Splitting water using renewable electricity to produce green hydrogen is seen by many as essential for achieving net-zero carbon emissions. Currently the cost and efficiency of such hydrogen production is a critical barrier to increasing the use of green hydrogen in replacing fossil fuel.

Using by the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science user facility at DOE’s Argonne National Laboratory, a group of scientists have recently demonstrated a new type of low-cost catalyst that could slash the cost and boost the efficiency of green hydrogen production through water splitting. Their results were published in the journal Science.

In 2021, to accelerate the development of affordable hydrogen, DOE launched its first Energy Earthshot–the “Hydrogen Shot”–with the goal of cutting the cost of green hydrogen to $1 per kilogram in one decade, the so-called “1-1-1” goal. Proton exchange membrane water electrolysis is seen as a key technology for meeting this goal.

A proton exchange membrane water electrolyzer consists of a cathode and an anode, separated by a solid proton-conducting membrane. During the electrochemical reaction, water is split at the anode into oxygen, protons and electrons. The protons then migrate across the membrane to the cathode where they re-combine with electrons to produce hydrogen.

The challenge with the current water electrolyzer technology is its use of iridium as the catalyst at the anode. Iridium is one of the rarest and most pricy elements on Earth. Its usage adds a significant capital cost and market uncertainty in meeting the 1-1-1 goal.  A low-cost alternative is needed. 

In a bid to replace iridium, a team of researchers led by scientists at Argonne explored a new anode catalyst made from manganese and lanthanum-doped cobalt oxide. The catalyst was produced using electrospinning of a metal-organic framework (MOF)-based precursor to create a highly porous crystalline structure with a large surface area, leading to a substantially increased electrocatalytic reaction efficiency. Furthermore, by controlling the manganese and lanthanum doping and distribution, they improved the catalyst conductivity and activity, as well as its stability in the acid environment of the electrolyzer. 

The team used several X-ray techniques to analyse the structure of the lanthanum and manganese-doped cobalt catalysts before, during and after water electrolysis. These included X-ray absorption spectroscopy carried out at beamlines 12-BM and 20-BM of the APS and high-energy X-ray diffraction at 17-BM. 

The anode was also found to be more stable than previous cobalt oxide catalysts. Interestingly, it was not that stable when first placed in the acidic electrolysis cell, but its stability improved once current started running through it. 

X-ray absorption spectroscopy showed that there was a major change in the crystalline structure under electrolysis conditions. According to the researchers, this is critical to decipher the enhanced efficiency and improved stability of this lanthanum and manganese-doped cobalt catalyst. Particularly, it helped the researchers to understand why the catalyst can be stable in the acid environment under the electrolyzer operating condition.

This structural change revealed by X-ray studies was unexpected and could help scientists improve their fundamental understanding of electrocatalysis using metal oxides. It also provides valuable insight into the direction for further improvement of these earthly abundant metal oxide materials as replacements for iridium, which would remove the major cost barrier for widespread uptake of green hydrogen production.  – Michael Allen

See: L. Chong¹, G. Gao², J. Wen¹, H. Li¹, H. Xu¹,  Z. Green³, J. D. Sugar⁴, A. J. Kropf¹, W. Xu¹, X.-M. Lin¹, H. Xu³, L.-W. Wang², D.-J. Liu^1,5, “La- and Mn-doped cobalt spinel oxygen evolution catalyst for proton exchange membrane electrolysis” Science 380 6645 609-616 (2023)

Author affiliations: ¹Argonne National Laboratory; ²Lawrence Berkeley National Laboratory; ³Giner Inc.; ⁴Sandia National Laboratories; ⁵University of Chicago

This work is supported by the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (D. Peterson, project manager), and by Laboratory Directed Research and Development (LDRD) funding of Argonne National Laboratory, provided by the Director, Office of Science, of the US DOE under contract no. DEAC02-06CH11357 through a Maria Goeppert Mayer Fellowship to L.C. Work performed at the Center for Nanoscale Materials and Advanced Photon Source, both US DOE Office of Science User Facilities, was supported by the US DOE, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. The work at Lawrence Berkeley National Laboratory was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy of the US DOE under the Hydrogen Generation program. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the US DOE’s National Nuclear Security Administration under contract no. DE-NA0003525. 

The U.S. Department of Energy's APS at Argonne National Laboratory is one of the world’s most productive x-ray light source facilities. Each year, the APS provides high-brightness x-ray beams to a diverse community of more than 5,000 researchers in materials science, chemistry, condensed matter physics, the life and environmental sciences, and applied research. Researchers using the APS produce over 2,000 publications each year detailing impactful discoveries and solve more vital biological protein structures than users of any other x-ray light source research facility. APS x-rays are ideally suited for explorations of materials and biological structures; elemental distribution; chemical, magnetic, electronic states; and a wide range of technologically important engineering systems from batteries to fuel injector sprays, all of which are the foundations of our nation’s economic, technological, and physical well-being.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC, for the U.S. DOE Office of Science.

The U.S. Department of Energy's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit the Office of Science website.