[en] The goal of present work is to investigate activity and stability of enzyme-based catalysts both for hydrogen and oxygen reactions in proton exchange membrane (PEM) systems. (authors)

[en] Efficient operation results from a proper control strategy. In the operation and performance of a Proton Exchange Membrane Fuel Cell (PEMFC), the hydrogen gas flow rate is one of the most essential control parameter in addition to operating pressure, water management, temperature and humidity. This is because of the high cost and amount of energy are required to produce the purity hydrogen gas. In this paper, a Proportional Integral Derivative (PID) feedback control system is used to control the hydrogen flow rate. A strategy is adapted to balance the hydrogen use based on the loading requirements, especially during start-ups and sudden power demands. This system is implemented using National Instrument (NI) devices powered by the LabVIEW program. This is due to its simplicity and customization flexibility for measuring, processing and recording data. Designed structure allows the real-time implementation of a robust control law that is able to address the related nonlinearities and uncertainties without incurring a heavy computational load for the controller algorithm. While it facilitating a fast sampling rate according to the needs of the power system. Test results from the controller show that the new fuel control system provides good performance by reducing the amount of wasted hydrogen gas compared with that of the previous open loop system by 30 % to over 80 % saved by the varied load. This improvement is beneficial for any PEMFC that experiences fluctuating power demand, especially for vehicle applications. (author)

[en] System integration was developed for fuel cell to control various parameters including voltage, current, power, temperature, pressure of gas (H/sub 2/), humidification, etc. The compact software has also been developed for monitoring different parameters of fuel cell system. System integrated was installed on fuel cell stack to manipulate these parameters. The compact software has been linked with the integrated system for visual monitoring of different parameters of fuel cell system during operation on PC. The installation of software and integrated system on fuel cell stack is the key achievement for the safe operation of fuel cell stack and for the provision of requisite power to any electric device for optimum performance. The compact software was developed for micro controller in KIEL. Control card and driver card are controlled by software-driven micro controller. A communication protocol was designed and developed. PC software has been developed to control and watch the values of all parameters of fuel cell such as voltage, current, power, temperature, pressure of hydrogen, pressure of oxygen, operational times and performance of the system on computer screen. (author)

[en] One major challenge of PEM fuel cells development is to overcome the activity and durability issues of the current anode materials which are susceptible to hydrogen impurities. To design stable and efficient catalysts with enhanced reformate tolerance, a comprehensive understanding of the underlying mechanisms is crucial. In this work, the CO and CO₂ tolerance of a series of Pt-based catalysts are tested in a PEM fuel cell. We report that the CO tolerance is the highest for PtMo/C followed by PtCoMo/C, PtRuMo/C, PtRuPb/C, PtRu/C, PtCo/C, PtFe/C, PtNi/C and Pt/C; while the CO₂ tolerance increases in the order: PtCo, PtNi> PtRuPb> PtRu> PtCoMo> PtRuMo> PtFe> Pt> PtMo. In situ XAS measurements in combination with FEFF8 calculations are performed to correlate the CO and CO₂ tolerance trends with the electronic properties of these Pt-based alloy catalysts. We find that the anode overpotential in the presence of CO₂ can be generally related to the experimental Pt d-band vacancy or calculated d-band center, and thus governed by the Pt electronic properties modified by the alloyed metal(s). No such correlation is observed between the anode overpotential in the presence of CO and Pt electronic properties, which highlights the key roles of Mo or Ru in improving CO tolerance via promotion and bifunctional mechanisms. Building upon these results a new ternary alloy PtCoMo/C was synthesized. This electrocatalyst shows the best reformate tolerance in low temperature PEM fuel cells by taking advantage of the bifunctional mechanism induced by Mo and the ligand effect induced by Co simultaneously. Our findings put forward a theory which gives a strong perspective for further research and development of new inexpensive catalysts with superior CO tolerance and durability

[en] Highlights: • Correlation between temperature profile inside an operating PEMFC and its performance was investigated experimentally for the first time. • In-house very fine sensor (6 $\mathrm{\mu }$m thick and 30 $\mathrm{\mu }$m wide) was fabricated and inserted into an operating PEMFC. • Local temperature measurement and visualisation inside an operating PEMFC were performed simultaneously inside an X-ray CT machine. • Vapour transport phenomena was discussed to reveal correlation between temperature profile and the PEMFC performance. -- Abstract: Water management is critical for the function of the proton exchange membrane fuel cell (PEMFC). The local through-thickness temperature gradient of the cathode gas diffusion layer (GDL) affect water management for a PEMFC. That has been known and been targeted for the discussion for several years. In this study, the effects of temperature gradient inside PEMFC was investigated by controlling it externally with a fine (testing diameter about 30 $\mathrm{\mu }$m) and thin (thickness about 6 $\mathrm{\mu }$m) thin-film thermocouple (TFTC), which has been developed using micro electromechanical system (MEMS) technology. In addition, X-ray computed tomography (CT) has been chosen as a method to visualise inside of an operating PEMFC. The simultaneously measurement of temperature gradient and liquid water distribution was firstly accomplished. In conclusion, in the case where the temperature of the cathode catalyst coated membrane (CCM) side is higher than that of the channel side, the PEMFC performance drastically decreased. The difference in PEMFC performance was caused by a difference the preferential sites for water condensation.

[en] In order to obtain the optimal output performance of the air-cooled self-humidifying proton exchange membrane fuel cell (PEMFC), the operating temperature, the air flow, purge interval and some other parameters must be controlled strictly. As a key factor, the operating temperature mainly determines the optimal output performance of the fuel cell. However, some intrinsic issues such as long adjusting time, over-shoot still exist inevitably for the traditional PID temperature-controlled method in circumstances of the load variation. Consequently, output performance of PEMFC decreases because the operating temperature of the fuel cell fails to reach, and the corresponding lifetime of PEMFC is also reduced. In this study, a segmented predict negative feedback control method, based on the advance proportional control one, is proposed and verified by experiments to overcome the shortcomings of PID temperature control. The results demonstrate that the optimal output performance of PEMFC can be realized by utilizing the proposed method for temperature control due to its excellent properties, simple controlling and small over-shoot

[en] Highlights: • A comprehensive review of researches on PEMFC degradation in start-stop condition. • Include degradation mechanism, accelerated lifetime tests and mitigation solutions. • Further researches should be taken from aspects such as material and strategy. The lifetime of the proton exchange membrane fuel cell (PEMFC) is the main issue restricting its commercialization. During real vehicular applications, the fuel cell engine mainly experiences four dynamic conditions: load changing, start-stop, idling, and high power. Since the start-stop condition has a great impact on the lifetime of fuel cells, it is necessary to fully understand the degradation mechanism of PEMFC under this condition. This paper discusses the background and progresses in related research, analyses the gas distribution process inside the fuel cells during start-stop, and summarises the main mechanism and factors that lead to the degradation. Then, solutions in terms of material improvement and system control are listed. This review can provide a basis for solving the degradation problem in PEMFCs and improving the cell lifetime.

[en] Enhanced Cross-flow split serpentine flow field (ECSSFF) for a rectangular cross sectional polymer electrolyte membrane fuel cells (PEMFCs) has been shown to be an effective layout compared to parallel serpentine designs. The concept of ECSSFF channel layout is extended to a square cross-sectional cell in this work. This is carried out with a detailed 3D and two-phase flow coupled with electrochemistry analysis in a computational environment using ANSYS®17.2. A detailed parametric study for fuel cell having square ECSSFF channel design is presented in this work. In addition, this layout is also evaluated for its efficacy at higher active areas up to 200 cm². The study on different channel to rib width ratios has indicated that the ratio of 1:1 results in peak performance at cell operating pressure and temperatures of 200 kPa and 70 °C for fully humidified anode reactants and 50% humidified cathode reactants. The performance of the square PEMFC with 4-channel ECSSFF design on cathode side is found to be superior to that with five parallel serpentine design and the proposed design is also found to be effective for higher active areas.

[en] This paper is meant to provide a basic introduction to electrochemical energy conversion. It should be a low-barrier entry point for reading the relevant literature and understanding the basic phenomena, approaches and techniques. Starting with some basics of electrochemistry to establish the most important techniques, I will touch upon established electrochemical processes which are carried out today on industrial scale to finish with an outline of state-of-the art research on proton exchange membrane fuel cells and electrolysers for water splitting.

[en] Highlights: • Modified serpentine flow fields were presented to improve PEMFC performance. • Secondary flow is first used to explain performance improvement of PEMFC with modified serpentine flow fields. • Secondary flow in the turn domain is very strong and the local current density is consequently increased. • The oxygen concentration distribution uniformity is analyzed for modified serpentine flow fields. -- Abstract: Modified serially–linked serpentine flow fields are proposed for proton exchange membrane fuel cells (PEMFCs) and their performances are numerically studied. The effects of the segment number and the channel path number on the cell performance are analyzed. Especially The effect of the secondary flow on the cell performance is particularly discussed. Numerical results indicate that the modified serpentine flow fields can obviously improve the cell performance in comparison with the parallel flow field. The cell performances can be improved by increasing the segment number or the channel path number in each segment. The reactant transport under the rib and the secondary flow in the channel are considered as the main causes for the high cell performance of PEMFC with modified serpentine flow fields. The secondary flow can be generated by the combination of the under–rib flow and the serpentine turn. In comparison with the parallel flow field, the modified serpentine flow fields have higher average oxygen concentration but lower uniformity of the oxygen concentration distribution.