Molecular catalyst switches between hydrogen and oxygen production

by Robert Schreiber
Berlin, Germany (SPX) Dec 26, 2025

Hydrogen production through water electrolysis is central to developing low-carbon energy systems, but current acidic electrolyzers depend on catalysts made from scarce metals such as iridium and platinum.

A team at the Singular Center for Research in Biological Chemistry and Molecular Materials (CiQUS) in Spain, led by Maria Gimenez-Lopez, has shown that a single molecular compound can function as a catalytic switch that shifts between oxygen evolution and hydrogen evolution depending on how it is assembled.

The researchers built a hybrid material that combines a vanadium-based polyoxometalate cluster with carbon nanotubes, creating a system whose behavior is controlled by the arrangement of organic TRIS+ cations surrounding the metal unit rather than by changes to the vanadium cluster itself.

Gimenez-Lopez explained that when the hybrid is simply mixed with nanotubes, the TRIS+ cations remain confined in the crystal structure, which steers the electrochemical reaction toward oxygen production through a defined oxidation pathway.

When the same components are allowed to assemble in a directed fashion, the TRIS+ cations are released, reorient toward the nanotube surface, and act as a proton sponge, producing a configuration that promotes hydrogen evolution under acidic conditions.

At the molecular scale, the vanadium cluster provides a stable and reversible electron reservoir in both states, while the accessibility of the TRIS+ cations shapes the local electrochemical microenvironment and determines whether water activation for oxygen release or proton reduction to hydrogen dominates.

Electrochemical measurements indicate that in its oxygen-evolving mode the material performs at a level comparable to commercial iridium catalysts, and in its hydrogen-evolving mode its efficiency approaches that of platinum, which is widely used as a benchmark in acidic water-splitting systems.

The work forms part of an ongoing research program at CiQUS that focuses on materials for energy storage and conversion, in which carbon nanotubes act as supports that help organize molecular units into architectures with specific catalytic functions.

Gimenez-Lopez emphasized that the results demonstrate a catalytic switch controlled by topology and microenvironment rather than composition, and the study proposes a design approach in which the reactivity of molecular catalysts is programmed through controlled assembly to obtain multifunctional, durable, and earth-abundant materials for electrolyzers.

The project involved collaboration with researchers at CICECO, University of Aveiro in Portugal, and received financial support from the European Union and regional funding schemes.

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