Researchers at Cornell University have discovered that a nitrogen-doped carbon-coated nickel anode can catalyze an essential reaction in hydrogen fuel cells at a fraction of the cost of the precious metals that are currently used. This new discovery could accelerate the widespread use of hydrogen fuel cells, which hold great promise as efficient, clean energy sources for vehicles and other applications.
It’s one of a string of discoveries for the Héctor Abruña lab in their ongoing search for active, inexpensive, durable catalysts for use in alkaline fuel cells. “This finding makes progress toward using efficient, clean hydrogen fuel cells in place of fossil fuels,” said Abruña, professor in the department of chemistry and chemical biology at Cornell University. The researchers report their findings in a paper in the Proceedings of the National Academy of Sciences.
Expensive precious metals, such as platinum, are currently utilized in hydrogen fuel cells to efficiently catalyze the reactions they employ to produce electricity. Although alkaline polymer electrolyte membrane fuel cells (APEMFCs) can utilize nonprecious metal electrocatalysts, they lack the necessary performance and durability to replace the precious-metal-based versions.
A fuel cell produces electricity via two chemical reactions – the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (OOR). Platinum, in particular, is a model catalyst for both reactions and is durable in the acidic environment of an APEMFC, Abruña said. But are there other materials that could perform the same functions?
According to the researchers, recent experiments with non-precious-metal HOR electrocatalysts have shown there are two major challenges to overcome: low intrinsic activity from too strong a hydrogen binding energy, and poor durability due to rapid passivation from metal oxide formation. To overcome these challenges, the researchers designed a nickel-based electrocatalyst with a 2nm shell made of nitrogen-doped carbon.
In a hydrogen fuel cell, this catalyst is used as the anode (where hydrogen is oxidized) and is paired with a cobalt-manganese cathode (where oxygen is reduced). The resulting completely precious-metal-free hydrogen fuel cell can output more than 200 milliwatts per square centimeter.
The presence of nickel oxide species on the surface of a nickel electrode is normally a problem, because these species slow the hydrogen oxidation reaction dramatically. But in the novel nickel-based catalyst, the nitrogen-doped carbon coating serves as a protection layer and enhances the HOR kinetics, making the reaction quicker and much more efficient. The carbon coating also prevents the formation of nickel oxides in the first place – producing electrodes with dramatically enhanced lifetimes. These electrodes are also much more tolerant to carbon monoxide, which rapidly poisons platinum.
“The use of this novel anode would dramatically lower prices, enabling the application of alkaline fuel cells in a wide variety of areas,” Abruña said.
This story is adapted from material from Cornell University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.
“The use of this novel anode would dramatically lower prices, enabling the application of alkaline fuel cells in a wide variety of areas.”Héctor Abruña, Cornell University