August 11, 2020

expert reaction to a study looking at converting bricks to energy storage units

A study, published in Nature Communications, looked at converting bricks to energy storage units.

Prof Richard McMahon, Professor of Power Electronics, University of Warwick, said:    

 “Energy storage is of great contemporary interest, especially in the electrical form. The paper by Wang at al. in Nature Communications describes work on creating super capacitors using brick material. The researchers have taken what seem to be generally available, at least in the US, bricks and cut small samples out of these bricks.

 “They have then put conducting coatings onto these brick samples to make the supercapacitors. In addition they have shown how it is possible to put a waterproof coating over the super capacitors and also indicated how they can be assembled into a module. I think it’s fair to say that one of the significant claims in the paper is that they have been able to apply the conducting polymer coating with success and good adhesion. They have created a short video showing a LED powered from one of the super capacitors made by their method.  They also claim figures for the achievable capacitance per unit volume which do not seem to be that far from commercial supercapacitors made by other technologies.

 “From a materials science perspective the work is intriguing and report some interesting features of this particular form of super capacitor.  On the other hand I think it’s fair to say that although this work is an interesting demonstration of a possibility it is a long way from practical application.

 “The first point is manufacturability.   Whilst it has been possible to make devices with presumably randomly chosen bricks if the devices were to be made at scale you would need to know more about the acceptable types of bricks, which of course reflects the clay from which those bricks are made and the conditions under which they are fired. Having said that it seems possible that sufficient process control could be implemented.

 “The samples that have been made are small and although some indication is given about how they can be made into bigger units it’s obvious that any useful application would require modules, comprising a number of devices, at least the size of a standard brick. There is also the practicality of how to bring out connections and if the capacitors are to be used in series the question arises as to how many could be series without insulation and possibly electrical safety issues.  Brick is a brittle material and so handling relatively thin sheets for assembly into modules could be an issue.

 “On the question of energy density it has to be said that this is low – supercapacitors have found certain energy storage applications but for most domestic, light industrial, commercial and distribution system uses much larger amounts of energy storage are needed.  If these uses are the intended areas of application, impracticably large numbers of devices would be needed and batteries provide an easier solution.  There is the further question of whether these modular ‘bricks’ could be used as structural elements.  

 “In summary, this is interesting work from a materials science perspective but it will be a long road to real applications and it’s hard to see how batteries would be seriously challenged.” 

Prof Dan Brett, Professor of Electrochemical Engineering, UCL, said:

 Is this a good quality study?

 “This is a novel proof-of-principle study that adopts a robust chemical, structural and electrochemical characterisation approach such that the findings can be believed.  Care should always be taken when interpreting area-specific properties (units per cm²) when considering devices, the operation of which is inherently a function of the 3D volume (cm³); comparison of supercapacitor performance using 2D parameters should therefore always be considered with caution.

 What is the key message should readers take from the research?

 “Electrochemical energy storage does not have to rely on fancy advanced nanomaterials but can be derived from low-cost (‘dirt-cheap’) or waste materials by taking a very practical approach to solving a problem. Energy storage units need not be discrete stand-alone devices but can be intimately integrated into a building’s fabric, in this case, the actual walls of a building.

 Does this proof-of-principle study indicate that significant amounts of electricity could one day be stored in brick buildings?

 “Heat has been the overriding area of interest when considering energy storage integration within the fabric of buildings. This study shows that there is potential to store electrical energy as well. The performance is a long way short of bespoke supercapacitors but the principle is proven and there is significant scope for improving the storage characteristics by optimising the structure and chemistry of the bricks.

 Are there caveats about the work that readers should be aware of – perhaps potential cost, reliability, manufacturing problems, issues with water etc?

 “The internal electrical resistance of the bricks is quite high, which limits the ability to deliver high rate performance (large currents). This brick format results in large electrodes which will require effective electron and ion transport through the structure to deliver large currents. However, as brick walls tend to be large structures a significant amount of energy can be stored overall such that many low current units (bricks) sum to a significant whole (wall or house).

 “It is important to realise the difference between a battery and a supercapacitor.  A battery can store energy for long periods, supercapacitors can store a large amount of energy rapidly, but cannot hold onto that charge for long due to internal self-discharge reactions. The need to store energy over a relatively short period of time in a building needs to be clear for it to be worthwhile. 

 “Failure is a key issue here.  For the approach to be practical, very long durability is required, it’s hard to imagine a ‘bricky’ being called out to swap out bricks in the walls of your home if they fail, even if the longevity is for many years. Having the bricks as load-bearing structures is therefore unlikely in my opinion. However, to be fair to the authors, they do not claim that the bricks will replace conventional building bricks or be load bearing but rather be integrated into architectural applications that use fired brick.

 “The fabrication approach requires a long time at elevated temperature to make the ‘bricks’, the cost and practicality should be explored further as processing time may increase significantly if the size of the bricks is increased.

 Any other comments?

 “Striving to combine the function of multiple approaches to a single solution to get the ‘best of both worlds’ is an admirable pursuit. However, the case must be made that the combined (hybridised) solution does the job better than multiple discrete units. Bricks are good for building houses and batteries are good at storing energy, combining the two without compromise will be a challenge. However, the authors do not promise this so care should be taken in how far the brick and mortar analogy is extended.” 

‘Energy storing bricks for stationary PEDOT supercapacitors’ by Wang et al was published in Nature Communications at 16:00 UK time on Tuesday 11^th August 2020.

Declared interests

None received.