Bifunctional behavior toward water splitting under strong acid conditions (1 m H2SO4 previously degassed) of a vanadium POM-based carbon hybrid catalyst incorporating non-innocent cations depending on its assembly with carbon nanotubes (CNT). Credit: Advanced Materials (2025). DOI: 10.1002/adma.202512902

Hydrogen production through water electrolysis is a cornerstone of the clean energy transition, but it relies on efficient and stable catalysts that work under acidic conditions—currently dominated by precious metals like iridium and platinum.

A research team from the Singular Center for Research in Biological Chemistry and Molecular Materials (CiQUS) in Spain, led by María Giménez-López, has made a fundamental advance toward Earth-abundant alternatives. Their work, published in the journal Advanced Materials, shows that a single molecular compound can act as a catalytic "switch," toggling between oxygen and hydrogen production.

How the molecular switch works

At the heart of the discovery is a hybrid material combining a vanadium cluster (a polyoxometalate) with carbon nanotubes. "The ‘switch’ is not in the metal cluster itself, but in how the organic cations around it are arranged," explains Giménez-López. "When the material is physically mixed with the nanotubes, these cations—called TRIS⁺—remain locked in the crystal structure. This steers the reaction toward oxygen production through a special oxidation mechanism.

"However, when we let it assemble in a directed way, the same TRIS⁺ cations are released, oriented toward the surface, and act as a ‘proton sponge.’ This simple change in molecular architecture turns the system into an exceptional catalyst for hydrogen."

At the molecular level, the vanadium cluster acts as a stable, reversible electron reservoir in both configurations. The final function—oxygen or hydrogen—is determined by the TRIS⁺ cations, which modulate the local electrochemical microenvironment depending on their accessibility.

Implications for catalyst design

When blocked, they promote water activation for oxygen release. When free and exposed, they capture protons and facilitate their reduction to hydrogen. Thus, the function switch stems not from changing the chemical composition, but from controlling the supramolecular architecture of the assembly.

Electrochemical data back this molecular switch. In its oxygen configuration, the material rivals commercial iridium. In its hydrogen setup, its efficiency approaches that of platinum, the benchmark. This work is part of Giménez-López’s research line at CiQUS, focused on designing new materials for energy storage and conversion, where the controlled use of carbon nanotubes as smart supports plays a key role.

"This work establishes that the catalytic switch is topological and microenvironmental, not compositional," the researcher emphasizes.

The study not only presents a promising candidate for more sustainable electrolyzers, but also proposes a new paradigm: the possibility of programming the reactivity of molecular catalysts by controlling their assembly, opening a rational path to design multifunctional, durable, and Earth-abundant materials.

More information: Eugenia P. Quirós‐Díez et al, POM‐Based Water Splitting Catalyst Under Acid Conditions Driven by Its Assembly on Carbon Nanotubes, Advanced Materials (2025). DOI: 10.1002/adma.202512902

Citation: A molecular switch for green hydrogen: Catalyst changes function based on how it’s assembled (2025, December 23) retrieved 23 December 2025 from https://phys.org/news/2025-12-molecular-green-hydrogen-catalyst-function.html

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