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New ruthenium oxide/graphene and CNT foam material improves supercapacitor performance

Microstructure of RGM electrode. (a) Schematic illustration of the preparation process of RGM nanostructure foam. SEM images of (b–c) as-grown GM foam (d) Lightly loaded RGM, and (e) heavily loaded RGM. Source: UCR. Click to enlarge.

Researchers at the University of California, Riverside have developed a novel nanometer scale ruthenium oxide (RuO2) anchored graphene and CNT foam architecture (RGM) for high-performance supercapacitor electrodes.

In an open access paper in the Nature journal Scientific Reports, the team reports that supercapacitors based on RGM show superior gravimetric and per-area capacitive performance (specific capacitance: 502.78 F g−1, areal capacitance: 1.11 F cm−2) which leads to a high energy density (for supercapacitors) of 39.28 Wh kg−1 and power density of 128.01 kW kg−1. The electrochemical stability, excellent capacitive performance, and the ease of preparation suggest this RGM system is promising for future energy storage applications, the researchers suggest.

Among all energy storage devices, supercapacitors (SC) have garnered substantial attention in recent years due to their ultra-fast charge and discharge rate, excellent stability, long cycle life, and very high power density. These characteristics are desirable for many applications including electric vehicles (EVs) and portable electronics. However, SCs may only serve as standalone power sources in systems that require power delivery for a short duration (<10 sec). This is due to their relatively lower energy density in comparison to other types of energy storage devices such as batteries and fuel cells. In often cases SCs are used as part of a hybrid system with other high energy storage devices in real applications. Therefore, boosting the energy density of SCs has become one of the most promising methods for the development of future high energy and high power density energy storage devices.

… There are two types of electrochemical capacitors: (i) electrochemical double layer capacitors (EDLCs), which are generally based on pure graphitic nanostructures including CNTs, graphene, carbon onions/spheres, template derived carbons, activated carbon, etc. and (ii) pseudocapacitors which are based on pseudocapacitive materials like V2O5, RuO2, MnO2, Co2O3, Co3O4, In2O3, NiO/Ni(OH)2, binary Ni-Co hydroxide, etc. which introduce fast surface redox reactions. … Among all pseudocapacitive materials, RuO2 appears to be the most promising material for SCs with the following advantages: i) simple and scalable synthesis, ii) high capacitance, and iii) rapid charging-discharging.

—Wang et al.

The UC Riverside team had previously developed high-quality graphene and carbon nanotube (CNT) hybrid hierarchical nanostructures—3D graphene foam conformally covered with densely packed CNT networks. In this latest study, the researchers anchored the RuO2 nanoparticles to the hybrid nanostructures.

The porous GM foam not only provides a large surface area for the loading of RuO– nano-particles but also facilitates electrolyte infiltration, they noted. The embedded CNTs in the CNT-RuO2 network layer work as a conductive framework.

Our innovative RGM architecture offers seamless connections at the graphene and CNT interface and enhances the interfacial integrity of major components (active materials and current collector) which improves the conductivity of the whole electrode compared with other reported hybrid RuO2 systems. Good electrolyte access, enhanced conductivity, and improved charge transport further lead to very high active material utilization, smaller internal resistance (ESR ~ 1V), superior rate capability, and cycling stability. In addition to a very high specific capacitance compared with other previously reported pseudocapacitive systems, symmetric ECs based on this innovative RGM hybrid foam architecture could be cycled reversibly in a operational voltage window of 1.5 V, which is much larger than the majority of aqueous electrolyte supercapacitors (~1.0 V). The high specific capacitance and extended operational voltage window lead to an impressive maximum energy density of 39.28 Wh kg-1 and power density of 128.01 kW kg-1.

—Wang et al.

The foam electrode was successfully cycled more than 8,000 times with no fading in performance.


  • Wei Wang, Shirui Guo, Ilkeun Lee, Kazi Ahmed, Jiebin Zhong, Zachary Favors, Francisco Zaera, Mihrimah Ozkan & Cengiz S. Ozkan (2014) “Hydrous Ruthenium Oxide Nanoparticles Anchored to Graphene and Carbon Nanotube Hybrid Foam for Supercapacitors,” Scientific Reports 4, Article number: 4452 doi: 10.1038/srep04452



It all sounds good:

39 Wh is almost exactly the amount of KE a 1500 Kg car doing 50kph has, so it would be useful for regenreative braking.

However, from Wikipedia ...
"Ruthenium is exceedingly rare, only the 74th most abundant metal on Earth"

So I don't think we will be seeing this in a Ford Focus any day soon.

However, it may inspire them to find a similar super-capacitive foam from a more abundant metal.


This is a huge breakthrough. These kinds of numbers are a game changer. As mahonj points out, they are using a rare element, but I have no idea how much "Ruthenium doping" this foam requires. For all we know it only takes a couple of nanograms of Ruthenium to make a kg of this new supercap...or it could take 100g to make a kg of supercap?

This is one paper I'll have to read...and then pass on to my daughter who's doing her undergrad in materials science/engineering :)

In all seriousness, I'm not sure how much we could mine if we decide this is a valuable element. Right now its spot price is only $72/oz and it mostly comes as a side effect of mining other metals. Very similar to Lithium until people found out that "stuff" may have some more uses. LOL


That is spectacular performance indeed.

Supposing that something like a transition metal can be substituted at a 50% penalty, that would still provide 150+ Wh and 500+ kW in an 8 kg unit.  That would make a batteryless hybrid a no-brainer.  The regenerative braking system would be the limiter, not the capacitor.


Could make a super BEV when combined with high energy density batteries.

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