Carbon monoxide, the ‘silent killer,’ becomes a boon for fuel cell catalysts

Researchers Dr. Gu-Gon Park, Dr. Yongmin Kwon, and Dr. Eunjik Lee from the Hydrogen Fuel Cell Laboratory at the Korea Institute of Energy Research (President Yi Chang-Keun, hereafter “KIER”) have developed a technology that uses carbon monoxide, typically harmful to humans, to precisely control metal thin films at a thickness of 0.3 nanometers. This technology enables faster and simpler production of core–shell catalysts, a key factor in improving the economic viability of fuel cells, and is expected to significantly boost related industries.

Core–shell catalysts refer to catalysts in which the inner core and outer shell are made of different metals. Typically, the core is composed of a low-cost metal, while the shell is made of platinum, which promotes the reactions* in fuel cells. This structure makes it possible to maintain high performance while using only a small amount of expensive platinum, making core–shell catalysts a strategic factor in improving the economic viability of fuel cells.

* Oxygen Reduction Reaction (ORR): In a hydrogen fuel cell, this is the reaction in which oxygen combines with hydrogen. The faster the reaction proceeds, the more quickly current can flow, making ORR a critical indicator for evaluating fuel-cell performance.

To achieve a high-performance core–shell structure, an atomically thick shell must be precisely coated onto the core surface. For this purpose, the “copper-underpotential deposition (Cu-UPD) method has been used for the precise shell thickness contral, in which a thin layer of low-cost copper is first deposited onto the core, followed by the replacement of platinum.

However, this approach demands highly precise voltage control to form an atomic-level copper layer, including extra steps to remove surface oxides. These factors make large-scale manufacturing of core-shell catalysts complex and time-consuming.

To solve this, the team developed CO Adsorption-Induced Deposition (CO AID), a method that uses the redox behavior of carbon monoxide. It enables precise metal coating without additional steps or reducing agents and cuts processing time to one-tenth of conventional methods.

The researchers turned their attention to carbon monoxide’s strong affinity for metal surfaces. CO readily adheres to metals, and when inhaled, it binds strongly to iron ions in the blood, preventing oxygen transport and posing serious health risks. This characteristic is the reason that CO is widely known as a hazardous gas.

Based on this insight, the team enabled carbon monoxide to adsorb onto the core metal surface as a single molecular layer. Platinum was then selectively reduced onto this layer, allowing the researchers to precisely control the shell thickness at the ultra-thin scale of about 0.3 nanometers.

With this approach, kilogram-scale quantities of core–shell catalysts can be produced in as little as 30 minutes to 2 hours, an impressive improvement over conventional copper deposition methods that take more than 24 hours. Moreover, since the process harnesses the inherent redox activity of carbon monoxide, it eliminates the need for electrochemical systems or additional reducing agents.

Using the newly developed method, the team fabricated core–shell catalysts by coating platinum onto metals such as palladium, gold, and iridium. Notably, the palladium-based platinum core–shell catalyst demonstrated about twice the ORR activity and 1.5 times the durability of commercially available platinum-on-carbon (Pt/C)* catalysts.

* Platinum-on-Carbon (Pt/C): A catalyst consisting of platinum particles dispersed on a carbon substrate. Its ease of production has made it the conventional benchmark catalyst in today’s fuel cells.

Dr. Gu-Gon Park, the lead researcher, explained, “This work originated from the idea of converting carbon monoxide’s toxicity into a tool for nanoscale thin-film control. By allowing materials to be precisely engineered at the atomic level and drastically reducing processing time, the technology presents a new synthesis paradigm with excellent prospects for commercialization.”

Dr. Yongmin Kwon, a member of the research team, noted, “Being able to manipulate the surfaces of metal nanoparticles at the atomic-layer scale using something as simple as carbon monoxide means this technology could have far-reaching implications—not only for fuel-cell catalyst production, but also for advancing nanoparticle manufacturing in areas such as semiconductors and thin-film materials.”

The research was conducted in cooperation with the Brookhaven National Laboratory (BNL). It was published in the November issue of ACS Nano (IF 16.1), a prestigious international journal in nanomaterials, and was selected for the issue’s inside front cover. The research was carried out with support from the Ministry of Science and ICT.