Manos Mavrikakis, a professor of chemical and biological engineering at the University of Wisconsin-Madison, is part of a research team that has discovered a new way of catalyzing an essential reaction that could make hydrogen fuel cells, a promising source of efficient, clean energy for vehicles and other applications, a much more affordable and practical energy solution.
The research, which includes collaborators at Cornell University and Wuhan University, was recently published in the Proceedings of the National Academy of Sciences.
Manos Mavrikakis“This finding makes progress toward using efficient, clean hydrogen fuel cells in place of fossil fuels,” says Professor Héctor D. Abruña of Cornell.
Hydrogen fuel cells are composed of an anode and cathode sandwiched around an electrolyte. At the anode, a catalyst separates hydrogen molecules into protons and electrons via the hydrogen oxidation reaction (HOR). The electrons then move toward the cathode, creating a flow of electricity.
Expensive precious metals, such as platinum, are currently used in hydrogen fuel cells to efficiently catalyze the reactions. Although alkaline polymer electrolyte membrane fuel cells enable the use of nonprecious metal electrocatalysts, they lack the necessary performance and durability to replace precious metal-based systems.
“The bottleneck for this technology to become widely adopted is the cost of the materials needed, including the electrocatalysts employed, which in most cases are expensive platinum-group elements,” says Mavrikakis. “In this work we demonstrated that cheap, non-precious metals, such as nickel, can be used effectively, both for the cathode and anode electrodes of the fuel cell.”
Recent experiments with nonprecious-metal hydrogen oxidation reaction electrocatalysts needed to overcome two major challenges, according to the researchers: low intrinsic activity from strong hydrogen binding energy and poor durability due to rapid passivation from metal oxide formation.
To meet these challenges, the researchers designed a nickel-based electrocatalyst with a 2-nanometer shell made of nitrogen-doped carbon.
Their hydrogen fuel cell has an anode catalyst consisting of a solid nickel core surrounded by the carbon shell. When paired with a cobalt-manganese cathode, the resulting completely precious-metal-free hydrogen fuel cell outputs more than 200 milliwatts per square centimeter.
Mavrikakis and his team, including postdoctoral researcher Roberto Schimmenti and 2020 PhD graduate Ellen Murray, used quantum mechanical modeling to explain the superior performance of the anode catalyst.
“It turns out that typical nickel nanoparticles tend to adsorb oxygen-containing reaction intermediates strongly, which leads to catalysts and fuel cell performance deterioration,” says Mavrikakis. “Whereas single nickel atoms embedded in a graphene-like sheath made of carbon and nitrogen atoms are resistant to oxidation and bind hydrogen atoms with the ideal strength needed for a highly efficient hydrogen oxidation reaction.”
A side bonus is that type of active site increases the tolerance for carbon monoxide impurities in the hydrogen fuel. This means the fuel cells do not need a special unit to remove carbon monoxide and can use less refined hydrogen, further reducing costs.
“The use of this novel anode would dramatically lower prices enabling the application of alkaline fuel cells in a wide variety of areas,” says Abruña.
Manos Mavrikakis is Ernest Micek Distinguished Chair, James A. Dumesic Professor, and Vilas Distinguished Achievement Professor.
Other authors include Yunfei Gao, Hanqing Peng, Yingming Wang, Chuangxin Ge, Wenyong Jiang, Gongwei Wang, Li Xiao and Lin Zhuang of Wuhan University; and Yao Yang, Francis J. DiSalvo and David A. Muller of Cornell University.
Work by the UW-Madison team was supported by the Center for Alkaline-Based Energy Solutions (CABES), an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences, under Grant Award No. DE-SC-0019445.
A version of this story was previously published by Cornell University.