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A 2018 study reported that sulfur-rich cobalt polysulfide, CoSx (x≈3.9), shaped into a silk-cocoon-like network, catalyzed the hydrogen evolution reaction (HER) with performance the authors described as comparable to commercial platinum-on-carbon (Pt/C). The headline results—42 mV overpotential at 10 mA cm−2 and a 41 mV dec−1 Tafel slope—are laboratory findings for HER, not proof of a complete, durable or commercially ready water-splitting system.
What does “silk cocoon-shaped” mean?
“Silk cocoon” describes the catalyst’s form, not its composition: the material contains no silk. Chao Wang and coauthors identify it as sulfur-rich cobalt polysulfide, CoSx with x≈3.9. They report a hydrothermal synthesis that forms hollow spheres interwoven with many nanofibers less than 10 nm across, connected into a three-dimensional conductive network. The Royal Society of Chemistry article describes the material and its preparation.
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Which part of water splitting did the catalyst address?
The study examined the hydrogen evolution reaction, or HER: the cathodic half-reaction that produces hydrogen during electrochemical water splitting. Water splitting also requires an oxygen-producing half-reaction at the anode. HER results alone therefore do not establish the efficiency or performance of a complete electrolyzer, which depends on both electrodes and the assembled system.
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What performance did the paper report?
In the 2018 paper, the authors report an HER onset potential of 0 V versus the reversible hydrogen electrode, a Tafel slope of 41 mV dec−1, and an overpotential of 42 mV at a current density of 10 mA cm−2. The authors’ abstract states: “Moreover, the overpotential to yield a current density of 10 mA cm−2 is only 42 mV.” These are values reported for that study, not independent replications or harmonized comparisons across catalyst studies. The paper’s DOI record identifies the article, published in Energy & Environmental Science in 2018.
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How should the comparison with platinum be understood?
The authors characterized the catalyst’s HER activity as comparable to commercial Pt/C, a common platinum-based reference catalyst. That is a study-specific comparison, not evidence that the material universally matches or outperforms platinum under every operating condition. The available article record does not establish directly comparable results against other catalysts tested under harmonized conditions.
Does this make it a practical or cheaper replacement for platinum?
The results make the material an interesting research candidate, but they do not show that it is a commercially available catalyst, a proven lower-cost replacement, or ready for industrial deployment. Chemistry World’s 31 July 2018 account framed the work as a potential lower-cost alternative to platinum-group catalysts; that is prospective context rather than demonstrated manufacturing cost or commercial use. Chemistry World’s report summarizes the work and its framing.
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The reported HER metrics also do not establish full-device energy efficiency, long-term durability, performance at industrial scale, or independent reproduction. The publication dates to 2018, and the cited sources do not document later product availability or deployment.
Where did the results appear?
Chao Wang and coauthors’ paper, “Facile synthesis of silk-cocoon S-rich cobalt polysulfide as an efficient catalyst for the hydrogen evolution reaction,” was first published on 7 June 2018 in Energy & Environmental Science, volume 11, pages 2467–2475. The journal article page provides the author and publication details alongside its abstract.
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