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New Swedish research suggests that low-platinum fuel cells for hydrogen vehicles, when scaled up for the same number of cells, can achieve efficiencies similar to or higher than commercial fuel cells. Its modeling is expected to serve as a bridge between materials science research and implementation in vehicles.
Scientists at Chalmers University of Technology in Sweden have modeled low-platinum (Pt) fuel cells for use in hydrogen fuel cell vehicles (FCVs). They have based their work on previous experimental findings on low loading Pt catalysts to approach the automotive application of the development.
“This is a modeling work, and from modeling to real application many challenges must be taken into account, for example, whether these catalysts or similar ones can be produced on a large scale,” the corresponding author, Tatiana, told pv magazine. Santos Andrade.
In hydrogen fuel cells, Pt is used as a catalyst material in the cathode to which oxygen is supplied in the process of producing electrical current. Commercialized FCVs, such as the Toyota Mirai, use 0.31 mg/cm2 of Pt at the cathode, while experimental researchers have managed to lower it to 0.01 mg/cm2 at the cell level.
“The amount of platinum is considered the bottleneck for the widespread commercialization of fuel cells,” the research group explained. “Platinum is reported to be responsible for around 40-55% of the total fuel cost of the cell. Due to the low kinetics of the oxygen reduction reaction that takes place at the cathode, the current Pt loading on that electrode is the critical part of the design, responsible for about 85% of the total platinum in the fuel cell.”
In their analysis, the team expanded on four types of low-charge fuel cells from the literature: two with 0.033-0.035 mg-Pt/cm2 and two with 0.01 mg-Pt/cm2. The systems were named E1 – 3.3 Pt, E2 -3.5 Pt, E3 – 1.0 Pt and E4 – 1.0 Pt, respectively. E1 and E2 were grouped as low-loading Pt catalysts, while E3 and E4 were ultra-low-loading Pt catalysts.
“The first two are catalysts formed by nanoparticles with a platinum-cobalt core on a platinum-free catalytic substrate with slightly different Pt charges,” the academics stressed. “The latter two are PtFe channeled mesoporous carbon (CMC) particles with slightly different channel porosity.”
Based on the energy efficiency curves of those cells, the researchers were able to scale them to the stack and system level and compare them to the Toyota Mirai. The Mirai has 370 cells with a surface area of ??237 cm2, a maximum power of 114 kW and a Pt cathode charge of 0.31 mg/cm2. The researchers compared the commercial system with two models: one in which the low-Pt fuel cell system has the same cell size of 370 cells, and another with the same maximum power of 114 kW.
In the same stack size scenario, the researcher found that E1 had a maximum power of 62-68 kW, E2 70-77 kW, E3 48-53 kW and E4 45-49 kW. However, although its power reached 52% of the commercial system in the best of cases, at lower power the fuel cell systems with low load Pt catalysts presented superior performance.
“When a power relationship is established (product of voltage and current), the large variation in efficiency at high power values ??for samples E1-E4 stands out,” the scientists noted. “The more drastic drop compared to the commercial FCV stack indicates that these materials demonstrated less stable performance in different power ranges.”
In the second model, when the target was the same power, E1 needed between 623 and 677 cells, E2 between 552 and 600, E3 between 795 and 864, and E4 between 860 and 935. “If you only take into account the number of Pt, even with the highest number of cells, the samples would still represent a Pt reduction of 81%, 82%, 93% and 92% compared to the commercial FCV for samples E1-E4, respectively. It can reduce the cost of the battery by around 27-45%,” they stressed.
Following these results, they modeled the system in an FCV and simulated it with the Worldwide Harmonized Light Vehicle Test Procedure (WLTP). The car had a battery with a state of charge (SOC) of 20%-95%, a 4kg hydrogen tank and a control strategy that switched between fuel cells and battery when necessary.
According to their results, in the case of the commercial car and the E1-E4, the power demand of the fuel cell is always less than 40 kW in the WLTP test. Therefore, all models could offer competitive results compared to the 628 km of autonomy of the reference car.
With the same frame size, the E1 had a range of 646 km-651 km, the E2 641 km-646 km, the E3 632 km-638 km and the E4 617 km-623 km. By optimizing the same maximum power, the E1 had a range of 662 km-665 km, the E2 654 km-656 km, the E3 632 km-638 km and the E4 646 km-647 km.
“In the development of catalysts, researchers often focus on improving maximum power, which is an important metric to take into account, while the entire efficiency profile of the fuel cell is often overlooked, for example at powers lows and mediums,” declared Andrade. “That may be a relevant factor in making the fuel cell suitable for vehicle applications, since the fuel cell is usually oversized for a vehicle. “I hope this article serves as a bridge between materials science research and vehicle application.”
Their findings are presented in the article “ Low platinum fuel cell as an enabler for the hydrogen fuel cell vehicle ,” published in the Journal of Power Sources. . |
