Plate Nº 21 · recorded November 11, 2026
Chemistry & MaterialsReported finding
Cobalt phosphide shields itself while making hydrogen
A 2026 study finds that cobalt phosphide changes its surface during electrolysis, forming a protective layer that supports hydrogen production and limits catalyst damage.
By Elena Vasquez4 min read707 words
In brief
- Cobalt phosphide remained stable for 24 hours at current densities exceeding 1 A cm⁻².
- The analysis covered 2,282 observations from approximately 886 catalysts in about 700 publications.
- The catalyst performed strongly across three pH environments: acidic, neutral and alkaline.
- The 2026 study appeared in the Journal of the American Chemical Society under DOI 10.1021/jacs.6c17411.
By Elena Vasquez
What did the catalyst achieve?
Cobalt phosphide remained stable for 24 hours at current densities exceeding 1 ampere per square centimeter while producing hydrogen, according to a 2026 study in the Journal of the American Chemical Society. Current density measures electrical current per unit area of catalyst, so the figure indicates demanding operating conditions.
The same catalyst delivered strong hydrogen-production performance in acidic, neutral and alkaline water, requiring comparatively little additional voltage. Those three environments span the pH range used in the study; pH describes how acidic or alkaline a solution is.
Computer models had suggested that cobalt phosphide, often written CoP, should become unstable under the electrolysis conditions used to split water and generate hydrogen. Experiments, however, showed that it stayed active and durable. The new study resolves that mismatch by showing that CoP does not remain chemically fixed while it works.
The paper treats CoP as a promising alternative to platinum for producing hydrogen from water. The reported results do not quantify any cost advantage over platinum.
CoP survives by changing rather than by remaining chemically unchanged.
Why does the surface protect the catalyst?
At lower voltages, hydroxyl groups form at phosphorus sites on CoP during electrolysis. A hydroxyl group is a chemical group containing oxygen and hydrogen. These P-OH groups help neighboring cobalt atoms activate water molecules and bind hydrogen more effectively.
As voltage increases, the surface changes again, becoming covered with hydrogen-containing species labeled Co-H and P-H. Those labels denote hydrogen chemically bonded to cobalt or phosphorus. The adjustment lets CoP maintain an effective balance between binding hydrogen and releasing it as a product across acidic, neutral and alkaline conditions.
The attached hydroxyl and hydrogen species also form a protective layer. These surface-bound molecules are adsorbates. They limit oxidation, a chemical process that can degrade the catalyst, and prevent cobalt and phosphorus from dissolving into the surrounding solution.
The same surface chemistry that helps make hydrogen also helps keep the catalyst intact.
How did researchers test the explanation?
The team combined AI-assisted analysis of previous studies, computer simulations and laboratory experiments. They analyzed 2,282 observations from approximately 886 cobalt phosphide-based catalysts drawn from about 700 scientific publications.
Researchers then used models to predict how the catalyst's surface would change during operation and tested those predictions with specially prepared CoP nanosheets. Nanosheets are ultrathin sheets of material, and making them for this test gave researchers a controlled catalyst surface to examine.
Advanced spectroscopic techniques detected the chemical species involved in the predicted changes. Spectroscopy uses the way matter interacts with energy to identify its chemical makeup. The experiments matched the model's description of the operating surface.
Tests with deuterium, a heavier form of hydrogen, provided further evidence that hydrogen was forming bonds with phosphorus. The catalyst also showed strong performance in all three pH environments and required comparatively little extra voltage to produce hydrogen.
It remained stable for 24 hours at very high current densities exceeding 1 A cm⁻², a measure of current per unit area. Together, the modeling, spectroscopy and deuterium results support both the proposed reaction pathway and the protective role of the changing surface.
Laboratory measurements matched the model's predictions at the catalyst surface.
What could this change for green hydrogen?
The authors say the findings could help researchers develop more affordable and versatile catalysts for green hydrogen production. More broadly, the work offers a design principle: scientists should consider how a catalyst's surface changes under real operating conditions, rather than focusing only on how the material looks when first made.
The experiments used specially prepared CoP nanosheets, and the reported durability result covers 24 hours. The findings do not establish performance in industrial reactors, a cost advantage over platinum, or durability beyond that test, so the result remains a laboratory advance rather than a commercial demonstration.
Zhongyuan Guo et al. published “Operando Surface Dynamics Govern the pH-Universal Activity and Stability of Cobalt Phosphide for Hydrogen Evolution” in the Journal of the American Chemical Society in 2026. The DOI is 10.1021/jacs.6c17411.
The practical lesson is to design catalysts around the surface they become, not only the surface they start with.
via phys.org/rss-feed/ (Source)
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Correspondent covering money, funding and market shifts around general science news at SciBeat.
384 articles
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