|ACAL Energy’s PEM fuel cell is said to be cheaper and more durable than any other hydrogen fuel cell currently on the market|
A UK-based clean energy firm’s revolutionary approach to hydrogen fuel cell technology, translates into cheaper, smaller and more durable fuel cells Dr. Andrew Creeth explains the science behind the technology.
Hydrogen fuel cells might be most commonly thought of in conjunction with cars but they can also provide electricity for stationary power systems. The US Department of Energy reported in 2011 that approximately 15,000 fuel cells were shipped globally in 2010 – more than a 40% growth since 2008.
Fuel cells are portable and can be transported easily, they are silent in operation (so ideal for use in or near residential areas) and they can be used either for continuous power or as emergency back-up systems.
The ‘plug-and-play’ nature of a fuel cell also means that they can be used to replace or supplement the grid infrastructure, or help meet peak grid demands.
However, you could argue that the biggest advantage of fuel cells is actually the fuel they use – hydrogen.
Hydrogen is a very high-energy fuel and is the most abundant energy source on the planet. Fuel cells are the highly-efficient way of converting a fuel into electrical energy because they do it in one step. Hydrogen fuel cells have a theoretical maximum energy conversion efficiency of more than 75%: nearly twice as efficient as a gas turbine when it comes to generator technologies. It is a clean, non-polluting fuel, and is a common by-product of many industrial processes. There is therefore huge potential to use hydrogen as a clean stationary power source.
The genius of hydrogen is that it can also play into the wider energy production picture. Currently, weather-dependent renewable power, such as solar or wind, is dogged by supply and demand problems. For example, on a very windy day, a wind farm will produce more power than is needed, so this excess capacity will go to waste.
But this excess power could be used instead to power an electrolyser, creating hydrogen as a means of storing the energy. A cell voltage of about 1.5V is enough to allow an electrolyser to split water into hydrogen and oxygen, so it is a very easy and simple way to extract hydrogen. This is why German utilities are already using electrolysers to make hydrogen from their surplus renewable energy. In this manner, fuel cells act just like normal batteries – providing portable, storable power that can be accessed on demand.
|At the heart of ACAL Energy’s fuel cell system is FlowCath, a liquid catalyst that replaces up to 80% of the conventional platinum catalyst|
Hydrogen is also a waste product from a variety of industrial processes, the largest being the chlor-alkali industry, which produces more than 100,000 tonnes of waste hydrogen per year, which equates to more than 100 million gallons of petrol. With little market for the element, the hydrogen is usually released, unused, back into the atmosphere.
However, if there was demand from fuel cell users, the chemicals industry could sell their waste hydrogen instead, thus creating a new revenue stream. One kilogramme of hydrogen provides roughly the same energy as one gallon of petrol. Hydrogen fuel cells can also be used for combined heat and power (CHP) applications – either domestically or commercially.
This ‘hydrogen economy’ model is attractive because it works in symbiosis with other established sectors. This in turn helps establish a well-distributed hydrogen infrastructure, which can link into existing or potential hydrogen producers. So whether you are operating a telecom base station, a chemical plant or a sewage treatment works, you should find it easy to access a source of hydrogen or potentially, as in the case of a chemical plant, use what would otherwise go to waste.
But although hydrogen makes an undeniably excellent fuel, a number of stumbling blocks associated with standard hydrogen fuel cells have held back the widespread adoption of the technology.
Standard proton exchange membrane (PEM) fuel cells are expensive, and contain fragile components that degrade quickly. The key component that makes up the PEM fuel cell is also its Achilles’ heel – the platinum catalyst assembly within the stack, which facilitates the reaction to produce electricity, is easily damaged. This limitation, coupled with the fact that the stack contributes up to 50% of the cost of the entire device, significantly limits the technology. These issues need to be addressed if the hydrogen fuel cell has any chance of becoming a viable technology for mass-market adoption.
To tackle this problem, we developed a revolutionary new approach to fuel cell technology. ACAL Energy-designed PEM fuel cells are cheaper and more durable than any other hydrogen fuel cell currently on the market.
With the ACAL Energy technology, a liquid catalyst – FlowCath® – replaces up to 80% of the platinum catalyst found in standard PEM fuel cells. This involved re-engineering the cathode (air) side of the fuel cell; removing the platinum and replacing it with a polyoxometalate liquid chemical solution – coined the ‘secret sauce’.
The advantages of this design technology are two-fold. In a standard PEM fuel cell, the cathode side of the cell (just 30% of the system) contributes 80% of the cost and is responsible for 99% of the durability issues. Because our architecture modifies this part of the system, it significantly enhances durability and reduces costs.
There are a number of durability mechanisms that the new technology addresses. Firstly the polyoxometalate is highly stable and does not degrade. In addition, no damaging intermediates in the reaction with air are formed in the cell which normally would degrade the catalyst assembly.
In standard PEM fuel cells, as the fuel and oxygen are pumped into the system, the membrane within the cell stack starts to degrade and the system wears down. As the fuel cell is switched on and off, the membrane moves between a dry and wet state. This cycling causes dimensional change and can lead to damage, which significantly limits the membrane’s lifetime.
In contrast, FlowCath – the liquid catalyst – dramatically improves the fuel cell’s durability. In the ACAL Energy system, the liquid catalyst is always in contact with the membrane so it avoids such extremes and therefore lengthens the fuel cell’s lifespan.
This in turn enables the system to operate at a higher temperature than would normally be the case for stationary applications. The hotter the fuel cell system, the higher the rate of heat loss. The ACAL Energy system operates at around 110°C, significantly higher than the 70°C normally observed. The higher temperature and robustness enables the fuel cell to operate at a higher power density.
|In a simulated automotive industry test the ACAL Energy fuel cell has reached 10,000 hours, equivalent to 300,000 road miles, with no sign of degradation|
Because the increased temperature increases the rate of heat loss, a simpler and cheaper heat exchange system is needed. For CHP systems, a more effective heat transfer is enabled, making the system more efficient and less expensive. The advantages offered by our technology mean that the FlowCath technology can be used for stationary applications such as in data centres, schools, hospitals, utilities, fixed line operators and telecom base stations at much lower cost. This has not previously been feasible; up until now, longevity and durability had only been possible with large amounts of platinum, which then makes the fuel cells prohibitively expensive for mass-market deployment and use.
ACAL Energy’s technology has effectively broken these old rules.
The ACAL Energy fuel cell technology has undergone robust durability testing in both stationary and automotive applications. Of greatest significance, the technology has been tested using an automotive standard test designed to push a fuel cell to its very limits. Our technology has exhibited no significant signs of degradation during the tests and the same trajectory is expected in stationary power system testing.
The hydrogen fuel cell has reached 10,000 hours, equivalent to 300,000 road miles, in a simulated automotive industry test consisting of a repeated 40-minute journey without significant sign of degradation. These results out-perform the previous industry benchmark of 5000 hours of testing with 20% degradation. Standard PEM systems tend to decay at a constant rate at approximately 30 µV/h whereas the FlowCath system shows no change for 8000 hours.
Concurrent stationary testing has also been running alongside the automotive application. So far, the cell has reached over 5000 hours; although somewhat behind the duration of the automotive test, the cell has not exhibited any decline in performance. On the basis of the results observed in the (significantly more demanding) automotive test, one would certainly expect the stationary cell to demonstrate equally robust results and for these results to follow the same trajectory.
With the ACAL Energy technology, the same fundamental system can be deployed in both stationary and automotive applications. FlowCath provides the levels of high durability and stability required in stationary applications and the power density and size associated with automotive applications. As a result, the technology can offer stationary durability at lower automotive price points.
After eight years of research and development – possible due to funding from investors such as the Carbon Trust, Solvay Chemicals Group and the Sumitomo Corporation – ACAL Energy is currently negotiating contracts with a number of large energy and automotive companies – leaders in the deployment of fuel cell platforms.
The FlowCath fuel cell technology has also been installed at Solvay’s UK chemical plant in Warrington,. The fuel cell – a 3 kw power unit – uses hydrogen that comes from a nearby chlorine production plant. This application is used as a back-up power unit supplying energy to the hydraulic water pump on the plant site. The rig has been running for hundreds of hours, and has endured over 250 stop-starts: so far the fuel cell has demonstrated 100% durability – an example of the robustness of the system that can be expected. The stop-start testing highlights a key benefit of the ACAL Energy system; the fuel cell can be used sporadically as back-up power, as well as a continuous power source.
FlowCath provides a breakthrough for fuel cell technology. The enhanced durability realized by the liquid catalyst means that the technology for both automotive and stationary applications can be aligned for the first time. Initial targeting of automotive companies will lower fuel cell costs, because the supply chain will be optimised for high volumes. This method will be advantageous for stationary applications that will subsequently benefit from the low costs associated with fuel cells produced by a large-scale supply chain.
Fuel cells represent a way to supplement power from the grid, and can provide a reliable back-up power source if mains power goes out. They are quiet, clean, energy-efficient – and like a giant battery, they can be plugged into a variety of situations and used in a variety of ways. This flexibility makes fuel cells the ideal power source of the future.
Dr. Andrew Creeth is chief technology officer at ACAL Energy Ltd, UK. www.acalenergy.co.uk