MTU carbonate-superstructured solid fuel cell (CSSFC) delivers enhanced power density at lower operating temperatures
09 April 2023
Solid oxide fuel cells (SOFCs) offer high energy efficiency and fuel flexibility, but require high operating temperatures. Although lowering the operating temperature of SOFCs can minimize material degradation and enable the use of less expensive materials, both electrolyte and electrode resistances increase exponentially with decreasing operation temperature.
Now, researchers at Michigan Technological University have demonstrated a carbonate-superstructured solid fuel cell (CSSFC) in which in situ generation of superstructured carbonate in the porous samarium-doped ceria layer creates a unique electrolyte with ultrahigh ionic conductivity of 0.17 S⋅cm−1 at 550 °C. The CSSFC shows enhanced power density with hydrocarbon fuels at lower operating temperatures. An open-access paper on the work appears in Proceedings of the National Academy of Sciences (PNAS).
… low-temperature SOFCs (LT-SOFCs) with hydrocarbon fuels suffer from polarization losses caused by temperature drop and carbon deposition (coking). This happens because 1) the hydrocarbon oxidation kinetics are extremely sluggish at lower temperatures due to the strong C–H bonds and 2) carbon deposition deactivates electrodes by covering catalytic sites.
… one of the key strategies to improve hydrocarbon oxidation and reduce coking for LT-SOFCs is to increase the oxygen ionic conductivity of electrolytes. … There exist two conventional strategies to enhance the oxygen ionic conductivity of electrolytes in LT-SOFCs, namely, reducing electrolyte thickness and developing fast ionic conductors. The ultrathin electrolyte film requires advanced techniques and inevitably increases fabrication cost and complexity. Although bismuth oxides exhibited impressive oxygen ionic conductivity due to their rich oxygen vacancies, their poor stability under SOFC operation conditions would hinder their applications. Therefore, other strategies are required to develop efficient ionic conductors.
—Su et al.
The team hypothesized that a continuous interface between molten carbonate and solid ionic conductor could constitute a fast transfer channel for oxygen ions—i.e., such a carbonate superstructure on solid ionic conductor would be an oxygen ionic superconductor.
To test this hypothesis, we fabricated a device by integrating a LiNi0.8Co0.15Al0.05O2 (NCAL) cathode, a porous Ce0.8Sm0.2O1.9 (SDC) electrolyte, and a Ni-BaZr0.1Ce0.7Y0.1Yb0.1O3–δ (BZCYYb) anode using a one-step dry-pressing procedure without high-temperature sintering in this work. The electrodes and the electrolyte remain porous and nanocrystalline structures in the system. Then, molten carbonate in the porous NCAL and SDC layers is in situ generated at cell operation conditions, creating the carbonate-superstructured fuel cell (CSSFC).
Furthermore, the CSSFC exhibited ultrahigh ionic conductivity of 0.17 S⋅cm−1 at 550°C, leading to an unprecedented high open-circuit voltage (OCV) and a very high peak power density (PPD) as well as excellent coking resistance with dry methane fuel at 550°C.
—Su et al.
(A) Schematic of conventional SOFC, porous SOFC, and the CSSFC. (B) The I-V-P performance of different fuel cell configurations with Ni-BZCYYb as anodes operated on CH4 at 550 °C. (C) The temperature-dependent Arrhenius plot of oxygen ionic conductivities of different electrolytes with or without carbonate modification. (D) DSC plots of different electrolytes in Ar atmosphere. Su et al.
Corresponding author Yun Hang Hu estimates that CSSFC fuel efficiency could reach 60%. By comparison, the average fuel efficiency of a combustion engine ranges between 35% and 30%. The CSSFC’s higher fuel efficiency could lead to lower carbon dioxide emissions in vehicles.
Resources
Hanrui Su, Wei Zhang, and Yun Hang Hu (2023) “Carbonate-superstructured solid fuel cells with hydrocarbon fuels” PNAS doi: 10.1073/pnas.2208750119
One of the hassles with SOFC is how fast they can get going.
It is unclear from this if any progress has been made in this aspect.
Posted by: Davemart | 09 April 2023 at 02:22 AM
The big news from this, given in the conclusions in the paper:
' We demonstrated a different type of fuel cell, CSSFC, withexcellent electrochemical performance and high durability atlower operational temperatures for hydrocarbon fuels. The peakpower density of a CSSFC employing a porous SDC electrolytelayer and a lithium-based cathode reached 215 mWcm2at550°C with dry methane fuel. Unprecedentedly high OCVswere achieved (such as 1.051 V at 500°C and 1.041 V at550°C). The CSSFC can be directly operated with varioushydrocarbon fuels. The CSSFC would be promising for com-mercial applications due to its excellent performance, easy fabri-cation, low cost, and fuelflexibility.'
So you can use a variety of hydrocarbon fuels, including methane, without first extracting the hydrogen, and certainly without the need for the very high purity hydrogen which is needed for typical PEM fuel cells and which substantially increases the cost of the fuel.
I would guess that an early application might be shipping.
Posted by: Davemart | 09 April 2023 at 03:53 AM
Leave them running on partial power they last longer
Posted by: SJC | 09 April 2023 at 09:10 AM
Just a note that BEVs are not the absolutely ideal solution which is often assumed.
You still really need a private plug to conveniently charge, which costs money, and even if you have super fast charging, still have to fool around waiting a few minutes to recharge on a longer journey, and that super fast charging both places considerable strain on the local grid and does not help the battery life.
In some respects a PHEV with a methanol RE is significantly better, as you can just pump in methanol swiftly and if needs be, don't have to plug your car in.
Downsides are carbon emissions, but it is perhaps possible to have net zero in an overall carbon cycle in making the fuel.
The other main objection is overall efficiency.
But the notion that efficiency is the be all and end all arose because of the relatively limited supply of renewable energy,.
That is rapidly becoming, if not irrelevant, way less important.
I don't find this line of argument entirely convincing, especially regarding closed loop production of methanol, but do think that the notion that batteries are a perfect solution is not correct.
In practice for several years there will be significant downsides to running a BEV, even though of course the users are a self selecting group for whom the downsides are less important.
A PHEV with a methanol RE would also be a very good solution, and better in some circumstances and places.
Posted by: Davemart | 09 April 2023 at 09:51 AM
A PHEV with a methanol RE would also be a very good solution, and better in some circumstances and places.
It depends. The PHEV needs a range of at least 150 miles so you don’t need to replace the High Power Lithium battery every 7 years, which in a Toyota RAV4 costs $5000. This PHEV would be really good for trucks, large SUV, and pulling trailers (so not for everyone).
Actually, China is already building these PHEV, e.g. Radar RD6 or the Geely Galaxy Range SUV.
https://www.greencarcongress.com/2023/02/20230227-geely.html
Geely also makes Volvo and LEVC London Taxi.
Posted by: Gryf | 09 April 2023 at 11:43 AM
@Gryf:
I am not too keen on very long ZEV range in present PHEVs, because if you use it very infrequently, petrol sours in the tank anyway, unlike hydrogen.
One metric which has improved considerably in batteries is cycle life.
You referenced elsewhere the 4,000 cycles of the LFP in a BYD.
That is pretty much overkill for a BEV in a consumer car, as it exceeds the rest of the life of the car, and switching them about is not as easy as it sounds.
It ignores also the rather different issue also of calendar life, which may be distinct from cycle life.
OTOH, for a PHEV with its smaller higher cycling battery, or even more so a hybrid, increased cycle life is an unalloyed benefit.
So a 20Kwh battery pack good for 70 miles or so of ZEV range gets perhaps 250,000 miles of life, which is pretty much spot on with the degradation cycle of a reliable car.
And as an additional point, even an old RAV4 needing a new battery is often worth the replacement at $5, comparable to other old car hassles like problems with the suspension etc.
If you have an aging BEV, forking out in the area of $20k for a new battery pack is far more problematic, and likely to result in the car being simply scrapped, with a lower total life in some cases than an ICE.
Posted by: Davemart | 09 April 2023 at 12:08 PM
Correction: The estimated cost to replace the battery on a Toyota RAV4 Prime is between $10,000 and $12,000.
https://rav4resource.com/toyota-rav4-prime-battery-replacement/
The $20K BEV replacement cost would be for an entire new battery. Typical cost is around $16,000.
https://www.currentautomotive.com/how-much-does-a-tesla-model-3-battery-replacement-cost/
Posted by: Gryf | 09 April 2023 at 12:30 PM
A 20 kWh PHEV battery typically gets a 30-40 mile range because the BMS limits use to the less than 80% capacity. So getting 250,000 miles of range would be a stretch.
Posted by: Gryf | 09 April 2023 at 12:35 PM
@Gryf
Fair enough, the limitation to 80% will be due to concerns about cycle life, which may not be so restricted as batteries such as the LFP you reference come into more general use.
But in any case, the differences are not substantial enough to affect the basic argument, as the ~150,000 miles implied by your reference are in the ballpark of consumer car use, whilst notions of 70KWh BEV batteries with a million miles etc are overkill, although never of course a bad thing.
The argument remains intact though, very high cycle life, which is certainly do-able, is way more useful in a hybrid or a PHEV hybrid than in a relatively big battery BEV.
Posted by: Davemart | 09 April 2023 at 01:01 PM
Simple math: You drive 150,000 miles. A PHEV with 30 mile range - 5,000 cycles. A Hybrid with 1.5 mile range - 100,000 cycles. A BEV with 250 mile range 600 cycles.
The same principle applies to laptops and cell phones, i.e. small battery more recharging and the battery dies.
Also, in the future, as BEV systems become more efficient (think Mercedes EQXX or Lucid Air) then battery size even for larger vehicles will be smaller just not too small.
Look at my original concept - 150 mile range, 4000 cycles then add Range Extender if you have a large vehicle and pull a trailer.
Posted by: Gryf | 09 April 2023 at 01:22 PM
@Gryf:
You seem to me to be confirming the basic point that I was trying to make, that increased cycle life is way more advantageous for smaller battery packs than large ones, so hybrids and PHEVs benefit more than large battery BEVs.
And we are not in disagreement that it is a good idea not to go OTT in specifying battery packs for BEVs.
As for the current cost of the pack specifically in a Toyota RAV 4, prices are all over the shop in replacements, including for instance from Nissan, and don't seem to bear much relation to current costs, let alone future ones, so perhaps it is not wise to attach too much importance to that current data point.
But as against that, smaller batteries are certainly more expensive than larger ones per KWh, and the pack in a Toyota RAV 4 has to work rather hard and be so specified to lug that size and weight around using only 18KWh or so, as against a comparable large BEV with perhaps 80KWh to do the job.
That is why tougher batteries with high cycle life are so important for cars with more modest battery packs, whether BEVs, PHEVs or whatever, rather than the big battery jobs which just throw a bigger battery at it.
Electric Hummers,or the pathway towards that type of solution, are a lousy answer in my view.
Posted by: Davemart | 09 April 2023 at 02:27 PM
@Davemart
We are getting closer to agreement. Generally, in the future large battery packs should not be necessary for most automobiles (btw many years ago I owned a 1966 Ford Fairlane GT/A with a 390 ci or 6.3 liter V8 engine, total overkill, like having a 90 kWh Mustang MachE).
So most automobiles could have between 30-40 kWh and the low end might be Sodium Ion. Again, if your requirements specify larger loads than a Range Extender might be an option. Leave large batteries to Commercial users.
Found an article which explains how a small Hybrid battery can meet the 10 year, 150,000 mile warranty requirement by using very low Depth of Discharge.
https://priuschat.com/threads/understanding-nimh-hypercycles-to-prolong-prius-hv-battery-life.64978/
Posted by: Gryf | 09 April 2023 at 02:47 PM
Gryf:
I just think that a whole range of options, some of which I like and some I don't, are opening up as numerous technologies progress and expectations change.
A couple I like are that here in Bristol there are a considerable number of deliveries by bicycle, and in Germany they are now offering passes on public transport for around 50 Euros per month, both unthinkable in the car centric 1960's as 'future transport!'
If you have to have a car, when real automated driving happens, likely within the next 5-10 years, not Musk Myth fake, then what you drive most times changes anyway as people specify their cars for extreme cases, when they have to load up to go on holiday etc.
If, and it is a big if, prices are allowed to reflect real costs in road space usage etc, then it is likely that a robocar you may hire will be one person if it is just you travelling.
And to power them we will plainly have a variety of good options, likely including through the road on the move charging, fuel cells able to use most light fuels, etc
I dunno which we will chose, although I have my own preferences, perhaps different options in different places, dependent on the legislative framework, density of population and what not.
There would appear to me to be little likelihood that fuel efficiency has to remain a top priority, as renewable energy clearly has considerable potential to carry on reducing in cost, so if it is cheap enough it makes not a lot of difference to the pocket if you turn renewable energy into methanol etc,
The bottom line is that I see a variety of options as likely, including lightweight ones with through the road charging and maybe a small methanol RE running just fine on maybe 10KWh of batteries.
But loads of other options are, or will be, available.
Similarly for energy, we can run the lot on renewables.
Nuclear would also do the job just fine, and factory produced small reactors are likely, in my view, to very greatly reduce costs.
Lots of options, and good ones, for energy and transport.
Lets hope we don't just chose the daft, inhuman, ones.
Posted by: Davemart | 09 April 2023 at 03:38 PM
Sorry, I was unclear.
Robocars are likely to mean in my view that cars are largely hired for the trip, not bought, and that consequently they are largely specified for the job, not overspecified to cover taking lots of people away on holiday, when we are just commuting on our own into the office etc.
So perhaps personal cars go the way of the personal DVD library.......
Posted by: Davemart | 09 April 2023 at 03:43 PM