Effect of different control strategies on rapid cold start-up of a 30-cell proton exchange membrane fuel cell stack

Many places experience extreme temperatures below −30 °C, which is a great challenge for the fuel cell vehicle (FCV). The aim of this study is to optimize the strategy to achieve rapid cold start-up of the 30-cell stack at different temperature conditions. The test shows that the stack rapidly starts within 30 s at an ambient temperature of −20 °C. Turning on the coolant at −25 °C show stability of the cell voltage at both ends due to the end-plate heating, however, voltage of intermediate cells fluctuates sharply, and successful start-up is completed after 60 s. The cold start strategy changes to load-voltage cooperative control mode when the ambient temperature reduced to −30 °C, the voltage of multiple cells in the middle of the stack fluctuate more drastic, and start-up takes 113 s. The performance and consistency of the stack did not decay after 20 cold start-up experiments, which indicates that our control strategies effectively avoided irreversible damage to the stack caused by freeze-thaw process.     

Review on zirconate-cerate-based electrolytes for proton-conducting solid oxide fuel cell

The performance of low-to-intermediate temperature (400–800?°C) solid oxide fuel cells (SOFCs) depends on the properties of electrolyte used. SOFC performance can be enhanced by replacing electrolyte materials from conventional oxide ion (O^2-) conductors with proton (H⁺) conductors because H⁺ conductors have higher ionic conductivity and theoretical electrical efficiency than O^2- conductors within the target temperature range. Electrolytes based on cerate and/or zirconate have been proposed as potential H⁺ conductors. Cerate-based electrolytes have the highest H⁺ conductivity, but they are chemically and thermally unstable during redox cycles, whereas zirconate-based electrolytes exhibit the opposite properties. Thus, tailoring the properties of cerate and/or zirconate electrolytes by doping with rare-earth metals has become a main concern for many researchers to further improve the ionic conductivity and stability of electrolytes. This article provides an overview on the properties of four types of cerate and/or zirconate electrolytes including cerate-based, zirconate-based, single-doped cerate–zirconate and hybrid-doped cerate–zirconate. The properties of the proton electrolytes such as ionic conductivity, chemical stability and sinterability are also systematically discussed. This review further provides a summary of the performance of SOFCs operated with cerate and/or zirconate proton conductors and the actual potential of these materials as alternative electrolytes for proton-conducting SOFC application.     

A fuzzy logic PI control with feedforward compensation for hydrogen pressure in vehicular fuel cell system

In a vehicular fuel cell system, alternative load and frequent purge action can lead to anode pressure varies with the hydrogen mass flow fluctuation. It's crucial to control the pressure difference between anode and cathode within a reasonable range to avoid adverse phenomena such as membrane failure, reactant starvation, or even water management fault. In this paper, an improved proportional integrative (PI) controller by the fuzzy logic technique that considers the engineer experience and knowledge on the hydrogen supply system behavior is proposed for hydrogen pressure control, in which the PI parameters are tuned by a fuzzy decision process. Furthermore, load current and purge action regarded as input disturbances are applied for feedforward compensation to reduce the pressure response hysteresis. A hydrogen supply subsystem based on the proportional valve is modeled, and corresponding parameters are determined by analyzing the response time and steady pressure fluctuation. The performance of the conventional PI controller, the fuzzy logic PI (FLPI) controller and fuzzy logic PI with feedforward (FLPIF) controller is validated. The presented results indicated that the FLPI controller significantly improves the dynamic response of hydrogen pressure compared to the PI controller, and the FLPIF controller can further reduce overshoot caused by disturbance. Finally, the proposed FLPIF controller is implemented on a rapid prototype platform of the hydrogen supply subsystem and an actual fuel cell system, exhibiting satisfactory performance.     

Composition-tunable PtCu porous nanowires as highly active and durable catalyst for oxygen reduction reaction

To accelerate the commercialization of fuel cells, many efforts have been made to develope highly active and durable Pt-based catalyst for oxygen reduction reaction (ORR). Herein, PtCu porous nanowires (PNWs) with controllable composition are synthesized through an ultrasound-assisted galvanic replacement reaction. The porous structure, surface strain, and electronic property of PtCu PNWs are optimized by tuning composition, which can improve activity for ORR. Electrochemical tests reveal that the mass activity of Pt_0.5Cu_0.5 PNWs (Pt/Cu atomic ratio of 1:1) reaches 0.80 A mg_Pt^?1, which is about 5 times higher than that of the commercial Pt/C catalyst. Notably, the improved activity of the porous nanowire catalyst is also confirmed in the single-cell test. In addition, the large contact area with the carrier and internal interconnection structure of Pt_0.5Cu_0.5 PNWs enables them to exhibit much better durability than the commercial Pt/C catalyst and Pt_0.5Cu_0.5 nanotubes in accelerated durability test.     

Thermal analysis and management of proton exchange membrane fuel cell stacks for automotive vehicle

The thermal management of a proton exchange membrane fuel cell (PEMFC) is crucial for fuel cell vehicles. This paper presents a new simulation model for the water-cooled PEMFC stacks for automotive vehicles and cooling systems. The cooling system model considers both the cooling of the stack and cooling of the compressed air through the intercooler. Theoretical analysis was carried out to calculate the heat dissipation requirements for the cooling system. The case study results show that more than 99.0% of heat dissipation requirement is for thermal management of the PEMFC stack; more than 98.5% of cooling water will be distributed to the stack cooling loop. It is also demonstrated that controlling cooling water flow rate and stack inlet cooling water temperature could effectively satisfy thermal management constraints. These thermal management constraints are differences in stack inlet and outlet cooling water temperature, stack temperature, fan power consumption, and pump power consumption.     

Enhanced hydrogen production through alkaline electrolysis using laser-nanostructured nickel electrodes

This study describes the fabrication of ultrafast laser-induced periodic nanostructures on Nickel sheets and their use as cathodes in alkaline electrolysis. For the first time, to the best of our knowledge, laser-nanostructured Ni sheets were used as cathode electrodes in a custom-made electrolysis cell at actual, Hydrogen producing conditions, and their efficiency has been compared to the untreated Nickel sheets. The electrochemical evaluation showed higher J_peaks, lower overpotential, and enhanced double-layer capacitance for the nanostructured electrode. A decrease in the Tafel slope was also found for the nanostructured electrode. The hydrogen production efficiency was found to be 3.7 times larger for the laser-nanostructured Nickel electrode, which was also confirmed by current-time measurements during electrolysis. Also, a novel approach is proposed to improve the stability of the current density during electrolysis and, therefore, the hydrogen production process by about 10%.     

Techno-economic analysis of hydrogen energy for renewable energy power smoothing

With the increasing proportion of renewable energy (mainly wind power and photovoltaic) connected to the grid, the fluctuation of renewable energy power brings great challenges to the safe and reliable operation of power grid. As a clean, low-carbon secondary energy, hydrogen energy is applied in renewable energy (mainly wind power and photovoltaic) grid-connected power smoothing, which opens up a new way of coupling hydrogen storage energy with renewable energy. This paper focuses on the optimization of capacity of electrolyzers and fuel cells and the analysis of system economy in the process of power output smoothing of wind/photovoltaic coupled hydrogen energy grid-connected system. Based on the complementary characteristics of particle swarm optimization (PSO) and chemical reaction optimization algorithm (CROA), a particle swarm optimization-chemical reaction optimization algorithm (PSO-CROA) are proposed. Aiming at maximizing system profit, the capacity of electrolyzers and fuel cells are constrained by wind power fluctuation, and considering environmental benefits, government subsidies and time value of funds, the objective function and its constraints are established. According to the simulation analysis, by comparing the calculated results with PSO and CROA, it shows that PSO-CROA effectively evaluates the economy of the system, and optimizes the optimal capacity of the electrolyzers and fuel cells. The conclusion of this paper is of great significance for the application of hydrogen energy storage in the evaluation of power smoothness and economy of renewable energy grid connection and the calculation of economic allocation of hydrogen energy storage capacity.     

Performance of surface ionic conduction single chamber fuel cell prepared by the sol gel method

The performance of surface ionic conduction single chamber fuel cell (SIC‐SCFC) prepared by the sol gel method was studied on electric characteristics due to the differences of the operating temperature and humidity, the electrode distance and electrolyte film depth, and multiple cells with the series and parallel connections. The SIC–SCFC was arranged the both anode of Pt and cathode of Au on the boehmite electrolyte. The open circuit voltage (OCV) of single cell achieved a maximum of 530mV in the dry gas mixtures of O₂/H₂=50% in room temperature operation, and but it became decrease as over 60%. The OCV was maintained the constant value between operating temperatures of 30°C to 80°C, and but it was decreased sharply at over 90°C because a humidity on the cell became lower as increasing operating temperature. Then, the cell property was improved to 120°C by adding to the humidity of 70% using a humidifier. The electrode distance and the electrolyte film depth of SIC‐SCFC found to be contributed to the reductions of the cell resistance and the surface roughness on the electrode, respectively. Moreover, the power property of SIC‐SCFC was significantly improved by cell stacks comprised of the series or parallel connection of a cell.     

Low-temperature constrained sintering of YSZ electrolyte with Bi2O3 sintering sacrificial layer for anode-supported solid oxide fuel cells

Solid oxide fuel cells (SOFCs) have strong potential for next-generation energy conversion systems. However, their high processing temperature due to multi-layer ceramic components has been a major challenge for commercialization. In particular, the constrained sintering effect due to the rigid substrate in the fabrication process is a main reason to increase the sintering temperature of ceramic electrolyte. Herein, we develop a bi-layer sintering method composed of a Bi₂O₃ sintering sacrificial layer and YSZ main electrolyte layer to effectively lower the sintering temperature of the YSZ electrolyte even under the constrained sintering conditions. The Bi₂O₃ sintering functional layer applied on the YSZ electrolyte is designed to facilitate the densification of YSZ electrolyte at the significantly lowered sintering temperature and is removed after the sintering process to prevent the detrimental effects of residual sintering aids. Subsequent sublimation of Bi₂O₃ was confirmed after the sintering process and a dense YSZ monolayer was formed as a result of the sintering functional layer-assisted sintering process. The sintering behavior of the Bi₂O₃/YSZ bi-layer system was systematically analyzed, and material properties including the microstructure, crystallinity, and ionic conductivity were analyzed. The developed bi-layer sintered YSZ electrolyte was employed to fabricate anode-supported SOFCs, and a cell performance comparable to a conventional high temperature sintered (1400 °C) YSZ electrolyte was successfully demonstrated with significantly reduced sintering temperature (<1200 °C).     

Black phosphorous nanosheets–gold nanoparticles–cisplatin for photothermal/photodynamic treatment of oral squamous cell carcinoma

To improve five-year survival rate of oral squamous cell carcinoma (OSCC), the development of a novel composite material of black phosphorus nanosheets (BPNSs) and gold nanoparticles (AuNPs) for tumor treatment was carried out. The purpose of this study is to evaluate the cytostatic effects of BPNSs, AuNPs loaded with cisplatin (CDDP) on human tongue squamous cell carcinoma cells lines (SCC-9), and 7,12-dimethylbenz anthracene induced cheek squamous cell carcinoma was validated in golden hamsters animal models. The results showed that BPNSs could efficiently inhibit the metastasis and growth of OSCC compared with CDDP and AuNPs. And a combination composite of AuNPs–BPNSs loaded with CDDP could more effectively inhibit the metastasis and growth of OSCC, which might be due to the high drug-loading capacity, excellent photothermal properties and the combination of photodynamic and photothermal therapy of BPNSs and AuNPs, as well as the synergistic effects of AuNPs, BPNSs and CDDP.