Selective Catalyst for Curbing Corrosion in Automotive Fuel Cells

Left: Hydrogen spillover is depicted, wherein TiO2 undergoes transformation into TiOOH under high hydrogen concentration conditions, which promotes hydrogen mobility on the surface and consequently produces conductivity. Right: Under relatively low hydrogen concentration conditions, the strong interaction between Pt and TiO2 leads to the covering of Pt by TiO2. Images courtesy of POSTECH.

A research team led by Prof. Yong-Tae Kim and PhD candidate Sang-Hoon You at Pohang University of Science and Technology (POSTECH) (Pohang, South Korea) had developed a selective catalyst that curbs corrosion in fuel cells used for hydrogen-powered automobiles. By tailoring the hydrogen oxidation reaction to match the concentration of hydrogen in the fuel cell, the team was able to hinder the corrosion of the fuel cells. 

Kim is a professor in the Department of Material Science and Engineering and Graduate Institute of Ferrous and Energy Materials Technology and You is a student in the Department of Material Science and Engineering. Their research was published in the energy journal ACES Energy Letters

Fuel cells are susceptible to numerous factors that deteriorate their durability. One of them is degradation, especially in the cathode catalyst, which is routinely exposed to start-up and shut-down events in automobiles. In particular, fuel cells designed for automotives experience recurring cycles of start-up and shut-down by nature. 

During normal vehicle operation, fuel cells are provided with a consistent supply of hydrogen with high concentration, but it temporarily declines when the car is turned off or started. Consequently, when external air mixes with hydrogen within the fuel cells, an unintended oxygen reduction reaction in the anode is triggered, leading to sudden potential jumps and carbon corrosion in the cathode. 

The POSTECH research team has engineered a catalyst (Pt/TiO2) comprised of platinum (Pt) deposited over a titanium diode (TiO2) that effectively halts corrosion in fuel cells employed in hydrogen-powered automobiles. The performance of this electrocatalyst comes from the robust interaction between two elements, and the ability of hydrogen spillover to modify the surface conductivity of the material in response to the hydrogen concentration in its vicinity.

When a vehicle suddenly stops or starts, the concentration of hydrogen within the fuel decreases correspondingly. As a consequence of this reduction in hydrogen concentration, there is an expansion of TiO2 onto Pt, which results in Pt being buried beneath the catalyst’s surface. This burying of the Pt, caused by expansion of TiO2, ultimately transforms the catalyst into an insulator due to the low conductivity of TiO2. This insulating effect hinders the catalyst’s ability to conduct electricity, thus preventing an unwanted reduction of oxygen that could cause sudden potential jumps in the cathode.

Conversely, during a standard vehicle operation, the concentration of hydrogen within the car remains high. Under such high hydrogen concentration conditions, the highly conductive Pt is exposed on the catalyst’s surface, and TiO2 reduction occurs, which promotes hydrogen mobility on the catalyst’s surface. This phenomenon, termed hydrogen spillover, enhances current flow and increases hydrogen oxidation reaction.

The POSTECH research team also performed a simulation test to compare the newly developed catalyst and conventional catalysts. The test results demonstrated that fuel cells using Pt/TiO2 catalyst exhibited three-times-higher durability, relative to traditional fuel cells. This indicates the team successfully increased the durability of fuel cells through the use of a selective oxygen reduction reaction and a hydrogen oxidation reaction based on the hydrogen concentration.

If this research can contribute to overcoming the existing durability challenges confronting fuel cells for hydrogen-powered vehicles, then it could potentially elevate the standing of Korean hydrogen-fueled automobiles in the next-generation mobility industry.

Source: EurekAlert!,