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The “silk-cocoon” catalyst is a 2018 laboratory material made from sulfur-rich cobalt polysulfide, not silk. Chao Wang and coauthors reported that it catalyzed the hydrogen evolution reaction (HER), the hydrogen-producing half of water splitting, with activity they described as comparable to commercial platinum-on-carbon (Pt/C). Their figures—42 mV overpotential at 10 mA cm−2, a 41 mV dec−1 Tafel slope, and an onset potential of 0 V versus the reversible hydrogen electrode—are results from that study, not proof of a complete or commercially ready electrolyzer.
What does “silk-cocoon-shaped” mean?
The name describes the catalyst’s shape, not its ingredients. The material is sulfur-rich cobalt polysulfide, written CoSx with x≈3.9. The authors describe hollow spheres interwoven with numerous nanofibers less than 10 nm thick, joined into a three-dimensional conductive network. They reported making it through a hydrothermal synthesis process. The Royal Society of Chemistry paper calls it “silk-cocoon structured S-rich cobalt polysulfide.”
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What part of water splitting did the catalyst target?
The study examined the hydrogen evolution reaction (HER), the cathodic half-reaction that produces hydrogen. It did not establish performance for a complete commercial water-splitting system. In particular, the reported HER measurements should not be read as full electrolyzer efficiency, output, or operating-life results.
What performance did the 2018 paper report?
The abstract of Wang and coauthors’ paper reports these HER measurements:
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| Reported measure | Study result | What it describes |
|---|---|---|
| Onset potential | 0 V versus the reversible hydrogen electrode | The reported potential at which HER activity begins. |
| Tafel slope | 41 mV dec−1 | A measure used to describe how current changes with applied potential. |
| Overpotential | 42 mV at 10 mA cm−2 | The extra potential reported to reach that current density. |
The authors state: “Moreover, the overpotential to yield a current density of 10 mA cm−2 is only 42 mV.” They also characterize the catalyst’s activity as comparable to commercial Pt/C. That is the paper’s comparison; the evidence cited here does not provide a harmonized, independent cross-study ranking of catalysts. The article abstract provides the reported figures and comparison.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What do these results establish—and what do they not?
The findings establish that the authors reported promising HER activity for this material under their laboratory study. They do not establish independent reproduction, commercial availability, industrial-scale operation, or long-term durability. Nor do the HER figures alone show how a full electrolyzer performs, since they describe one half-reaction rather than the entire system.
The paper appeared in Energy & Environmental Science, volume 11, pages 2467–2475, and was first published on 7 June 2018. Its DOI is 10.1039/C8EE00948A. The journal’s article page lists publication metadata and the abstract. Chemistry World later presented the work as a possible lower-cost alternative to platinum-group catalysts; that is prospective context, not evidence of demonstrated cost savings or commercial deployment. Chemistry World’s 31 July 2018 account summarizes the study.
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