Durability study of HTPEMFC through current distribution measurements and the application of a model

In this work, a life study of a single 50 cm² high temperature proton exchange membrane fuel cell (HTPEMFC) has been carried out and experimental results are used to assess the causes of performance degradation in PBI HTPEMFC. Current distribution measurements, electrochemical characterization and physicochemical post-mortem analyses are combined with a CFD model that uses local parameters to determine that coalescence of catalyst particles (catalyst agglomeration) can be considered one of the main reasons responsible for the PBI fuel cell short life, according to electrochemically active area (ESA) and charge transfer resistance measurements. According to the current density distribution information, this agglomeration apparently occurs over the whole electrode surface. Increase of membrane resistance also contributes to the loss of fuel cell performance, but the significance is not as large as the effect of the catalyst. The model has been demonstrated to be a suitable diagnostic tool to identify degradation causes.     

Design of a cost-effective on-grid hybrid wind–hydrogen based CHP system using a modified heuristic approach

An economic model and optimization procedure is developed in this paper for grid-connected hybrid wind–hydrogen combined heat and power systems for residential applications in northeastern Iran. The model considers various significant factors: energy production cost, electrical trade with local grid, electrical power generation from the wind/hydrogen energy system, thermal recovery from the fuel cell, and maintenance. Also, various tariffs for purchasing and selling electrical energy from the local grid are considered for the hybrid system operation. The optimization objective is to minimize the system total cost subject to relevant constraints for residential applications. To achieve this aim, an efficient optimization method is proposed based on particle swarm optimization. The proposed algorithm performance is compared with that for the imperialist competition algorithm. The results show that the hybrid system is the most cost-effective for the residential load, and the results of the proposed algorithm are more promising than those for the alternative algorithm.     

Thermal management of solar cells using a nano‐coated heat pipe plate: an indoor experimental study

With temperature increasing, the photovoltaic efficiency of solar cells is reduced significantly. Such an efficiency loss may offset the efficiency improvement because of the development of the photovoltaic technology. This paper provides a novel approach for efficiency loss recovery of solar cells. Specifically, a nano‐coated heat pipe plate was integrated with the solar panel to remove heat from the hotspots on solar cells. This study concerns the indoor experiments of a commercial solar cell thermally managed with a heat pipe plate. The temperature rise and non‐uniformity on the solar panel were quantified in different light irradiances. With thermal management by the heat pipe plate, the solar panel shows a temperature‐rise reduction of 47–50%. This implies that half of the efficiency loss of the solar cell can be recovered. In addition, the temperature variation within the solar panel is reduced to 1.0–2.5 °C, which is beneficial in prolonging the longevity of the solar cell. In the experiments, the heat pipe plate can provide a cooling flux of 380 W/m² with light irradiance below 1000 W/m². By incorporating the heat pipe plate with a water jacket, the heat removal flux could be improved to 600 W/m², leading to a solar cell temperature of a few degrees higher than the ambient. Copyright © 2016 John Wiley & Sons, Ltd.     

Research on the influence of PV cell to thermal characteristics of photovoltaic/thermal solar system

In the paper, we analyzed internal thermal transmission characteristics of water‐heating photovoltaic/thermal (PV/T) solar collector covered by photovoltaic (PV) cell, established photothermal conversion model of PV/T solar system, and analyzed the influence of PV cell coverage to photothermal characteristics of PV/T solar system. Results show that the thermal efficiency of PV/T solar system by optimizing PV cells coverage can reach 68%. In addition, by designing four water‐heating PV/T solar system prototypes with PV cell coverage of 0.4, 0.56, 0.7, and 0.82, respectively, we conducted experimental researches for the four prototypes and found that the four prototypes can achieve thermal efficiencies of 58%, 51%, 64%, and 67%, respectively, in heating 250 L of water to 50°C. The experiment results are consistent with theoretical analysis results, indicating that it is feasible to improve thermal characteristics of PV/T solar system by optimizing PV cell coverage. Copyright © 2017 John Wiley & Sons, Ltd.     

Single medium microbial fuel cell: Stainless steel and graphite electrode materials select bacterial communities resulting in opposite electrocatalytic activities

A graphite electrode and a stainless steel electrode immersed in exactly the same medium and polarised at the same potential were colonised by different microbial biofilms. This difference in electroactive microbial population leads stainless steel and graphite to become a microbial cathode and a microbial anode respectively. The results demonstrated that the electrode material can drive the electrocatalytic property of the biofilm opening perspectives for designing single medium MFC.This new discovery led to of the first demonstration of a “single medium MFC.” Such a single medium MFC designed with a graphite anode connected to a stainless steel cathode, both buried in marine sediments, produced 280 mA m^?2 at a voltage of 0.3 V for more than 2 weeks.     

Influence of Cladding-Peripheral Hydride on Mechanical Fuel Failure under Reactivity-Initiated Accident Conditions

In order to investigate the influence of hydrogen embrittlement on fuel failure under reactivity-initiated accident (RIA) conditions, pulse irradiation experiments were performed with unirradiated fuel rods at the Nuclear Safety Research Reactor (NSRR). Fresh cladding was pre-hydrided so that the other factors of cladding degradation, such as irradiation damage and oxidation, were excluded. Hydride clusters are circumferentially oriented and localized in the cladding periphery in order to simulate ‘hydride rim’ which is formed in high burnup PWR cladding. The present study demonstrated hydride-assisted pellet-cladding mechanical interaction (PCMI) failure which has been observed in high burnup fuel experiments. The fuel enthalpy at failure was lower when the cladding had a thicker hydride rim where surface cracks were easily generated. It indicates that the failure limit is highly correlated with the stress intensity factor assuming that the crack depth is equivalent to the hydride rim thickness. Hence, we conclude that hydride rim formation is the primary factor of decreasing the failure limit for high burnup fuels. Based on the experimental results together with an analysis on cladding mechanical state during PCMI, the present study suggests a process of through-wall crack generation which is originated with brittle cracking within the hydride rim.     

Influence of doctor blade gap on the properties of tape cast NiO/YSZ anode supports for solid oxide fuel cells

In this study, various tape cast NiO/YSZ anode support layers with similar geometric properties are fabricated by varying the doctor blade from 100?µm to 200?µm with an increment of 25?µm. The mechanical properties of the anode support layers are investigated by three point bending tests of 30 samples for each doctor blade gap. The reliability curves of the flexural strength data are also obtained via two-parameter Weibull distribution method. The effects of the doctor blade gap on the microstructure and the electrochemical performance of the anode support layers are determined via SEM investigations and single cell performance-impedance tests, respectively. The apparent porosities of the samples are also measured by Archimedes’ principle. The results indicate that the doctor blade gap or the resultant tape thickness influences the microstructure of tape cast NiO/YSZ anode supports significantly, yielding different mechanical and electrochemical characteristics. At a reliability level of 70%, the highest flexural strength of 110.20?MPa is obtained from the anode support layer with a doctor blade gap of 175?µm and the 16?cm² active area cell with this anode support layer also exhibits the highest peak performance of 0.483?W/cm² at an operating temperature of 800?°C. Thus, a doctor blade gap of 175?µm is found to have such a microstructure that provides not only better mechanical strength but also higher electrochemical performance.     

Lightweight reactor design by additive manufacturing for preheating applications using metal hydrides

Thermal energy storage systems based on metal hydrides can be a solution for preheating fuel cells (FCs). They can provide thermal energy at temperatures below −20 °C during startup, while heat at 50 °C during operation is sufficient for regeneration. The challenge of such a system in mobile applications is the final weight specific thermal power. In this study, a reactor design based on additive manufacturing techniques for ~300 g of metal hydride is presented. Here, a reactor (passive) to hydride (active) mass ratio of 0.97 is realized, still reaching high weight specific thermal power of up to 2.1 kW/kg_MH at −20 °C and 8 bar (LmNi_4.91Sn_0.15). Considering the example of preheating a FC from −20 °C in ~120 s, the performance of LaNi₅ and LmNi_4.91Sn_0.15 is studied. While LaNi₅ requires higher regeneration temperatures than LmNi_4.91Sn_0.15 (>40 °C compared to >20 °C), its performance is less sensitive to operative variations due to its nearly ideal thermodynamic characteristic.     

Parameter identification of proton exchange membrane fuel cell via Levenberg-Marquardt backpropagation algorithm

It is essential to develop an accurate model of proton exchange membrane fuel cell (PEMFC) for a reliable operation and analysis, in which unknown parameters usually need to be determined. The inherent nonlinear, strong coupling, and diversification of PEMFC model seriously hinder traditional methods to identify the parameters. For the sake of overcoming these thorny obstacles, Levenberg-Marquardt backpropagation (LMBP) algorithm based on artificial neural networks (ANNs) is proposed for PEMFC parameter identification. Furthermore, the performance of LMBP is thoroughly evaluated and compared with four typical meta-heuristic algorithms under three cases. Simulation results indicate that LMBP performs a higher accuracy and faster speed for parameter identification. In particular, accuracy and convergence speed can achieve as much as 99.8% and 95.9% growth via LMBP, respectively.