On the anode side, slight Pt corrosion is only visualized under open circuit conditions, while on the cathode side, evident Pt agglomeration in the catalyst layer and different Pt precipitation behaviors in the membrane are observed under all the conditions. The highest amount of Pt precipitation occurs in the cells held at open circuit voltage and cycled at low loads, which also exhibit the most pronounced performance degradation. In addition, the PA redistribution between the membrane and electrodes contributes to the cells’ resistance and performance differences.

A computational fluid dynamics model for high-temperature polymer electrolyte fuel cells (PEFC) is developed. This allows for three-dimensional (3D) transport-coupled calculations to be conducted. All major transport phenomena and electrochemical processes are taken into consideration. Verification of the present model is achieved by comparison with current density and oxygen concentration distributions along a one-dimensional (1D) channel. Validation is achieved by comparison with polarization curves from experimental data gathered in-house. Deviations between experimental and numerical results are minor. Internal transport phenomena are also analyzed. Local variations of current density from under channel regions and under rib regions are displayed, as are oxygen mole fractions. The serpentine gas channels contribute positively to gas redistribution in the gas diffusion layers (GDLs) and channels.

One of the main hurdles in achieving optimum performance for the high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) is to come up with just the right combination of material parameters for membrane electrode assembly (MEA) construction. In this study, we investigate the effect of platinum (Pt) loading, cathode catalyst layer (CCL) thickness and the phosphoric acid doping level (PADL) on the performance of a polybenzimidazole (PBI) based HT-PEMFC MEA. The range for each parameter is carefully chosen to address the need of optimizing cell performance at minimum cost. These experiments build on some of the results obtained by Fang et al [1], but with different operating conditions and analysis procedure and a greater emphasis on CCL characterization. It is very important to reduce CCL thickness as it is a limiting factor for effective diffusion of oxygen to the so-called triple phase boundary (TPB). The CCL thickness is varied between 60 µm and 120 µm to analyze the reduction potential. The Pt loading should be as low as possible to reduce cost. The cathode loading for most commercially available HT-PEMFC MEAs is close to 1 mg/cm2. Therefore, this value is used as the upper limit, and 0.6 mg/cm2 is selected as the lower limit. PADL is vital in HT-PEMFC MEAs because phosphoric acid provides the protonic conductivity in the PBI based membrane. A higher doping level improves protonic conductivity, but also floods the pores within the CCL, thus impeding smooth diffusion of oxygen to available TPBs. A range of 15 mg/cm2 to 25 mg/cm2 is selected for the PADL based on literature values and previous experience. All the gas diffusion electrodes (GDE) are prepared by the doctor blade method. Two types of catalyst (20 wt% and 40 wt% Pt/C), spacers with different thicknesses and inks with different proportion of ingredients are used to control the thickness and Pt loading of GDEs. As for the PADL, the doping level of all the membranes is kept at 15 mg/cm2, and 25 mg/cm2 PA doped MEA is obtained by adding extra 5 mg/cm2PA on both cathode and anode GDEs. A series of designed experiments similar to those presented in Rahim et al [2] is performed using the selected ranges of each parameter. A total of nine MEAs with different parameters are evaluated using polarization curves and electrochemical impedance spectroscopy (EIS) in single cells with an active area of 14.44 cm2. The impedance measurements are performed in the low current density regime (up to 100 mA/cm2) and with a very high cathode stoichiometry (operation as a differential cell – constant conditions inside the cell with hardly any depletion of oxygen between inlet and outlet). This makes it possible to characterize the CCL on the basis of characteristic fuel cell parameters by almost eliminating the mass transport losses within the CCL. Cell impedance is measured at four selected current densities of 10, 20, 50 and 100 mA/cm2. The impedance spectra are fitted with an equivalent circuit model (ECM) to extract the ohmic resistance (RΩ) of the cell, the activation resistance (Ract), the protonic resistance (Rp) and the double layer capacitance (Cdl) of the CCL. All of these cell parameters are found to be a strong function of current density in agreement with some of the observations made by Wippermann et al [3], especially concerning the RΩ. Finally, a comparison is made between all MEAs and the optimum level for each material parameter is analyzed based on the obtained cell parameters and a discussion of the underlying physics. References [1] Liu F, Mohajeri S, Di Y, Wippermann K, Lehnert W. Influence of the Interaction between Phosphoric Acid and Catalyst Layers on the Properties of HT-PEFCs. Fuel Cells 2014;14:750–7. doi:10.1002/fuce.201300272. [2] Rahim Y, Janßen H, Lehnert W. Characterizing membrane electrode assemblies for high temperature polymer electrolyte membrane fuel cells using design of experiments. Int J Hydrogen Energy 2017;42:1189–202. doi:10.1016/j.ijhydene.2016.10.040. [3] Wippermann K, Wannek C, Oetjen HF, Mergel J, Lehnert W. Cell resistances of poly(2,5-benzimidazole)-based high temperature polymer membrane fuel cell membrane electrode assemblies: Time dependence and influence of operating parameters. J Power Sources 2010;195:2806–9. doi:10.1016/j.jpowsour.2009.10.100.

A comparative study of four different high temperature polymer electrolyte membrane fuel cell (HT-PEFC) polybenzimidazole (PBI) based membrane electrode assemblies (MEAs) is undertaken utilizing the design of experiments (DOE) method, a very valuable statistical optimization method, much underutilized in fuel cell research. Single cell voltages are examined as a response (target variable) at two levels (high and low) of four factors (controlled variables); anode and cathode stoichiometry, operating temperature and current density. This yields a two-level, four factor (24) full factorial DOE. The data is used to form a linear regression model for each MEA, which is in turn utilized to predict the cell voltage at random values within the selected ranges of the four factors for validation. The main effects and two factor interactions of each factor are compared to determine their effect on the cell voltage and the underlying physics is examined to determine the best performing MEAs. The PBI based MEA has a much higher tolerance to carbon monoxide (CO) in the fuel stream in comparison with Nafion based MEAs due to the different proton conducting mechanism as well as a higher operating temperature, thus enabling reliable operation of HT-PEFC stacks with reformate containing upto 3% CO.